Mini 0r Micro Amps.... I Must Be Missing Something?

[guy n. cognito]

3. Inability to load in where you are being paid to play.
4. Wasting energy (although what I proposed weighs about the same... PF-500 versus the XLS 1500 and a preamp.)

I did not mean to make a general statement about all manufacturer's amplifiers, my listing is for the companies that make the small heads. If if you do a search on the smaller amps, there are many complaints, which I did not expect when I was searching the threads. To me, it appears that many of them were with the PF-500, but to be fair, they probably outsold most of the other amps as well and they have probably remedied these problems as fast as they found them. I am a big Ampeg fan, starting with my B-15N which I have had a long time.

I'm also not advocating using heavy rigs. I'm wondering out loud, what is the advantage to hauling something that weighs a few pounds less and half the size?

In order to use a pre / power setup, it must be mounted in a road case. That case is going to be large enough that it must be carried by itself, meaning one trip from the car just to carry your amp.

Not only are micros reliable and plenty powerful, but they can also fit in a gig bag and be carried over the shoulder with something else in your hands. Less trips makes me a happier person.

A Genz Benz Shuttle 9 is small and light. I've never encountered a gig where I needed more than 900 watts.

 

[popgadget]

My amp choices are a WT-400, Shuttle 9.0, Streamliner 900 or a Crown XTI-2002 racked with a Demeter HBP-1.
I like the Demeter/Crown the best, but use the Shuttle or Streamliner far more often because they do a great job and are so easy to move. In reality at the typical volumes that I play, there is no practical advantage to hauling the rack. The differences in performance is minuscule in my applications.

 

[joelb79]

They don't. How are you interpreting those graphs? FYI a typical mainstream Class-AB power amp will have a similar graph.

I probably cannot interpret what that distortion actually looks like unless it was under an oscilloscope. 10% distortion where and how? at what frequency? what does the resulting waveform look like? The chart contains different frequencies as well indicating it was done with a tone generator and not a full range musical signal I would think. That's about all I can interpret at this point; sure does leave a lot to the imagination. And of course, that would be only how that amplifier responds given that input, frequency and output power.

The spec is pointless to a bass guitar signal, but it is a starting point on expected performance of the amplifier.

Let me get the gist of this; that the chart is wrong, invalid and had no point even though the manufacturer is the one producing it? Regardless of implementation, that is the spec sheet of the power section of at least 2 bass amps. you can wish they never produced the chart, but it's still there.

Perhaps an expert can explain the chart then?

I found this about AES17 Measurements and THD: Invalid Link Removed

8.5 Total harmonic distortion and noise (THD + N)

NOTE The characteristic to be specified is the transfer characteristic and dynamic non-linearities in
the EUT. The results are indicative of anomalies in device behavior but may not be indicative of
audible performance.

Harmonic distortion and noise is the ratio of the output noise and distortion level to the output signal level.
Both levels shall include all harmonic, inharmonic and noise components. All components shall be included
because harmonics often alias above the folding frequency and often appear anywhere in the audio band.

8.5.1 Total harmonic distortion and noise versus frequency

The measurement should be conducted with a sine wave at – 1,0 dB FS and repeated with a sine wave at – 20
dB FS. The test signal present in the output should be removed by means of a standard notch filter and the
remaining signal bandwidth limited to the upper band-edge frequency or 20 kHz, whichever is lower. The
level of the filtered signal should be measured and reported as a ratio to the unfiltered signal level. The
measurement should be repeated at each octave frequency from 20 Hz to one-half the upper band-edge
frequency.

8.5.2 Total harmonic distortion and noise versus level

The measurement should be conducted with a sine wave at 997 Hz. The test signal present in the output should
be removed by means of a standard notch filter and the remaining signal bandwidth limited to the upper bandedge frequency or 20 kHz, whichever is lower. The level of the filtered signal should be measured and reported as a ratio to the unfiltered signal level. The measurement should be repeated at each level from 0 dB FS to – 80 dB FS in steps no larger than 10 dB

This should be kept in mind when interpreting that chart/graph from ICEPOWER since this is the measuring standard they used.

This is also applicable showing how testing is done by AES17 measurement standards: http://www.audiotech.com.tw/AES17 Filter.htm

 

[fdeck]

No problem. I'll borrow the link that you provided for the graph:

Now I'm not "officially" an expert, but am a pretty serious electronics enthusiast, and have a day job involving scientific instruments. I'll start with where the graph takes off sharply, around 60 W. The horizontal axis is likely to be an RMS value for a sinewave into 8 Ohms resistive, so it corresponds to a voltage of Sqrt(60*8) = 21.9 V RMS, or an amplitude of 31 V (62 V peak-to-peak). Because the curve rises so rapidly, I'm going to guess that the main distortion mechanism is "hard" clipping. So this is a basically linear amp with a hard clipping threshold of 31 V when driving an 8 Ohm load. The slightly elevated distortion level at the lowest frequencies is probably due to some amount of crossover distortion. I don't know why the distortion level is elevated at high frequency, and would be interested in looking at a comparable curve for a Class-AB amp. But all of those curves are below what I am guessing is the threshold for audibility. This is a high fidelity amplifier, perhaps even unnecessarily so for bass guitar use.

