2. amps-preamps
  3. 1400094668

HT input anomaly on Grounded Grid Preamp

Recently, I completed building a Transcendent Sound preamp, with a home theater input. It was confirmed as being wired correctly by Bruce at Transcendent.

However, with the HT inputs in use, all the other inputs were nearly muted, and instead of having unity gain, the attenuator had to be turned up to use the HT input.

I have since been using a normal input for HT, and have converted the HT input to an output, for my subwoofers.

No one has been able to puzzle out this issue, from the preamp's designer, to John Chapman at Bent Audio, or anyone else so far. I know it's not much info, but I'll supply what info I can. Anyone care to take a crack at it?

Thanks and regards,
Dan
Ag insider logo xs@2xislandmandan
response34's avatar
response34
169 posts
 
It sounds to me that there is certainly something not correct in the wiring. I have been designing and building tube preamps for years and many with HT bypass. It is a very simple configuration and the volume control should have absolutely no effect.
A HT bypass should simply take the signal from the inputs and direct it to the outputs with nothing in between.
the only purpose of the HT bypass is to simplify the system allowing your amplifier(s) to be used both with your preamp or pre/pro without having to swap cables.
how is the HT switching done on your unit? Passive toggle switch? Rotary switch?
Ag insider logo xs@2x
islandmandan OP
1,260 posts
 
Hello Response34. I thought the thread died without any replies.

The HT jacks were connected to the L/R outputs of the rotary switch, which are then connected to the attenuator inputs.

I have since started using a normal input, and just adjusting gain until it matches the pre-pro. The extra jacks I then converted to an additional output pair for my subwoofers.

I would very much like to know what was wrong, for future reference, and to just make sense of it.

Thank you, and regards,
Dan
truemaineiac's avatar
truemaineiac
249 posts
 
Did the pre-amp designer look at it?
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