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

[aankrom]

 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