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Quilter Bass Block

#84
teemuk said:
If it's similar to their guitar amps the power amplifier actually models some most distinctive characteristics of a generic push-pull, class-AB tube (power) amplifier. So depending on design it may introduce some degree of "coloration" to the signal reproduction chain, even when not particularly overdriven. At least their related patent describes a scheme to model high output impedance, and resulting weaker "damping factor", of generic tube (musical instrument) power amps, which in turn introduces "non-linearity" to overall frequency response because gain of power amplifier with low damping factor is effectively somewhat dependent on load impedance that varies with frequency. Frequency-dependent gain characteristics will enhance all resonant frequencies and frequencies that otherwise present a higher-impedance load. Usual effects are low end boost due to speaker's resonant frequency near their low frequency limit and gradually increasing enhancement of upper mid-range and higher frequencies due to inductivity of voice coils in general. Crossover networks, piezo tweeters and alike will introduce more "complex loads" where load impedance may peak at various different frequencies. Power amplifier with low damping factor will enhance all such peak frequency bands .

Additionally the patent describes means to emulate certain ovedrive characteristics that - at least by generic acknowledgment - are traditionally introduced by such aforementioned tube power amps: Clipping distortion is similarly somewhat gradual and "soft", and the dynamically changing clipping threshold due to "power supply sag" characteristics is also effectively modeled. Power tube grid overdrive and resulting dynamic effects like bias shifts, related introduction of crossover distortion under sustained loading, and related "blocking distortion" characteristics are also modeled.

So if it's anything like the design in their guitar amps it should be a power amplifier with characteristics and performance very similar to aforementioned tube (musical instrument) power amps. ...Particularly those aimed for guitar rigs because many "classic" tube power amplifier designs for bass amplification actually tried to - in great degree - reduce or eradicate effects of many aforementioned characteristics, particularly "sponginess" of amps with sagging power supplies, "fizzyness" and "farting out" of amps that introduce bias shifting during sustained overdrive, and excessively enhanced low end, overall signal "coloration", "flabbyness" and poor transient response of power amps with low damping factors.

I realize it's solely a matter of preference, but many bass guitar players - especially those employing more "modern" playing techniques and tonal landscapes overall - tend to prefer more "sterile" power amplification (whether tube or SS) when it comes to bass guitars. Distinct warmth, coloration, distortion, dynamic variance et cetera that works when you amplify an electric guitar may be too excessive and disturbing when one amplifies a bass guitar. The trend to prefer solid-state amplification is much more prominent with bass guitar players than it is with guitar players, and to very large degree due to generic "solid-state" characteristic of having no particular distinct characteristic, just amplifying the signal accurately and without coloration. Designs with "stiff" power supplies and high damping factors introduce characteristics perhaps more favourable to bass amplification, like overall frequency response linearity (even to complex loads like x-way bass cabs with passive X-overs) and improved definition of signal transients.

So, no disrespect to Quilter and his/theirs designs intented, but if one has interest in these amps because they are solid-state (and because traditional "linear" solid-state-ish performance is therefore expected), then it might be worthwhile to acknowledge that these amps most likely are not quite similar to such but rather categorize under label of musical instrument power amplifier, which loosely means something along the lines of: "I'm actually a signal processor / effect unit disguised as a power amplifier, and I WILL color the signal while I amplify it. That's the sole purpose of my design.". So if your preference was actually higher fidelity, more linear and accurate signal production, - the solid-state cliché - then you most likely want to steer away from employing (power-amplifying) effect units that had totally different design goals. They made this solid-state amp intentionally perform similarly to certain tube power amps.

On the other hand, there are bass guitarists who do prefer and enjoy such signal coloration effects, generally considered "tubey". For them these kinds of (intentionally signal-coloring) solid-state musical instrument power amplifiers offer characteristically similar alternatives to generic tube musical instrument power amplifiers. Yes, differences to generic, "Hi-Fi-er" power amp designs probably were somewhat underlined. But - IMO - this generalisation particularly applies to more distinctly guitar-amp-like designs. By its performance the Quilter power amp design, for example, is essentially more similar to classic vintage Bassman/Marshall power amp than it is to any classic tube power amp favoured by bassists, particularly anything even resembling the SVT. Keep in mind that classic tube power amp designs for bass guitars were - for good reasons - rarely too similar with classic tube power amp designs for electric guitars. But those are what Quilter's designs prominently "model". Not a bad thing at all, on contrary, and certainly more choices for bass guitarists overall, but just something to be aware of and keep in mind. Don't expect a Quilter amp to be a traditional solid-state amp. It's intentionally going to feature characteristics of certain tube power amps, which - however - some people do regard unpreferable in bass amplification.

