This resistor is there to provide certain isolation between amp input and outside world. In most cases you don't really need it, and presently, I'm not using such. Even replacing Caddock or Vishay with a short, brings improvement in low level detail and neutrality.
Sometimes using that resistor may equalize some brightness that other GC components may introduce, and in such cases Vishay S102 works quite well as it adds certain smoothness and more body. Caddock, OTOH, seems to be more neutral, preserving same signature of trebles, but it may be somewhat bright.
The value of that resistor is not critical; National suggests 1k, I've been using 220R ( I was probably influenced by Alephs schematics
). But anything between 220R and 1K should be fine. Higher resistor value brings slightly stronger signature, but this is very slight effect.
So, you can remove that resistor, and the circuit should be working fine without it (in most cases at least). You may even notice an improvement.
Sometimes using that resistor may equalize some brightness that other GC components may introduce, and in such cases Vishay S102 works quite well as it adds certain smoothness and more body. Caddock, OTOH, seems to be more neutral, preserving same signature of trebles, but it may be somewhat bright.
The value of that resistor is not critical; National suggests 1k, I've been using 220R ( I was probably influenced by Alephs schematics
). But anything between 220R and 1K should be fine. Higher resistor value brings slightly stronger signature, but this is very slight effect.So, you can remove that resistor, and the circuit should be working fine without it (in most cases at least). You may even notice an improvement.
The reason I asked is because on a preamp I am working on right now I have a small problem with humm and hiss when connected to my GC. Nearly none however when connected to headphones.
The preamp is a opa2228 with 2 buf634s one for each channel.
Well, I put 1K resistors on the outputs of the BUF635s and a 1.75K resistor in sereies with the power ground running from the power supply to my star ground. The helped a lot for the humm, but I am not sure if I am harming the circuit.
The power supply is fed by a 30V wall wort and vortual ground is created with a simple volateg divider with 4.7K resistors.
Could I use even higher values for my isolation resistors, as I still have some humm?
The preamp is a opa2228 with 2 buf634s one for each channel.
Well, I put 1K resistors on the outputs of the BUF635s and a 1.75K resistor in sereies with the power ground running from the power supply to my star ground. The helped a lot for the humm, but I am not sure if I am harming the circuit.
The power supply is fed by a 30V wall wort and vortual ground is created with a simple volateg divider with 4.7K resistors.
Could I use even higher values for my isolation resistors, as I still have some humm?
Banned
Joined 2002
Russ White said:The reason I asked is because on a preamp I am working on right now I have a small problem with humm and hiss when connected to my GC. Nearly none however when connected to headphones.
The preamp is a opa2228 with 2 buf634s one for each channel.
Well, I put 1K resistors on the outputs of the BUF635s and a 1.75K resistor in sereies with the power ground running from the power supply to my star ground. The helped a lot for the humm, but I am not sure if I am harming the circuit.
The power supply is fed by a 30V wall wort and vortual ground is created with a simple volateg divider with 4.7K resistors.
Could I use even higher values for my isolation resistors, as I still have some humm?
I'm Also starting to have Problems with my gain clone's and passive pre-amp When connecting another amp ithe other amps hum useing a active xover it hums too. Disconnecting the gain clone amp and using any other type of amp it works just fine and no hums. What could it be ?
Yes, interestingly my preamp work fine when I connect it to my Adcom and my Denon. the humm/his problem only comes when I connect to my GC. It as if I have a ground loop on the inputs to the GC. But I don't know how I could as the grounding is done on the PCB. I do not have CG connected at all.
BTW I have romoved all resistors from ground and the outputs now. Sounds excellent as a headphone amp, but I really buuilt this premp for my GC, so I am really bummed
BTW I have romoved all resistors from ground and the outputs now. Sounds excellent as a headphone amp, but I really buuilt this premp for my GC, so I am really bummed
Banned
Joined 2002
Solved!!! :d
My preamp sounds awesome now with my GC. I had decoupling caps at the power pins of the OPA2228 but I hadn't thought to put them at the pins of the buffers. I put 0.1uf mylar caps right on the chips between th rails. VOILA!!! No more hiss, no more hummm!!!!
Thanks so much for the help Peter. I shorted R1, and think it does indeed sound better. the highs have much more air now.
Life is good!!
My preamp sounds awesome now with my GC. I had decoupling caps at the power pins of the OPA2228 but I hadn't thought to put them at the pins of the buffers. I put 0.1uf mylar caps right on the chips between th rails. VOILA!!! No more hiss, no more hummm!!!!
Thanks so much for the help Peter. I shorted R1, and think it does indeed sound better. the highs have much more air now.
Life is good!!
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