B1 Buffer Preamp

[AndrewT]

try your passive 50k pot.
If you like what you hear you have saved a lot of time and money.

I would add a buffer to reduce the pot's 12k75 output impedance to something more sensible.

[AlanElsdon]

As suggested by Andrew I am posting this question - I have balanced outputs on my computer sound card and would like to use them into the B1 buffer I will be building - how can this be best achieved?

Andrew suggested two very closely matched B1s which is possible (I will be getting two sets of boards), but I would like to achieve this in one B1 if at all possible.

Alan

[udailey]

you could make a balanced line driver and balanced line receiver. Receiver in front of B1 and driver on the back end unless your amp has RCA inputs in which case you would simply use a balanced line receiver in front of the B1 and no driver, just straight to amp from there.
This way you only need one B1 board, but you would need one receiver for each channel. You can make a stereo BLR with a OPA2134.
Uriah

[rhysh]

Originally posted by AndrewT
try your passive 50k pot.
If you like what you hear you have saved a lot of time and money.

I will do just this. Do you not think there will be problems with interference or HF roll off?

[AndrewT]

Do you not think there will be problems with interference or HF roll off?

I'm absolutely sure it will mess up the frequency response, but you seem intent on using an unbuffered 50k pot.

[woodturner-fran]

Would some 2SK117 work OK in this circuit?

From the manual: ....you can use substitutes having Idss 5-10mA and transconductance numbers from 5-30mSiemens


From the SK117 datasheet: Idss 1.2-14mA and Yfs 15mS


Am I reading that all wrong or should they work?

Fran

[AndrewT]

if you already have them then it's worth trying.
sk170 are renowned for high Yfs, low pinch off voltage and low noise.

[rhysh]

Originally posted by AndrewT
I'm absolutely sure it will mess up the frequency response, but you seem intent on using an unbuffered 50k pot.

Im happy to use a buffer if necessary, but it is another stage in the signal path. I can use a 10K pot if this would help anything?

R

[Braun_]

Originally posted by rhysh



Im happy to use a buffer if necessary, but it is another stage in the signal path. I can use a 10K pot if this would help anything?

R

If you reffer to the potentiometer as the volume control of the Buffer,
I mounted a clone of the Buffer published on Nelson Pass website with 10k pot. For my earings, it work just as fine.

Here some pics...

[rhysh]

I Think i should explain my situation more clear.

Should i use the B1 after my stepped attenuator or not? This is before my preamp. The preamp has no attenation onboard.

Plain and simple