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solid state reverb drive ciruit.... hummmmm
solid state reverb drive ciruit.... hummmmm
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Old 23rd May 2020, 05:36 AM   #11
JMFahey is online now JMFahey  Argentina
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Originally Posted by Davidscott59 View Post
okay, thanks for the suggestions. I think probably the biggest issue is that I have the tank sitting about 2" from the power transformer! Its a very small box I have it all mounted in. Dang! and I do remember the Fender amps always have the spring mounted to the bottom of the box. I will do some experimenting with moving the tank away and see what happens. and try those other suggestions. will let you know!

Well I have discovered another issue with this! when I play my guitar through this, the low freq (bass) are cut. so somehow I have created a band pass filter. because it is very treble sounding. I don't know where to look to fix this.
You have many bass cutting treble peaking at work there

1) you are driving a pure inductor (input coil) with a constant current signal from U1b .
Which creates a 6db/oct rising frequency response, increasing treble nd cutting bass big way.

That said, THAT is the way to drive a reverb tank.
Anything else gives you muddy boingy sound, so dont change that.

2) R9 + 10uF (C4 combined with C5) also cut bass boost treble big time, again suspect that is done on purpose.
You may increase capacitors to, say, a maximum of 100+100uF in series, but dont overdo it.
Too much bass signal makes reverb sound like door closer or bed mattress springs

3) C6 and R10 cut bass below 160Hz but believe me, you dont want those frequencies hitting the springs.

As is, its an almost Miracle cheesy springs provide useful sound, dont try your luck too much

I make my own reverb tanks and use springs designed to hang toys from the ceiling, go figure!
Design/make/service musical stuff in Buenos Aires, Argentina, since 1969.
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Old 23rd May 2020, 06:07 AM   #12
PRR is offline PRR  United States
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solid state reverb drive ciruit.... hummmmm
> The TL072 isn't designed to drive loads much lower than 2k, yet here its driving 150 ohms. Is that going to be an issue?

Everybody does it. (Well, some beef-up.)

The tank only needs ~~30mA to saturate. Most older chip opamps would do 10mA very accurately but 30mA clean enough for this job. The reverb is NOT the main signal path, a little distortion phattens-up the reverb, it's fine for a basic system. If you want ULTIMATE REVERB then the sky is the limit. (Considering the quality of presently available tanks, I would not bust my butt over it.)
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Old 23rd May 2020, 07:35 AM   #13
Mark Whitney is online now Mark Whitney  Netherlands
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C4 and C5 are way too small with an equivalent capacitance of 11uF. U1b is, therefore, a highpass filter of about 1KHz. 100uF gets you down to 100Hz and 1000uF to 10hz. Try using LTspice to simulate the circuit.
Regards Mark.
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Old Today, 04:39 AM   #14
Davidscott59 is offline Davidscott59  United States
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thanks for the info. I will look into experimenting with the caps. First I still need to figure out where the HUMMMM is coming from and eliminate this, or none of the other fixes will be of any use.
I got to thinking, I have seen commercial reverb units that are in small boxes no more than the size of a Fender bassman head. They don't have 60hz hum issues? so I wonder how they isolate the tank from the xfmr? I wonder, could I create a faraday cage for the tank to isolate it from the mains 60hzs?
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Old Today, 12:40 PM   #15
Kay Pirinha is offline Kay Pirinha  Germany
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Did you assure your reverb tank's driver coil has got both terminals fully isolated from the chassis?
Best regards!
"I spent a lot of money on booze, birds and fast cars. The rest I just squandered." (George Best)
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