---

Back to the topic, master volume arrangement of Quilter amps is indeed also different to popular master volume arrangements that simply attenuate input signal to power amplifier while retaining a "fixed" output power rating. Such amps basically control perceived loudness simply by "having less to amplify" and their headroom limit remains fixed. The dilemma encountered, and already few decades old, is that if we want to use such power amp as an effect processor that intentionally generates harmonic distortion (and other associated effects) it must be overdriven past producing its rated output power, which is the point where the amp still introduces very low amounts of any harmonic distortion, and effectively that means the rig is often going to be operating at disturbingly and unacceptly loud volume levels.

Reducing output power, or more particularly just the overall "headroom", amount of produced output power where signal is still amplified within the specs quoted by that "@ x % THD" - line, can shift overdrive to take place at lower perceived loudness levels. This is not a new idea by any means. It's basically the key operating principle of schemes like PPIMVs, current starved PIs, pentode/triode switches, user adjustable power supply voltages (e.g. "Power Scaling") and alike: Basically, instead of attenuating the input signal, reduce the rated output power at which harmonic distortion still meets quoted specs. For example: Instead of 1% of THD getting exceeded at 100 watts of output power, make the amp exceed that 1% of THD in the signal already when its producing merely, say, 1 watt of output power. Various different methods to accomplish that goal are legion, and if goal is to simultaneously achieve archetypal "tube power amp-ish" overdrive characteristics not all schemes even manage to capture every nuance of such performance in stunning great detail and realism.
It may sound counter intuitive but Quilter's analog modeling circuit - albeit being entirely solid-state - for example, fairs much more realistic results in replicating performance and behaviour of overdriven push-pull, class-AB biased tube power amp than what any PPIMV or current-starved-PI -based design achieves using real, genuine vacuum tubes. Many dynamic effects overlooked or ignored by inherent nature of such circuit designs have been taken into consideration in Quilter's design and the overall result is therefore much more "realistic" than remotedly close attempts to model real tube power amp / power tube distortion by means of phase inverter distortion, which sounds very similar but lacks all related dynamic effects and nuances that explain great deal of touch sensitivity, feel, and warmth associated to tube amp overdrive. Note that such characteristics, however, may not neccessarily at all correlate with subjective preferences of what is "good tone" or even "tube amp tone", though.

But yeah, Quilter amps call for "new" approach to handle loudness control, an approach again more traditionally favoured by those guitar players: Instead of decreasing overall loudness while retaining a fixed threshold of headroom, reduce that headroom and effectively distortion will appear at lower loudness levels. This is of course just another introduction of the age old dilemma of how to define musically useful concepts like "dynamics"; Is it amp's capability to accurately reproduce high signal transients without distortion, high dynamic range so to speak, or is it increased sensitivity to generate musical effects like harmonic distortion, or perhaps increased amount of "dynamic" characteristics within such effects?

Compression, by definition, limits dynamic range of the signal and signal clipping distortion is form of compression. Then again, there are distinct effects in performance of archetypal push-pull, class-AB tube power amp circuit that are in many ways similar to expanding signal's dynamic range: Signal clipping compresses, but power supply sag can make envelope and amount of that compression very dependent on overall signal dynamics. e.g. Harder sustained overdrive automatically reduces output signal's amplitude, which in turn mimicks more pronounced envelopes of signals that do not have their dynamic range and crest factor reduced by signal compression. Crossover distortion from bias shift during sustained overdrive of power tubes is another dynamically variant effect that affects timbre of amp's distortion, effectively causing the amplifier to introduce and gradually shift between different kinds of patterns of harmonic distortion when ovedriven lightly, overdriven more heavily, and depending on time constants of that sustained overdrive condition. So it can again make the amp react more touch sensitively and "dynamically" to ovedrive even though the overdrive is inherently reducing signal's dynamic range by clipping compression.

