subjective impressions of transistors for pre-amp

[kye]

Hi All!

I have been using a passive pre-amp for some time now, and it has some 'interesting' passive circuitry in it as well (caps resistors), so i'm now looking at buffering it by putting in an active stage.

I don't really need much gain (perhaps none and at most a few dB) and am looking at starting with an emitter-follower circuit to kick things off.

the question is, what transistor to use? I could buy every transistor ever made and implement all of them and pick the one I like, but I figure people may be able to make some recommendations..

so, anyone want to recommend some transistors/fets for a single-stage line-level low-gain circuit that you have used and liked the sound of?

thanks in advance..

Kye.

[janneman]

I think your question is too general. What is your source (impedance), what do you want to drive? Do you have a power supply voltage set or is that open?

Do you expect an audible difference between transistors in a well-designed preamp (Well designed as in: " isolate the result from the component non-linearities" )?

Jan Didden

[rabbitz]

Have a look at this buffer and I played with it some time ago and still have to complete it.

Extremely nice sounding which was better than all the op amp pre's I tried (OPA2134, OPA627, AD843). I used the BC546 as that's what I had. You can tweak R3 by going lower than the 120R down to about 60R.

[CBS240]

Hi Kye

Do a search in this forum for "diamond buffer"

[kye]

hi jan,

the source impedance is a CD player (Marantz cd67mkII SE - can't find any specs on it) so probably a reasonably normal load, and the load would be a filter network that i'll try and make to be a larger impedance but may be smaller at some freqs (perhaps down to 1k? if I use a few 10k resistors to ground in it)..

I'm not sure what kind of differences are possible or likely from individual components, although I am aware there are differences between things that "measure the same", which is why I asked specifically for subjective impressions.

I am hoping someone will come on and say "I tried the same circuit with 50 different bipolars and my impressions were that..." and I could benefit from their experience..
I see at this page here (about half way down) there are comments on how different bipolars sounded in the same circuit, but i've not heard people compare jfet circuits or seen this kind of comparison anywhere else.

i'm kinda new to the whole thing of circuit design (which i'll also be playing with) so just trying to see what knowledge was around..

Kye.

[kye]

Hi Rabbitz..

that's the same pages I got my initial inspiration from!
I have a few BC546s, BC557s, BC639s and BC640s from some Jaycar kits where I fried some components and bought replacements so i'll probably start with them.. my dad (pure engineering background) says they're not very good as they have a low beta (Hfe) so won't be as linear as higher beta ones, but since I have them on hand I figure i'll try them.

I was half hoping there would be a strong recommendation towards some magical device with good figures that everyone swears by and uses, although I guess opinion is likely to be quite diverse.

I wonder what types are used by the really high-end people like Krell or Musical Fidelity who have the time to try everything on the market and see what they like?

Kye

[CBS240]

Why limit yourself with just a single stage? There really is no perfect linear "ideal" transistor. If there was, SS amp circuits would be quite simple. How 'bout a cascoded jfet differential, driving a common base diff as a VAS, with neg feeback for better liniarity.


On a side note,

Could this circuit work as a preamp? and if not, why? Assuming +V & -V are regulated.

I personally have fallen in love with this jfet from Fairchild because of the small capacitances, high impeadence, and relative linearity, regardless of such small current. I have used them in a prototype pwr amp circuit by multiple cascoding to limit Vds to about 6V, with a topology somewhat similar to this.

http://www.fairchildsemi.com/ds/KS%2FKSK595H.pdf

[hihopes]

I have been using that 3 bjt buffer for some time noe and I am very impressed with it. I have tried quite a lot of different transistors in it and given a fair amount of feedback to NUUK about them. He does not have it all on his site. I am currently driving one of these buffers with another and very pleased with the results.
The sound of the buffer is affected by the different transistors, but I find this a great advantage, because I can "tune" the sound to suit my system. Transistors are so cheap, it is no hardship to buy half a dozen each of a whole bunch of diffrerent types. Once you know the "sound" of each type, you can even "mix and match" if you want to.
The transistors that I have settled on as most suitable for my system at the moment are ZTX1053a. KSP2222a are quite a lot cheaper and sound very similar. (not the ordinary 2222a - the 75v ones!) There are a few others that I have found to be good. If you would like to know more, just say so.
BTW. Whatever you decide to build, start off with a really good power supply, or at least use decent regulation. What you listen to in the end is your power supply modulated by the audio signal.
Cheers,
William

[routhun]

Hi William,

Would you mind posting your 3 bjt buffer schematic? Buffer using 3-BJTs is a simple and seems quite interesting to me.

Thanks,
Routhu

[janneman]

Originally posted by kye
[snip]I am hoping someone will come on and say "I tried the same circuit with 50 different bipolars and my impressions were that..." and I could benefit from their experience..
I see at this page [snip]Kye.

Hi Kye,

I read you, but I always have the logic problem in cases like this. Acknowledging that these things are subjective, there is no link between someone else's impressions and your or mine. In other words, your impressions / preferences may be completely the opposite of someone else's, so the value of someone else's experiences for you is zero.
So, why bother? Built something that can handle the electrical specs like load, freq response, output level, imput impedance etc and enjoy

Jan Didden