GC passive pre-amp dissapointment

[adason]

here is a buffer without capacitor in the signal path
http://home.c2i.net/semfielec/buffer/buffer.htm
ed

 

[dsavitsk]

A couple of notes on Nuuk's buffer:

1) I built mine with all Kiwame carbon resistors. I didn't think much of it at the time, but I recently built another with all Holco and PRP metal films. The metal film version sounds horrible. Unlistenably sterile. The Kiwame's give the circuit a warmth and presence that is missing with metal film resistors.

2) I added 0.22 uF Wimas at the + and - voltage input points and it added a good punch to the bass (fwiw, my PS is a welborne ps1 with the 0.1 film caps replaced by 4.7uF ones).

-d

 

[Nuuk]

I have noted similar changes to the sound when using carbon film resistors with Gainclones! I am just finishing another GC variation at present then I will turn my attention back to the buffer and try those variations myself.

 

[filholder]

Hi Nuuk,

Can i just ask you on your PSU design which out of UAR and LAR are the N and P resistors.

Sorry i trouble you just couldnt work it out last night, but then i had had a drink or two so that isnt saying too much.

Thanks,

Fil

 

[Upupa Epops]

" Warmth of carbon resistors, sterility of metal ones " - all is about distortion, guys and at any music you can't find it prescribed .

 

[Nuuk]

Can i just ask you on your PSU design which out of UAR and LAR are the N and P resistors.

N is the UAR and P is the LAR. My apologies for the confusion and I have now updated the information on DD to make it clearer.

 

[postpunk]

dsavitsk; I just tried, like you described, small caps on the+/- V inputs. I used 1uf low impedance electrolytics. The sound got less hard on my ears Thanks for the idea!

Upupa; Do you think that the buffer is a good design? I asked a Swedish engineer and he thought that it at least SHOULD have low distortion. Thanks for you input, it is much valued.

 

[filholder]

Cheers Nuuk,

Thanks for that.

P.S.
I like the new colour sceme at DD much better now, the old one was a bit vibrant to look at for extended periods!!!

Thanks,

Fil

 

[Nuuk]

2) I added 0.22 uF Wimas at the + and - voltage input points and it added a good punch to the bass (fwiw, my PS is a welborne ps1 with the 0.1 film caps replaced by 4.7uF ones).

We'd better make it clear - are these in series or to ground?

 

[Nuuk]

I like the new colour sceme at DD much better now, the old one was a bit vibrant to look at for extended periods!!!

I always aim to please Fil. And of course I have to cater for those of you who like a drink or two while viewing the site.

 

[postpunk]

Nuuk; mine, at least, are connected to ground.

 

[Upupa Epops]

To postpunk : Good designed buffer with ultralow distortion is good thing. If have high input and low output impedance, you can find many applications, where you can use it.

 

[postpunk]

Upupa; Yeah, but how do you like the design of this particular buffer with the discrete regulators?

 

[postpunk]

Adding small value capacitors after the discrete regulators.. why does that make the amp sound audible different? Can that be, from a technical point of view?

Perhaps I have made a mistake somewhere?

I mean, if hearable differences arise from such a small(?) change, there must be distortion involved?

This distortion issue worries me. If I had an oscilloscope, would it be easy to measure if there are big differences after adding caps and such? I can't say that I dare to trust my ears.

 

[filholder]

Hi Nuuk,

Having nearly finished the main board of your PSU design i am about to start building the second stages of regulation. I am going for the simpler repeat design but will probablyt go with twin second stages ie one for each channel. You talk about adding some capacitance on this second psu but dont really say where. Would it be before or after the regulators or both. And should these be bypassed as well?

So for the constant questions, i really am very new to all this.

Thanks very much for all yours help,

Phil

 

[postpunk]

I am not Nuuk, but the caps should be added before the second regulators. I think that Nuuk (?) would have bypassed them, that seems to be common practice.
Edit: OTH he does not write on the page about bypassing them. It is probably unnecessary to do that before a regulator.

 

[filholder]

Hi postpunk,

Thanks, what sort of values should i use? I have got lots of duorexii 100uf and some 1000uf as well would these be any good. Also what value of bypass 1.0uf then 0.1uf sound any good. And like you said all this is before the regulator and nothing after is that right?

fil

 

[postpunk]

Of your available values I think that you should use 1000uf before the regulators, and use the 1uf and 0.1uf after the regulators, like in the first stage.
Sorry I was not clear, don´t bypass the electrolytics before the regulator, after the regulator you put the filmcaps 1uf, 0.1uf. Like in the first stage.

 

[filholder]

Ok so no bypass caps.
Fair enough.

edit.

Ok that sounds fine. Thanks for the help.

Cheers,

Fil

 

[Nuuk]

Sorry for the delay in replying - I have been wall-papering and completing my discrete regulated IGC! (Don't tell Carlos )

10uF is plenty to put on the inputs of the second regulator stage(s). That is 10uF from rail to ground and no need to bypass them IMHO.