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Bijou All Tube Futterman Headphone Amplifier - Page 67

post #991 of 3981
8/1/08 at 7:47pm
Quote:
Originally Posted by regal View Post
I think I saw a few questions about a mod to run the 6N1P at 5 ma like I did with the 6DJ8. This really isn't a good configuration for the 6N1P on this amp. At 5 mA and 100V a-k the 6N1P would need less than 0.5V cathode bias. This would lead to clipping in all but the most sensitive headphones.
Right. Will not work. 6N1P is not a direct sub for 6922, although it is often claimed to be. It wants to run at much higher voltage, hence the bias issue here.
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post #992 of 3981
8/1/08 at 8:09pm
I have my fingers and toes crossed for good sound from your amp running each side single ended Pabbi. If that works out, then getting it set-up in balanced config. should come soon after.
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post #993 of 3981
8/2/08 at 1:04am
Not sure whether to be happy or sad... or neither..

In checking, all the amps have output to some smaller portable headphones - maybe I need to rerun the tests with the Senns, just to make sure it wasn't just the source driving the phones.

I decided to pull all the SE (TRS pin) wiring to isolate balanced first (fewer wires for sure), as this is (only) how I intend to use this amp - SE was for meets just for SE only phones. Sod all that.

The results were mystifying -

Left channel: Back board: Pin 2, signal, Pin 3 no signal (output wired to pin 3)
Front board: Pin 3 signal, Pin 2 signal (output wired to pin 2)
*** May check this again - non-sensical.

Right channel: Back board: Pin 2, no, Pin 3, yes (output wired to pin 3
Front board: pin 2, yes, Pin 3, no (output wired to pin 2)

I was very careful to run Pin 2 with white from input to final output, and Pin 3 with red all the way, just to avoid mixing phase.

No difference.

Maybe a bad Neutrik? I do have another set to try - tomorrow.
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post #994 of 3981
8/2/08 at 1:34am
I wouldn't think that this is a faulty Neutrik, but wiring is high on the list. The reason for doing single-ended tests, would not be for the final configuration, but it would indicate if on-board components and solder joints for the amplifier boards are working. I realize what a messy thing it is to have wiring for SE and balanced at the same time.
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post #995 of 3981
8/2/08 at 1:51am
I'm inclined to agree with amphead about the jacks.

Assuming that the nonsensical thing is just a wiring mistake, this test seems to say that all boards are amplifying. Is that correct? If so, do you get a reasonable amount of power from each board? You should be able to drive the headphones to loud levels from each board. Yes? No?
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post #996 of 3981
8/2/08 at 2:54am
Yes, I was getting loud levels from each amp, but through some crappier phones. I'll rerun tomorrow through the 650 just to make sure the output is much louder than what I experience through the jacks. I agree on wiring, but I might have another look at the output terminals - could NOT having the NFB or using just a two position connector on the NFB terminal have any effect?
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post #997 of 3981
8/2/08 at 3:21am
No, when NFB is removed, the amplifier will run louder and usually noisier(without heater mod). It does however, have more detail which is why I think that I prefer the amp without it. I will be doing another test to find out later. If you have an unacceptable amount of buzz or hum and your heater wires are tightly twisted, try the heater mod. Edit: My amp sounds very good and the only component change that could improve it, would be better input tubes than the 6DJ8 national "made in USSR". I would want to keep the bias the same and find better input tubes. Trying the 6n6p as input tubes again, produced lower volume overall, some distortion on loud vocals/horns etc. , they are definitely suited for output tubes only.
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post #998 of 3981
8/2/08 at 9:31pm
woot home at last. So I've almost got my amp dead quiet. I replaced my blown up C7, grounded the case, nfb/volume pots....and moved my amp away from my surge strip which was the reason for the deafening buzz lol. So now I've hooked up my magic wand (long grounded piece of aluminum) which I waved around the case and wiring to diagnose areas of high EMF interference. As expected the input/output wires which are still uncased since I havent drilled the front plate yet, got quieter when I waved the wand over them. So I expect once those wires are inside the case that will be solved.

