Transformer simulation

[ProfPep]

I'm doing some experimenting with Pultec type passive EG's.

The proper Iron I've got lives in the rack with it's associated devices.

Has anyone any suggestions for transformer simulating circuitry that I can use on my breadboarded circuits to get a reasonable, (I'm no way asking for perfect) response? Something I can put across the inputs and outputs to approximate the presence of a transformer, without the cost? I can ise load resistors, but that somehow seems to miss something.

For reference, I'm playing with an EQ design, but using reed relays to switch the caps, taps and resistors. What I intend to end up with is something that performs like a Pultec, has certain frequency differences, (like 50Hz rather than 60Hz - I'm in Europe!), and once that's sorted, can be controlled by a micro, to allow 'snapshot/recall'. I'd orginally thought of servo driven pots, but came to the conclusion that 0.5dB steps, on a selector would actually be better for repeatability and matching.

I have this control surface idea that has a shaft encoder with an integral push button for each band, rotating goes from cut to lift, press and rotate switches frequency bands . Q is on a separate control. Display is via LED's or an LCD panel, and the reeds keep the control system isolated from the audio.

I know, it will never fly..... but it should be fun finding out. I just don't want to have a pair of exotic ironmongery on the bench for the next 6 months, not doing a lot.

 

[haima]

what exactly do you want to "simulate" about the transformers?

you COULD make some opamp circuits which have a particular input and output impedances - that might help you get the frequencies right... but it seems to me you'd be best to keep the exotic iron sitting on the bench with the circuit - if you want to hear exactly what your finished product will sound like...

edcor makes cheap and pretty good transformers - around $10usd - could be worth a look.

sound like an interesting take on the pultec circuit - keep us posted how it goes.

for me, i'd be against the frequency & boost/cut being on the same encoder - it requires an extra brain process to remind yourself what "mode" you are in, before you twist the knob.

but i'm a one function, one knob kinda guy...

 

[haima]

also - one of the cool things about the circuit, for some people, is the different sounds you can get by cutting AND boosting simultaneously...

so you may not want to limit the choice to only cutting OR boosting...

just a thought!

 

[ProfPep]

Thanks.

Good point on the 'boost and cut simultaneously', I was going off the old Pultec guide about not using both at once, and forgetting that you can get 'creative' with that.

I've had a few HUI ideas - I began with "Up" and "Down" button for each function which is probably the cheapest. A good compromise on hardware and panel space might be to use knobs for boost and cut, and use buttons for the frequency selection.

I used to call some FX pedals I made for friend "SABLA's" - which stands for "Sounds A Bit Like A", as in a "SABLA TS9". That's more like what I'm trying to get here, rather than a true clone.