Popular trend in bass amplification has been, however, to favour moderately linear, high power amps, with "stiff" power supplies, high headrooms and minimal chances to overdrive even if exposed to signals with HUGE dynamic range. Such performance may even be essential when one employs "slap" techniques to play bass guitar. Low frequency harmonic distortion will also more profoundly than high frequency harmonic distortion introduce the kind of intermodulation distortion that usually doesn't fit too well to generic musical contexts so greater degree of linearity is required than from, say, guitar amp. IOW, amplifying bass signals in decent magnitude of "cleanness" requires more headroom than amplifying mid-range or higher frequencies because relatively lesser amounts of harmonic distortion are tolerable due to effects of IMD involving low frequencies. For example, many intentional "harmonic generation" and "distorting" circuits / effects for bass duties rely on distorting mid-range and higher frequencies only, which gives a bit of "edge" to the tone by enhancing higher order harmonic content. BUT if low frequencies were also distorted in similar magnitude the tone would become unbearable, muddy "farting" because IMD would rise alarmingly high.
While guitar amps, especially when it comes to producing modern high-gain tones, can practically hi-pass filter at @1kHz in order to reduce IMD such technique seldom works in bass amplification. Reproduction of fundamental at full gain may not be neccessary for "strong" bass, but response that extends below mid-range definitely is. So strong, musically-pleasing, "clean" bass calls for greater output power than amplifying more mid-range oriented content.

Additionally, seeming effects of expanding dynamic range with dynamically varying envelope characteristics of the overdrive is also very popularly considered as "squishyness", which can benefit a guitar amp of certain nature, but very rarely bass amp. Perhaps even contrary. Trend of popular features to include in bass amps have for years been built-in signal compressors and limiters (not dynamic range expansion) and "stiff" power supplies to guarantee authoritive, sustained and clean reproduction of bass. High damping factors are also popular preference due to resulting flatter frequency response to all kinds of loads, improved transient response, and tighter control of the cone movement. Solid-state guitar amps have for few decades popularly employed schemes that artifically decrease damping factor and therefore introduce performance more similar to that of tube amps. Implementation is trivial and very cheap, yet implementation of that feature to solid-state bass amplifiers have never enjoyed equal popularity. There must be a reason for that, which probably is very similar to reasons why many bass guitarists also prefer solid-state amplification over tube-based. And it's not just weight, size and cost, though they are admittably part of temptation.

Anyway, what one prefers to employ as bass amplifier is naturally matter of individual and subjective preference. It is just generally interesting to see an intentionally "tube-ish" amplifier being introduced to market crowd that largely has not favoured too "tubey-ish" amplifiers. Whether they have realized that or not.
Click to expand...
Could you explain this in greater detail?
 
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#87
Nice carry bag included!

quilter_bag.jpg
 
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#88
Specifications (from the [Invalid or Expired Link Removed]):

Power Output:
225 watts-16 Ohms, 450 watts-8 ohms, 800-watts, 4 ohms (2 Ohm use possible, but may experience clipping at high volume.)

AC Power Req.:
100–240Vac, 50–60 Hz, 250 W typical, 1000W peak.

Signal Connections:
PASSIVE INPUT: ¼" mono (full gain), 2 meg
ACTIVE INPUT: ¼" mono (-10dB gain), 30K
LINE INPUT: XLR 10K balanced, 1V full scale.
LINE OUTPUT: XLR, quasi-balanced, 400 ohms, 1V full scale

Controls:
GAIN CONTROL MUTE BUTTON (with red warning LED)
DEPTH CONTROL (100Hz Hi-Q bass control)
CONTOUR CONTROL (Low-mid scoop, flat, treble cut)
MASTER CONTROL (adjusts peak power from 0 to 800W)
PILOT LIGHT (“winks” if the amplifier is driven into thermal limiting)

Speaker Connections:
4-8 ohms, 90V, 25A peak
Dual ¼” jacks, 8 ohms each
Speakon (2 wire) 4-8 ohms.

Headphone Out:
3.5mm mini-jack, 20 ohms per side, 2V peak.

Dimensions:
H x W x D 8.5”(218mm) x 7.5” (190mm) x 3” (76mm)

Weight:
3.7 lbs (2kg)

Approvals:
UL recognized, tested to conform to FCC/CE limits for Class B devices.
 
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#91
The amp looks promising. How much of that promise it fulfills will, as with most things, depend on the execution. How will it feel? Is the power management obtrusive (will it squish my low end dynamics)? How's it high-passed? The simple tone controls could be nice if well-implemented, annoying if not.

XLR for the power-amp input -- I see pros and cons to that, depending on your use. Would have to think it through. No aux-in.

If I picked up something like this, I'd be looking for a small, robust power-amp that will work well with a variety of sources and without imparting a lot of color or altering dynamics. If it doubles as a simple, toneful bass amp, as this purports to, great.

