[serengetiplains]

Wow, this is one seriously good amplifier.  Really good job, Bruno!   

[serengetiplains]

And also fascinating that those tiny caps are also bypassed as well.

I think all the electrolytics on the board may be bypassed.  I haven't really looked, but it would seem good practice to boost a little more cap action for HFs.

[serengetiplains]

Here's the temporary bypass-capacitor wiring.

[serengetiplains]

And with that, correction, 5.25" woofer, I'm getting 30-40Hz bass, a bit in the 20s, moreso than when the amp was unbypassed.  That's some woofer control.

[serengetiplains]

I was looking at the pin-out for the comparator chip.  It has a Vss.  Google tells me that's a negative supply?  It then looks like the buffer supplies supply the comparator, which looks to operate differentially.  Perhaps it must?  Cough.

[Ric Schultz]

Can you give more details of your bypassing?  What power supplies were bypassed and with what values of what brand of Teflon caps are you using?  Are you orienting the outside foil to the the lower power supply polarity or to ground?  I find the outside foil direction to be very important.

[kc8apf]

That pin out is for a PIC micro controller from Microchip. It has a comparator built-in but is really a fully programmable little processor. I hope it isn't in the analog path. Maybe it is doing some fancy feedback and controlling the output FETs.

[poseidonsvoice]

And with that, correction, 5.25" woofer, I'm getting 30-40Hz bass, a bit in the 20s, moreso than when the amp was unbypassed.  That's some woofer control.

You measured that change in LF response?

Anand.

[serengetiplains]

Can you give more details of your bypassing?  What power supplies were bypassed and with what values of what brand of Teflon caps are you using?  Are you orienting the outside foil to the the lower power supply polarity or to ground?  I find the outside foil direction to be very important.

I bypassed one output electrolytic on what I assumed was each output rail.  I grabbed and used a few caps just to test proof of concept.  For the final implementation, I generally want the most, best capacitance in the least amount of space, with foils oriented as you suggest.

[serengetiplains]

That pin out is for a PIC micro controller from Microchip. It has a comparator built-in but is really a fully programmable little processor. I hope it isn't in the analog path. Maybe it is doing some fancy feedback and controlling the output FETs.

Thank you, kc.  I think that chip is in the analogue path, perhaps functioning also as a gate driver, but I barely know how this amp works.  The unused connector on the top of the amp seems to be for programming that chip, which might be a place to install good regulators.  I suspect the chip is involved in the feedback loop.

[TomS]

Thank you, kc.  I think that chip is in the analogue path, perhaps functioning also as a gate driver, but I barely know how this amp works.  The unused connector on the top of the amp seems to be for programming that chip, which might be a place to install good regulators.  I suspect the chip is involved in the feedback loop.

If you look at section 8 of the data sheet it is for control and monitoring:
The microprocessor has three main functions: to provide an interface for controlling the amplifier, to
monitor the supply voltages in order to prevent spurious operation during power up/down and to
detect error conditions.

[serengetiplains]

If you look at section 8 of the data sheet it is for control and monitoring:
The microprocessor has three main functions: to provide an interface for controlling the amplifier, to
monitor the supply voltages in order to prevent spurious operation during power up/down and to
detect error conditions.

Here is a description from the data sheet.

[serengetiplains]

You measured that change in LF response?

Anand.

No.  I gave only quick listening impressions.

[serengetiplains]

Back to the comparator for a moment.  That chip performs probably the most important function in the amp, and as such would be the most important source of nonlinearity and distortion.  A little jitter on that delicate oscillator and ...

[serengetiplains]

Here are a few paragraphs from one of Cyril Bateman's articles talking about electrolytics.  In the Ncore, electrolytics are in effective series with the output.  The output FETs connect the output from these capacitors to one's speakers.  One is therefore listening, at all times, to electrolytic capacitors.  For me, electrolytics are the weakest link in the audio chain.

