I am finishig up an Aleph P1.7 preamp, but since I will only be using it for unbalanced sources, I was thinking of eliminating the input caps for the negative input and the output caps for the negative outputs- as both of these will be shorted to ground anyway - just using a short wire as I have seen done in the X2 preamp. Ánybody got any objections to that - please let me hear them
Regards
Hans
Regards
Hans
you can leave out (short) both input caps ( Papa put them probably for Foolproof convenience ) , but you MUST leave in output caps ;
both outputs are on substantial DC potential , before caps .
use your fave poison there , but be sure that you bypass them with at least 1uF of some different poison
both outputs are on substantial DC potential , before caps .
use your fave poison there , but be sure that you bypass them with at least 1uF of some different poison
Bill Fuss said:ZM, could you explain, in your own unique way, why it would be beneficial to AC short the unused output to ground. I can't get my head around the idea.
Bill
say that you're that way not wasting any percent of output amplitude .. meaning that - what's on input - it will be on output
( amplified) ;
if you leave one output (differential ) leg just flapping around , who knows what is happening with all these left-one electrons .... anarchy in the UK ?
shortly - you'll have less output voltage ( and how much less strictly depends of load connected to output ) with that ( neg ) leg flapping around ...
go to Jensen site , there is ton of nice handy pdfs .... and they're certainly better in Engrish than I am
Bill Fuss said:Buhl, there is DC at the gate through the divider Rs on the input, but dont know if it would harm your source or not.
Bill
you're right !!!!
mea culpa , maxima !
seems that I was even more confused than usual .....
buhl - do not short these caps , unless you move both feedback resistors (R48 and R63 , in Papa's original pdf ) from adjacent drains to adjacent preamp outputs ( after output caps ) ........
analog_sa said:But surely he can use lower quality caps for the unused phase with no ill consequencies.
if we are splitting ( as usual ) hair - no ;
if we are practical - certainly !
wise !
Bill Fuss said:
... why it would be beneficial to AC short the unused output to ground.
This will also help.
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Babowana said:This will also help.
Aleph P has SuSy topology?
Bill Fuss said:I was wondering about that post from NP also. I started searching threads to no avail and got sidetracked. I think that post was from an X preamp discussion. Someone please enlighten us.
Bill
almost SUSY , but not completelly - due to common source degeneration of input differential ;
if you decrease R51 and R66 to few ohms ( up to 10 ) , connect just one - lower - CCS ( with doubled current comparing to previous situation ) to middle point between them ( off course - deleting trimpot ....... ) , you'll have fully functional SUSY center of universe
then - just set adequate gain of circ with values of R48/R5 and R63/R6 - for left and right side , respectively
Thanks for the all the replys guys! - I knew that there would be DC fed back from the feedback resistor, and I would defenetly keep the input cap
But back to my original question, I am not sure that everybody noticed that I will be running strictly unbalanced? They reason is that I saw that the balanced input circuit from the X2 (which I am not happy to post due to the IP of Nelson) only uses the positive output and leaves the drain of the negative side just hang (connected to positive supply).
I guess I will go for the all cap everywhere - better safe than sorry!
Regards
Hans
But back to my original question, I am not sure that everybody noticed that I will be running strictly unbalanced? They reason is that I saw that the balanced input circuit from the X2 (which I am not happy to post due to the IP of Nelson) only uses the positive output and leaves the drain of the negative side just hang (connected to positive supply).
I guess I will go for the all cap everywhere - better safe than sorry!
Regards
Hans
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