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

[Tom Wiltshire]

Be sure to make sure that you can drive the springs pretty hard. I had an old yamaha organ and the best thing about it apart from the crazy yamaha "vertical leslie" inside was the reverb spring circuit, which was able to supply a classic reggae organ stab sound. Boing! Boing! BerBoing!

Unfortunately several parts of it have now died. I wondered about fixing it, but for the tenner it cost me, I might as well just find another one.

T.

On 11 Sep 2011, at 05:31, Dave Brown wrote:

> 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
> 
> 
> 
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