design help needed

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).

Reply to
Jim Anable
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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

Reply to
The unknown Posterchild

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.

Reply to
The unknown Posterchild

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

Reply to
Pooh Bear

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......

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Let me know if that's of any interest.

Wasn't that actually Rupert the Bear ?

Yup.... ;-)

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Graham

Reply to
Pooh Bear

There was a book in the early eighties called "Electronic Projects for Musicians" by Craig Anderton which covered basic amplifiers and filters for musicians with limited technical background. It might still be in print.

Bob

Reply to
Bob Stephens

try here as well

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martin

Reply to
martin griffith

Pooh you designed that mixer?

What did you use for micpres - discrete or opamp?

EQ

Reply to
tempus fugit

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

Reply to
Pooh Bear

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

variable

I've

still

has

compared to

Reply to
tempus fugit

[snip]

I'm glad you said it ;-)

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

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

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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!

Reply to
The unknown Posterchild

--
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.
Reply to
John Fields

The integrated parts make

LOL

Like myself

most of

perfromance.

find

used.

pres

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.

Reply to
tempus fugit

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.

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As long as you can get way with it. ;-)

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

Reply to
Pooh Bear

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?

Reply to
The unknown Posterchild

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

Reply to
Pooh Bear

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

Reply to
Pooh Bear

I read in alt.binaries.schematics.electronic that Pooh Bear wrote (in ) about 'design help needed', on Thu, 8 Sep 2005:

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.

--
Regards, John Woodgate, OOO - Own Opinions Only.
If everything has been designed, a god designed evolution by natural selection.
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Reply to
John Woodgate

I read in alt.binaries.schematics.electronic that The unknown Posterchild wrote (in ) about 'design help needed', on Thu, 8 Sep 2005:

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'

No.

Yes, very much so.

--
Regards, John Woodgate, OOO - Own Opinions Only.
If everything has been designed, a god designed evolution by natural selection.
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Reply to
John Woodgate

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