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tomcat 5th June 2002 10:11 PM

sound quality of different transistors?
Hi all,

I'm curious if anyone has quantified the differences in sound quality between devices, small signal and output? There has been a lot of work done over the years on the differences between tubes; ie 2A3/300B, 12AX7/12AT7, etc, but not much in the solid state field as far as I know and my cursory search of the net has found apart from some obscure mention here and there.

This question crossed my mind after the huge difference I noticed replacing the ouput devices in my Digi-125 amp with the Toshiba 2SC5200/2SA1943 used in the AKSA amp.
At the time I was emboldened by the success of this experiment enough to consider replacing the small signal devices with MJ15030/1531's but in the end I decided on Toshiba's 2SC4793/2SA1832 which were alittle closer in Hfe/fT to the original BC546/556 devices.

After a lot of fiddling around removing/replacing the devices I plugged the amp back in and sat back for a listen. To my utter dismay and disapointment the music now sounded flat and totally uninvolving. Quickly I pulled the amp apart and reinstalled the original small signal devices, took about half hour and bingo the music was back again!

Obviously the small signal devices were responsible for this remarkable and very obvious change for there was nothing subtle about it...

Anyone have similar experiences/comments/opinions they would like to share?


JonMarsh 5th June 2002 11:06 PM

You might stop and think a little bit about the difference between the contribution of the circuit as well as the transistor. Also, ponder the concept of "voicing". I don't think you'd expect to take a speaker, replace one tweeter with a different tweeter, and expect only an improvement in the sound. The tweeter's performance in a given speaker must be "voiced" to the speaker, including the characterisitcs of the tweeter (impedance, frequency response, dispersion, etc), as well as the designer's goal for the speaker.

A well designed circuit is built around the performance and the characteristics of the parts used- regardless of the merits of one transistor or another, if you modify a circuit with a different device, and the cicrcuit wasn't designed around that device, you'll probably get different, or rather, indifferent results, regardless of the relative tradeoffs and quality merits of the devices.



Pete Fleming 5th June 2002 11:38 PM

Tomcat, have you tried doing a search on this topic? Yes I believe the different devices make a huge difference to the sound produced. Good on you for giving it a go and remaining objective enough to realise that just because you went to the effort of changing something it was going to sound better.

Aud_Mot 6th June 2002 03:11 AM

I have wondered the same thing. There has always been plenty of discussion about XYZ brand caps sounding better than ABC brand caps.

I have never heard of any body "auditioning" brand ABC of bi-polar transistors against brand XYZ bi-polar.

Nelson Pass has, on more than one occasion, said he doesn't understand Audio Amature's neurosis about cap types, when "active devices introduce much more distortion."

tomcat: Did you allow for any break in or warm up period for your new components? Maybe that is an interesting idea for a project. A transistor burn in / tester / stresser.



alfsch 6th June 2002 11:11 AM

I tried different transistors on a standard-design power amp:
- input: bip (BC546b),mosfet(BS107),j-fet(BF245b); sound differce was obvious: ref bip, the fet had finer hi-range, but less resolution on low level( less room), the mosfet bad / sharp highs, maybe by their bigger inp capacity;
- output: power bip, mosfet; ref bip, the mosfet had more room and a little finer hi;
since that time i made my power amps with bip input and mosfet output, this was the optimum configuration for me; but dont forget, this is only one part of the amp-sound, the design begins at the power supply and ends at the kind of wires you use, all parts make a change in sound quality...


tomcat 7th June 2002 06:15 AM

Thanks to all who have replied thus far.

It's given that there are a certain number of circuit topolgies, be they tube or solid state that can use any number of output devices.

For instance had I asked the same question about tubes, there would, I am sure been a flood of correspondence on the sound quality of various output tubes in a given circuit using say, a PP60.

Some would insist that the KT66 is the only tube to use, others the EL37. But what of the humble 6BG6 or the venerable run off the mill old workhorse, everybodies ex military surplus 807? This tube is so plentifull they are almost dime a dozen. Yet nobody except a handfull take it seriously for audio because of it's industrial background, yet it is one of the sweetest sounding tubes around.

The same principle applies to solid state circuits. The Digi-125 is general purpose circuit similar in concept the tube one mentioned above and originally designed to use either the 2N3055/2955 pair or the MJ802/4502 o/p pair.
I can vouch that the latter devices sound much nicer/sweeter than the former.