BUT...heres the wierd part. As is, the buzz level is noticeable but relatively quiet at full volume with minimum nfb, and becomes hardly noticeable somewhere between 3/4 and 7/8 volume with minimum nfb. BUT...when both pots are grounded and I touch the one of their casings it gets DEAD QUIET. If the pot that I'm touching is ungrounded it gets loud and buzzy, but if its grounded its dead quiet. So...my amp is dead quiet if I sit there and hold one of the pots in my hand lol. Also it was near dead quiet with a dry finger, completely quiet with a wet finger touching it. Any idea what would cause this and/or how to make the effect permanent w/o me touching it all the time.

edit: i only have to touch one to make the setup quiet...doesn't seem to matter which one.
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post #999 of 3981
8/2/08 at 10:41pm
You keep poking a wet finger around in a tube amp, and you'll be
running dead quiet too. (Sorry, couldn't resist).
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post #1000 of 3981
8/2/08 at 10:48pm
lol ya i know, but the other hand was insulated and like i said the input/output wires are outside of the casing away from the boards/power cords.
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post #1001 of 3981
8/3/08 at 12:14am
Amp boards are all fine - quite good (outrageous) output from each into the Senns.

When plugged in via the jacks, with the (100k) attenuators 100% open (99k ohms) it sounds good, albeit faint. No hum. Fully closed is 0k, so the attenuators *seem* to be working, as they do respond in getting louder (relatively speaking) as they are turned up and lower when down.

Sadly, I need to check the Azur (source) again, though I don't have any other (functioning) balanced amps available. In reading Tangent';s troubleshooting from long ago, should I be able to check input signal with a voltmeter?

Back to ground (once again)... the inside of the Nabu is clear annodized - IEC and star are screwed into some standing metal offsets that are tack welded to the sheetmetal - all the stars are touching one another via soldered eyelets, very snugly via the screw pressure. BUTT, I did not grind down to bare metal on the case (through the annodize) - worthwhile?

Again, thanks for your patience.
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post #1002 of 3981
8/3/08 at 12:32am
chobint, that's really good news. The peculiar finger grounding feature might go away what you get everything enclosed.

pabbi1, what happens if you connect the balanced source but take the SE outputs from pins 2 & 3 on the O/P as in the SE test. Do you get signal from the amp boards?
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post #1003 of 3981
8/3/08 at 1:49am
No, it sounds like pass through signal from the source. Same as through the XLR balanced.
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post #1004 of 3981
8/3/08 at 2:04am
so the amps put out a nice healthy signal when fed SE and loaded SE.

but they put out the weak signal when fed balanced but loaded SE?

If so, this means that either the balanced signal is not big enough to drive the amp (hard to believe) or the balanced signal is not ground referenced.

the attenuators should handle the ground referencing. but maybe they are not.

we need to be able to measure the amplitude of the signal at the amp inputs with respect to ground when running in balanced mode. do you have a way to do that?
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post #1005 of 3981
8/3/08 at 2:59am
Quote:
Originally Posted by runeight View Post
so the amps put out a nice healthy signal when fed SE and loaded SE.

but they put out the weak signal when fed balanced but loaded SE?

If so, this means that either the balanced signal is not big enough to drive the amp (hard to believe) or the balanced signal is not ground referenced.

the attenuators should handle the ground referencing. but maybe they are not.
Completely agree. Since these are stereo attenuators , I _tried_ to do this by running the input ground to one channel, tying it to the other, then running seperate input grounds to each amp board. I also tried untying the channels to see if one channel would work - not so much.

Quote:
Originally Posted by runeight View Post
we need to be able to measure the amplitude of the signal at the amp inputs with respect to ground when running in balanced mode. do you have a way to do that?
No, at least not that I am aware. No scope nor access to one that I've found.
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