So in this case, it's possible to boil the entire graph down to a pretty simple behavior of linear response up to "hard" clipping where the waveform just gets flattened at the top. Any bass waveform is likely to be flattened in the same way, since the circuit is probably running from a "stiff" regulated power supply. The dynamic headroom is probably negligible, or at least, I wouldn't count on any.

The curve goes through 10% at around 100 Watts. Now it's not my choice to rate things this way, but a lot of mainstream bass amps use the 10% point for where they pin down their power ratings. It's one reason why I'm not a big fan of power ratings. That 31 V (i.e., 62 V peak to peak) is more meaningful to me. If a power rating is specified at 1% distortion, then I'd feel safe just computing the clipping voltage directly, but at 10%, it requires a look at the shape of the curve as we've done here.

At least, that's my take on things. I'm betting that from a bass player standpoint, the only thing that really matters is that hard clipping behavior, which means that in a well designed bass amp, the designer needs to add some circuitry to tailor the behavior of the amp when it approaches the clipping threshold, such as some sort of soft clipping, limiting, compression, or maybe a combination thereof. Both of the "micro" heads that I own seem to incorporate such features.

 

[joelb79]

I agree with everything you just said. Guess my understanding was not far off; especially after a read through of AES17. I do realize that I'm nitpicking an already hi-fi amplifier.

 

[JimmyM]

If this "there is no difference due to topology" stuff was true, then how come I hear a vast difference between all-tube and traditional solid state? And how come I hear a slightly less vast but no less significant difference in every single micro I ever played vs. trad solid state? Quite frankly, it's starting to insult my intelligence a little, this business about there being no difference in tone based on topology.

Reminds me of the story I read about Geoff Emerick, who engineered later Beatles albums. All the Beatles albums but one were done using a board with an all-tube design. When they started working on Abbey Road, they had replaced the tube board with a SS board, and the Beatles, George Martin, and Geoff Emerick could tell a big difference for the worse, but the engineers there swore up and down that it sounded the same, claiming that they took measurements.

And how about the last Tube Challenge I did, where almost 75% of those who voted successfully picked out my REDDI tube DI vs. my Sansamp VT? I did my darndest to make them sound as close as I possibly could, too, and a significant majority totally recognized which was which.

So let's stop the nonsense, eh? Clearly there is a difference in topologies, and it ain't just EQ points.

 

[guy n. cognito]

If this "there is no difference due to topology" stuff was true, then how come I hear a vast difference between all-tube and traditional solid state? And how come I hear a slightly less vast but no less significant difference in every single micro I ever played vs. trad solid state? Quite frankly, it's starting to insult my intelligence a little, this business about there being no difference in tone based on topology.

Reminds me of the story I read about Geoff Emerick, who engineered later Beatles albums. All the Beatles albums but one were done using a board with an all-tube design. When they started working on Abbey Road, they had replaced the tube board with a SS board, and the Beatles, George Martin, and Geoff Emerick could tell a big difference for the worse, but the engineers there swore up and down that it sounded the same, claiming that they took measurements.

And how about the last Tube Challenge I did, where almost 75% of those who voted successfully picked out my REDDI tube DI vs. my Sansamp VT? I did my darndest to make them sound as close as I possibly could, too, and a significant majority totally recognized which was which.

So let's stop the nonsense, eh? Clearly there is a difference in topologies, and it ain't just EQ points.

Methinks you misunderstand that comment........

 

[Chef]

I think I see what both fdeck, and Jimmy are saying.
I think, and I could be wrong, that fdeck is saying "many bass players don't push the power plant into distortion." And, given that, smaller probably sounds pretty good to most folks.

I think what Jimmy is saying is that smaller is never gonna sound like tubes and big transformers. And, that real tube amps with real iron do their thing, at and around the limits of THD, differently than the micro stuff. Both points I'd also have to agree with.

So, as far as I can tell, both of you guys are right.

 

[fdeck]

Chef, thanks for the comment. And I certainly don't mean to dis Jimmy. I'd clarify just a bit, saying that the hard clipping limit is a danger zone for solid state amplifiers, and turning a power amp module into a bass amp involves dealing with clipping in some way. For instance, neither of my micro heads can be readily driven into hard clipping. One of them appears to have a built in optical compressor, and the other has a soft clipping behavior plus a less aggressive compressor. What that means is, the designer who integrated the power amp module into a bass amp has done something about clipping.

 

[Chef]

I'm no engineer, but I kinda get that.

Tube amps can take that clipping, in all kinds of varying degrees, and make it a musical thing, as opposed to "a danger zone."

 

[fdeck]

I'm no engineer, but I kinda get that.

Tube amps can take that clipping, in all kinds of varying degrees, and make it a musical thing, as opposed to "a danger zone."

Exactly right. A classic tube amp circuit is the only power amp that handles clipping in a bass-friendly way "out of the box." With Class-AB solid state and Class-D, it has to be deliberately designed into the circuit, which means there is a possibility for success or failure, as well as a learning curve for the industry as techniques improve.

