we are lucky on this forum to have folks like scott dorsey, john
hardy, dan kennedy, john lagrou, and others who are top pros in their
field. i would like to take advantage of this, and request that you
guys please give the rest of us a "primer" on preamp electronics
design basics.

1. what is the simplest preamp design? ie, what exactly is required
in the circuit and why?

2. what are the basic problems with the simplest possible design?
(noise, fidelity, whatever)

3. what are the approaches to turning the basic design into a
reasonably clean and useable mic preamp? (better parts, additions to
the basic circuit, etc.)

4. what are the primary philosophies of top-end preamp design? ie,
why does a grace preamp sound so different from an HV3 when they are
both designed to be clean and transparent, or why tubes vs
transformers for more "colored" preamp dsigns?

jnorman wrote:

4. what are the primary philosophies of top-end preamp design? ie,
why does a grace preamp sound so different from an HV3

You can read some of Michael Grace's thoughts here
http://www.gracedesign.com/support/tech3.pdf

"Kurt Albershardt" wrote in message


jnorman wrote:

4. what are the primary philosophies of top-end preamp design? ie,
why does a grace preamp sound so different from an HV3

You can read some of Michael Grace's thoughts here
http://www.gracedesign.com/support/tech3.pdf

I'm not saying it's all snake oil, but there's some really hilarious stuff
the

"By terminating the destination end of the output cable with a 300 Ohm
resistor, the load resistance matches the output source resistance to create
a 600 Ohm balanced transmission line. Matching the impedance at or near the
characteristic impedance of the cable eliminates signal reflections in the
wire which greatly improves transient performance and preserves harmonic
integrity. This type of termination is very advantageous for driving very
long lines because it provides maximum power transfer through the cable and
virtually eliminates the effects of cable capacitance and inductance."

Arny Krueger wrote:

"Kurt Albershardt" wrote in message


jnorman wrote:

4. what are the primary philosophies of top-end preamp design? ie,
why does a grace preamp sound so different from an HV3

You can read some of Michael Grace's thoughts here
http://www.gracedesign.com/support/tech3.pdf

I'm not saying it's all snake oil, but there's some really hilarious stuff
the

"By terminating the destination end of the output cable with a 300 Ohm
resistor, the load resistance matches the output source resistance to create
a 600 Ohm balanced transmission line. Matching the impedance at or near the
characteristic impedance of the cable eliminates signal reflections in the
wire which greatly improves transient performance and preserves harmonic
integrity. This type of termination is very advantageous for driving very
long lines because it provides maximum power transfer through the cable and
virtually eliminates the effects of cable capacitance and inductance."

As classicly used by telephone companies ;-)

Graham

In article ,
Pooh Bear wrote:

As classicly used by telephone companies ;-)

Graham


Yeah, over thousands of feet where it actually is a transmission line
for audio frequencies. All audio is lumped parameters. Certainly
anything to do with mic preamps. But it's a pretty common mistake.

DC

Dave Collins wrote:
In article ,
Pooh Bear wrote:


As classicly used by telephone companies ;-)

Graham



Yeah, over thousands of feet where it actually is a transmission line
for audio frequencies. All audio is lumped parameters. Certainly
anything to do with mic preamps. But it's a pretty common mistake.

And if it *was* a transmission line, it sure looks like a 300-ohm (not
600) line to me.

Harvey Gerst has an excellent discussion on just that topic over at
PSW, with some of the designers you mentioned participating. 14 pages
of it:

http://recpit.prosoundweb.com/viewtopic.php?t=7774

jp

(jnorman) wrote in message . com...
we are lucky on this forum to have folks like scott dorsey, john
hardy, dan kennedy, john lagrou, and others who are top pros in their
field. i would like to take advantage of this, and request that you
guys please give the rest of us a "primer" on preamp electronics
design basics.

*snip*

"John Penovich" wrote in message
om

Harvey Gerst has an excellent discussion on just that topic over at
PSW, with some of the designers you mentioned participating. 14 pages
of it:

http://recpit.prosoundweb.com/viewtopic.php?t=7774


Most significantly it lays the groundwork for this excellent link:

http://www.mil-media.com/docs/articles/preamps.shtml

Arny Krueger wrote:

http://www.mil-media.com/docs/articles/preamps.shtml

Thanks, couldn't find that one earlier.