I just took at look at this page (linked to, along with the manual, on the product page), which I find interesting: [Invalid or Expired Link Removed]. Talks about "warmth" and damping factor, among other things. Not sure exactly how I feel about what's said, but hearing and playing the thing will be, ultimately, where it's at. There's the amp, your cabs, your instrument, your touch, and your individual interpretation of what constitutes a stiff response, warmth, etc., and how much of each is desirable.
 
#92
teemuk said:
If it's similar to their guitar amps the power amplifier actually models some most distinctive characteristics of a generic push-pull, class-AB tube (power) amplifier. So depending on design it may introduce some degree of "coloration" to the signal reproduction chain, even when not particularly overdriven. At least their related patent describes a scheme to model high output impedance, and resulting weaker "damping factor", of generic tube (musical instrument) power amps, which in turn introduces "non-linearity" to overall frequency response because gain of power amplifier with low damping factor is effectively somewhat dependent on load impedance that varies with frequency. Frequency-dependent gain characteristics will enhance all resonant frequencies and frequencies that otherwise present a higher-impedance load. Usual effects are low end boost due to speaker's resonant frequency near their low frequency limit and gradually increasing enhancement of upper mid-range and higher frequencies due to inductivity of voice coils in general. Crossover networks, piezo tweeters and alike will introduce more "complex loads" where load impedance may peak at various different frequencies. Power amplifier with low damping factor will enhance all such peak frequency bands .

Additionally the patent describes means to emulate certain ovedrive characteristics that - at least by generic acknowledgment - are traditionally introduced by such aforementioned tube power amps: Clipping distortion is similarly somewhat gradual and "soft", and the dynamically changing clipping threshold due to "power supply sag" characteristics is also effectively modeled. Power tube grid overdrive and resulting dynamic effects like bias shifts, related introduction of crossover distortion under sustained loading, and related "blocking distortion" characteristics are also modeled.

So if it's anything like the design in their guitar amps it should be a power amplifier with characteristics and performance very similar to aforementioned tube (musical instrument) power amps. ...Particularly those aimed for guitar rigs because many "classic" tube power amplifier designs for bass amplification actually tried to - in great degree - reduce or eradicate effects of many aforementioned characteristics, particularly "sponginess" of amps with sagging power supplies, "fizzyness" and "farting out" of amps that introduce bias shifting during sustained overdrive, and excessively enhanced low end, overall signal "coloration", "flabbyness" and poor transient response of power amps with low damping factors.

I realize it's solely a matter of preference, but many bass guitar players - especially those employing more "modern" playing techniques and tonal landscapes overall - tend to prefer more "sterile" power amplification (whether tube or SS) when it comes to bass guitars. Distinct warmth, coloration, distortion, dynamic variance et cetera that works when you amplify an electric guitar may be too excessive and disturbing when one amplifies a bass guitar. The trend to prefer solid-state amplification is much more prominent with bass guitar players than it is with guitar players, and to very large degree due to generic "solid-state" characteristic of having no particular distinct characteristic, just amplifying the signal accurately and without coloration. Designs with "stiff" power supplies and high damping factors introduce characteristics perhaps more favourable to bass amplification, like overall frequency response linearity (even to complex loads like x-way bass cabs with passive X-overs) and improved definition of signal transients.

So, no disrespect to Quilter and his/theirs designs intented, but if one has interest in these amps because they are solid-state (and because traditional "linear" solid-state-ish performance is therefore expected), then it might be worthwhile to acknowledge that these amps most likely are not quite similar to such but rather categorize under label of musical instrument power amplifier, which loosely means something along the lines of: "I'm actually a signal processor / effect unit disguised as a power amplifier, and I WILL color the signal while I amplify it. That's the sole purpose of my design.". So if your preference was actually higher fidelity, more linear and accurate signal production, - the solid-state cliché - then you most likely want to steer away from employing (power-amplifying) effect units that had totally different design goals. They made this solid-state amp intentionally perform similarly to certain tube power amps.

