[sdiy] Arp 2600 reverb tank impedance

[Harry Bissell]

You are measuring DC resistance, not impedance.

You could feed a sine wave (from your ARP if its working) and put a resistor
in series with the tank. I'd choose a resistor that is much higher than what you think
the tank is... if you think the tank is 1Kohm, try at least a 10Kohm.

Feed a 1KHz sine wave into the series connected resistor and coil. Measure the
voltage drop across the resistor. Use ohms law to find the current that is flowing at
1KHz. This current is the same everywhere in a series circuit.

Now measure the voltage drop across the coil. You know voltage and current, solve for
resistance. Because this is a 1KHz signal, its the 'resistance' at 1KHz or in other
words, the impedance.

There are meters to find this sort of thing but I'm assuming you don't have one...
Your meter must be pretty good to make this measurement... a real cheap one
might not be accurate at 1KHz... You could use a scope to do this as well...

Careful, don't hook the VCO direct into the reverb tank, the signal will be too hot
for sure. If your signal level is too high, the coil will saturate and give you the
wrong reading (impedance will read much lower than it should be...)

H^) harry


----- Original Message -----
From: James Dunn <james at 4thharmonic.com>
To: synth-diy at dropmix. xs4all. nl <synth-diy at dropmix.xs4all.nl>
Sent: Mon, 24 May 2010 06:14:59 -0400 (EDT)
Subject: [sdiy] Arp 2600 reverb tank impedance

I'm still working on fixing the reverb tank in my 2600 and am probably 
going to buy a new tank but I don't know what the specs are... I'm 
pretty sure the input transducer on mine is faulty because it gives a 
reading of 1.7 ohms (and my DMM always shows a minimum reading of 0.6 
ohms so this is more like an input impedance of around 1 ohm - which 
sounds too low for a reverb tank?).

Anyway, if someone with a 2600 could confirm what the input and output 
impedances are that would be great. My tank is a 17", vertically 
mounted, Gibbs Special Products Corporation tank marked only as 1122. 
It's from a grey-faced 2600.

thanks

James
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-- 
Harry Bissell & Nora Abdullah 4eva