comparing 2 same amps (old vs new)

[MaxwellsEq]

Hi all,

Just wanted to share an observation & perhaps get some feedback from the experienced & knowledgeable ASR members. So I purchased a second Musmys E-406 amp (original post here) with the intention of eventually having a true vertical bi-amp setup once I upgrade my main speakers (Martin Logan ESL) to a higher-end pair like the ML Classic ESL-9.
View attachment 500822

The first one I had for about 7 months now, and has probably between 600-1,000 hours of usage. It is still working reliably & remarkably well... sounds as good as the day I got it. So, before I disconnected the cables on the back, I did one more REW in-room measurement test. Then I plugged everything on the brand-new amp, without any changes to how the cabling (DAC > preamp > amp). Then after a bit of warmup, I measured with REW. Here are the graphs:

LEFT channel = red (new) | blue (old)
View attachment 500823
LEFT channel = green (new) | yellow (old)
View attachment 500824

Definitely consistent, however the difference is I actually had to lower the preamp volume by around 3db on the new amp before taking a snapshot of the graphs. It seems the newer amp is about 3db louder than the old. So I asked AI (Gemini) if this is normal (comparing old vs new), here's Gemini's answer:
View attachment 500825

Let me know what you guys think... is what Gemini AI claiming realistic? =)

In room measurements with a microphone tell us:
1. A lot about your room
2. Quite a lot about your loudspeakers
3. Absolutely nothing about your electronics unless they are significantly broken.

Rerun the experiment with a 4 Ohm dummy load and take the measurements across the speaker terminals with a test set or ADC and REW.

 

[voodooless]

Best way to check the gain is to measure the pre-amp voltage of a 1 kHz sine with a cheap DMM, then connect the amps one-by-one to the same pre-amp channel, and again measure the output of the amps. Write down all the numbers. This should give you the gain of each amp. Should be trivial to see the diffrence form this.

Also, check the bal/single-ended switch? Maybe if wired incorrectly, it could result in lowered gain, but that will be highly dependent on the internal circuits.

 

[SSS]

Best way to check the gain is to measure the pre-amp voltage of a 1 kHz sine with a cheap DMM, then connect the amps one-by-one to the same pre-amp channel, and again measure the output of the amps. Write down all the numbers. This should give you the gain of each amp. Should be trivial to see the diffrence form this.

Also, check the bal/single-ended switch? Maybe if wired incorrectly, it could result in lowered gain, but that will be highly dependent on the internal circuits.

Right. This was sugested in my erlier post. Measurement of the amps directly.

 

[SSS]

Sorry, the automatisch Word replacement ist horrible. Dort know how to omit.

 

[Svend P]

with the intention of eventually having a true vertical bi-amp setup

That is a waste of amplifiers. It will not make a difference

Bi-amping 101

This article provides a quick look at how bi-amplification works. The conventional scheme is to split the signal into two frequency bands before the power amplifiers that drive the speakers. The bass (LF) amp sees only LF signals and drives only the LF driver (woofer). The treble (HF) amp sees...

www.audiosciencereview.com

 

[SSS]

Biamping as described above ist the Kind of aktive speakers. With conventional speakers the xover ist still in the Signal chain. So no need for dividing filters prior the amps. Benfit is that the hi amp does not need to deliver high current of the bass signal. This can give better quality for mid and hi. Depending on quality of the amps the q gain may be negligeable.

 

[Svend P]

Biamping as described above ist the Kind of aktive speakers. With conventional speakers the xover ist still in the Signal chain. So no need for dividing filters prior the amps. Benfit is that the hi amp does not need to deliver high current of the bass signal. This can give better quality for mid and hi. Depending on quality of the amps the q gain may be negligeable.

Not really.

"There is no net system power increase at the speakers assuming the amps have the same voltage rails (e.g. inside an AVR or multichannel amplifier with the same power voltage rails to all amps). If you had a 100 W amp before, and bi-amp with two 100 W amplifiers, passive bi-amping does not give you 200 W to the speaker. You have split the load into two frequency bands, but the maximum power is the same to the speaker. That is, 100 W to the lows and 100 W to the highs is the same as having a 100 W amp that covers the entire frequency range. It is not the same as driving the speaker with a 200 W amplifier; to increase the power, you need to increase the voltage rails. There is not an effective increase in power headroom as there is for an active approach."

 

[khaliss]

thanks all for the feedback, much appreciated =)

 

[SSS]

Not really.

"There is no net system power increase at the speakers assuming the amps have the same voltage rails (e.g. inside an AVR or multichannel amplifier with the same power voltage rails to all amps). If you had a 100 W amp before, and bi-amp with two 100 W amplifiers, passive bi-amping does not give you 200 W to the speaker. You have split the load into two frequency bands, but the maximum power is the same to the speaker. That is, 100 W to the lows and 100 W to the highs is the same as having a 100 W amp that covers the entire frequency range. It is not the same as driving the speaker with a 200 W amplifier; to increase the power, you need to increase the voltage rails. There is not an effective increase in power headroom as there is for an active approach."

I did not mention power increase. It is just the amp for mid and highs speaker part has less load to carry which may ore may not improve sound quality.

