design discrete mic pre?

I think you won't get much better performance, unless you invest in a high quality transformer (i.e. Jensen). With discrete transistors you might achieve a slightly better noise floor however linearity and distortion are probably worse unless you invest into special matched parts like MAT04 or LM394.

This is the one that I was thinking about:

And that's kind of what I was wondering - will it sound much different from what I have now? I've heard many people say that a discrete micpre sounds so much better, but I wonder myself.

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It is certainly possible, but I doubt you will notice any improvement over a design using an SSM2017.

There is a fairly simple design here for example:

Gareth.

Thanks Gareth.

I've got that MAT datasheet already, and this is one of the things that got me thinking in the discrete direction. I'd still have to figure out a way to get rid of the opamp to be all discrete, od I could use fig. 4, but it is only a single ended input; I'd need to figure out how to make it balanced.

I should note that the SSM I'm using now is REALLY low noise, so it's not really the noise level that I want to improve upon. I guess I'm wondering if one will actually sound better. I know that I can hear a difference (a big one) among different mic pres I've heard, but then some of them may indeed be crap in the first place. I often wonder if I would hear much of a difference between my SSM design and one of the high end ones.

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It may be possible to get slightly lower noise with discrete parts as Ban said, but the SSM2017 is very low noise and I doubt that you would notice any improvement. I'm not really an expert on this though, and I have no idea what the pre amp you have now sounds like either :)

Have a look at this datasheet:

Figure 4 is a circuit diagram for a pre-amp with about 1/2 the noise and distortion of the SSM2017. it uses the MAT03 low noise transistor pair and an op amp to get the advantages of both (low noise and low distortion).

You could reduce the noise still further by putting several MAT03s in parallel as in Fig 3a. However that will get very expensive, and I doubt you will notice any difference.

It would be an interesting experiment to get some of these people who say that discrete pre amps sound much better and do some blind tests to see if they can actually tell the difference.

An opamp is in the end nothing but a circuit made from transistors, just in a small case. You can also build an OpAmp from discrete transistors and use that as a sensitive preamplifier. Elector had a circuit like this many years ago, with 5 parallel input transistors to reduce noise. IIRC it was meant as preamp for a moving coil pickup (those were the days!).

But I doubt that a good preamp from discrete transistors would be audibly better than one made with a good OpAmp, and vice versa. For example a noise floor of -100 db is not audibly worse than -105 dB. There is a lot of fetishism in this area, and some people are making good money from it.

In addition, what kind of musik is the amp intended for, and in what environment will it be listend to? Dance musik with little dynamic in a loud bar has lower requirements than recording classical musik in a studio.

Back in '82 I built a transformerless mic preamp to use with my Technics SVP-100 digital audio recorder. I was messing with a commercial mic preamp with a Triad (not Jensen) input transformers and was measuring nasty THD at 30 Hz-- like 10% or more. Looking back now it may have been 60 Hz hum raising the noise floor since the HP THD meter simply nulled out the fundamental and called the rest distortion.

I copied the mic preamp out of an EV (Tapco?) board but used matched transistors and resistors. With the AKG C451s, it hears better than I do (even 23 years ago when I could still hear). The transformerless unit measured 0.01% at 30 Hz. BTW, I was recording classical pipe organ with true 32' stops (17 Hz) so the low THD seemed needed. It certainly made some nice recordings

I have som SSM2017s to rebuild that thing 'real soon now'. Where's my round tuit?

Good Luck GG

Hi Dr.

These are things that I wrestle with - I know that an opamp is what you say, so how can it sound different? My 1st mic pre was an all transistor design. It never really got off the ground, and after much work and frustration, I tried an 072, which sounded infinitely better than my transistor design. I'm a little more knowledgeable in electronics now though, so I was wondering.... This is why I wonder what the big deal is about discrete - and why I wouldn't mind trying one just to see.

Agreed.

I record primarily classical guitar, but am looking at recording a rock band in the near future.