Solid state spring reverb power supply

[Ben79]

I'm looking to build the above and need a 15v dual power supply which I thought I might as well build myself too.

I'm wondering what kind of current draw the circuit would have running 4 tl072 opamps for a 3 spring medium length tank.

I know I need a centre-tapped transformer, some are marked 15-0 15-0, would that enable me to achieve the same result?

They are also sometimes marked in milliamps and sometimes VA. I know volt amps is AC power rating but I'm not sure what kind of value I should be looking for.

Any other advice? Should I go for a toroidal to reduce noise?

Is this what I need? http://www.ebay.co.uk/itm/2X15V-30Va-To ... SwVNxaAQbh

I guess using regulators means I can shop around for a cheap transformer that doesn't need to be 15v on the button.

Thanks.

[crochambeau]

Are you driving the springs with the TL072?

I'm wondering what kind of current draw the circuit would have running 4 tl072 opamps for a 3 spring medium length tank.

TL072 are not high current devices. Their current draw will be dictated by the circuit they are in, but over all I would expect them to want to remain in 10-20 ma range. Your spring might want more juice, depending on input impedance.

I know I need a centre-tapped transformer, some are marked 15-0 15-0, would that enable me to achieve the same result?

Yes, you simply tie the two secondaries together (low of one to high of the other, and this node becomes your common reference) to create a center tapped equivalent circuit.

They are also sometimes marked in milliamps and sometimes VA. I know volt amps is AC power rating but I'm not sure what kind of value I should be looking for.

Any other advice? Should I go for a toroidal to reduce noise?

Is this what I need? http://www.ebay.co.uk/itm/2X15V-30Va-To ... SwVNxaAQbh

I guess using regulators means I can shop around for a cheap transformer that doesn't need to be 15v on the button.

Thanks.

Those eBay transformers are probably good for around 1 amp per winding. (I MIGHT BE WRONG, but) I figure VA as a product of voltage (at secondary) and amperage. in this case, a 30 va xfrmr having two 15 volt secondaries I would apply 15 va per secondary. Since the secondary is 15 volts, 15 (va) /15 (volts) = 1, in amps. If you look at the eBay pic, they have a 12 volt same va, and you can see they've got 1.25 amp rating, which figures as well.

Toroidal might make a difference if everything is close together. I would suggest situating the *pickup* end of the reverb pan on the far side from the PT (regardless of type) as it will be the one dealing with the smaller currents.

[Ben79]

Thanks Croc, that's clear, I know what I'm doing now.

I think the circuit uses the TL072s to drive and recover. It's an old PCB kit that was sold bundled with a tank for DIY. Originally it was 4x LM741 but someone has replaced them I guess to lower the noise.

[crochambeau]

Did it come with a tank? If you're providing that part I think you'll want a higher impedance input...

but since I've never built one with opamps I very well may not know what I'm talking about - so take it with a grain of salt.

[Ben79]

Yeah the tank and PCB were bundled so should be compatible but it quite likely wasn't intended for guitar.

[imJonWain]

+1
You won't need any more current then the opamps can draw and tl072 can't put out much over 20mA so figure a bit more then that per op amp, not a whole lot in your case.

Lot's of good info here on reverb driving and recovery stuff, especially for figuring out impedance related things.
http://sound.whsites.net/articles/reverb.htm

Most opamp driver and recovery circuits look really similar to the ones in the above link.

I am working on a PCB for an effects loop/reverb driver and recovery circuit combination based off of the designs from that link that I plan to replace the stock one in my Laney with.

[Ben79]

It doesn't seem to matter how many times I try, I can't get my head round the real world meaning of impedance.

I didn't get the kit in the end but I'm still determined to build a reverb unit of some kind. One day.

[crochambeau]

It doesn't seem to matter how many times I try, I can't get my head round the real world meaning of impedance.

Impedance is reflected load or nominal source resistance. Getting the two to match up is not nearly as important as it was 60 years ago.

Take these TL07n opamps for example. A stage has an output capability rated at 20ma, and they're powered by 30 volts. Plug those *maximum* ratings into Ohms Law and it will return 1500 ohms as being the absolute minimum resistance acceptable.

Resistance is a DC measurement, the AC equivalent is impedance. In many ways they are interchangeable, unless you're talking moving coils, inductive or reactive loads - in those cases the reflected impedance will shift depending on signal frequency, and a "nominal" figure is offered.

I have reverb tanks that reflect a 20 ohm DC resistance on input, which is a coil that drives the spring. AC impedance MAY be much higher at typical frequencies, but as the frequency drops it will get nearer to a DC state and the reflected impedance will itself shift toward that 20 ohms... which in the case of a TL07n would likely cause component failure.

So: impedance is used when dealing with AC signal because often a static resistance won't cut it. It's not incredibly important inside fuzz circuits and so forth because those are largely resistive loads and impedance will only factor in when calculating curves (like EQ, etc) that are frequency related. From a frequency perspective, impedance is a curve and resistance is a straight line.

It becomes critical when transmission of power is at play, and as small as it is, a spring reverb is just a little power amp pushing a spring.

[Ben79]

I appreciate your bold effort to help me here!

I've read that over a few times and I'm starting to get it. So impedance is important to know because if it's too low then too much current will flow and whatever is delivering it will overheat and fail....is that correct? I'm not sure what 'reflected' means in this context though.

And audiowise it's useful because it....can tell you how much resistance and hence loss there will be to certain frequency ranges?

[crochambeau]

I appreciate your bold effort to help me here!

I've read that over a few times and I'm starting to get it. So impedance is important to know because if it's too low then too much current will flow and whatever is delivering it will overheat and fail....is that correct? I'm not sure what 'reflected' means in this context though.

And audiowise it's useful because it....can tell you how much resistance and hence loss there will be to certain frequency ranges?

Yeah, impedance is basically resistance for all intents and purposes, you just can't nail a hard value on it because it shifts with frequency. So we dumb it down into "high" and "low" ranges...

I said reflected because in the case of stuff like transformers much of the load is not defined by the transformer itself but by circuitry past it.

[imJonWain]

If you're still interested in making your own spring reverb I finished my buffer/effects loop/reverb PCB layout today. It's meant to go in a tube amp, specifically a Laney AOR Series 1 combo (which also has the needed transformer built in), just before the PI. But with a few adjustments to the buffer, mixer, and reverb recovery gain you could use it elsewhere. For power you just need a 30v CT PT that's good for 250 or 500mA to be safe. Hammond has one for $20 and I'm sure there are cheaper options too. So you could use it to build a decent and cheapish solidstate spring reverb tank setup

Here's a link to my post on diy stompboxes.
http://www.diystompboxes.com/smfforum/i ... c=119509.0


I'm gonna go over it a few more times for mistakes and probably have 10 made so I'll be selling the extras at my cost + shipping.

[Ben79]

Sounds great, I'd definitely be interested in buying a PCB.