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gareth magennis gareth magennis is offline
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Default Pultec EQP clone problem

Right, I have this Pultec EQP-1A clone that apparently was motorboating, but only when attached to a patchbay.
Turns out the manufacturer knew certain serial numbered units were prone to this and offered a mod to fix the problem.
Customer took the unit to a tech who carried out the mod as described in an email from the company.
Only now the unit is something like 12dB down in level than before.

I have removed the mod, and there is in fact about 12dB drop in level with it fitted, the customer is correct.

Original Pultec schematic he
http://www.gyraf.dk/gy_pd/pultec/pultech.gif


The mod is to wire a 100 ohm resistor in parallel with a 0.1uF capacitor directly accross the output transformer secondary.

The pultec schematic shows a 1k resistor in series with a capacitor on the output, the unit is question has a factory fitted 2k2 resistor across the output, but no cap.

I am not having much joy from the company on this matter, but it seems to me that putting 100 ohms across the output transformer is going to reduce the output level rather drastically.
This transformer is directly connected to pins 2 & 3 of the output XLR, so essentialy there is 100 ohms across pins 2 & 3.
Transformer secondary measures 113 ohms DC disconnected.

I have been trying to suggest that either this 100 ohms is incorrect, or the 100 ohms in parallel with the 0.1uF capacitor is not intended to be put across the output, but should in fact be installed somewhere else.
Maybe on the grounding circuit to prevent the motorboating under certain conditions I can't create on the bench.


Any thoughts on this? I'm getting rather frustrated.


Cheers.