Greater Toronto Area DIY meetup

[Mikett]

Originally Posted by wlowes

Happy New Year to all as well.

Sounds like you are going to be having some great sound with the help of Benchmark. What speakers are you using with them? They are compact enough that you could bring them to an audio meet in the future?

Early on I expected to be isolated until Sept of this year, so if anything I think I'll be pleasantly surprised. If I recall, our host was waiting for a hip replacement. That may have been delayed in 2020. If so best of luck getting it scheduled.

I'm pretty happy with the sound system. About the only project planned is to implement Andrea Mori's final 5mHz clock to replace his already very good 45mHz WTMC. Otherwise the next thing will be a little room treatment. Maybe some subs to get the low registers filled in.

Interesting because I was using the Neurochrome 86 which was clearly better than a Leach fully regulated LOW TIM III, Fully regulated Leach Super Amp with match transistors, Borbeley Mosfet. The AHB2 simply changed the characteristic of a pair of Polk LSIM 707s. These speakers are much more demanding than what they say. What they say of the AHB2 was so quick to perceive, the dynamics and extension was immediate then the articulation of instruments and voices is so good. You hear the real performance. I use my system to watch TV as well. The ease with which you hear the space of the rooms people are in is also interesting. I am happy I sprung for them because they will finally end the quest of what I was looking for since 1977.
It's not a warm sound nor is it etched. The low end has dynamics and it a full bass but not wooley and slow and it has fantastic extension all the bass your speaker can naturally provide, it will bring out. It has SLAM when it call for it. The Neurochrome 86 sounds similar in character but it is unable to have the same bass control and punch but it gets close in the same direction. The AHB2 is much more open than the Neurochrome 86 despite similar specs. The AHB2 has excellent high end resolution, never sounding harsh but the deatils are all there. As soon as you push the volume level, the Neurochome 86 is not in the same league but I do my listening at lower levels, not even close to what the 86 limits. And it is here where the AHB2 is uncanny....you hear a lot more from the AHB2 at LOW listening levels. It is so tuneful and full sounding at low levels. That aspect is excellent for me.
I have yet to test it with my older B&W 802Fs. Maybe those speakers really needed this amp to come alive! The LA4 is certainly plays a part as well. It sounded as transparent as my passive but the passive was too lifeless.
My amplification journey now takes a stop.

[wlowes]

I think we have similar goals in what we expect from our system. I think the magic happens with the accurate reproduction of low level information together with dynamic range and transient response. From what you have said and I have quickly read, the Benchmark sounds like it hits all the right spots. It would be interesting to compare it to some Pass designs. There is DIY meeting in the making!
I noticed it uses low amount of feedback. I was listening (as best you can on YouTube) to a Gryphon Mephisto compared to a mega watt Boulder amp. Even over YouTube I commented that the Gryphon sounds like low feedback. Quick look at it's marketing blurb and sure enough, great specs without feedback.

[Mikett]

Power Amplifiers - A "First Watt" ABX Test - Benchmark Media Systems

The above article by Benchmark makes for interesting reading. First it actually follows the same philosophy as Pass's First Watt. The both of them are on the same page. Pass prefers to go the Class A route, Benchmark takes another direction to achieve the same goals. The last amp I was using was the Leach Super Amp, 300W per channel fully regulated and I was now tiring of the size of it as well as the heat it produced.

Then when the pandemic began I started to play more with "chip amps" and they possessed something about them that was correct but not all was right. Just beyond a certain level of output they fell apart. Then the Neurochrome 86 was tried and it had a difficult time handling the low frequencies at moderate levels. I imagine they would be perfect for much more efficient speakers. I then wondered if I should disassemble the Super Leach, remove the four 500VA toroids and use it for the Neurochrome 686. Again the size and heat produced swayed me. So I bit the bullet.

What is also interesting is that beyond the Fletcher Munson effects, which I thought was responsible for my turning up the volume to enjoy the music, it might have been the very aspect of the First Watt philosophy and the level and characteristic of distortion at low output levels that was the problem. So maybe Pass and the article above has merit, Tube SET probably don't have the crossover distortion being single ended but we do know they add some nice sounding distortion into the output. Again heat and the longevity of tubes was an issue for me.

I'll bring the Neurochrome setup/ stack at the next meet. When?

[rdf]

Tube SET probably don't have the crossover distortion being single ended but we do know they add some nice sounding distortion into the output.

Another mechanism may be at play. If the amplifier's distortion is low order and approximately the magnitude of the speaker's it can reduce distortion reaching the listener. It's measurable and potentially significant.
The REW plots below used a pentode SET with ~0.35 THD @ 1 watt, predominantly 2nd order with the 3rd about 0.03%. 4th is about 100db below fundamental. The speaker is an ancient tweaked PSB Alpha Mite used for bench testing. The measurements were quick and dirty at a distance of under 1 foot, the speaker on a paint can and the mic resting on a bench vice.
Distortion reduction is clear on either side of the 3kHz crossover point when speaker phase is reversed. REW gives THD2-9 figures of 0.487% and 0.141%. I would expect one polarity adds distortion as well. For completion this needs to be followed up with equivalent plots using a standard low distortion amplifier. This SET also permits 'tuning' the level of the 2nd harmonic with minor bias/B+ changes, suggesting more effective cancellation is possible. I would also anticipate more broadband cancellation from a crossover-less full range driver.
SET feed-forward?