GC passive pre-amp dissapointment

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Jump to Latest
F

filholder

Member
Joined 2005
Hi Nuuk,

Wall papering eh, there is another skill i have yet to master.
You say 10 uf, is 100 uf too much ? I dont really want to put in another order to farnell (and most maplin electorlytics seems rubbish)and all i have are film caps up too about 1.0uf and these duorex ii electrolitic which are 100 and 1000 uf.

No good?
 
P

postpunk

Member
Joined 2004
Nuuk; Since I have already revealed myself as a illiterate moron, would you please tell me if there is a reason not to use bc547 for all three transistors in the buffer circuit? :)

Edit: any other reason than the sound, I mean. I have trouble finding those other types mentioned on your site.
 
Nuuk

Nuuk

Member
Joined 2003
decdun.me.uk
Nuuk; Since I have already revealed myself as a illiterate moron, would you please tell me if there is a reason not to use bc547 for all three transistors in the buffer circuit?
Click to expand...

Always glad to help a moron or two! :D

To answer your question, no it doesn't matter too much. You can use almost any type of NPN transistor so all three being BC547's doesn't matter. You would of course want to use the same transistors for each channel! ;)
 
Nuuk

Nuuk

Member
Joined 2003
decdun.me.uk
Edit2: I have built it with only bc547, and I find that the treble is a bit sharp (could be my linn helix speakers, though). Is it possible that this can be helped by substitution of Q2 to ZTX 653?
Click to expand...

I'm not too sure to be honest. But didn't Shoog say that he adjusted the tone of the buffer by changing one of the resistor values? Have a search and see if you can find his post. ;)
 
dsavitsk

dsavitsk

diyAudio Member
Joined 2005
diyaudio.ecp.cc
Upupa Epops said:
" Warmth of carbon resistors, sterility of metal ones " - all is about distortion, guys :D and at any music you can't find it prescribed :cool: .
Click to expand...

I am not one to care at all about distortion measurments. If it sounds good, it is good. Reality has no bearing on my judgment.


Nuuk said:


We'd better make it clear - are these in series or to ground? :att'n:
Click to expand...

To ground. In theory, these are only useful if there is some impedence from the PS to the buffer. My PS is connected by a 18" umbilical, so putting some caps close to the circuit is helpful. As such, you should use the fastest caps you can. If, however, your PS is very close to the circuit, then this is just adding some caps to the rails which may or may not be a good thing.

-d
 
rabbitz

rabbitz

Member
Joined 2003
Nuuk said:


I'm not too sure to be honest. But didn't Shoog say that he adjusted the tone of the buffer by changing one of the resistor values? Have a search and see if you can find his post. ;)
Click to expand...

It's done by changing the R3 value and here's a quote from Andrew Rothwell.

"Most people will tell you that more bias current is a good thing but I don't think you need to go mad. The 120R resistor sets the bias current. You could go down to maybe 60R for 10mA bias current, or even lower for even more bias current. The limiting factor is the heat dissipation in the transistors."

Hope this helps.

Has anyone ever had a buzz in this buffer either constant or at certain volume settings?
 
Nuuk

Nuuk

Member
Joined 2003
decdun.me.uk
here's a quote from Andrew Rothwell.
Click to expand...

And that's from the horse's mouth (if he'll forgive me calling him a horse!). :D

Has anyone ever had a buzz in this buffer either constant or at certain volume settings?
Click to expand...

No, not a buzz. I get very feint pops when using the stepped attenuator but not bad enough to worry me. Otherwise both my examples of this buffer are dead quiet. ;)
 
dsavitsk

dsavitsk

diyAudio Member
Joined 2005
diyaudio.ecp.cc
The temporary home of my buffered passive pre.

An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.

Inside the case: Kiwame resistors, Kimber Kaps, Wimas on the rails. Vampire 18ga cast copper wire and Cardas jacks.

An externally hosted image should be here but it was not working when we last tested it.

The PS is a modified Welborne PS-1 using an extra BrianGT board for the rectifier.
 
dsavitsk

dsavitsk

diyAudio Member
Joined 2005
diyaudio.ecp.cc
Shoog

Shoog

Member
Joined 2002
Nuuk,
If your running Firefox, does that mean your running a Linux. If so would you care to do me a copy. I've been searching fro weeks for a reasonably prices copy of SuSe 9.2 professional. I really want to dump windows.

I believe I increased the value of R3, but I would have to check. I was using salvaged transistors from switch mode power supplies. With R3 as per the diagram it sounded real harsh. After altering it really mellowed out.
What's with regulating the power supply. IMHO this buffer just don't need it. It has very high PSRR and works quite happlily with about 1000uf on each rail. Tying the rails together with a 0.1uf cap can't hurt though. Requlation seems like overkill bigtime.

Shoog
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Top Bottom