On the other hand, there are bass guitarists who do prefer and enjoy such signal coloration effects, generally considered "tubey". For them these kinds of (intentionally signal-coloring) solid-state musical instrument power amplifiers offer characteristically similar alternatives to generic tube musical instrument power amplifiers. Yes, differences to generic, "Hi-Fi-er" power amp designs probably were somewhat underlined. But - IMO - this generalisation particularly applies to more distinctly guitar-amp-like designs. By its performance the Quilter power amp design, for example, is essentially more similar to classic vintage Bassman/Marshall power amp than it is to any classic tube power amp favoured by bassists, particularly anything even resembling the SVT. Keep in mind that classic tube power amp designs for bass guitars were - for good reasons - rarely too similar with classic tube power amp designs for electric guitars. But those are what Quilter's designs prominently "model". Not a bad thing at all, on contrary, and certainly more choices for bass guitarists overall, but just something to be aware of and keep in mind. Don't expect a Quilter amp to be a traditional solid-state amp. It's intentionally going to feature characteristics of certain tube power amps, which - however - some people do regard unpreferable in bass amplification.

---

Back to the topic, master volume arrangement of Quilter amps is indeed also different to popular master volume arrangements that simply attenuate input signal to power amplifier while retaining a "fixed" output power rating. Such amps basically control perceived loudness simply by "having less to amplify" and their headroom limit remains fixed. The dilemma encountered, and already few decades old, is that if we want to use such power amp as an effect processor that intentionally generates harmonic distortion (and other associated effects) it must be overdriven past producing its rated output power, which is the point where the amp still introduces very low amounts of any harmonic distortion, and effectively that means the rig is often going to be operating at disturbingly and unacceptly loud volume levels.

Reducing output power, or more particularly just the overall "headroom", amount of produced output power where signal is still amplified within the specs quoted by that "@ x % THD" - line, can shift overdrive to take place at lower perceived loudness levels. This is not a new idea by any means. It's basically the key operating principle of schemes like PPIMVs, current starved PIs, pentode/triode switches, user adjustable power supply voltages (e.g. "Power Scaling") and alike: Basically, instead of attenuating the input signal, reduce the rated output power at which harmonic distortion still meets quoted specs. For example: Instead of 1% of THD getting exceeded at 100 watts of output power, make the amp exceed that 1% of THD in the signal already when its producing merely, say, 1 watt of output power. Various different methods to accomplish that goal are legion, and if goal is to simultaneously achieve archetypal "tube power amp-ish" overdrive characteristics not all schemes even manage to capture every nuance of such performance in stunning great detail and realism.
It may sound counter intuitive but Quilter's analog modeling circuit - albeit being entirely solid-state - for example, fairs much more realistic results in replicating performance and behaviour of overdriven push-pull, class-AB biased tube power amp than what any PPIMV or current-starved-PI -based design achieves using real, genuine vacuum tubes. Many dynamic effects overlooked or ignored by inherent nature of such circuit designs have been taken into consideration in Quilter's design and the overall result is therefore much more "realistic" than remotedly close attempts to model real tube power amp / power tube distortion by means of phase inverter distortion, which sounds very similar but lacks all related dynamic effects and nuances that explain great deal of touch sensitivity, feel, and warmth associated to tube amp overdrive. Note that such characteristics, however, may not neccessarily at all correlate with subjective preferences of what is "good tone" or even "tube amp tone", though.

But yeah, Quilter amps call for "new" approach to handle loudness control, an approach again more traditionally favoured by those guitar players: Instead of decreasing overall loudness while retaining a fixed threshold of headroom, reduce that headroom and effectively distortion will appear at lower loudness levels. This is of course just another introduction of the age old dilemma of how to define musically useful concepts like "dynamics"; Is it amp's capability to accurately reproduce high signal transients without distortion, high dynamic range so to speak, or is it increased sensitivity to generate musical effects like harmonic distortion, or perhaps increased amount of "dynamic" characteristics within such effects?

Compression, by definition, limits dynamic range of the signal and signal clipping distortion is form of compression. Then again, there are distinct effects in performance of archetypal push-pull, class-AB tube power amp circuit that are in many ways similar to expanding signal's dynamic range: Signal clipping compresses, but power supply sag can make envelope and amount of that compression very dependent on overall signal dynamics. e.g. Harder sustained overdrive automatically reduces output signal's amplitude, which in turn mimicks more pronounced envelopes of signals that do not have their dynamic range and crest factor reduced by signal compression. Crossover distortion from bias shift during sustained overdrive of power tubes is another dynamically variant effect that affects timbre of amp's distortion, effectively causing the amplifier to introduce and gradually shift between different kinds of patterns of harmonic distortion when ovedriven lightly, overdriven more heavily, and depending on time constants of that sustained overdrive condition. So it can again make the amp react more touch sensitively and "dynamically" to ovedrive even though the overdrive is inherently reducing signal's dynamic range by clipping compression.

