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design help needed

  • Thread starter The unknown Posterchild
  • Start date
T

The unknown Posterchild

Jan 1, 1970
0
I want to build a preamp for my acoustic guitar, which will have a condenser
mic and a few transducers as input.
I would like to be able to fine tune each input and have it go through an
onboard mini-parametric and or graphic eq.

Anyone have any ideas where I can find this info?

Thanks to an earlier request, I have seen some basic opamp stuff and some
basic FET preamps (terms which I don't really understand too well yet) but
none appears to fit my needs.

Thanks in advance
 
P

Pooh Bear

Jan 1, 1970
0
The said:
I want to build a preamp for my acoustic guitar, which will have a condenser
mic and a few transducers as input.
I would like to be able to fine tune each input and have it go through an
onboard mini-parametric and or graphic eq.

Anyone have any ideas where I can find this info?

Thanks to an earlier request, I have seen some basic opamp stuff and some
basic FET preamps (terms which I don't really understand too well yet) but
none appears to fit my needs.

Do you really need a full blown parametric or graphic on the inputs ?

A decent mixer from the better manufacturers will offer a parametric mid at
least as well as LF, HF and an HPF.

Graham
 
T

The unknown Posterchild

Jan 1, 1970
0
I don't really need anything...my limited knowledge is my handicap and I
just asked for what I had read about as being the "ideal."

LF = low frew? ie: Bass
HF = Hi Freq? ie: Treble
HPF = high pass filter? (no clue...you win)

Any guidance from the bear in the red sweater would be appreciated.
 
J

Jim Anable

Jan 1, 1970
0
The said:
I want to build a preamp for my acoustic guitar, which will have a condenser
mic and a few transducers as input.
I would like to be able to fine tune each input and have it go through an
onboard mini-parametric and or graphic eq.

Anyone have any ideas where I can find this info?

Thanks to an earlier request, I have seen some basic opamp stuff and some
basic FET preamps (terms which I don't really understand too well yet) but
none appears to fit my needs.

Thanks in advance

Please don't take offense, but if you don't understand the meaning of
FET and opamp, aren't you biting off a bit too much?

There are plenty of good commercial units out there. You don't also
built your car from the ground up, do you?

Personally, I'd go with a decent Fishman setup. Most standard acoustic
electrics will have at least three bands of tone, many have four. If
you still think you need a parametric, take a hard look at your amp and
speakers to see if they aren't the real problem. If not, throw a
parametric in the effects loop (or in line with recording, if that's the
issue).

If you are looking for parametric because of feedback, some preamps have
a built in notch filter (or you can get a feedback eliminator).
 
P

Pooh Bear

Jan 1, 1970
0
The said:
I don't really need anything...my limited knowledge is my handicap and I
just asked for what I had read about as being the "ideal."

LF = low frew? ie: Bass
HF = Hi Freq? ie: Treble
HPF = high pass filter? (no clue...you win)

Yes - correct on all counts !

And don't forget the mid freq control ( variable frequency ). So you get 3 EQ
sections and a filter.

Here's one I made earlier......

http://www.studiomaster.com/c1.html

Let me know if that's of any interest.
Any guidance from the bear in the red sweater would be appreciated.

Wasn't that actually Rupert the Bear ?

Yup.... ;-)

http://pers-www.wlv.ac.uk/~fa1871/rupage.html


Graham
 
T

tempus fugit

Jan 1, 1970
0
Pooh you designed that mixer?

What did you use for micpres - discrete or opamp?
 
P

Pooh Bear

Jan 1, 1970
0
tempus said:
Pooh you designed that mixer?

What did you use for micpres - discrete or opamp?

A bit of both.

The 'front end' is a low noise long tailed pair type configuration with variable
gain ( the 'pot' is connected inter-emitter ) followed by a fixed gain
differential op-amp stage.

It's not actually changed very much since I first came across it in 1979. I've
tinkered with it a bit but this circuit and its various derivatives is still
widely used throughout the pro-audio industry. The main change since 1979 has
been reducing the noise level slightly.

