[sdiy] Driving high impedance reverb springs with IC amps + transformer?

[Dave Brown]

I found the paper I used when I designed mine.  It is very good.
http://roymal.tripod.com/reverb.htm

I must have found the specs for my tank and designed mine around a maximum current.  The paper mentions a typical of 10 mA.  At +/-9VDC, you have plenty of headroom for 10 mA of current.  The transducers in the reverb are not all that large so I doubt you need more than this.  I'm sorry I'm not more help but I did this about 10 years ago and just don't remember the details.  Mine does work very nicely, though.  Give it a try and see.  There aren't many parts for the driver.  Just use a guitar amp or something with low level inputs as the recovery amp.  That way you can test your driver and see how much drive capability it needs.

Someday I will probably come across my design notes.  This was back in the paper era.

Dave

-----Original Message-----
From: aankrom [mailto:aankrom at bluemarble.net] 
Sent: Saturday, September 10, 2011 5:42 PM
To: Dave Brown
Cc: synth-diy at dropmix.xs4all.nl
Subject: RE: [sdiy] Driving high impedance reverb springs with IC amps + transformer?

 Would this overcome the lack of drive due a relatively lower voltage  swing from a +/-9V supply vs. say a +/-15V supply? I know I'm still  concerning myself with voltage here. I'm just trying to avoid things  like crossover distortion from a buffered op-amp, etc... I'll have a  look at your design. I've seen some interesting synth DIY reverb module  designs. I was tempted to use the Polyfusion design, (with some parts  replacements here and there. I dunno why I'm stuck on +/-9V because I  just remembered I'm going to be using this in a 5 channel stereo mixer -  and of course I'd use +/-15V for that.

 On Sat, 10 Sep 2011 10:29:41 -0700, "Dave Brown" <davebr at earthlink.net>
 wrote:
> Think about driving it with current instead of voltage.  Put the input 
> in the feedback loop of an op-amp.  The reverb tank input needs to be 
> floating as neither end will be grounded.  My reverb design for my 
> modular used a tank with an 800R input impedance so it is similar.  
> There are a number of good ap notes out there although I don't have 
> any bookmarked.  You can see my design on my site at 
> http://modularsynthesis.com/modules/DJB-002/djb002.htm
>
> The schematics are there, but not much else.  It was my second module 
> and I wasn't putting that much detail there.  Even the schematics are 
> hand drawn.
>
> Dave
>
> -----Original Message-----
> From: synth-diy-bounces at dropmix.xs4all.nl
> [mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of aankrom
> Sent: Saturday, September 10, 2011 10:02 AM
> To: synth-diy at dropmix.xs4all.nl
> Subject: [sdiy] Driving high impedance reverb springs with IC amps + 
> transformer?
>
>  I have a reverb tank with an input impedance of 600 Ohms. There's a 
> simple circuit I found online to drive reverb tanks with an LM386 amp.
>  I've heard that driving a tank with too much DC bias can magnetize 
> the core of the input driver - which is probably bad. Also, since I 
> plan to  use
> +/- 9V, I probably won't have enough swing to really drive the tank.
>  Then I had an AHA! I could use one of those cheap 1KCT:8Ohm audio 
> transformers from Radio Shack. I could drive the 8 Ohm side with the 
> amp  IC (I like LM380's better...)and drive the tank with the 
> secondary. If I use the tap it'd be 500 Ohms, which should be close 
> enough. Also the xformer will isolate the tank from DC. The small size 
> will cut low end,  but for reverb, this is probably a good thing. I'm 
> just wondering if I'm overlooking anything, like maybe should I let 
> the transformer output
> -->
> reverb input float or should I ground it? I thought if I grounded the 
> center tap, I could switch the phase of the reverb audio by switching 
> which primary lead I use. Will I really get enough swing using a +/- 
> supply?
> Might I get too much? Should I load the amp IC with a resistor,  that 
> is, might this help protect the tank? If I burn an LM386, big deal.
>  I have a million of them.
>
>  AA