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Totally transparent combo bass amp?
- Thread starter fretlessman71
- Start date
The Tom Lees article is the one I was talking about. Any chance you could post higher resolution images so it's a bit more readable? Understandable if the answer is no due to fair use policy.
I think @Mark Reccord 's frequency response plots look flatter than they are because of the 10dB per subdivision setting used to take the measurement. However, if you look at the Figure F. in the Tom Lee article rather than the optimally flat, one of the traces seems to indicate fairly flat response...When I reviewed this article previously, I found some of the traces a bit confounding.
Over 300W at 4% THD. Your amp is making really good power.
I just ran a few FR sweeps of my preamp, which is not exactly the same as the SVT's but close and designed to be pretty flat with EQ zeroed (same tone circuit topology, different part values to tweak it to my liking). You can see what +1dB and +4dB at 100Hz looks like on my analyzer and the SVT plots I did a while back aren't anywhere near that boosted. I'm confident in my statement that my SVT is within ±1dB when the knobs are flat. Obviously this is only one data point and I can't speak for every SVT. Maybe there's some anomaly that makes mine flatter than normal but I've used lots of other old SVTs and they all sound pretty much the same to me at the same settings so my suspicion is that mine is pretty normal.
Cheers!
I used that FRFR speaker with the Genz Benz amp and also tied it into the power amp from my GK combo that replaced the GB. Now I'm running a Genzler amp plus Elf 2x8 cab which is good enough so the FRFR is no longer in use. But boy did it sound good when I was using it.
There is no combo in the traditional sense that can sound like an eq'd flat 8x10 behind you. Quid pro quo the quest is a non starter. Then there's the Trace vintage SMX 810 combo.
- Apr 3, 2003
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- Editor-in-Chief, Bass Gear Magazine
Keep in mind that our testing - by design - includes the sonic influence of both the preamp section and the output section. I will also say that the testing was done with "used" tubes. We might see somewhat different results with newer or just different tubes.
I recently had a good deal on an Ampeg B2 15" combo. As I read trough the TB reviews and opinions, all I hear is flat and transparent and under powered....
Before this thread started I was thinking to myself " This Amp (eq. flat) is close to the acoustic sound of my bass (eq. flat)". And I love it.
So you're asking if such a thing exist?.... I don't know, and I'm not smart enough to understand the tech-side of it, but my gut says that this B2 is close to what you're looking for.
I always forget my Mark Bass CMD K1 Super Combo was advertised as extremely transparent till I try out any of these new combos. Only then do I think "my K1 is way more transparent than any of these!"
Absolutely and in the measurements I did of my SVT I measured the preamp response, the power amp response and the combined response. I don't think I bothered to post the combined response because I think we were talking about preamps and the combined response looked exactly like the preamp one. I think I measured at 10W or so. Enough to get the dummy load resistors warm but not hot. I think you'd see the low end begin to roll off as you approached the limits of the power amp. My sense of it based on my own observations and understanding of how the SVT works at the circuit level is that it should be pretty flat with EQ zeroed and filters out. I don't think tubes would account for the delta between our measurments but I could certainly be wrong about that. I don't think there's much different between the two amps, certainly no major design changes between 1974 and 1978 so it's curious that they measure so differently. There's a big difference between ±4dB and less than ±1dB. Oddly enough, the curves you got for the V4-B in a while back are more what I would expect from both that amp and the SVT as their preamps are nearly identical function-wise.
Differences can come from out of spec components in the PEC tone modules used in many Ampeg amps. The modules are a network of carbon composition and ceramic capacitors, mounted on a substrate and coated. Even within an amp, the components can read differently. In the B-15 for example, you might have two identical channels but people claim that they do not sound the same. The tonal difference usually comes down to the PEC module in each channel. Both the carbon composition resistors and ceramic capacitors drift with time. Interestingly, the resistors seem to be the worst offenders. I've never tried baking a module to see if driving out the moisture has any effect on the readings.
PEC module
PEC schematic
In amp schematic
PEC module
PEC schematic
In amp schematic
My hypothesis is that it's something like out of tolerance parts in the James tone stack. It's pretty finicky about resistor and cap values and the impedance driving it and so out of tolerance parts could account for changes in response. I somehow don't think that component drift would make the response flatter, but I suppose it's possible.
- Feb 12, 2006
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- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
There are all kinds of possible causes for variability, but I sure don't remember seeing flat to 1dB. I remember closer to what Tom measured.
Component tolerances in many cases were 10-20%, and with tube stages that don't use much local AC feedback and no global feedback, variations are entirely expected.
Component tolerances in many cases were 10-20%, and with tube stages that don't use much local AC feedback and no global feedback, variations are entirely expected.
Why don't we just play bass lines with sine, square, and sawtooth....
(sound clips @ around 1:00 to 2:00)
(sound clips @ around 1:00 to 2:00)
… and then...
We make the amplification perfect...
(measurably perfect just doesn't necessarily sound good to me)
We make the amplification perfect...
(measurably perfect just doesn't necessarily sound good to me)
I recently had a good deal on an Ampeg B2 15" combo. As I read trough the TB reviews and opinions, all I hear is flat and transparent and under powered....
Before this thread started I was thinking to myself " This Amp (eq. flat) is close to the acoustic sound of my bass (eq. flat)". And I love it.
So you're asking if such a thing exist?.... I don't know, and I'm not smart enough to understand the tech-side of it, but my gut says that this B2 is close to what you're looking for.
Swink, congrats on your purchase. The B2 was my first Ampeg combo about a decade ago. I picked it up at a Music Go-Round for not much, as it was beaten up but fully functional. I had not read reviews or opinions at that point and, other than its colossal weight, thought it was a great buy. Now that I look back, I'd agree it was underpowered as I was using it with a community band of around 25 musicians unless I used a GK 115 cabinet with it, where I threw a lot more air out.
At home, I thought it sounded pretty nice, especially with the EQ to mess with. It was certainly built like a brick as I found out during the restoration process. I ended up selling it but then had the chance for a buy-back, which at that point I was onto lighter-weight amps. Now, I might re-consider knowing it would occupy a corner of my music room.
Hey, if you take a picture of your B2 and post it in our Combo Club I'll give you a membership number. We're just a few away from 200 members and we'd love to have you along if you're interested!
I figure that in this particular circuit, the LF/HF tone stack is the most likely place for this kind of FR variation to occur. Like I said above earlier, my measurements are congruent with how the circuit should work and that bears out in simulation and on my bench with my DIY preamp, albeit using new and much more tightly toleranced parts than the old SVTs used. But these are still only a few data points so it's entirely possible that my SVT is the anomaly. I'm certainly not going to die on that hill.
Depends what you're measuring and how you're measuring it.
Frequency response is one of a bunch of parameters that contribute to an amp's sound. Distortion, harmonic and intermodulation, both amount and composition is a huge factor. Lots of amps that might have identical frequency responses can and do sound quite different. I would never draw the conclusion that two amps sound the same from only the FR plots because that's not enough information to come to that conclusion.
Depends what you're measuring and how you're measuring it.
Mark, we have argued in the past. You may not admit, but you have just agreed with me [c:
Why wouldn't I admit it? I will happily agree with the idea that a flat frequency response isn't the only thing responsible for an amp's sound and that perfect measured response isn't necessarily desirable from a human perception of sound standpoint. I don't think I would ever have argued against that, while also admitting that my memory is faulty.
Forgive me if I don't recall, but what have we argued about in the past?
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Is it necessary for an amp to have 8 10" speakers in order to be considered? I'm confused.