Popular trend in bass amplification has been, however, to favour moderately linear, high power amps, with "stiff" power supplies, high headrooms and minimal chances to overdrive even if exposed to signals with HUGE dynamic range. Such performance may even be essential when one employs "slap" techniques to play bass guitar. Low frequency harmonic distortion will also more profoundly than high frequency harmonic distortion introduce the kind of intermodulation distortion that usually doesn't fit too well to generic musical contexts so greater degree of linearity is required than from, say, guitar amp. IOW, amplifying bass signals in decent magnitude of "cleanness" requires more headroom than amplifying mid-range or higher frequencies because relatively lesser amounts of harmonic distortion are tolerable due to effects of IMD involving low frequencies. For example, many intentional "harmonic generation" and "distorting" circuits / effects for bass duties rely on distorting mid-range and higher frequencies only, which gives a bit of "edge" to the tone by enhancing higher order harmonic content. BUT if low frequencies were also distorted in similar magnitude the tone would become unbearable, muddy "farting" because IMD would rise alarmingly high.
While guitar amps, especially when it comes to producing modern high-gain tones, can practically hi-pass filter at @1kHz in order to reduce IMD such technique seldom works in bass amplification. Reproduction of fundamental at full gain may not be neccessary for "strong" bass, but response that extends below mid-range definitely is. So strong, musically-pleasing, "clean" bass calls for greater output power than amplifying more mid-range oriented content.

Additionally, seeming effects of expanding dynamic range with dynamically varying envelope characteristics of the overdrive is also very popularly considered as "squishyness", which can benefit a guitar amp of certain nature, but very rarely bass amp. Perhaps even contrary. Trend of popular features to include in bass amps have for years been built-in signal compressors and limiters (not dynamic range expansion) and "stiff" power supplies to guarantee authoritive, sustained and clean reproduction of bass. High damping factors are also popular preference due to resulting flatter frequency response to all kinds of loads, improved transient response, and tighter control of the cone movement. Solid-state guitar amps have for few decades popularly employed schemes that artifically decrease damping factor and therefore introduce performance more similar to that of tube amps. Implementation is trivial and very cheap, yet implementation of that feature to solid-state bass amplifiers have never enjoyed equal popularity. There must be a reason for that, which probably is very similar to reasons why many bass guitarists also prefer solid-state amplification over tube-based. And it's not just weight, size and cost, though they are admittably part of temptation.

Anyway, what one prefers to employ as bass amplifier is naturally matter of individual and subjective preference. It is just generally interesting to see an intentionally "tube-ish" amplifier being introduced to market crowd that largely has not favoured too "tubey-ish" amplifiers. Whether they have realized that or not.
Click to expand...

With no disrespect in any way to Teemuk whom we appreciate and treasure dearly, Pat Quilter wanted to chime in and make one notable correction. What follows is Pat's addition to the conversation.


Hello Teemuk and to the Forum

It’s a pleasure to see an expert who understands the nuances we have worked on to achieve authentic vintage tone in our guitar amps. Rest assured, however, that the Bass Block is a whole different animal than our guitar amps, and uses more conventional pro-audio Class-D technology to provide high sustained headroom, good cone control, and artful signal processing, to achieve a sense of bottomless linearity for the bass guitar, which has become a modern full-range instrument.

Unlike our guitar amps, which have an intentionally low damping factor for greater warmth and tone, the Bass Block uses conventional voltage feedback to achieve a "stiff" output impedance, to maintain tighter control on large bass speakers. The actual damping factor for the Bass Block is approximately 40, which may not seem very high, but it is sufficient to reduce load-dependent frequency variations to less than 0.2dB, while leaving just a bit of "warmth" to avoid an overly sterile sound.

There's a lot more to effective bass performance than damping factor however. Amps that "don't deliver" probably suffer more from lame pre-amp voicings, inadequate power supplies, poorly behaved clipping, and lack of thermal capacity - all possibly acceptable in consumer gear but not to be compared to standards in the pro-audio field, like the many reliable QSC amps that we have made over many decades.

The Bass Block starts with a solid pro-audio power platform, derived from the very successful QSC K-series speaker series, but with higher current FETs to meet the needs of high current bass speakers. The Bass Block has a well-regulated power supply that supports 90V peak outputs, and the output current limit is sufficent to drive full voltage down to about 2.5 ohms, to ensure robust performance into real-world 4 ohm cabinets. We combine this with an artfully designed preamp with bass-specific EQ points and a very effective multi-section "bottomless" limiting system that prevents obtrusive clipping without limiting the dynamics or smooth surge of power.

