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Old 20th August 2004, 10:55 AM   #1
Klaus is offline Klaus  Germany
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Default coupling cap in Aleph Amp

Hi guys,

and the tweak goes on… Finally I have reached the coupling capacitors of the negative input of my DIY Aleph4 mono amp. Sorry, if this issue was handled here before, I did not find it.

The issue: the original pass design uses a 220uF electrolytic cap at the negative input branch. It decouples the output DC offset from the 10k input resistor and so the complete negative input. This cap has no defined polarity and voltage pre-load. This brings the poor polarized electrolytic to sound not optimal. As far as I understand the cap value shall be that big not to change the feedback factor 100k versus 10k at low frequencies. 220uF just have 72Ohms of impedance at 10Hz.

The old trick to make DC-unloaded electrolytics sound good: use two in line electrolytics with inverted polarity and pre load the center pin via a high resistance with a DC, e.g. 12V created by an easy Zener regulator.
BUT: here it does not work too well! The load up current through the 220uF cap flows via the 100k resistor to output ground and creates DC offset voltage of easily some hundreds mV for many ten minutes... I have tested it, the sound was much better, but with 4MOhm and 2 x 220uF the DC offset starts with 150mV with a RC-time constant Tau = ca 20min. No go!

So next thoughts: why this 220uF cap? If the cap is out, the 10k and the input branch gets full output DC offset. Is that any problem? The tricky cap pair or a smaller one could be put at very first income position, no problem with loading them. What do you think about this solution?

Of cause, the easiest way would be to use bipolare electrolytics like Black Gate NX in the original Pass design. I will test this in parallel…

Thanks for your comments on!

Regards

Klaus
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Old 20th August 2004, 02:05 PM   #2
Henrik is offline Henrik  Denmark
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Klaus - take a look here
Aleph questions

Regards
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Old 20th August 2004, 07:26 PM   #3
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Perhaps it exists, but I have never seen any credible
demonstration that you need to have an existing polarizing
voltage on an electrolytic that only sees a few millivolts.
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Old 21st August 2004, 12:53 AM   #4
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Off-topic

I'd like to know. Thanks for your responce.
Is the manufactured voltage rating of the electrolytic capacitor indicated with respect to DC only or both DC and AC? Brief reason?
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Old 21st August 2004, 01:46 AM   #5
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The spec is for DC voltage. Ordinarily you look to the
ripple current spec to assess the maximum AC voltage,
and this assumes that the cap is not being significantly
(if at all) operated with a reverse voltage.

The coupling caps you cite might see 1 mA or a few mV on
a bad day, and they can take that until they slowly dry out.
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Old 23rd August 2004, 07:12 AM   #6
Klaus is offline Klaus  Germany
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Hi,

Thanks, Henrik, for the link.

Well, no doubt, any Aleph sounds almost perfect with a normal electrolytic in. But guys who are interested in tweaking and so getting really 100% performance out of any device should just test it. The sound improvement is really remarkable.

I have also tested the version "without any cap", but without stronger adjustments it disturbs the hole well matched circuit. My Aleph block runs from less than 10mV DC up to over 200mV. To compensate this change the bias could be adjusted, but maybe the matched balance would be disturbed. I will not test it.

So I will buy 220uF 6.3V Black Gate NX plus 0.1uF NX bypass. They shall be such a kick. Compared to the total amount of an Aleph amp the 10€will be ok.

Regards

Klaus
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Old 7th September 2004, 12:58 PM   #7
Klaus is offline Klaus  Germany
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Default tests finished, BG wonderland...

Hi,

I have finished my tests on the Aleph amp coupling caps. Here are the experiences for interested guys…

1. 220uF 25V Panasonic FC electrolytic plus 10nF ERO1830 bypass: I have frequently wondered why my fully tweaked Aleph Amp still sounds somewhat soft and a bit coated with a layer of distortions, specially at the heights – this mentioned restrictions in spite of the fact that I love the sound of the Aleph and prefer it to all other solid state amps I know! Well, after this test I understood…

2. test with the "tricky polarized" coupling cap: two times two parallel 220uF FCs antiparallel in line create a over all 220uF cap with middle pin to apply polarization voltage. 10nF bypass, of course. The polarization was done by a well noise free 12V source. BUT: this circuit causes massive DC offset in the aleph circuit for many ten minutes, no go! Just for test issues. But the test results were impressive: the sound is more tight and solid, more transparency and more neutral. Leaner Bass with more punch and crystal clear hights, better focus. And all positive properties of the Aleph remain, they are just enhanced. This would have been the ultimate solution – if the circuit would allow it…

3. 220uF Black gate NX + 0.1uF NX bypass + 10nF bypass: unbelievable! All enhancements from test #2, but even clearer, deeper room, more dynamics. The sound is as clear as with good solid state amps with tons of feedback. But still the lovely Aleph sound remains. I burned the BGs in for 6 day at the FM-tuner noise. BUT, there must be a "but". Like at other tests with BGs at PSU I got this special BG sound character: I would call it "to clear to be true". The sound is hard to the limit of being to cool, artificial, the musicians play at fresh autumn wind in a concrete tunnel without enough warmth. Hopefully the BG will burn in further; otherwise I have to learn to love it…

What are your BG experiences, similar effects? Thanks for feedback.

