Hello all,
I recently saw a demo of an old school Pultec eqp-1a and was wowed by it. It reminded me of a fully adjustable loudness contour that you find on many stereos...but on steroids! However, I almost choked on my cup of water when I saw what this thing is going for on Ebay. Further, it is a mono unit, not stereo. Given that it only has three tubes in it, I would figure that one could build the thing for around $300. So that is what I am asking. Is there a kit for this tone control out there? If not has someone built something like it?
I recently saw a demo of an old school Pultec eqp-1a and was wowed by it. It reminded me of a fully adjustable loudness contour that you find on many stereos...but on steroids! However, I almost choked on my cup of water when I saw what this thing is going for on Ebay. Further, it is a mono unit, not stereo. Given that it only has three tubes in it, I would figure that one could build the thing for around $300. So that is what I am asking. Is there a kit for this tone control out there? If not has someone built something like it?
Actually all the data is on the internet.
The difficult part is obtaining the 3 transformers: input, interstage and output transformers.
Input transformer for impedance matching, passive filter where the magic happens, interstage for coupling then a classic good audio amplifier to compensate for the passive filtering stage. Very nice.
The difficult part is obtaining the 3 transformers: input, interstage and output transformers.
Input transformer for impedance matching, passive filter where the magic happens, interstage for coupling then a classic good audio amplifier to compensate for the passive filtering stage. Very nice.
Did you try searching?
DIY Pultec - Google Search
IMHO the amount of information ALREADY available is mind-boggling. We should not be typing stuff already written.
DIY Pultec - Google Search
IMHO the amount of information ALREADY available is mind-boggling. We should not be typing stuff already written.
Yes, however, two of the transformers are really for the balanced signal, of which I wouldn't have a need for in a standard pre-amp build. Right off the bat the first input transformer could be done away with and not affect the sound. The interstage could be done away with as well, but I wouldn't know how that would affect the sound. Generally inductive coupling is better than capacitive coupling, so hard to say here. The output transformer is a bit tricky as it has some kind of feedback circuit and my guess is that one certainly would affect the sound. But this transformer averages about $370. Which would make a stereo EQ already expensive. Ideally, doing away with all the iron could make a $300 to $400 a possibility.
I have come across this variant though and it looks interesting:
It is called "Gyraf" or G-Pultec:
http://www.gyraf.dk/gy_pd/pultec/gy_pd_sch.gif
Note that even though it does have an input and output transformer, it is solely for balanced operation and they can be done away with.
The only other esoteric part there is the multi-tapped inductor, but I believe that part can be had for about $35.
The single tube amplification does make this variant at around $300 - $400 doable.
I would say the operation would probably be close to the original, but the sound quality. That might differ given that buffer amplifier is quite a different circuit. The original uses two tubes in the circuit as well. The only way to know is if someone built this variant and did comparitive sound tests with the original.
Yes, it is mind boggling and hence why I cut to the chase and asked the more direct question here.
It doesn't bother me.
Thanks!
Geo