Getting back to damping factor, the term expresses the ratio between the amp's internal impedance, and the impedance of the load, which is mostly the resistance of the voice coil. The presence of the voice coil resistance will always put a limit on how much "control" the amp can put on the cone motion; once the amp resistance is well below the voice coil resistance there is very little change even for "infinite" damping. It would be more enlightening to look at the inverse term, which is called "regulation" - the percentage of voltage drop from no-load to full-load. A damping factor of 1:1 (very low) equates to a regulation of 50%, which would allow a highly audible 6dB change in frequency response vs speaker impedance peaks and dips. 10:1 equates to a regulation of 9%, yielding less than 0.8dB frequency loading effect, which is already "pretty good". At 40:1, we're at 2.5% regulation, or 0.2dB - and 1000:1 or 10000:1 will only cut this negligible effect closer to zero. (In contrast, our guitar amps are designed with a high output impedance, causing a very audible frequency vs impedance response of up to 12dB, which brings out the full tone of guitar speakers).

So bottom line: good bass performance starts with a foundation of a reasonably "stiff" amplifier, with the all-important high voltage and current reserves to cope with speaker impedance changes, and a power supply having adequate capacity to support heavy low frequency transients. Using this foundation, we add a good-sounding preamp that has been artfully voiced to bring out the best qualities of the modern bass guitar, plus a nice set of real-world convenience features, all in a 4-pound package.

It's true that modern bass speakers are much closer to conventional pro-audio practice than guitar speakers, and are tuned to perform well with stiff amplifiers; we have found however that chasing that last couple of percent of regulation has no benefit in transient response, and if anything, it's better to leave a small amount of warmth in the response.

Those readers seeking an old-school tube-amp bass sound will like our 200-watt Tone Block series, which play louder than you would think due to the “inflationary” properties of our guitar-amp output impedance. These are well suited for bass players who like to exploit overdrive. The Bass Block will “growl” a bit when pushed, but never really bottoms out.

Best regards
Pat Quilter
 
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#93
chrisparks said:
With no disrespect in any way to Teemuk whom we appreciate and treasure dearly, Pat Quilter wanted to chime in and make one notable correction. What follows is Pat's addition to the conversation.


Hello Teemuk and to the Forum

It’s a pleasure to see an expert who understands the nuances we have worked on to achieve authentic vintage tone in our guitar amps. Rest assured, however, that the Bass Block is a whole different animal than our guitar amps, and uses more conventional pro-audio Class-D technology to provide high sustained headroom, good cone control, and artful signal processing, to achieve a sense of bottomless linearity for the bass guitar, which has become a modern full-range instrument.

Unlike our guitar amps, which have an intentionally low damping factor for greater warmth and tone, the Bass Block uses conventional voltage feedback to achieve a "stiff" output impedance, to maintain tighter control on large bass speakers. The actual damping factor for the Bass Block is approximately 40, which may not seem very high, but it is sufficient to reduce load-dependent frequency variations to less than 0.2dB, while leaving just a bit of "warmth" to avoid an overly sterile sound.

There's a lot more to effective bass performance than damping factor however. Amps that "don't deliver" probably suffer more from lame pre-amp voicings, inadequate power supplies, poorly behaved clipping, and lack of thermal capacity - all possibly acceptable in consumer gear but not to be compared to standards in the pro-audio field, like the many reliable QSC amps that we have made over many decades.

The Bass Block starts with a solid pro-audio power platform, derived from the very successful QSC K-series speaker series, but with higher current FETs to meet the needs of high current bass speakers. The Bass Block has a well-regulated power supply that supports 90V peak outputs, and the output current limit is sufficent to drive full voltage down to about 2.5 ohms, to ensure robust performance into real-world 4 ohm cabinets. We combine this with an artfully designed preamp with bass-specific EQ points and a very effective multi-section "bottomless" limiting system that prevents obtrusive clipping without limiting the dynamics or smooth surge of power.

