GC passive pre-amp dissapointment

[dsavitsk]

Someone asked if there was buzz in any other ppl's buffers at any volume setting, and yes, I have a buzz when my volume is at the lowest setting. I had this problem with the 50k pot too.

Try a resistor in series with the input (after the pot.) Something in the range of 470R to 1K should work to eliminate the noise. Quality counts here, b/t/w. I have had good luck with both Kiwame and PRP resistors in this spot.

-d

 

[Upupa Epops]

Buzzing by minimal volume setting ? Something is wrong designed, active circuits or grounding.

 

[Shoog]

Hi there,
I wouldn't sware to the fact that I increased the restance value. I am running mine with +/-18V rails. The transistors are a mix from PC power supplies (matched between buffers).
Its all so long ago now I don't remember the details and I don't want to poke around the case.

Shoog

 

[carlosfm]

Buzzing by minimal volume setting ? Something is wrong designed, active circuits or grounding.

Indeed, looks like bad grounding layout.

 

[postpunk]

dsavitsk; I did as you said, 470r in series after the pot, and the buzz is gone Thanks for the help

 

[postpunk]

Upupa, Carlos ; Let me explain this buzz.. When I turned the pot fully counter clockwise the buzz came all at once, almost like a bang, and when I then touched the grounded chassis it made difference to the tonality of the buzz. But if I turned the pot up by only 1mm, it got as silent as umm... silence. I don´t understand why, but with the 470r resistor it is ok.

 

[Upupa Epops]

To postpunk : 470 R connected in series with brush ? Do you have a scope ? Buzzing can have two reasons : ground loop or oscilation of active circuit. Look at first by scope at output of amp, if isn't there ( by buzzing ) hf oscilations. Do you have some internal pics of this preamp ?

 

[filholder]

Here is my build of Nuuks psu.

Been very busy at work finishing a pop video and a series of bog roll adverts so not nearly enough time of late to get on with the serious matter of building my buffer.

 

[filholder]

And this is the current state of the Buffer board. It currently has the second stage of rectification for one channel and i am about to do the same for the other channel.

Hopefully all be together by the weekend but lots of deadlines at work might mean it gets put back.

fil

 

[Nuuk]

Here is my build of Nuuks psu.

Good work so far Fil. Nice and neat! I must redo mine sometime. When you keep changing/adding parts, it gets a little untidy.

My next job though is the 'delayed' start for the buffer output.

 

[Upupa Epops]

To Nuuk : If you can " delay ", send me a mail .

 

[dsavitsk]

To postpunk : 470 R connected in series with brush ? Do you have a scope ? Buzzing can have two reasons : ground loop or oscilation of active circuit. Look at first by scope at output of amp, if isn't there ( by buzzing ) hf oscilations. Do you have some internal pics of this preamp ?

What I was told is that when the pot is set to full-minimum position, it shorts out R2 and this affects the bias voltage for Q2 which causes the noise.

 

[Nuuk]

To Nuuk : If you can " delay ", send me a mail

OK Upupa! I am going to be trying the method discussed here . (Still waiting for the parts from Farnell)

 

[Upupa Epops]

Your circuit have delayed switch on, but haven't immediate switch off ( reset ) after mains switch off. It is not good. I have better circuit .

 

[Nuuk]

Upupa, the parts have just arrived so I will try that circuit and see how things are when I switch off. But if you have a 'better' solution, then I would be interested!

 

[filholder]

Hi all,

This thread had been dead for a while i know however i have just finished my Nuuk design psu and buffer. Havent had chance yet due to work to actually listen to it, 70hrs per weeks at the moment unfortunately.

I have also got a new 10k log alps pot to stick in so there is a way to go.

One thing i was wondering was wether the resistors ihave built it with are 1/8 watt 1% metal film. Are these too low power?
Also one channel is gving about 15.15 -/+ and the oterh 14.85 +/- will this level of difference be audible and how would i get around it. Will i need to change the resistor on the regs or should i use apot?

Any advice greatfully recieved.

Fil

 

[Nuuk]

One thing i was wondering was wether the resistors ihave built it with are 1/8 watt 1% metal film. Are these too low power?

They're fine Fil.

Also one channel is gving about 15.15 -/+ and the oterh 14.85 +/- will this level of difference be audible and how would i get around it. Will i need to change the resistor on the regs or should i use apot?

No problem at all!

Now steady on - 70 hours a week is a bit excessive isn't it? When will you ever have time for listening? I hope at least you are being paid enough to pay for the resistors!

 

[filholder]

Thanks Nuuk,

lol

Needed some reassurance, and thank you for your concern but yeah when i finally am allowed a night/day off i have usually scrapped enough together for my pick n mix in Maplin.

 

[filholder]

Here are the latest pics of my 'Nuuk' buffer for my LM3886 power monoblocks. As yet work has kept me from actually hearing the results but maybe on the weekend i will get a chance.

fil

 

[filholder]

and here is the P2P wiring