Aleph J Schematic

[schultzsch]

no, I use the second version of the schematic above with 6sl7 as amplifier stage and 6sn7 as buffer, with a separate casing psu

 

[Zen Mod]

with 6SL7 you're having way too much gain

not exactly most clever solution , looking from signal leveling point of view - too much attenuating and then too much amplifying

with funny J , all you need is gain of 2-3x , at least I prefer stages like that to purely passive

I also like iterations with just proper buffering , so no gain at all

 

[schultzsch]

you are sayng about pot which lowers the signal and then 1st stage which is amplifing too much?

 

[buzzforb]

Vfet pre.

 

[Zen Mod]

@ Schultzch - yes , exactly

buzz - you have any possible part candidate for that pre ?

anyway - why using part with questionable triodish characteristics not easily available, when you have part which is exactly triodishly triode itself , easily available ?

 

[buzzforb]

Yes
Being difficult?
I actually use beautiful triode 6v6. Waiting for, not really, SUsy 6V6, althought that just might counteract loveliness of triode.

 

[schultzsch]

as source signal I use an experimental board with pcm1794 and 100R i/v resistors (signal taken single ended) as for this the gain it fits pretty well at this moment.
after I finish with the amps I would like to do a dual mono pcm1794dac and active i/v .. any recommandation for i/v?

 

[buzzforb]

D1 or maybe Xformer feeding OPA1632 directly into AJ balanced input.

 

[Zen Mod]

Yes
Being difficult?
I actually use beautiful triode 6v6. Waiting for, not really, SUsy 6V6, althought that just might counteract loveliness of triode.

send me exact schematic you're using now , and I'll give you what you want

you know that it will be bal in bal out , and that will inevitably kill some of second harmonic sweetness

you can gain some of it back , but not entirely

it will help if you give me voltages here and there ( and gain figure , too ), to save me too much looking at graphs

then say what gain figure you want

those things are easypeasy ; what is not easypeasy is when you want DC coupling all the way

 

[Zen Mod]

....Xformer feeding OPA1632 directly into AJ balanced input.

yes

hard to beat

 

[buzzforb]

I may when time comes. Too far in the hole to worry about now. I may not do it and just keep it as part of SE rig. It is the killing of the sweetness that I am not excited about, as that is the reason for it in the first place.
I do have question. I think 6v6 pre has about 15dB of gain. I should only need 10 more, max for Altec rig, correct.

 

[Zen Mod]

and the question is ?

 

[schultzsch]

removed C3 from the game just from curiosity
for the quiet nights I`m thinkinig to use a switch and a 2x10cm wire to interrupt C3R24 network.would there be any sound degrading or possible oscillation apearance? from the wire/switch part

 

[Zen Mod]

instead of switching out/in of C3 , proper SE operation can be with switch across R20-R23 group

that way - there is no more CCS modulation and these resistors are no more in series with speaker output

 

[schultzsch]

and C3 remains connected?

 

[Zen Mod]

yup

 

[schultzsch]

wil try
btw managed to mount that timmer, you gave me the schematic for , in the tube preamp and works nice, now I turn on confidently my amps

 

[Zen Mod]

 

[francolargo]

r27 as a pot to jack up the bias. more bias makes it sound better. but adds heat.

OK! My plain A-J boards check out, which is a relief! I tested a SE signal into each side of each board using a junk speaker and first impressions are favorable. One side measured 8.73 V across R8 rather than 8.3... That board seems to have a bit more gain and a little less control than the one that measures 8.3... Thoughts?

So, I'm planning to remove R27 and install multi-turn trimmer pots. Question: does increasing the resistance at R27 increase or decrease the bias?

TIA,

Frank

 

[francolargo]

Answer to my own question: I don't have much thermal headroom to raise the bias anyway, so the R27 pots are sitting at 64k. With that amount of current, the temperature rise is ~32 degrees above ambient with silent airflow, 27 degrees with the fan 'barely noticeable', and 24-25 degrees with the fan at full speed of 1200rpm. If you are curious, images are the air tunnel, the front panel fan control with thermal readout, and the profile of the air exhaust. The power supplies have 75 degree thermal cutoff switches on the heatsinks.

Cheers,

Frank