help with stand alone reverb effect

[pughcityblues]

I have been working on a stand alone reverb box based on the unit in a Fender Blues jr.  I have the correct spring tank and have built the circuit from the Blues Jr schematic.  I have a normal dry signal, but when I add the wet signal with the pot, it just adds static.  I know that I could have an impedence problem, and it is quite possible that I may have a ground problem.  I need some help.  Any suggestions?

[PRR]

Welcome.

> Fender Blues jr.

We don't have all amp plans memorized; on a quick search I see Fender made two Juniors. Please link to the plan you are working from. Or if you prepared your own plan, even better, post that.

> when I add the wet signal with the pot, it just adds static.

Wiring error.

Let us start with the DC voltages, all 8 pins of the chip. Hint: should be one +15V, one -15V, and all others should be nearly zero.

[pughcityblues]

Thank you for replying so quickly.  I have 15 volts across pins 4 and 8 just as illustrated on the diagram.

[thermionix]

You should have 30v across pins 4 and 8.  Did you build with a bipolar power supply?

[pughcityblues]

I built it with a single 15v AC/DC power supply tbat feeds both op-amps.  When I touch pins 4 and 8 with my volt meter on each op-amp, it reads 15v and the polarity is correct.

[thermionix]

From "ground" (0v) to pin 8 you should read +15VDC.  From ground to pin 4 you should read -15VDC.  From pin 4 to pin 8 you should read 30VDC (+ or - depending on which meter probe you put where)

Is that what you are getting?  I'm not sure what you mean by AC/DC power supply.

Edit:  After re-reading your last post, I don't think you're using a bipolar power supply.  You need someting with basically 3 wires (or connections) coming out of it.  +15V  0V  -15V

It sounds like you are using a standard (unipolar?) power supply, with just 0V and +15V, and have pin 4 going to 0V and pin 8 going to +15V.

[pughcityblues]

The power supply is a 120v AC to 15v DC converter.   I get 15v DC across pins 4 and 8.  Pin 4 to ground is about -1.5v DC on each op amp.  Pin 8 to ground is about +13.5v DC on each op amp.

[pughcityblues]

Ok.  Is the 0v lead connected to ground?

[thermionix]

You were posting while I was editing.  But yeah, you have the wrong kind of power supply.  You can probably still get the circuit to work with the power supply you have, but it will take some circuit changes, and you might end up with less headroom.

I'll wait now and let the smarter folks here weigh in on that.

[thermionix]

Ok.  Is the 0v lead connected to ground?

Now we're simul-posting.  Yeah 0V would go to ground, if you had the right bipolar power supply.

[pughcityblues]

I have found a 15v dual output bipolar kit for about $30 online.  I think I will try it instead of modifying the circuit.  Thanks for Your help.