Comments from the real experts on this forum led me to appreciate this aspect of amp design, which I wouldn't have guessed myself.

 

[Chef]

True Story.
If they all sounded the same, we could wrap this amps forum up and go home

You are correct in that all bass amps sound a bit different.

 

[fdeck]

Does that mean the thread is locked?

 

[Chef]

not at all, lol...carry on!

 

[KJung]

True Story.
If they all sounded the same, we could wrap this amps forum up and go home

I was on my stupid iPhone trying to respond to Jimmy, and got caught up in my 'quoting' shorts. I don't believe there is a difference in power amp topologies for the most part, but I SURE do think there are editing 'ease of use' differences between the iPhone app and my PC I had to power up my laptop to undo my mess!

Jimmy, god bless you, and keep rockin' the big iron if it floats your boat!

 

[JimmyM]

You are correct in that all bass amps sound a bit different.

And you don't think that's in any way due to topology? Let me ask this...if the major amp companies could make micros that sound identical to their trad SS amps, don't you think they'd do it?

Chef, I really only included the tube/trad SS stories to illustrate how there was a time manufacturers and fans of the new technology swore that SS sounded the same as tube and was 100% its equal. This is the same thing for today's musician.

The one topic that keeps getting brought up in defense of the new technology, PA amps, could be a legit argument. I don't know enough about them and never really owned any to make any kind of comparison. I do know that pretty much nobody uses anything but class D anymore, but the PA industry almost immediately switched over to SS power amps in the 70's as well because they were smaller and could give them more power than tube power amps, not because they sounded better. And yeah, if I'm running a touring PA, do I want 20 60 lb. 2000w amps in racks or 20 10 lb. 2000w amps in a small fraction of that rackspace? I know a guy who still lugs the big iron for PA because he feels class D isn't as good. I also know a guy who switched over because of budgetary and old age concerns, and he likes it but says it took some getting used to. Me, I don't know...I can only go by what people tell me. It's generally well liked by the PA community, but does that mean it's as good? I don't know. I only have to bring one amp myself

 

[arai]

A lot of people hear with their eyes.

 

[JimmyM]

A lot of people hear with their eyes.

LOL! Yeah, OK.

 

[agedhorse]

At the request of a few TB members who have asked for specific explainations on this topic, and the confusion that it's generating, I'm going to post some general discussion information here rather than answer in e-mails and PM's. There's a lot of inaccurate statements that have been made based on some significant misunderstandings of the product.

1. Whenever relying on published data, it really pays to understand what this data means, how it's generated, the specific conditions and measurement metrics that are used, and why they are stated the way they are.

2. If the application uses a module in BTL mode, the single ended data bears no value to the discussion, it does not apply. BTL mode carries some unique benefits in class D amplifiers driving primarily inductive loads. One of these is the increase in power delivered by recycling back EMF through the power supply, the other is the lack of power supply pumping and resultant (possible) asymmetrical current limiting when an amp is driven hard. This does not occur in traditional linear amps, is not reflected in purely resistive published ratings, but can have a significant influence on real world performance (if properly taken advantage of).

3. The power supply can be stiff, but it can also perform virtually identically to a "linear" (line frequency transformer) supply... ie. dynamic impedance can be the same. Most are in fact have significant dynamic impedance, which can be harnessed as an additional variable to maipulate within the design.

4. The THD curves are somewhat misleading (aside from folks citing the single ended specs. for a BTL application) in that there are dynamic elements to these curves, but the specs. show static curves. Understanding how these numbers change with the dynamics of the power supply are crutial to exploiting the maximum DYNAMIC performance from any power amplifier.

5. The Shuttle 9.0/9.2 and Streamliner 900 are using the module to generate 900 watts RMS into 4 ohms. This appears to be puzzling to some because the module lacks a 4 ohm BTL rating. Understanding the details of the internal architecture of the SMPS and the class D sections, as well as the inter-relational aspects between the two open up new territory that is designed in but requires considerable expertise to extract safely. I have been working with IcePower products for many years (I come from the pro audio industry where their initial products found favor) and we worked hand in hand with IcePower's own engineers to identify and exploit these "hidden" features. This engineering is not for the faint of heart, and additionally, our specific designs were performance, safety and reliability tested at their (IcePower's) engineering lab in Denmark. I do not believe this is true of any other bass amp product using their components.

6. Class D bass amps do not all sound the same, and if one were to think about it I suspect that this is rather obvious in fact. There are a couple of dominating factors in what make a bass amp sound and feel different. The preamp design is probably the biggest influence on the sound, our Streamliners sound considerably different than our Shuttles. Feel is another aspect that separates the different products, and attention to dyamics management throughout every stage of the preamp and power amp are critical to the feel and playability.

7. There are a number of well respected class D bass amps out there, they all sound different, they all have their fans and detractors. In fact, this is probably the best time ever to be a bass player. There are more outstanding choices available than ever before, rather than bitching about the petty dislikes how about celebrating how many really good options that are now available?

 

[fdeck]

Thanks!