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M³ Project Announcement - Page 14

post #196 of 565
9/27/04 at 9:53pm
moresl,great work!
as always logical and in order,especially mosfet parts.
About the feedback loops,I agree with peranders.it maybe more short.
like this,shorter feedback and shorter opamp power supply +/- rail tracks.



sorry for my ugly pic

digi
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post #197 of 565
9/28/04 at 1:44am
Hi digi01, thanks for your suggestion. I was going to say that the power rails are also available on the left side but you fixed the picture and beat me to it. At any rate, we left some space near the TLE2426 because there may be additional parts to go there. The power supply is an area where we are still working on (whether there should be a separate TLE2426 per channel, whether there should be capacitance multiplier, or FET isolation for the op amp power, or additional regulators, etc.).

But you're right, unlike the PPA, the M³ has a bigger pcb so there is some "wiggle room" to allow us to move things around to tighten up the layout. There are "no fly zones" on the left and right sides, though (corresponding to the front and rear panel areas of the case), so that switches, RCA phono jacks, power connector, phone jacks, etc. won't interfere with parts on the board.
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post #198 of 565
9/29/04 at 7:19pm
Speaking of power supply, is a Condor P/s (a la the Dynahi) a possibility, or is this topic still premature?
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post #199 of 565
9/29/04 at 7:53pm
Thread Starter 
Like the PPA, the M³ is designed to use a single rail supply. It should work on anything from a wallwart to a STEPS as long as the outputs are isolated, not tied to AC ground. A dual rail supply would be overkill.
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post #200 of 565
10/4/04 at 7:02pm
Any update on the board and heatsink approaches (a or b)? Current estimate on board dimensions? How are the listening tests progressing?
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post #201 of 565
10/4/04 at 8:10pm
Thread Starter 
Quote:
Any update on the board and heatsink approaches (a or b)?
We will let you know. AMB has been busy at work, and I will be out of town from 10/11-10/25, so it may be a while.
Quote:
Current estimate on board dimensions?
8x6" is a rough maximum, and we may go smaller.
Quote:
How are the listening tests progressing?
NeilPeart and Raif came over and did some listening. I don't want to put words in their mouths, but they were very helpful, and will be doing more listening after we make some progress with the power supply section. I missed Raif because I was at the annual Bay Area Carnivorous Plant Society plant show, but AMB told me he was able to distinguish 2 .vs. 3 channel operation in double blind tests. Pretty cool!
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post #202 of 565
10/4/04 at 8:21pm
It was quite an amazing listen, especially considering the whole thing was built on a protoboard.

I am going to keep my mouth shut, considering how early it is in the game, but I am impressed already.

Thanks alot to amb too, as I roughly doubled my amp engineering knowledge while at his house. I swear he built every piece of electronics I saw in there.
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post #203 of 565
10/4/04 at 9:58pm
Raif: Did you a/b against AMB's (highly modded) SDS?

Morsel: Thanks for the schedule update.
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post #204 of 565
10/4/04 at 10:45pm
Quote:
I was at the annual Bay Area Carnivorous Plant Society plant show
You mean designing high-end headphone amplifiers wasn't an esoteric enough hobby?
If you don't mind a very brief thread-jack, what kind of carnivorous plants?
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post #205 of 565
10/8/04 at 6:49pm

No multiloop here?

Hi!
Even though it feels like I´m somewhat banned here...I would like an answer anyway...
Wy don´t u use multiloop in this configuration? Is because the use of AD8610 with it's nice buildup u don't feel it's important?
(hope I haven't miss a explanation to this in the earlier posts)
And I hope no one did get offended by my q...

would be interesting to know the answer...

/qpedejo
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post #206 of 565
10/8/04 at 8:07pm
Quote:
Originally Posted by pabbi1
Raif: Did you a/b against AMB's (highly modded) SDS?

yep
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post #207 of 565
10/8/04 at 8:52pm
And, is M³ vastly superior to the modded AMB SDS? Details, por favor?
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post #208 of 565
10/9/04 at 4:33am
Thread Starter 
Multiloop would increase DC offset in this circuit configuration.

M³ will be better than a modded SDS Labs because it will not suffer from the SDS Labs power supply problem bleeding hum into the input stage and because it has 3 channels instead of 2. There are other reasons, but those are a couple of good ones.

I'm going out of town for a couple of weeks starting Monday. I may be too busy to post again until I get back at the end of October. We will let you know when we have news to report.
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post #209 of 565
10/9/04 at 6:34am
Quote:
Originally Posted by Qpedejo
Hi!
Wy don´t u use multiloop in this configuration? Is because the use of AD8610 with it's nice buildup u don't feel it's important?
That's a perfectly reasonable question. If you study the topology of this circuit and understand it, you'll find that the op amp's output will "sit" at about +3.5 to +4V due to the biasing requirement for the output MOSFETs (i.e., the op amp is not driving the "center" of the bias voltage span). This means that if you were to connect a Jung-style inner feedback loop here, it will adversely affect the amp's total output DC offset voltage. Indeed I've experimented with exactly that on the breadboard prototype, and proved it to be true (the offset went from a fraction of a mV to ~30mV). Not a good thing. The purpose of multiloop is to reduce distortion, but as it turns out, the M³ prototype measured as well or better than a multiloop'ed PPA wrt. distortion.

Hope that answers your question.
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post #210 of 565
10/9/04 at 6:49am
Quote:
Originally Posted by pabbi1
And, is M³ vastly superior to the modded AMB SDS? Details, por favor?
Yes, due to M³'s 3-channel configuration, I have observed an improvement in the overall sound, particularly in the bass, which is taut and more controlled. This is also confirmed by NeilPeart and Raif during their listening tests. I was also able to observe actual elimination of ground pollution with my function generator and scope.

Moreover, while my modded SDS Labs MOSFET amp is good, I found that with sensitive low-Z cans there is audible hum due to the proximity of the AC power transformer to the low-level circuits on Sheldon's pcb layout. In retrospect I wish that I had designed my own pcb for that amp, but it doesn't matter now. The M³ will fix that and be better for a number of other reasons too.
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