BAD PCB and kits Now Available

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JimiB
Posts: 6
Joined: Thu Jan 15, 2009 9:53 am

Re: BAD PCB and kits Now Available

Post by JimiB »

whats the voltage on the rails of the BA? (I am wondering if a 2520 will work)
Also I have a BA that I built a while back - can I swap the op-amp I have in there with a 99V with out changing parts?

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Joe Malone
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Re: BAD PCB and kits Now Available

Post by Joe Malone »

JimiB wrote:whats the voltage on the rails of the BA? (I am wondering if a 2520 will work)
The BA and BAD both have a opamp voltage regulator made on the PCB using T1 #BD681 and Z2 30v to 47v 400mW zener. For +/-24v opamps like the JLM99v and Hybrid this doesn't need to be fitted but for 2520 with want +/-16v to +/-18v the #BD681 and 33v to 36v zener need to be fitted to give the opamp the right voltages.

If going to run a 2520 etc that needs the BD681 and 33v zener just mention it in the comments box when checking out of the web store and I will put the parts in for free into the BA or BAD kit.
JimiB wrote:Also I have a BA that I built a while back - can I swap the op-amp I have in there with a 99V with out changing parts?
Yes you can swap opamps without any changes if they can run on the same voltage rails.
Joe :-)
JLM Audio
Capturing Audio without Injury

chrisp
Posts: 184
Joined: Sun Mar 04, 2007 11:46 am
Location: Sydney, Australia

Re: BAD PCB and kits Now Available

Post by chrisp »

Joe (or anyone)

The BAD PCB has separate GAIN paths for each opamp (although they are usually wired with a double gang pot so that both apply equal amounts of gain). It also has an INSERT path (I O 0v) which can be used as a volume control (or a unbalanced signal point for connecting an eq or comp etc). The following assumes a 1:4 input and 1:2 output tranny.

Although not pictured in the connection diagram, it seems possible to run both amps at pretty much full gain (by connecting both Rgain resistors to directly to 0v rather than going through a pot) and using the insert point as a volume control. The volume control acts like a fader (in fact, you could use a fader), going from silence through to max (equal to 86db of gain), rather than a gain control that would always have 18db of signal gain from the transformers even when gain is turned right down.

As a gloss on this, you could then retain a separate INPUT GAIN control for the first amp, leaving the second one strapped to max gain. The volume control would then act as an OUTPUT LEVEL control, going from a minimum of zero signal to maximum level represented by the amp 1 gain plus 52db of gain (12 from the input tranny, 6 from the output tranny and 34 from amp 2).

Are there any issues with the above? In particular, is running a 99V at 34db gain continuously any sort of an issue, either in terms of heat generation or otherwise?
Chris P
---------------------------------------------------------
I do lots of things. I believe eclectic skills are best.

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