Regards

Klaus
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Old 7th September 2004, 02:16 PM   #8
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Default Re: tests finished, BG wonderland...

Quote:
Originally posted by Klaus
Hi,

I have finished my tests on the Aleph amp coupling caps. Here are the experiences for interested guys…

1. 220uF 25V Panasonic FC electrolytic plus 10nF ERO1830 bypass: I have frequently wondered why my fully tweaked Aleph Amp still sounds somewhat soft and a bit coated with a layer of distortions, specially at the heights – this mentioned restrictions in spite of the fact that I love the sound of the Aleph and prefer it to all other solid state amps I know! Well, after this test I understood…

2. test with the "tricky polarized" coupling cap: two times two parallel 220uF FCs antiparallel in line create a over all 220uF cap with middle pin to apply polarization voltage. 10nF bypass, of course. The polarization was done by a well noise free 12V source. BUT: this circuit causes massive DC offset in the aleph circuit for many ten minutes, no go! Just for test issues. But the test results were impressive: the sound is more tight and solid, more transparency and more neutral. Leaner Bass with more punch and crystal clear hights, better focus. And all positive properties of the Aleph remain, they are just enhanced. This would have been the ultimate solution – if the circuit would allow it…

3. 220uF Black gate NX + 0.1uF NX bypass + 10nF bypass: unbelievable! All enhancements from test #2, but even clearer, deeper room, more dynamics. The sound is as clear as with good solid state amps with tons of feedback. But still the lovely Aleph sound remains. I burned the BGs in for 6 day at the FM-tuner noise. BUT, there must be a "but". Like at other tests with BGs at PSU I got this special BG sound character: I would call it "to clear to be true". The sound is hard to the limit of being to cool, artificial, the musicians play at fresh autumn wind in a concrete tunnel without enough warmth. Hopefully the BG will burn in further; otherwise I have to learn to love it…

What are your BG experiences, similar effects? Thanks for feedback.

Regards

Klaus
Klaus ,

Check out this link

http://www.blackgate.jp/english.htm

Try running the BG's back to back as per this article .

Failing that, upgrade the Aleph to X Aleph...all the fuzz will disappear.

macka
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Old 7th September 2004, 02:18 PM   #9
lucpes is offline lucpes  Romania
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Default Re: tests finished, BG wonderland...

Quote:
Originally posted by Klaus
220uF Black gate NX + 0.1uF NX bypass + 10nF bypass: unbelievable! All enhancements from test #2, but even clearer, deeper room, more dynamics. The sound is as clear as with good solid state amps with tons of feedback. But still the lovely Aleph sound remains. I burned the BGs in for 6 day at the FM-tuner noise. BUT, there must be a "but". Like at other tests with BGs at PSU I got this special BG sound character: I would call it "to clear to be true". The sound is hard to the limit of being to cool, artificial, the musicians play at fresh autumn wind in a concrete tunnel without enough warmth. Hopefully the BG will burn in further; otherwise I have to learn to love it…
Remove the 10nF ERO cap, the black gates are good enough in this position and a bypass might do more worse (read constricted, soft, artificial sound). Try only the 220uf BG for a couple of days then add the 0.1uf NX to see if it improves over the single cap.
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Old 7th September 2004, 03:53 PM   #10
Klaus is offline Klaus  Germany
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Hi again,

@ macka: thanks for back to back hint, but it means two BGs per block… I will check the Aleph x soon!

" Remove the 10nF ERO cap, the black gates are good enough in this position and a bypass might do more worse (read constricted, soft, artificial sound). Try only the 220uf BG for a couple of days then add the 0.1uf NX to see if it improves over the single cap."

I have not described it in detail, not to bore you. I checked in detail how the sound improvements of the BGs are created, step by step with hours of listening not to get lost. First I tested the 220uF BG without anything. Good… Then the NX0.1 bypass came in – much better, but to cool… The small 10nF bypass improves the scenario much without any negative influence. They clean up last effects and give stronger and more neutral coloration. This special type of small low voltage (63V AC/100V DC) polypropylene caps with ultra low inductance seem to be the only thing which can really do so. I can not imagine that the 0.1NX can "clean" that perfect HF effects. I use this 10nF caps everywhere, at PSU, at speaker cross over and at coupling caps. The improvements are everywhere the same, the character as well.

Regards

Klaus
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