Toft Audio console mod question???

[Jettison]

Is it possible to remove and jumper the mic pre op-amp on each channel input in order to make each channel a "micpreless" input-only channel. Would this mod make the quieter and open up the headroom of the console?
This question is obviously inspired by the recent issue of the mag.
Just wondering if it's possible or even worth it.
thanks
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You traded the Cadillac for a microphone?

[The Scum]

Before you actually cut into the thing, try this:

Run your recorder outputs into the insert returns. You may lose auxes and/or EQ, but you'll be bypassing a bunch of circuitry without modding anything.

If you like what you hear, then look at bypassing the mic pres...if you simply remove the chipsand jumper the signal, you'd lose the balanced input, if that's important to you.

[Jettison]

Ah ha. I see what you're saying.
Well I've had this thing open and done so many repairs on it that I can't even count. So i'm not really afraid of getting under the hood.
I also am running 24 inputs from my DAW back to it for mixing. I have the 3200 and use 25-32 for the pres and misc. mixdown BS. I need the eq and aux sends.
So, do the op amps balance the signal in addition to amplifying it?
What does "balanced" mean anyway.
Would they be noisier or lose headroom if they weren't balanced? I guess I don't yet know how those chips really work.

Can you explain it?

It's not really important. I like the sound of the board. I don't need the pres so if removing them gives it more headroom then I might try it.
I'll start with insert trick first.
Thanks for the input.
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You traded the Cadillac for a microphone?

[Jim Williams]

Both the mic and line inputs feed the that 1510 mic preamp chip. The line signal is attenuated 20 db, then jacked back up by the mic pre chip. THD measures .04% through the stereo mix outputs at +4dbu/1k hz.

The monitor input feeds a TL072 opamp. If you use the EQ to monitor you can mix through the rotary fader. This is prefered but the console cries out for a fader reverse switch.

Sonically to me the 1510 is a weak spot in this design. I'm finishing up a modular replacement for the that 1510, SSM2017/2019, INA217 mic pre chips. It's a 1" square module with 20 components. It's a plug in preamp, or as I call it, the PIP. Specs are 200k hz bandwidth, 3000 volt/us slew rate, 100 ma output current, .0006% THD, .0002% IMD, -129.6 db EIN. It should be ready in a couple of weeks if it goes to plan. The idea is to create a user replacable mic preamp to insert into Toft, Amek, Trident S-20, DAV, Safe Sound etc.

I've also done extensive mods to the Toft console. I got -3 db at 90k hz bandwidth, mic/line in to stereo mix out. THD dropped from .04% to .003%. 10 hz is flat, 1.9 degrees of phase shift at 20 hz, monitor in to stereo mix out. Levels are clean, .003% THD up to +27 db output levels, the stock console crunches out well before that due to insufficiant loop gain in the 5532 suming opamp. It now sounds best with the meters pegged.

I obtained major improvements in stereo crosstalk, a stock console measures -58 db , 20 ~20k hz. Modifed it measures - 80 db at 10k right, - 74 db left. I also removed all residual power supply hum as none of the input modules have an electrolytic psu decoupling cap. I installed large low impedance caps and 60 hz psu noise went from -71 dbu to -110 dbu.

The EQ's were modified with super fast low noise opamps. Wima polyprop film caps were used. Frequencies were adjusted, hi mids sweep to 22k hz, low mids sweep down to 50 hz. I also moved down the 60 and 120 hz shelf EQ.
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Jim Williams
Audio Upgrades

[Brian]

Jim,
I'd like to know more about this thing you're designing/manufacturing. I've been looking into doing something like that but, since you already did and you're way better than me at it, I'll just buy yours. You, I like.
So, I'm guessing this will also work in a soundcraft with a seriously upgraded power supply (which I have)??
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Oh shut up.

[Jim Williams]

It's designed with 8 pins to plug into an 8 pin dip socket. So in that way it's intended to retrofit those 8 pin dip preamp chips, the SSM2017/2019, that 1510 and BB INA217. I suppose it can be used in any place where that pinout is used. Layouts are done and Gerber files are going out. It's pretty tough doing miniture PCB's as most I do are large and have plenty of room to work with. This one is 1 inch square with 20 parts and the pin sockets.

I originally went with all surface mount parts, but good .1% tolerance metal film resistors. It turns out since surface mount is top side only and no through hole access, the routing I couldn't complete without a zillion vias added. I went with 1/8 watt through hole metal film resistors as they added bottom routing capability. They are mounted on end so the same 0805 sized surface mount 2 mm lead spacing was preserved.

My eyes hurt after this one.
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Jim Williams
Audio Upgrades

[Brian]

I can't even see well a that size anymore.

I'm really interested in trying these out. I think that the pre's are my only weak section in my board and they ain't bad now, BUT, I'd like to get about 12 channels modded to see the diff to start, probably kick, snare, oh's, 2 bass, 2 gtrs, 3 vox channels, heck mix out's too. I want to put an xformer on a switch on the mix and sub outs, just on the output jacks on the subs. maybe I'll change my mind on that and just put a switch on them.

Hmm, maybe do one channel all the way with them, just to see.

Need a crash test dummy for PIP?
I'll rename my board from Clara to PIP.

My IC's are already socketed.

How far is Carlsbad from Loma Linda?
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Oh shut up.

[Jim Williams]

Turn right at the Medical Center and drive down the I-5 for about 40 miles.
I'll let you know when they are done as I will need guinea pigs.
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Jim Williams
Audio Upgrades

[The Scum]

Wait a second - red flag:

[Brian]

[Brian]

[The Scum]

DIP8 only tells you the package the thing is in. It tells you nothing about the function of the chip. I could give you a DIP8 micrprocessor, but if you plugged it into you board, all you'd get is smoke.

You say yourself that the soundcraft pre is transistors and a TL072...so it sounds like the ones I'm familiar with. The 072 is a DIP dual opamp. It has the same pinout as most other dual opamps.

The module Mr Williams is discussing is a replacement for the THAT1512, INA217, etc chips. These are basically a single mic pre on a chip - add power and a couple passive components and voila...instant mic pre. The internal details of these chips looks something like the Soundcraft pre (differential transistor pair in front of an opamp), but it's all wrapped up in one chip. And the pinout and connections are nothing like an 072.

So I'm very skeptical that the module described above will fit your board. It definitely wont be plug'n'play - it would mean significant revision of the Soundcraft circuit.

[Brian]

Thanks for your excellent reply.

Correct me if I'm wrong, but, I believe this existing dual mono to dual dip8 adapter on the market right now will work. It takes two single opamps, such as OPA128
etc. and makes them compatible with a regular dual dip8 socket.
http://cgi.ebay.com/2X-Mono-to-Dual-Opamp-PCB-SOIC8-DIP8-OPA627AU-AD8610_W0QQitemZ220319369633QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item334c0ec9a1&_trksid=p3286.m20.l1116
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Oh shut up.

[The Scum]

That socket would let you swap the 072 out for a pair of single opamps (heh heh, why not try a pair of TL071s?).

The chips that Jim is replacing aren't opamps at all, and the pins aren't set up anything like a single opamp. They're mic pres on a chip.

Also, the adapter you linked adapts 2 surface mount singles into a dual DIP socket.

[Brian]

I slouch corrected. I haven't started working with the That 1510 yet and someone told me that it's pinout was compatible with a TL072, but, I shouldn't have taken their word for it?
I'm pretty aware that many chips use a dip 8 socket and aren't pre's or opamps, I'm not THAT far gone, yet.
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Oh shut up.