B1 Buffer Preamp

[stefanobilliani]

Originally posted by salas
These are just terminal resistors so to avoid thumps when switching inputs due to the fact that the original single rail B1 has an input capacitor. And you need one for each input. At least I guess so.
Nelson can explain what he got with and without them, I never made the single rail B1.

Yes you need one for each input . I believe they are for avoid parasistic oscillations .

And to comment the udailey post about PS buzzing , I can tell that it comes either from the circuit layout ( wich need a coherent ground plane IMHO ), from Bad contacts at the output , and also from the amp to which the B1 is connected . I mean you could connect batteries at the B1 and still have the buzz.

[udailey]

I just bought a bunch of copperclad FR4 and CEM (whatever that is) from ebay. I will redo the B1 at some point soon, but I will also try batteries and see if it is the supply on the B1. The amp did not buzz before though when I had just some pots attached to the inputs.
Uriah

[AndrewT]

Hi,
your buzz sounds like a signal return or grounding fault.
What precisely did you change when you inserted the B1?

[stefanobilliani]

I very much like this , but cant explain why .

[Skorpio]

Originally posted by stefanobilliani
I very much like this , but cant explain why .

I think your zener will have to be reversed...

[udailey]

Check this out. When I touch the volume pot for the right channel the buzz increases. If I touch the bare lead of ANYTHING on the B1 the buzz increases. However, I, just this morning, turned on only the amp. No B1, no CDP. There was a faint buzz. So, then I turned on the B1 and the buzz immediately increased in volume. Do you think I have a ground loop somewhere or is this probably a buzz in my transformer that is getting into the B1 and being amplified?
Uriah

[udailey]

Andrew,
What I changed: I only put the B1 between the CDP and the Amp connected by RCA cables. I then removed the pots on the amp and now the signal goes into a 1k resistor and then there is a 22k to ground then the input pin of the amp.
I think, now, that there is a buzz/humm somewhere in the amp that somehow gets to the B1 and then gets amplified. The only way I can imagine it getting to the B1 is through the ground so maybe I need a DC blocking cap on the ground coming from the wall. Do you agree that this might help? Maybe I am starting to get OT since it seems like this sound is only amplified by the pots in the B1 because it already existed in the Amp.
Uriah

[stefanobilliani]

Originally posted by Skorpio



I think your zener will have to be reversed...

Ohh yes ! of course

Originally posted by udailey
so maybe I need a DC blocking cap on the ground coming from the wall. Do you agree that this might help? Maybe I am starting to get OT since it seems like this sound is only amplified by the pots in the B1 because it already existed in the Amp.
Uriah

On the wall wart is ok to make the rectifier bridge and a first bank of capacitors . I use 20000 u F . Then inside of the B1 box I used another bank of capacitors plus the voltage regulator .

Remember that the pots of the b1 only attenuate what is at its input . Moreover The B1 almost has not noise , thats why also is convenient to have the pots at the input . Personally I didnt noticed any change in noise varying the position of the pots . So it may be something else .
Check out the ground arrangements.

[04dgmsilv]

I don't think I've seen this question asked in the thread, but I've been reading it over the course of a few days.

Can the B1 be used to drive two sets of outputs? (i.e. main full range amp and a set of subs) Possibly another output be connected at the source-drain connection between QX00 and QX01?

[Professor smith]

nelson pass, what would happen if you put the volume pot after the b1 circuitry?