Baldwin takes on Moog in 1973. Read the Ebay Info, pretty funny. http://www.ebay.com/itm/73-BALDWIN-SYNTHA-SOUND-VINTAGE-ANALOG-HARPSICHORD-MINIMOOG-SYNTHESIZER-GRETSCH-/160829607910?pt=Keyboards_MIDI&hash=item2572310fe6#ht_17544wt_1415
No Moog, but an interesting instrument anyway.
Here’s their filter design: http://www.synthfool.com/docs/Other_Misc/Baldwin_Synthasound_Filter/
Is that what’s called a stepladder filter ? 
I do believe so!
Sounds pretty cool, Listen http://www.youtube.com/watch?v=TsrZWsVPfK0 Here is an inside view http://www.youtube.com/watch?v=TsrZWsVPfK0
Uh, is it me, or the second link is the same as the first…?
I saw that! Really cool synth, and I’d love to have it in my collection, but for that price? NO WAY. 
Agreed. Somethings wrong with it, at that price.
Here is the inside view http://www.youtube.com/watch?v=IxWYsFjKqeE Sorry for the mix up. 
748 opamp? YUCK!
I have to agree. However, can’t one replace that with a modern, more efficient op-amp? I’m pretty sure there are several modern equivalents out there.
Forgive, MC. He’s an engineer. 
No engineer would design a circuit using a 748 today.
As for equivalents, there are likely several possibilities, but then…again.. you should probably be an engineer to choose them.
I’ve seen the results of inexperienced “hey, this opamp has better specs and the same pinouts” and often it’s not a better result.
If you put a better opamp in a circuit originally designed around a older one, you may get high freq oscillations, radio reception, offsets and other unexpected problems.
I have to agree with Kevin on this. Unless an op amp is in the final audio stage and produces higher than normal audible hiss, or even possibly distortion, or is defective, I wouldn’t replace it.
In my beloved Mini, there are several original 741 from Raytheon 1973 on the oscillator board, and if one eventually fails, I’m going to replace it with…a 741. That’s the way Bob Moog designed the circuit, that’s the way it will stay. That’s probably what contributes to the imperfections of the waveforms, the noise in them that prevents them from locking up together when closely tuned. All those things we love about a Mini.
But some of you might say; aren’t you going to replace the whole keyboard contacts with an optical system soon ? What about keeping the Mini original then ?
I’m not crazy enough not to improve the playability of it. And once Kevin’s OptoKey is installed, no one will be able to tell that it’s in there, unless they look in the back of the Mini and see 2 DIN MIDI connectors at the end of cables.
But the electronic boards that create and modify the sounds have to stay as close as humanly possible to the original designs IMHO.
The difference between the original contacts and the OptoKey (besides the obvious) is that it could be considered an “upgrade” by one person, a “repair” by another.
Someone who wants everything stock, but still has horrible key contacts might not want it, but needs it.
Someone who wants their Mini to play as well or better than before might not need it, but wants it.
As a repair, it fixes a common problem.
As an upgrade, the note to note CV precision is more accurate, stable and there’s now some simple (but fast!) MIDI I/O.
I DID use a 741 opamp for the CV too because all the DIP opamps in a Mini remain the same type and it likely won’t pass on any MCU noise.
A better opamp might amplify things I wouldn’t want.
If someone decides to upgrade an earlier design’s opamps, they better have a clear understanding of what the circuits do and how they work.
I have no problem with anyone working on their own synth and experimenting tho. It’s their synth.
But if you’re paying for upgrades, make the tech explain the circuits and upgrades.
If they can’t, they shouldn’t be upgrading it.
Phrases like “all opamps replaced with better kinds” might be true, but doesn’t mean things are necessarily better.
Normally you don’t want a background 80khz tone, LFO or clock clicks in your audio or knowing if your air conditioner turns on, etc. 
I’ve seen Arp 2600s, Oberheim SEMs and Moog modules where all opamps were changed to one particular “better” kind.
While they were better in some locations, they were worse in others.
For example, I wouldn’t recommend one replace their Mini’s older VCO 741 opamps in locations IC3, IC5 and IC10.
All the other locations, including the buffer board, can usually be upgraded with certain better opamps (LT1006, LF411, etc, etc, etc.)
If one was playing on stage under lights, certain IC locations might benefit from various upgrades because of less thermal drift.
But for the most part, stock 741s are fine.
The greatest benefits are not realized via opamp bandwidth, but in terms of offset, drift and noise.
Upgrading some synth with faster opamps seems at first like one will suddenly have less noise and greater frequency response.
In fact, the opposite can be true if a better opamp is installed in a location that wasn’t designed for it.