(John Penovich) wrote:

Harvey Gerst has an excellent discussion on just that topic over at
PSW, with some of the designers you mentioned participating. 14 pages
of it:

http://recpit.prosoundweb.com/viewtopic.php?t=7774

Some of the participants in that discussion of preamp design include Geoff
Tanner, Dan Kennedy, Mark McQuilken, John Le Grou, Tim Ferrant, and John Hardy.

Harvey Gerst
Indian Trail Recording Studio
http://www.ITRstudio.com/

I've decided that, for me at least, as long as the mike preamp is
considerably better than the microphone, there's little to gain from
using an expensive one. The preamps that come with a Mackie mixer
are better than my mikes. Are yours?

Cheers,

Norm Strong


"Harvey Gerst" wrote in message
...
(John Penovich) wrote:

Harvey Gerst has an excellent discussion on just that topic over at
PSW, with some of the designers you mentioned participating. 14
pages
of it:

http://recpit.prosoundweb.com/viewtopic.php?t=7774

Some of the participants in that discussion of preamp design include
Geoff
Tanner, Dan Kennedy, Mark McQuilken, John Le Grou, Tim Ferrant, and
John Hardy.

Harvey Gerst
Indian Trail Recording Studio
http://www.ITRstudio.com/

"normanstrong" wrote:

I've decided that, for me at least, as long as the mike preamp is
considerably better than the microphone, there's little to gain from
using an expensive one. The preamps that come with a Mackie mixer
are better than my mikes. Are yours?

Cheers,

Norm,

Generally speaking, we use the board's preamps for most things. For certain
mics and/or certain sounds, we use outboard preamps to get what we want. I'm
not a big fan of Mackie preamps. When we were looking around for our first
decent board for the small studio, we passed on the Mackie, Behringer,
Soundcraft, and several other boards, in favor of the Soundtrac Topaz. Not only
because the Topaz had more features and a better EQ (IMHO)than the other boards,
but because it had better sounding preamps, to my tired ears, anyway.

As far as your statement that "The preamps that come with a Mackie mixer
are better than my mikes", I don't understand that at all. The Shure SM57 comes
alive thru a really nice preamp. The Mackie does nothing for the SM57. Are you
saying that you don't even have an SM57 that would benefit from a better preamp?
Or are you saying you don't even have a mic as good as an SM57 in your mic
collection, so it doesn't matter to you?

Harvey Gerst
Indian Trail Recording Studio
http://www.ITRstudio.com/

"Harvey Gerst" wrote in message
...
"normanstrong" wrote:

I've decided that, for me at least, as long as the mike preamp is
considerably better than the microphone, there's little to gain
from
using an expensive one. The preamps that come with a Mackie mixer
are better than my mikes. Are yours?

Cheers,

Norm,

Generally speaking, we use the board's preamps for most things. For
certain
mics and/or certain sounds, we use outboard preamps to get what we
want. I'm
not a big fan of Mackie preamps. When we were looking around for
our first
decent board for the small studio, we passed on the Mackie,
Behringer,
Soundcraft, and several other boards, in favor of the Soundtrac
Topaz. Not only
because the Topaz had more features and a better EQ (IMHO)than the
other boards,
but because it had better sounding preamps, to my tired ears,
anyway.

As far as your statement that "The preamps that come with a Mackie
mixer
are better than my mikes", I don't understand that at all. The
Shure SM57 comes
alive thru a really nice preamp. The Mackie does nothing for the
SM57. Are you
saying that you don't even have an SM57 that would benefit from a
better preamp?
Or are you saying you don't even have a mic as good as an SM57 in
your mic
collection, so it doesn't matter to you?

I have 3 AKG C451's, 2 Nak CM-300's and 3 RadShack PZM's. No Shure
mikes.

So far as I can tell, mikes vary in noise level, frequency response
and output impedance. As long as the preamp has the right impedance
level for the mike used, has a smoother and more extended frequency
response than the mike, and adds little noise to the self noise of the
mike, it should be good enough. Anything else falls into the
category of mystery; I don't do mystery. If you feel I've missed
something pertinent, please feel free to correct me.

