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Bijou All Tube Futterman Headphone Amplifier - Page 72

post #1066 of 3981
8/12/08 at 1:16am
So I performed amphead's grounding mod and it did wonders to eliminate half the noise. Also this mod seems to have increased the amps sensitivity to source noise. Placebo effect?? donno but it seemed worth mention. The other half of the noise was from a physically audible, loose tranny case, which was also vibrating noise into my right channel 6922 which gets a bit microphonic at max volume with sensitive headphones(earbuds). While all this noise was only audible(to me) on the earbuds and not my k701's, the changes seem to have helped smooth out the choppiness in loud vibrant mids. go figure

Next step will be upgrading bypass caps, any opinions on audiocap theta vs auricap?
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post #1067 of 3981
8/12/08 at 2:00am
Happy to hear that the ground mod has reduced noise with your amp.
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post #1068 of 3981
8/12/08 at 3:04am
i apologize in advance for my newbishness.
which would actually be the bypass caps? what other caps can be replaced with good effect?
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post #1069 of 3981
8/12/08 at 4:12am
C6 on the amp board.
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post #1070 of 3981
8/12/08 at 4:51am
do i have to do anything about c5 since its in parallel with c6?
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post #1071 of 3981
8/12/08 at 5:46am
Quote:
Originally Posted by koike View Post
do i have to do anything about c5 since its in parallel with c6?
To my humble opinion, as long as the electrolytic C5 is in the signal path, it will largely (≥98%) determine/limit the sound quality of the amp, no matter what you use for the bypass cap C6.
The bypass cap C6 is intended to lower the ESR of the electrolytic C5 a bit.
Due to (unpredicted) interactions of the 2 caps (C5 and C6), the sound can be (positively or negatively) influenced, but sound wise you won’t win much!

If you are using high impedance headphone (≥ 300Ω), you can best replace the electrolytic C5 entirely for a MKP film cap (≥ 100µF). C6 can be a high quality (PIO, Teflon, silver mica…) cap or omitted completely.
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post #1072 of 3981
8/12/08 at 4:56pm
gents, if i solder all caps etc to the underside of the board, will i get the boards in a 40mm case (tubes poking out) ?
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post #1073 of 3981
8/12/08 at 5:20pm
doublepost -
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post #1074 of 3981
8/12/08 at 5:24pm
Quote:
Originally Posted by adamus View Post
gents, if i solder all caps etc to the underside of the board, will i get the boards in a 40mm case (tubes poking out) ?
It depends on the caps you use, but I don't see why not. If the default electrolytes don't fit on the board, you could always just off-board them, or find smaller axial ones.

This is, of course for the amplifier board.
The caps used on the PSU are too big, and the heatsink should be mounted on the top.
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post #1075 of 3981
8/12/08 at 5:28pm
cheers, looks like for simplicity i should use the 80mm case.
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post #1076 of 3981
8/12/08 at 6:05pm

output caps

Quote:
Originally Posted by amphead View Post
I have to say that with the K701's, don't go any lower than 460uF for your total output capacitance.
So I purchased those rubycon photocaps off ebay (thanks for the link), and will be running a setup similar to amphead with a 410uf electrolytic, a 1uf bypass cap, and a filler cap to boost my total output capacitance to 460ish. My question is, if you noted a solid increase in SQ going from 410uf to 458uf, is it feasible to believe that the amp stands to gain from increasing the total output capacitance to 470uf, 490uf or 510uf+? (i dont even know if those values are reasonable)

The reason I ask is because parts express(local) offers ruby gold capacitors in values of 47uf, 70uf, and 100uf. They also offer dayton audio metalyzed capacitors in values of 40uf, 50uf, 60uf, 75uf, 90uf, and 100uf.
Edit:Is it okay to use a film cap for my second 47uf+ output cap? I always notice people saying don't use film caps with low ohm headphones (k701's here).
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post #1077 of 3981
8/12/08 at 7:31pm
Film will certainly be better(and large), you can go 47uF or 70uF it will extend very slightly deeper with the latter. I used the caps that I had on hand for that. Edit: one small issue with photoflash caps is that you have to solder on leads to the terminals. And the terminal with knurled top is the negative side.
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post #1078 of 3981
8/12/08 at 7:53pm
cool, thats what I was hoping to hear. I think I'll compromise between the two at 60uf for a stock 471uf. And of course thanks for the heads up. My potentially fried future caps are very grateful : D
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post #1079 of 3981
8/12/08 at 10:51pm
Thread Starter 
Quote:
Originally Posted by adamus View Post
gents, if i solder all caps etc to the underside of the board, will i get the boards in a 40mm case (tubes poking out) ?
You need at least 2 inches (50mm) if you want the caps upright. I think 60mm will give you some breathing room for the necessary spacers etc for safely mounting the board underside..dB
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post #1080 of 3981
8/13/08 at 3:14am
great, thanks for the advice. I am ordering a few cases from modushop.biz. Its either 40mm or 80.
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