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1970s Design Indulgence

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peterb View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote peterb Quote  Post ReplyReply Direct Link To This Post Posted: 04 Feb 2019 at 3:50pm
The musical differences of capacitor types is nicely highlighted on this website, all be it as a key component of loudspeaker crossovers. A bit of light reading perhaps! 

Peter
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Hood/Hart 30W MosFet Integrated amp.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Richardl60 Quote  Post ReplyReply Direct Link To This Post Posted: 04 Feb 2019 at 5:20pm
Wow, must take dedication to listen to all of those capacitors!!!
 
The Alcap ones my speakers use do not appear to be listed here but I have heard of a small number of these - I was steered away from some of the more exotic caps (two are set out) by Jerry At Falcon Accoustics so as not to unduly change my speakers characteristics but do wonder with the number shown and Grahams research over long term availability of other components how many may bite the dust and no longer be available?
 
Whilst most keen ears agree that cables also make a difference, so do plugs and different connectors in my experience so there could be a full time job here for someone (as claimed can fuses and solder - neither of which I have tried!).
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 05 Feb 2019 at 6:35am
After removing the "imaginary" emitter resistor and combining its value in the NFB divider resistor, the "life" in the music departed.

The "imaginary" resistor is actually real, but its contribution has not been properly explained by anybody on earth yet, as far as I know, and I've dug deep.

It is depicted in the (repeated) diagram below as R2, and R4 is the NFB divider resistor (R3 is bypassed because it is only required for the DC bias level).



The actual values changed to R2: 0 ohms; R3: 620 ohms; R4 560 ohms; R8: 12k ohms; C5: 100uF.

This has now changed to R2: 180 ohms; R4: 390 ohms; R8: 8.2k ohms (C5 remains 100uF as the turnover frequency here is much below 1Hz).

R2 is therefore the "imaginary" resistor. Although its action can be explained, the differences cannot be measured by any conventional means, and therefore its explanation can be called into question.

Regardless, it's for keeps (I think...) because the sonic qualities reflect what the explanation explains.

The junction R7/R4 (via C3) is the negative feedback node. With R2 = 0, the signal at that point is not discontinuous with the input signal, and that can be mathematically proven. However, should distortion be present in the fed back signal it becomes discontinuous and an error voltage will be generated to eliminate it.

Now, if distortion is present, the discontinuity will mean R4 is not purely an extension of the intrinsic emitter resistance (re), and therefore it must have an effect on the value of gm. And as the value of gm works with the value of Cdom to set the stability values of the amplifier, these will change for the duration and magnitude of the distortion to some extent.

The duration and magnitude of the distortion will vary with signal amplitude and frequency and so it is always changing. It is therefore always generating an error voltage to some degree, and therefore the stable point is always changing. And because it is generating an error voltage the gm must increase rather than decrease.

The increase in gm should be countered by an increase in Cdom, but that is fixed, and so any error voltage leads to a narrowing of phase margin. Even the slightest narrowing will take it more toward ringing.

Therefore gm needs to be made more linear, but for reasons that the explanation against it being absolutely linear would take some digesting, I will simply state it can only be made more linear.

So by taking a proportion of Re from R4 and placing it in series with the emitter outside the NFB node (R2), we have made gm less prone to changes influenced by the need for distortion-eliminating error voltages.

We still have the same open-loop gain and so the error voltages should not be any larger. And so measurable distortion should remain the same.

So, the action of the "imaginary" resistor has now been explained, and I only hope it will stand scrutiny, because the audible improvement (yes, improvement) is undeniable.

But, as I will continue to state, improvements can be fleeting because of other factors so this will now be subjectively tested for a further lengthy period.

(erratum: C3 is now shown where it should belong)

Edited by Graham Slee - 05 Feb 2019 at 6:36am
Not simple enough for Google-Bot to understand...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote musicdude Quote  Post ReplyReply Direct Link To This Post Posted: 11 Feb 2019 at 8:10am
Hi Graham, I was reading about your search for a suitable power supply reservoir capacitor. Have you looked into Nichicon caps? You might find a suitable cap in the LKS or LKG series. They are made for audio. I know they are Japanese made but it's good quality and they last.
I use Nichicon in my recap projects with very good results.
Andy

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Post Options Post Options   Thanks (1) Thanks(1)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 11 Feb 2019 at 12:38pm
I agree about Nichicon audio electrolytics. The Fine Gold types are very good if a bit signatured. If the LKS or LKG are as good we would not have a problem. Unfortunatly there is no stock of the 4700uF 100V in either, available from Mouser or Digikey, and no UK supplier does them. This puts us back to using the largest size radials which is 1000uF 100V, which I am doing at present. The sound has been pretty good but it's also about what it sounds like after days of being switched on.

With all electrolytics there is capacitance vs frequency stability, which means that a 100uF 100V at 100Hz is 95uF 100V at 10kHz. This being far worse for lower voltage ratings. The effect of this value difference is quite subtle but it is heard as a sound changing distortion especially with low voltage electrolytics. The thing is that such distortion cannot be measured because THD uses single frequency sine waves and even on a sweep it has to be slow enough for the analyser null-out to keep up. Intermodulation distortion measurements cannot read it either. So we have a situation where analogue measurements have not progressed in years, and therefore any new distortions heard are not believed - if it cannot be measured they cannot exist!

But they bloody-well do!!!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote musicdude Quote  Post ReplyReply Direct Link To This Post Posted: 11 Feb 2019 at 3:55pm
It's a shame, also here in the US they both don't stock the 4700uF 100V in either KG or KS. Cry   You can only trust the measurement equipment to a certain degree but the ear is the best equipment. They pick up the slightest change.                      
It's funny you would mention the FG series. I used them to replace some blackgates in my Yamaha M-80. I wasn't 100% satisfied with the FG, something was not right... After half a year I replaced them with KZ series. After a burn in of 3!!! months the sound became just right to my ears! Everything sounds now just right! Thumbs Up


Edited by musicdude - 13 Feb 2019 at 1:46am
Andy

ProJect Xtension 10 with Clearaudio Charisma V2, Reflex M, Majestic DAC, CuSat50, modified Kenwood DP-8020, Yamaha M-80, Revel F-52.
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