Norm Strong

normanstrong wrote:
I've decided that, for me at least, as long as the mike preamp is
considerably better than the microphone, there's little to gain from
using an expensive one. The preamps that come with a Mackie mixer
are better than my mikes. Are yours?

Compare the sound of an SM-57 into a Mackie and then into the Great River.
Very substantial difference, mostly due to loading it's true, but a very
substantial difference.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

jnorman wrote:
we are lucky on this forum to have folks like scott dorsey, john
hardy, dan kennedy, john lagrou, and others who are top pros in their
field. i would like to take advantage of this, and request that you
guys please give the rest of us a "primer" on preamp electronics
design basics.

1. what is the simplest preamp design? ie, what exactly is required
in the circuit and why?

It has to have a differential input and it has to have gain. I think you
can do that with a single long-tailed pair, or with a step-up transformer
and a single transistor stage.

2. what are the basic problems with the simplest possible design?
(noise, fidelity, whatever)

You get noise, you get poor linearity, you don't get enough gain.

3. what are the approaches to turning the basic design into a
reasonably clean and useable mic preamp? (better parts, additions to
the basic circuit, etc.)

Constant current sources, for one thing. Trying to get less gain per stage
and getting more stages. Using higher voltage rails for more headroom.
Using follower outputs for more current drive.

Take a look at a typical tube preamp, though. Two, sometimes three gain
stages. A lot of the gain is from the input transformer. It's pretty
simple, and you can do the same thing with FETs if you want.

4. what are the primary philosophies of top-end preamp design? ie,
why does a grace preamp sound so different from an HV3 when they are
both designed to be clean and transparent, or why tubes vs
transformers for more "colored" preamp dsigns?

You can make very transparent tube preamps too. The problem is that there
are widely varying philosophies. Since you cannot make anything completely
transparent (especially given the widely varying loading requirements of
different mikes), you are stuck with making tradeoffs between different kinds
of coloration. And different people make different tradeoffs.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

jnorman wrote:

1. what is the simplest preamp design? ie, what exactly is required
in the circuit and why?

I think the simplest possible preamp would be an input transformer
followed by a single unity-gain active stage.

The transformer would have to have a high turns ratio in order to
provide all the gain necessary.

The active device would have to have a nearly infinite input impedance
and an output impedance near zero.


2. what are the basic problems with the simplest possible design?
(noise, fidelity, whatever)

The transformer will have a limit to its operating level and bandwidth,
will cause distortion, and will be bulky and expensive. The high ratio
required to obtain the necessary gain will compound every one of these
limitations.

The active device will require peripheral components including a power
source, and will have limits to its linearity and bandwidth, in
addition to adding noise.

There is no control over the gain, and the output signal is unbalanced.
There are no utility features such as input pad to prevent overload,
polarity switching, phantom power, etc.

The preamp will be susceptible to interference from environmental
noise, be it sound pressure, electrical, or magnetic.

3. what are the approaches to turning the basic design into a
reasonably clean and useable mic preamp? (better parts, additions to
the basic circuit, etc.)

Adding more active stages to allow for a lower-ratio transformer.
Adding a gain control or an input attenuator. Adding still more gain
stages to compensate for losses in the attenuator or gain control.
Adding a differential amplifier or transformer for balanced output.
Adding contol over polarity, an input pad, and phantom power. Housing
the whole thing in an enclosure to protect it from damage and noise.
Adding a control surface to allow the user to easily and effectively
manipulate all the features you just added. Some connectors to allow
quick and easy interfacing with different microphones and destinations.

4. what are the primary philosophies of top-end preamp design? ie,
why does a grace preamp sound so different from an HV3 when they are
both designed to be clean and transparent, or why tubes vs
transformers for more "colored" preamp dsigns?

Dunno.

ulysses

On 11 Nov 2003 11:42:42 -0800, (jnorman) wrote:

we are lucky on this forum to have folks like scott dorsey, john
hardy, dan kennedy, john lagrou, and others who are top pros in their
field. i would like to take advantage of this, and request that you
guys please give the rest of us a "primer" on preamp electronics
design basics.

