design discrete mic pre?

T

tempus fugit

Guest
Hey all;

I'm thinking about building yet another mic preamp. I've currently got one
built around the SSM 2017, and it sounds pretty good. However, I notice that
many of the high end designs use discrete (i.e. all transistor) designs. How
feasible is it for a hobbyist to build/design something like this? I've seen
some schems on the net that use a transistor input stage with an opamp as a
follower, but I'd like to try an all discrete design if possible. I suppose
I should also mention that I'm a musician how doesn't have a lot of spare
time. I'm pretty happy with my current (SSM) micpre, and could easily build
another (I need another micpre), but if it isn't going to take tons of
fiddling and redesigning, I wouldn't mind trying another option.

Thanks
 
tempus fugit wrote:
Hey all;

I'm thinking about building yet another mic preamp. I've currently
got one built around the SSM 2017, and it sounds pretty good.
However, I notice that many of the high end designs use discrete
(i.e. all transistor) designs. How feasible is it for a hobbyist to
build/design something like this? I've seen some schems on the net
that use a transistor input stage with an opamp as a follower, but
I'd like to try an all discrete design if possible. I suppose I
should also mention that I'm a musician how doesn't have a lot of
spare time. I'm pretty happy with my current (SSM) micpre, and could
easily build another (I need another micpre), but if it isn't going
to take tons of fiddling and redesigning, I wouldn't mind trying
another option.

Thanks
Click to expand...
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.
--
ciao Ban
Bordighera, Italy
 
tempus fugit wrote:
Hey all;

I'm thinking about building yet another mic preamp. I've currently got one
built around the SSM 2017, and it sounds pretty good. However, I notice that
many of the high end designs use discrete (i.e. all transistor) designs. How
feasible is it for a hobbyist to build/design something like this? I've seen
some schems on the net that use a transistor input stage with an opamp as a
follower, but I'd like to try an all discrete design if possible. I suppose
I should also mention that I'm a musician how doesn't have a lot of spare
time. I'm pretty happy with my current (SSM) micpre, and could easily build
another (I need another micpre), but if it isn't going to take tons of
fiddling and redesigning, I wouldn't mind trying another option.

Thanks
Click to expand...
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:

http://sound.westhost.com/project13.htm

Gareth.
--
-----------------------------------------------------------------------
To reply to me directly:

Replace privacy.net with: totalise DOT co DOT uk and replace me with
gareth.harris
 
tempus fugit wrote:
This is the one that I was thinking about:

http://sound.westhost.com/project66.htm

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.
Click to expand...
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:

http://www.analog.com/UploadedFiles/Data_Sheets/23265255MAT03_c.pdf

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.

--
-----------------------------------------------------------------------
To reply to me directly:

Replace privacy.net with: totalise DOT co DOT uk and replace me with
gareth.harris
 
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.

Thanks

"Gareth" <me@privacy.net> wrote in message
news:HuGdnR0c36EO697fRVnyuw@brightview.com...
tempus fugit wrote:
This is the one that I was thinking about:

http://sound.westhost.com/project66.htm

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.

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:

http://www.analog.com/UploadedFiles/Data_Sheets/23265255MAT03_c.pdf

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.

--
-----------------------------------------------------------------------
To reply to me directly:

Replace privacy.net with: totalise DOT co DOT uk and replace me with
gareth.harris
Click to expand...
 
tempus fugit wrote:

Hey all;

I'm thinking about building yet another mic preamp. I've currently got one
built around the SSM 2017, and it sounds pretty good. However, I notice that
many of the high end designs use discrete (i.e. all transistor) designs. How
feasible is it for a hobbyist to build/design something like this? I've seen
some schems on the net that use a transistor input stage with an opamp as a
follower, but I'd like to try an all discrete design if possible. I suppose
I should also mention that I'm a musician how doesn't have a lot of spare
time. I'm pretty happy with my current (SSM) micpre, and could easily build
another (I need another micpre), but if it isn't going to take tons of
fiddling and redesigning, I wouldn't mind trying another option.
Click to expand...
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.
 
Hi Dr.

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!).
These are things that I wrestle with - I know that an opamp is what you say,
Click to expand...
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.

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.
Click to expand...
Agreed.
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.
Click to expand...
I record primarily classical guitar, but am looking at recording a rock band
in the near future.
 
This is the one that I was thinking about:

http://sound.westhost.com/project66.htm

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.


"Gareth" <me@privacy.net> wrote in message
news:RaqdnTT_Y-k5Y9_fRVnysg@brightview.com...
tempus fugit wrote:
Hey all;

I'm thinking about building yet another mic preamp. I've currently got
one
built around the SSM 2017, and it sounds pretty good. However, I notice
that
many of the high end designs use discrete (i.e. all transistor) designs.
How
feasible is it for a hobbyist to build/design something like this? I've
seen
some schems on the net that use a transistor input stage with an opamp
as a
follower, but I'd like to try an all discrete design if possible. I
suppose
I should also mention that I'm a musician how doesn't have a lot of
spare
time. I'm pretty happy with my current (SSM) micpre, and could easily
build
another (I need another micpre), but if it isn't going to take tons of
fiddling and redesigning, I wouldn't mind trying another option.

Thanks

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:

http://sound.westhost.com/project13.htm

Gareth.
--
-----------------------------------------------------------------------
To reply to me directly:

Replace privacy.net with: totalise DOT co DOT uk and replace me with
gareth.harris
Click to expand...
 
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
 
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