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Bijou All Tube Futterman Headphone Amplifier - Page 103

post #1531 of 3981
10/8/08 at 12:23am
Quote:
Originally Posted by chobint View Post
As always not 100% here but, it looks like a grounding loop at your RCA's. They appear to be grounded to both starG and thru the input board. And all the noise from the starquad shield could potentially be going thru your input ground, which can cause some bad noise from my experience. I think (?) its always best if shielding is separately grounded to starG.
i tried this. hum is louder, again starts at 1/2 volume, but now lasts all the way to full clockwise.
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post #1532 of 3981
10/8/08 at 1:11am
Quote:
Originally Posted by chobint View Post
As always not 100% here but, it looks like a grounding loop at your RCA's. They appear to be grounded to both starG and thru the input board. And all the noise from the starquad shield could potentially be going thru your input ground, which can cause some bad noise from my experience. I think (?) its always best if shielding is separately grounded to starG.
I second this. The green wire from the RCAs to the star ground shouldn't be there. And it should not connect the L and R together.

JR
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post #1533 of 3981
10/8/08 at 2:11am
It may take quite a bit of experimentation Fishski13. It sometimes becomes the challenge you fight for quite awhile. Try to enjoy the process of fixing it, and it will be worth the time spent. I kept trying/experimenting until the noise was gone.

Pabbi, I have installed 2 of the amp boards, but I have to back-up one step on the attenuators. The key hole isn't securing the right attenuator from rotating. I may have to mount them with the attenuators mounted at 90 degrees/left rotated. There was a pre-existing hole that ended up causing trouble for the attenuators key(the post that holds it at 0 degrees). If mounting at 90 degrees is OK with you, that would solve the problem. Edit: it would only change the look from the inside of the amp and would function just fine.
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post #1534 of 3981
10/8/08 at 4:34am
am i correct ina ssuming that if i've shorted Input to Input Ground with the pot connections intact, my noise issue is from pot and/or pre-pot?

my ground loop breaker is 10R 5Watt in parallel with a 0.1 uF cap inserted between IEC ground to star ground. should i try to place the ground loop breaker between both L/R Input star ground connections to actual star ground, or from the PS star ground to actual star ground?

i will investigate my pot wiring tomorrow.

thanks.
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post #1535 of 3981
10/8/08 at 9:20am
update...as i said before, the buzzing got worse after re-wiring correctly. this was with the interconnects from my DAC1 inserted, but the DAC1 was turned off. i just turned it on this morning and the buzz is the quietest i've heard yet, but now the pot has some faint noise, crackling, but only when the pot is rotated.

i will also try moving the star ground position, and maybe try adding some aluminum mass. it's currently on one of the alodined internal dividers. i also reflowed all ground crimps when doing the rewire last evening.

[IMG][/IMG]
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post #1536 of 3981
10/8/08 at 10:01am
Quote:
Originally Posted by amphead View Post
Pabbi, I have installed 2 of the amp boards, but I have to back-up one step on the attenuators. The key hole isn't securing the right attenuator from rotating. I may have to mount them with the attenuators mounted at 90 degrees/left rotated. There was a pre-existing hole that ended up causing trouble for the attenuators key(the post that holds it at 0 degrees). If mounting at 90 degrees is OK with you, that would solve the problem. Edit: it would only change the look from the inside of the amp and would function just fine.
Way fine by me - substance over form, always.
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post #1537 of 3981
10/8/08 at 4:49pm
as always, disclaimer I'm not a pro at this but, do you mean to say that the noise occurs from pot travel? or from when the volume is turned up? if it's dead silent besides during pot travel then you're looking good amp wise, and a new pot *should* fix it.
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post #1538 of 3981
10/8/08 at 9:33pm

Regal's mod completed

I've just completed Regal's mod and everything is working ok. The sound is noticeably improved with both the 6N1P's and the 6H30's. I did learn a valuable lesson though... when I was adjusting the trim pot on the PS, I must have leaned a little too close to the heatsink with the screwdriver as I got a huge spark (I'm reasonably sure I didn't actually touch it). Fried the mosfets and smoked R4. Luckily, I had spares. I wrapped my screwdriver with electrical tape to avoid a reoccurance.

What a difference with the 6H30's. Much, much improved.
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post #1539 of 3981
10/8/08 at 10:00pm
Thread Starter 
Quote:
Originally Posted by huskydawg9 View Post
I wrapped my screwdriver with electrical tape to avoid a reoccurance.

May I suggest isolating the heatsink instead ..dB
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post #1540 of 3981
10/8/08 at 10:24pm
Quote:
Originally Posted by dBel84 View Post
May I suggest isolating the heatsink instead ..dB
Actually the heatsink is isolated. I'm not sure where the spark came from as I only heard it.
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post #1541 of 3981
10/9/08 at 12:18am
Quote:
Originally Posted by fishski13 View Post
am i correct ina ssuming that if i've shorted Input to Input Ground with the pot connections intact, my noise issue is from pot and/or pre-pot?

my ground loop breaker is 10R 5Watt in parallel with a 0.1 uF cap inserted between IEC ground to star ground. should i try to place the ground loop breaker between both L/R Input star ground connections to actual star ground, or from the PS star ground to actual star ground?

i will investigate my pot wiring tomorrow.

thanks.
Yes, I would say that the first conclusion would be that the noise is pre-pot or in the pot. But this is not always true because shorting the input completely shorts the the pot to ground. If there is noise generated at the pot this can also short out that noise.

I would suggest trying another pot as cheap and dirty as you can just for the test.
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post #1542 of 3981
10/9/08 at 2:18am
chobint, Alex, and amphead,
thanks guys.

the "hum" and "crackle/scratchy" are 2 different issues, and the act of me touching the volume knob has no effect on their quality or quantity.

scratchy when wiper is moving, but this noise disappears when the wiper is stationary.

the hum is a "zzzzz" sounding buzz that occurs now at about 3 o'clock and disappears at 4 o'clock. i took out my SPL meter - the buzz "pegs" the needle at 51 dB - so, very quiet.

the gain of Bijou is a bit high for my tastes when driving the K701 w/o NFB. with the higher Z HD650, gain is fine. i tend to ride the volume a bit, and like to have a bit of travel on the volume knob to get the perfect volume - so i've opted for a single 4 deck balanced TKD pot. having 2 stereo pots to fiddle with may drive me crazy with the K701.

just ordered another set of boards from Jeff for a balanced Bijou. the Bijou is a phenomenal music maker - the best i've heard.
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post #1543 of 3981
10/9/08 at 4:08am
another couple of questions:
if driving balanced, the increased voltage gain results in a doubling of gain seen by the headphones? so...if the gain is a bit on the high side for me already now, unbalanced, should i instead go with a 4-deck balanced attenuator (vs. TKD pot), where i can tailor the attenuation curve for the increased gain by running balanced?

or is there an easier way by reducing gain from the amplifying stages, without sonic detriment?
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post #1544 of 3981
10/9/08 at 7:29am
Fishski13, that is probably better answered by Runeight. However, from listening to Pabbi's amp which has the equivalent of a 4-gang attenuator. The HD650's high impedance tames the higher gain very well, and it sounds beautiful.

Pabbi, time for some pics. I need to mount 2 more amp boards and then wiring begins.........

Top view.


Front view:
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post #1545 of 3981
10/9/08 at 2:16pm
its maaaahoooosive.

looks a cracking job so far though amphead.
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