Author Topic: Other uses for TA7125P?  (Read 1350 times)

digi2t

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Other uses for TA7125P?
« on: March 31, 2013, 10:26:05 AM »
Having gone to great lengths to track down this hen's tooth of an IC, I now have a dilemma...

What else can I use it for?

I still have not been able to track down a datasheet. I've sent two info requests to Toshiba, but nothing yet. As this schematic shows, it's a 7 pin SIP VCA (lower right corner)



I set it up alone on the breadboard, using the surrounding components as on the schematic. I plugged in my guitar to the 1uF going to pin 1, and output from the 3.3uF to my amp. For a control voltage, I kept the 0.1uF cap, the diode, and the 330K resistor. I connected this to a 1M pot, and then to +9 vdc. Working the pot did indeed vary the volume output.

Since breadboarding the entire circuit, and fiddling with it extensively, I decided to abandon this design. Slackers Slacktave front end did help, but it was too glitchy, and really didn't blow up my skirt soundwise. I thought that it might get me into Schumann PLL territory, but it didn't.

I know there's lots of other circuits that I can use the other components on, but the TA7125P? Anyone have any ideas? How about combining it with an LFO for a vibrato circuit?
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mictester

Re: Other uses for TA7125P?
« Reply #1 on: February 04, 2021, 05:47:17 AM »
I found that I had a few of these VCA chips. I decided to experiment with one to see how much use it is.

My conclusions are that it behaves very like an MC3340, but with lower noise. The gain control range seems to be about 60dB, and the distortion varies with gain, but never gets above 0.5%.

I've tried two configurations: straight through and in the negative feedback loop of an op-amp. The feedback version works best, with low noise and an element of distortion cancellation going on. Gain through the VCA is then sort of proportional to the reciprocal of the control voltage - the control law is a smooth curve.

It's a pity that this chip is so rare, as it's a useful part. I think that I might have the data sheet for it, but it's probably buried in the "probably won't use these" file! If I find it, I'll put it on line.

digi2t

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Re: Other uses for TA7125P?
« Reply #2 on: February 04, 2021, 02:53:10 PM »
I found that I had a few of these VCA chips. I decided to experiment with one to see how much use it is.

My conclusions are that it behaves very like an MC3340, but with lower noise. The gain control range seems to be about 60dB, and the distortion varies with gain, but never gets above 0.5%.

I've tried two configurations: straight through and in the negative feedback loop of an op-amp. The feedback version works best, with low noise and an element of distortion cancellation going on. Gain through the VCA is then sort of proportional to the reciprocal of the control voltage - the control law is a smooth curve.

It's a pity that this chip is so rare, as it's a useful part. I think that I might have the data sheet for it, but it's probably buried in the "probably won't use these" file! If I find it, I'll put it on line.

I must have about 20 of these, but still no application for them (other than the Jap Synth). I have a pinout sketch, but nothing more. If you do have a datasheet for it, please post it. I`ve never been able to find one.
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iainpunk

Re: Other uses for TA7125P?
« Reply #3 on: February 04, 2021, 03:14:51 PM »
you could use it for an envelope retainer pedal.
its a pedal that has an enfelope follower and a VCA, in in between those an FX Loop, so if you put in a fuzz, you retain the attack and decay of your playing dynamics, i still want to make one of those one day, if i can finally free up a breadboard!

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