A couple of companies make an integrated version that costs a bomb compared to
doing it with discretes and an op-amp.


Graham
 
T

tempus fugit

Jan 1, 1970
0
These would be SSM2017 or 2019?
Actually, they're very inexpensive, because no one ever seems to carry them,
so I end up having to contact AD directly for samples.

The million dollar question: Does the version with the discrete front end
sound different or better than the IC version?

Thanks
 
P

Pooh Bear

Jan 1, 1970
0
tempus said:
These would be SSM2017 or 2019?

Yes - and there's also a similar part from That. And indeed a TI / Burr Brown
part, the INA103 IIRC. Yup. And there's the older INA217 too.

http://focus.ti.com/docs/prod/folders/print/ina103.html

Actually, they're very inexpensive, because no one ever seems to carry them,
so I end up having to contact AD directly for samples.

As long as you can get way with it. ;-)
The million dollar question: Does the version with the discrete front end
sound different or better than the IC version?

Since I've never had occasion to use the integrated parts I really don't know. I
really doubt it there's very much difference though. The integrated parts make
life simple for those who never designed with discretes. ;-)

I actually have TI / BB's PGA2500 digitally controlled gain mic amp in the
office right now. That's a new development that's likely to be popular.

There's much talk about the sound of mci pres. My own suspicion is that most of
the 'routine' ones like my own designs are very alike in their perfromance.

To be honest I just tend to hone the tech figures as opposed to trying to find
fault with the sound.

I expect you start getting interesting colourations when a transformer is used.
I'm sure you do in fact. It seems likely to me that the 'interesting' mic pres
sound that way on account of their flaws.

Graham
 
T

The unknown Posterchild

Jan 1, 1970
0
After a day of pounding my head against the wall, I think I got it done!

http://get-noticed.com/darkwood/preamp schematic dual preamp.jpg

2 condenser mics into separate preamps, blended by a dual gang volume
control into a simpe tone control network, then into the volume control then
out.

I'd like some comments/critiques on the design.
Thanks for your support!
 
P

Pooh Bear

Jan 1, 1970
0
The said:
After a day of pounding my head against the wall, I think I got it done!

http://get-noticed.com/darkwood/preamp schematic dual preamp.jpg

2 condenser mics into separate preamps, blended by a dual gang volume
control into a simpe tone control network, then into the volume control then
out.

I'd like some comments/critiques on the design.
Thanks for your support!

That tone control is passive and won't work with linear taper pots. It's typical
of 1950s and early 1960s thinking ! For example I've been building audio
circuits since .... 1969 and never once done a passive tone control !

Yeah - it's designed around the 10% taper log pots that were once common ( the
end-stop values are a giveaway ).

These days, 'log' pots have a15% taper So it won't be flat with the controls
centred.

An active 'tone control' stage is much, much better and likely to be far, far
quieter and less prone to hum - etc pickup too !

In fact all the R values are horribly high and it simply will have trouble
feeding any amplifier that doesn't have about 1 megohm input impedance. The
output impedance is absurdly high !

It'll stink. Where on earth did you find such a retarded 'circuit' btw ? The
toob nuts weren't involved by any chance ?

Graham
 
J

John Fields

Jan 1, 1970
0
That tone control is passive and won't work with linear taper pots. It's typical
of 1950s and early 1960s thinking ! For example I've been building audio
circuits since .... 1969 and never once done a passive tone control !

---
With so much experience under your belt, it seems that you'd have
caught the fact that there are couple of FET's in there.
---
Yeah - it's designed around the 10% taper log pots that were once common ( the
end-stop values are a giveaway ).

These days, 'log' pots have a15% taper So it won't be flat with the controls
centred.

An active 'tone control' stage is much, much better and likely to be far, far
quieter and less prone to hum - etc pickup too !

In fact all the R values are horribly high and it simply will have trouble
feeding any amplifier that doesn't have about 1 megohm input impedance. The
output impedance is absurdly high !

It'll stink. Where on earth did you find such a retarded 'circuit' btw ? The
toob nuts weren't involved by any chance ?