1. what is the simplest preamp design? ie, what exactly is required
in the circuit and why?

2. what are the basic problems with the simplest possible design?
(noise, fidelity, whatever)

3. what are the approaches to turning the basic design into a
reasonably clean and useable mic preamp? (better parts, additions to
the basic circuit, etc.)

4. what are the primary philosophies of top-end preamp design? ie,
why does a grace preamp sound so different from an HV3 when they are
both designed to be clean and transparent, or why tubes vs
transformers for more "colored" preamp dsigns?

It is important to understand that painting the box certain shades of
various colors, can have a dramatic impact on the sound of the unit.
Certain shades of blue and green can often cause a marginally designed
preamp to sound amazing. Cool looking knobs will enhance this effect

For instance, if you want a vintage sound, paint the preamp olive drab
or utility gray and chose those cool "chicken head" or "pelican head"
knobs. Wrinkle and hammertone paints give a dramatic vintage sound ;-)


Ed

Edvard wrote:

It is important to understand that painting the box certain shades of
various colors, can have a dramatic impact on the sound of the unit.
Certain shades of blue and green can often cause a marginally designed
preamp to sound amazing. Cool looking knobs will enhance this effect

For instance, if you want a vintage sound, paint the preamp olive drab
or utility gray and chose those cool "chicken head" or "pelican head"
knobs. Wrinkle and hammertone paints give a dramatic vintage sound ;-)

You are rigth. But why the smilie?
This preamp tuning does not only work with analog preamps.
It is often successfully used on digital plugins that try to simulate
analoge stuff.

And if you want a warmer sound just put a tube visible(!) into the
preamp. You need only connect the heaters or simplier put some orange
LEDs behind it.
It is a lie that a tube has to be in the signal path to get the warm
vintage effect.

jnorman wrote:

we are lucky on this forum to have folks like scott dorsey, john
hardy, dan kennedy, john lagrou, and others who are top pros in their
field. i would like to take advantage of this, and request that you
guys please give the rest of us a "primer" on preamp electronics
design basics.

1. what is the simplest preamp design? ie, what exactly is required
in the circuit and why?

I'm going to rule out transformers because of cost. The circuitry may be
simple but it won't find its way into a practical 'simple preamp' design.

You need a differential input, typically a long tailed pair and a means
of converting the differential output at the collector loads to a single
ended signal - usually an op-amp suitably configured.

2. what are the basic problems with the simplest possible design?
(noise, fidelity, whatever)

Common general purpose transistors are noisy w.r.t. 200 ohm sources. Best
choice is typically pnp ( higher carrier mobility in the base region
results in lower flicker noise ) and large geometry ( lower intrinsic
resistance has lower thermal noise ). Devices originally designed for
moving coil pre-amp designs work very well.

The input stage also needs to be run at several milliamps to get the
benefit of the noise improvements because of the emitter dynamic
impedance ( 27 / Ie ( mA ) Ohms, true up to a few milliamps ).

Single transistor gain stages have poor linearity and generate plenty of
THD esp at high signal levels. This is overcome by 'compound'
arrangements or indeed using the op-amp stage to close a feedback loop to
the input transistor emitters. There are more elaborate methods too.

3. what are the approaches to turning the basic design into a
reasonably clean and useable mic preamp? (better parts, additions to
the basic circuit, etc.)

Better parts for the input transistors especially for noise.
More advanced circuit design ( more bits ).

4. what are the primary philosophies of top-end preamp design? ie,
why does a grace preamp sound so different from an HV3 when they are
both designed to be clean and transparent,

Don't know them so can't comment.

or why tubes vs transformers for more "colored" preamp dsigns?

That's easy. Some ppl like technically inaccurate designs since they
produce a 'warm sound'.

Valves produce little gain compared to transistors per stage, and rarely
have much feedback applied around them, so a valve design will produce
plenty of nice 2nd harmonic distortion.

Transformers do all sorts of stuff to the signal. Kinda where do you want
me to begin ?


Regds, Graham