Since then I have tried several other o/p devices including the MJ1004/1005 pair (hard sounding)and the 2SC2987A/2SA1227A (smooth, but oh so,,, ho-hum) devices before I stumbled on to the 2SC5200/2SA1943 as used in the AKSA, and these really made the Digi sing!

So there are differences, much greater than many imagine or, those who are in the know are prepared to concede.
Because if some can (as many claim) hear the difference that resistors, caps and cables can make in their systems, then surely they could tell the difference in sound quality between output devices as it would be just as audible.

Surely the onus is on those of us who have the ability to build our own (ss) amps and discover the sonic differences between components to share our discoveries/knowledge/experiences with others of the same ilk.

Logical, No? Or is that too much to ask. Hmmm???


jan.didden 7th June 2002 06:32 AM

different transistors?
You are obviously ignoring Jon Marsh's post above. I think he made it clear that if you just change some active device in an amp, you really built yourself a different amp, unless you make sure that the new device is propperly 'integrated' in the amp as far as biasing, compensation, etc is concerned.
If you don't do that, any results and this whole exercise is meaningless.
Sorry, I don't want to spoil your fun, but if you just want to play around, then that's all you are doing.

Cheers, Jan Didden

rdarnall 7th June 2002 08:16 PM

I'd like to make some comments about a few statements previously made...

"A well designed circuit is built around the performance and the characteristics of the parts used- regardless of the merits of one transistor or another, if you modify a circuit with a different device, and the cicrcuit wasn't designed around that device, you'll probably get different, or rather, indifferent results, regardless of the relative tradeoffs and quality merits of the devices."

I believe this statement is true and false.

True, in that any particular device has a certain set of general operating parameters and limits (voltage, current, power diss., etc...) that the circuit is to accomodate or follow.

But I disagree with this statement in that the device parameters can vary way too much even for the same "part number." I'm speaking particularly of transistors, although any device suffers from the same manufacturing variables, even something as simple as a resistor. These variances are more problematic in analog circuits than digital, I believe, simply because of the need for linearity.

Let's say you want to design a transistor amplifier (any type you want) and you want to use part 2Nxyz. Perhaps you would look at the spec sheets for its parameters, design, build, and test it. Then you decide that your design is the greatest thing since slice bread and go out and buy 100 more so you can build more and sell them to all your friends. Well, you put another 2Nxyz in, and the tests come back significantly different. That's because the first 2Nxyz is not the same as the others. You designed your circuit off of the spec sheets and that's only a guide.

Even worse is when you get out your curve tracer and design your circuit to that.

you cannot expect to replace components with "better" parts (or even same parts) and expect better overall performance. Unless, perhaps it's a circuit-dependent design rather than a device-dependent design. A device-dependent design relies mostly on the parameters of the device for its performance, but a circuit-dependent design allows for variations between parts while still maintaining its designed parameters. But alas, the real word is made up of compromises and both are always in effect.

tomcat 7th June 2002 09:50 PM

Thanks rdarnall for clarifying what I was trying to say that obviously a couple of others overlooked.
If what they are saying were true, how is it that so many have been able to build both the early and the latter versions of the JLH SE 10w amp, as in both versions there are devices that are, either obsolete or hard to get so substitutes had to be found... And find them they did, with good results, even the small signal devices not just the outputs. In one example one chap changed from one device (I think it was 2n3055) to MJ 15003's and noticed an instant improvement! This is a good example of a circuit dependant design that you were referring to.
Another one I saw posted recently on this forum was the "Hiraga 20w" somebody built using the 2n3055 and BF149 (from memory) sounding quite nice... as most of the devices in this circuit are as rare now as hens teeth too, yet it worked (in this one example) with these common and easy to get devices.... So it is possible, in the tube fraternity they (I think) call it tube rolling, what can we call it with SS devices? Any Ideas?? Anyone??
tomcat :D

900gripen 8th June 2002 11:32 AM

The Digi 125 Amplifier was designed for use with a number of different output transistors. Indeed I have built examples with
2N3055/MJ2955, TIP3055/TIP2955, MJE3055/MJE2955, MJ802/MJ4502 and MJ15003/MJ15004 output pairs. Probably the best sounding of these were the modules I built using the MJ802/MJ4502 combination. There are now more linear devices such as the Toshiba pair you have tried, and it seems that there may be adaptations of the original circuit that use these and other
modern output devices.

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