 

[khaliss]

regarding vertical bi-amping, i've read the thread linked above awhile back, I've also watched some videos about the topic on youtube. I know there's not much measurable evidence that it will make a difference... but since these amps are fairly inexpensive, I don't mind investing some $$$ for the hobby, just to find out for myself if they do (or not) =)

I can always keep it as a spare amp if it ends up doing nothing special for my ears! LOL

 

[SSS]

regarding vertical bi-amping, i've read the thread linked above awhile back, I've also watched some videos about the topic on youtube. I know there's not much measurable evidence that it will make a difference... but since these amps are fairly inexpensive, I don't mind investing some $$$ for the hobby, just to find out for myself if they do (or not) =)

I can always keep it as a spare amp if it ends up doing nothing special for my ears! LOL

Good idea!

 

[DVDdoug]

I tested twice (at least on the new amp) to make sure the resulting graphs have consistency. The measurement microphone sat on top of my listening chair, it never moved, even for a fraction of an inch (there is no wind/breeze that could have moved it inside my listening room LOL)

Yes! You did an excellent job!!! Like I said, "Your curves are remarkably close." Measuring the same amp twice probably wouldn't look any better.

I was once doing some high-frequency experiments with an SPL meter on a mic stand. When I moved-around behind the meter the readings changed by several dB.

...Unrelated when the mic (or SPL meter) isn't moved, but you also hear large variations in high frequency test tones when you move your head slightly because the direct-and-reflected and right-and-left signals mix in-and-out of phase at different locations. We don't notice it with constantly-changing music but we can hear it with constant test tones.

the amps are heavy (about 47 lbs each), but I will try to find time to remove them from the rack... and put them side by side, open the cover, and take a closer peek inside to compare both.

There may be big differences in the design, but the gain is normally set by one (or maybe two) resistors in each channel so that may be the only difference. If they are through-hole and color coded it should be easy to compare the colors. You don't have to "decode" the resistance to see a difference. Sometimes the resistance is printed on the part so that's easy as long as it's not rotated so it's unreadable.

Capacitors and transistors/MOSFETs don't directly affect the gain. It would be resistors (or a completely different design).

 

[khaliss]

thanks Doug... it would be a shame if for some reason the manufacturer changed resistors just to increase the gain (both are advertised as 28db gain from Ali's product page). I don't see a revision number on the chassis sticker on the back, or any sort of indication that it's a different version (everything looks the same front & back)

 

[pablolie]

AIs don't tend to give sources; they're *literally* just saying "well, I read about it on the internet". ...

ChatGPT now cites sources. The copyright lawsuits were coming in too often @OpenAI HQ, I guess. I have prompt programmed my Plus personal account to always, unfailingly cite sources. I don't believe anything that does not come from a credible source.

To stay on topic, the differences between the two amps look insignificant to me. Even with the best electronic parts, +/-1dB (SINAD) can easily happen (actually pretty impressive to keep it there), manufacturing tolerances and such.

 

[antcollinet]

I did not mention power increase. It is just the amp for mid and highs speaker part has less load to carry which may ore may not improve sound quality.

It doesn't. Unless the amp is clipping (running out of voltatage). In which case you need a bigger amp - not two of them.

 

[mike70]

The "I" in "AI" is very, very overvalued... you need to know about the question domain. Is a good helping tool, not a good master.

 

[RexrothPigeon]

it gets things right about 80% of the time

I wouldn't keep an advisor with this failure rate on staff.

 

[threni]

ChatGPT now cites sources. The copyright lawsuits were coming in too often @OpenAI HQ, I guess. I have prompt programmed my Plus personal account to always, unfailingly cite sources. I don't believe anything that does not come from a credible source.

To stay on topic, the differences between the two amps look insignificant to me. Even with the best electronic parts, +/-1dB (SINAD) can easily happen (actually pretty impressive to keep it there), manufacturing tolerances and such.

I tried ChatGPT the other day. I was trying to force it to provide documentation for some code it claimed existed (but which doesn't). It referred me to "Source 1.1.12" in a document. It didn't exist in that document. I challenged it. "Source 1.1.12 is a hypothetical citation...". Not really worth bolling the ocean for I would argue. I would check not only that you have a source, but that the source exists and is accurate and relevant.

 

[RexrothPigeon]

I tried ChatGPT the other day. I was trying to force it to provide documentation for some code it claimed existed (but which doesn't). It referred me to "Source 1.1.12" in a document. It didn't exist in that document. I challenged it. "Source 1.1.12 is a hypothetical citation...". Not really worth bolling the ocean for I would argue. I would check not only that you have a source, but that the source exists and is accurate and relevant.

For regular questions I ask, most of the sources are...wait for it...reddit posts

 

[pablolie]

I tried ChatGPT the other day. I was trying to force it to provide documentation for some code it claimed existed (but which doesn't). It referred me to "Source 1.1.12" in a document. It didn't exist in that document. I challenged it. "Source 1.1.12 is a hypothetical citation...". Not really worth bolling the ocean for I would argue. I would check not only that you have a source, but that the source exists and is accurate and relevant.

Check your sources is a number one requirement when you use any tool anywhere for any endeavor that you are authoring. That's just me. Has always been that way, IMO. Nothing new that AI tools add to it unless you are willing to plagiarize others' work.
I own several patents and I was part of a lawsuit against OpenAI. Never got compensation, but the system now provides sources if you ask for them. Which has always been and will always be mandatory for public intellectual property.