---
Blah, blah, blah.

Look at the circuit again. it's not passive. You fucked up. Admit it
or piss off. Or not, it doesn't make much difference. No matter
what, you were wrong and all your grandstanding can't change that.
 
T

tempus fugit

Jan 1, 1970
0
The integrated parts make
life simple for those who never designed with discretes. ;-)


LOL

Like myself
I actually have TI / BB's PGA2500 digitally controlled gain mic amp in the
office right now. That's a new development that's likely to be popular.

There's much talk about the sound of mci pres. My own suspicion is that most of
the 'routine' ones like my own designs are very alike in their perfromance.

To be honest I just tend to hone the tech figures as opposed to trying to find
fault with the sound.

I expect you start getting interesting colourations when a transformer is used.
I'm sure you do in fact. It seems likely to me that the 'interesting' mic pres
sound that way on account of their flaws.

Indeed. The late 60s Rupert Neve designs are very sought after, and even
Rupert himself concedes that just about anything nowadays sounds better, and
it was probably the xformers themselves that were adding most of the sought
after sound to the pre.
 
P

Pooh Bear

Jan 1, 1970
0
tempus said:
The integrated parts make

LOL

Like myself


Indeed. The late 60s Rupert Neve designs are very sought after, and even
Rupert himself concedes that just about anything nowadays sounds better, and
it was probably the xformers themselves that were adding most of the sought
after sound to the pre.

Very true and indeed the modern 'copies' make a great fuss of the fact that
they've closely copied the transformers.

Those early transistor circuits weren't exactly terribly linear by today's
op-amp standards either. 'Fractions of a per cent ' THD are quite normal. In
those days 0.1% was considered really good going. Todays mic pres routinely
deliver 0.0xx to 0.00xx and better THD.

Grahams
 
T

The unknown Posterchild

Jan 1, 1970
0
What makes it active? the N FETs? ..they are in the preamp phase...
I admit to scouring the net and stealing what I found...
Before today, I didn't kniow a fet from an accompli

I am going to separate the bass and treble to separate tone controls...with
center being neutral and less and more being left and right. Does that mean
I need more amps on the + side of the controls?

Bear with me...really..up till today I never tried doing this..does it show?
 
J

John Woodgate

Jan 1, 1970
0
I read in alt.binaries.schematics.electronic that Pooh Bear
The output impedance is absurdly high !

So is the input impedance.

Oh, I see; the OP is using crystal microphones.(;-)

And the 'balance' control is wired as a master volume control.
 
J

John Woodgate

Jan 1, 1970
0
I read in alt.binaries.schematics.electronic that The unknown
<[email protected]>) about 'design help needed',
What makes it active? the N FETs? ..they are in the preamp phase... I
admit to scouring the net and stealing what I found... Before today, I
didn't kniow a fet from an accompli

John Field's comment is misleading. The **tone control** circuit is
passive. It strongly attenuates the signal. You will end up with only a
few tens of millivolts output from your 'preamp'
I am going to separate the bass and treble to separate tone
controls...with center being neutral and less and more being left and
right. Does that mean I need more amps on the + side of the controls?
No.

Bear with me...really..up till today I never tried doing this..does it
show?

Yes, very much so.
 
T

The unknown Posterchild

Jan 1, 1970
0
let's see...circuits came from...

tone: http://amps.zugster.net/articles/tonestacks/
preamp: http://www.till.com/articles/GuitarPreamp/index.html
balance + volume: http://sound.westhost.com/pots.htm

as for resistors and caps ..it's what the circuits said.
I thought they were modern audio log pots...

I am still looking for an active tone control circuit but can't seem to
understand what I should be looking for,,,some kind of opamp circuit for
that?

...and since I am not using pickups but condenser microphones, the amp
circuit may have to change a bit.

I don't do electronics math so I have no idea about impedance issues with
the output

Thanks again for the input.
 
T

T N Nurse

Jan 1, 1970
0
Pooh Bear said:
That tone control is passive and won't work with linear taper pots.

It's a Baxandall circuit. It's fine with linear pots.
 
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