Gyraf Pultec - question about filterboard levels

Hiya,

I finished a gyraf pultec the other day - All the voltages are as they should be on the main board but the eq is putting out an extremely low volume level and I need to overdrive the heck out of its input in order to get a reasonably usable output level.

I followed the signal through the circuit and the level drops 10x once it gets through the filterboard regardless if bypass is on or not. Is the level supposed to drop and the gain be made up by the buffer stage? Any help diagnosing this would be appreciated as I am going nuts trying to figure this out.

thanks!

> Is the level supposed to drop and the gain be made up by the buffer stage?

Yes.

So I have a problem with my buffer stage. I'll poke around there once my eyes and brain stop hurting.

thanks PRR

It seems my problem was more fundamental. I am glad I got a chance to scrutinize the schematic in search for the problem. I tend to paint by numbers unless there is something wrong.

My issue is that I am using the eq as an insert in summing amp. The insert is the usual TRS sharing tip and ring for the + of the send & receive (definitely not balanced). I am putting this unbalanced send into the transformer balanced input of the eq. It works perfectly if route the signal directly from my DA converter into the eq. I realize there is an input for an unbalanced but shouldn't I be able to send tip & ground only to the balanced input section?

the passive pultec filter networks needs to be driven from a proper source, 1. balanced and 2. capable of driving low impedances.

Yeah... I need to install a 2nd jack for the unbalanced inserts.

BTW excellent sounding inductors Max! My Pultec (when used properly) sounds incredible. I have been using it all afternoon. Big thanks to Jakob for putting this together and all of you who worked out your problems on the forum. :guinness: :guinness: :guinness: The advice on draining the power caps saved my life a few times last night. I can just imagine that big ass popping spark happening on my heart instead of on my screwdriver. :shock:

The LM317 gets extremely hot. I sawed down a massive aluminum finned heatsink and it still gets blazing hot. I've read some other posts and I guess this happens but I am probably going to make some cut some vents into the case.

I can just imagine that big ass popping spark happening on my heart instead of on my screwdriver.

Click to expand...

um, don't use a screwdriver, just add draining resistors and wait until the caps are discharged while watching the voltage drop with a multimeter. This has been discussed on the board some time ago... 470k on the big caps, or something like that...