Getting back to damping factor, the term expresses the ratio between the amp's internal impedance, and the impedance of the load, which is mostly the resistance of the voice coil. The presence of the voice coil resistance will always put a limit on how much "control" the amp can put on the cone motion; once the amp resistance is well below the voice coil resistance there is very little change even for "infinite" damping. It would be more enlightening to look at the inverse term, which is called "regulation" - the percentage of voltage drop from no-load to full-load. A damping factor of 1:1 (very low) equates to a regulation of 50%, which would allow a highly audible 6dB change in frequency response vs speaker impedance peaks and dips. 10:1 equates to a regulation of 9%, yielding less than 0.8dB frequency loading effect, which is already "pretty good". At 40:1, we're at 2.5% regulation, or 0.2dB - and 1000:1 or 10000:1 will only cut this negligible effect closer to zero. (In contrast, our guitar amps are designed with a high output impedance, causing a very audible frequency vs impedance response of up to 12dB, which brings out the full tone of guitar speakers).

So bottom line: good bass performance starts with a foundation of a reasonably "stiff" amplifier, with the all-important high voltage and current reserves to cope with speaker impedance changes, and a power supply having adequate capacity to support heavy low frequency transients. Using this foundation, we add a good-sounding preamp that has been artfully voiced to bring out the best qualities of the modern bass guitar, plus a nice set of real-world convenience features, all in a 4-pound package.

It's true that modern bass speakers are much closer to conventional pro-audio practice than guitar speakers, and are tuned to perform well with stiff amplifiers; we have found however that chasing that last couple of percent of regulation has no benefit in transient response, and if anything, it's better to leave a small amount of warmth in the response.

Those readers seeking an old-school tube-amp bass sound will like our 200-watt Tone Block series, which play louder than you would think due to the “inflationary” properties of our guitar-amp output impedance. These are well suited for bass players who like to exploit overdrive. The Bass Block will “growl” a bit when pushed, but never really bottoms out.

Best regards
Pat Quilter
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Great info, Chris. My basis for tonal comparison for something with these design goals might be a GK 800RB, but with more headroom - is that reasonable? Where am I off, if at all?
 
#97
First gig report playing thru my spankin new QBB800; 3 gigs with 3 different bands with 3 great drummers. All were blowen away by the new amp.
I've been a GK guy for many moons; 1001RB and NEO 12 and 15 cabs. During the first song on the first gig the drummer and I just started grinning at each other; I could tell right away this was a much better sounding set up for me, (which says a lot). This amp responds very well to my playing style, (lots of dynamics - whisper to a roar, when appropriate), and each note carries a different weight to it than my GK head; this is hard to verbalize but bottom line this is a very responsive and musical amp. Very easy to dial in a great sound, minimal tweaking on the first gig; plug and play after that. For reference, I play older P basses strung with EB Cobalt Flats through either the GK NEO 12 or 15 or both depending on the gig.
 
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#99
Mike Barry said:
First gig report playing thru my spankin new QBB800; 3 gigs with 3 different bands with 3 great drummers. All were blowen away by the new amp.
I've been a GK guy for many moons; 1001RB and NEO 12 and 15 cabs. During the first song on the first gig the drummer and I just started grinning at each other; I could tell right away this was a much better sounding set up for me, (which says a lot). This amp responds very well to my playing style, (lots of dynamics - whisper to a roar, when appropriate), and each note carries a different weight to it than my GK head; this is hard to verbalize but bottom line this is a very responsive and musical amp. Very easy to dial in a great sound, minimal tweaking on the first gig; plug and play after that. For reference, I play older P basses strung with EB Cobalt Flats through either the GK NEO 12 or 15 or both depending on the gig.
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This is a great review, esp. with the comparison to an amp a lot of people are familiar with. This description fits one of my gigs to a "T" - if I can get a sense of how it would do for more aggressive styles (e.g., punk), it might tip me over.
 
#100
Mike Barry said:
First gig report playing thru my spankin new QBB800; 3 gigs with 3 different bands with 3 great drummers. All were blowen away by the new amp.
I've been a GK guy for many moons; 1001RB and NEO 12 and 15 cabs. During the first song on the first gig the drummer and I just started grinning at each other; I could tell right away this was a much better sounding set up for me, (which says a lot). This amp responds very well to my playing style, (lots of dynamics - whisper to a roar, when appropriate), and each note carries a different weight to it than my GK head; this is hard to verbalize but bottom line this is a very responsive and musical amp. Very easy to dial in a great sound, minimal tweaking on the first gig; plug and play after that. For reference, I play older P basses strung with EB Cobalt Flats through either the GK NEO 12 or 15 or both depending on the gig.
Click to expand...

Thanks for sharing!

Question: Did you plug directly into the BB800 or did you have some pedals in the signal chain?
 

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