Spring Reverb Circuit Problems

Jump to Latest
#41
Kay Pirinha said:
In contrast to your first posting it appears you've got an 8 Ω input impedance reverb tank. No opamp ever will suffice to drive it alone. You definitively need a more powerful drive circuit (add a »power« stage, consisting of a complementary transistor pair etc.). No use to mess with the recovery.

Best regards!
Click to expand...
Fully agree.

Forget the OpAmp drive, instead drive the tank "as if it were a small speaker" replacing drive OpAmp with a TDA2030 or LM1875 chipamp, fed from, say, +/-15V rails.

Add a 10-15 ohm 2W resistor in series with input coil, leave the rest of the reverb circuit as-is.

If not clear, will add a simple hand drawn schematic if you need to.

Now I understand why you found such a weak reverb result.
 
#42
Thanks a lot to you both for the input!
After tweaking it a bit (skipping a resistor and a cap and solidifying some wiring), its actually not too bad now, the mix knob when max'd out has a huge amount of verb. I'll have to give it a real world test today.

I know that 2nd link (care and feeding of reverb tanks) which is where I got the top part of the circuit from. In reading that first link just now I see where he's saying "low impedance (about 8 Ohms) input transducers are well suited to being driven with a small power amp IC". So i might be heading in that direction if this doesn't pan out!
 
#44
Ok, tell us what you have.
It would be great if it can be fed from +/-15V rails, since you already have them. .
Most any chipamps will do, as long as it stands those rails.

Or a "12V car type" one if it can be fed from a single +15V rail.
Most can.
 
#45
Post #38 shows the driver strapped as a transconductance amp (current drive). Most but not all 12V car amp chips can do this. Depends if they have internal NFB or not, and if it can be effectively overridden. The stuff from the TDA200x family actually like being used that way.
 
#47
LM386 isn’t powerful enough. It’s really only good for loads of about 20 ohms up. Ive had trouble with BA4506’s - they are finicky and like to oscillate. Doing something funky with the feedback is risky. With the built in resistors, the maximum Zout and gain are limited, but probably close enough to current drive. If it’s stable that way.
 
#49
TDA2030’s are perfectly happy transconductance strapped so they’re probably your best bet. Widely used for practice guitar amps, driving the speaker in the same way. The TDA2003 12 volt single ended CFA version works well too, but only available surplus nowadays. Still plenty of stock worldwide and I never seem to have problems with fakes. The TDA2030 however, is often faked.
 
#53
Oh, I have, dotneck! But there's a big difference between reading them and fully absorbing them! I'm workin' on it though. What part in particular would you point out in this case?

Thanks, wg_ski - Parts are ordered!

I use Tayda a lot by the way, in case any one's looking for a cool supplier. Did an order last month, 10days via USPS from Asia.
 
#54
BJT output to drive any reverb (like below). BD139/140 pair and one op-amp.
That is the ARP2600 synth reverb circuit. VERY clean unit (sounds good).
OS
 

Attachments

  • image_2024-02-05_203613446.png
    image_2024-02-05_203613446.png
    100.6 KB · Views: 71
#56
I suggest to keep it simple.

Replace original 1/2 TL072 driving tank by a good Chipamp, TDA2003 is fine, connected as in the datasheet, gain will be 20X something.

Don't worry about transconductance or constant current amplification, regular voltage drive is fine.

In any case I suggested adding a 10 ohm resistor on series with drive coil, which in practice solves that problem.

After you successfully build it, you may tweak sound.

Build and listen at it, post some samples here.
 
#57
Hey JMFahey, thanks for the post - I will be giving that a go for sure.

You've helped me a bunch in the past, glad to have your insights again.

Once its sounding good (and we listen TO it and not AT it) I will post those samples! ;-)

I might look into some filtering (these springs don't usually sound great with a ton of super low end and super high end).

Cheers!
 
  • Like
Reactions: JMFahey
#58
Post 38 “the updated schematic” showed it transconductance strapped, so I assumed that’s what Gonecat wanted to do. Whether you really want to depends on the tank. This one is apparently lower impedance than most, and if a 5532 won’t drive it adequately there’s no hope of TL07x. TDA2003 ought to drive anything, assuming 11 volts peak to peak is enough.
 
#59
I must admit, I have no idea what transconductance is, I just looked it up and I still don't.
All I was trying to do was combine those two circuits so I had a blend/mix knob on this thing.
TDA2003 is on the way, so we'll give that a shot!
 
#60
Parts arrived, but in a bone-headed move I got TDA2030AL's instead of TDA2003's. (2030 Datasheet). But from what I can see, they are fairly interchangeable.
JMFahey wrote earlier saying to hook it up according to the datasheet - but to clarify, aside from plugging in the chip (power, ins, outs), what other changes might I need to make to the surrounding circuitry?
 
You must log in or register to reply here.
Top Bottom