[poseidonsvoice]

And with that, correction, 5.25" woofer, I'm getting 30-40Hz bass, a bit in the 20s, moreso than when the amp was unbypassed.  That's some woofer control.

You measured that change in LF response?

Anand.

No.  I gave only quick listening impressions.

Wow. I am humbled.

Anand.

[*Scotty*]

serengetiplains, I am attempting to put your listening impressions into to some kind of context.
How many operating hours are on your modules? Also have you considered doing further listening tests using a mono signal or only one stereo channel and listening to the sound of the modded and unmodded amplifiers in an A/B comparison? This would eliminate the variable of attempting to evaluate the sound of the modded amp with a signal that differs from the one being fed to the unmodded amp.
 If the sound of the basic unmodded Ncore was found wanting when compared to a TACT amp a substantial amount of the HF short coming could be attributed to the electrolytic power supply caps not being fully broken in. It could take perhaps 300hrs to fully break the power supply caps as well as the output filter components.
 A subjective phenomena I have noticed when listening to stereo systems is that when the high frequencies above 10kHz are are extended or improved, there is also an improvement in bass definition and apparent extension. When in fact however, there has been no actual change the bass at all only the highs have been changed. The bass can go from being muddy sounding and lacking in extension to being tight, well defined and appearing to have another half octave of extension.
 It would also be helpful if you listed your system components, we know you have a modded Tact amp and that is all. could you provide a link to the rest of Cyril Bateman's article it looks like interesting reading.
From the part you quoted, it appears that he referring to consequences of using an unpolarized electrolytic capacitor as a coupling cap with no biasing voltage present. This is certainly one of the worst case applications for an electrolytic cap that might be seen in consumer electronics.
Scotty

[serengetiplains]

Scotty, I'm listening through AAD 7001 speakers with upgraded crossovers.  They have a passive radiator on the back, and claim a 25Hz frequency response.  I've been hearing some of that lately.  Anand, the sub-40Hz is down in level, but I wasn't straining to hear what I reported.  The rest of my system is a Mac Mini and an Audioquest DragonFly DAC, a few pieces of cheap wire and some power conditioners (two regenerators in series feeding the amps).

The right channel is stock, so I've been flipping between stock and modified.  It's a quick and easy test. Differences between the channels are easily heard.

I've heard bass tonality change from a change in HF response.  This is not all that's happening here.  From my above reference to woofer excursion, I infer that bass frequencies are also being affected.  The L woofer (bypassed amp) is visibly and audibly better controlled than the R.  Thirty years ago I owned a Marantz amplifier that had peak-LEDs on it.  After I bypassed electrolytics on that amp with some teflon caps, I got a full 30 degrees further movement of the volume control before those LEDs lit.  The lesson of that experiment has stayed with me.

I think the Bateman series of articles is out of print.  I sourced my copy at the local university library.  The articles ran from Jul-Dec in Electronics World.

And yes, the electrolytics on the Ncores are still breaking in---the amps have been plugged in for maybe 48 hrs.  I've learned to hear the sonic signature of new capacitors---fwiw, teflons are the absolute worst and sometimes sound dreadful when first used.  Because I have a stock and modified Ncore in my system now, I can hear relative differences despite the entirely moving playing field this setup represents.

[*Scotty*]

I think I have found the articles you referenced online.
http://www.scribd.com/doc/2610442/Capacitor-Sound
What is interesting is that he found that bypassing electrolytic capacitors with film shunt capacitors gave no useful reduction in distortion and the lowest distortion electrolytic power supply caps were a pair series connected bi-polar capacitors.
Fascinating reading.
Once again there appears to no measurable reason for an observed sonic improvement, it figures.
For what it's worth I have also heard improvements from bypassing electrolytic power supply caps with film types.
Scotty

[TomS]

Here is a description from the data sheet.
...

What I shared was from the NC400 data sheet, not the PIC.