PAS-2 tone control bypass

billinrio wrote:I was never satisfied with the tone control performance of my PAS-2. On my system it did little for the high frequencies and
made the lower ones tubby.  Therefore, I always left them "flat".  But since the PAS-2 isn't a PAS-3x the controls were never really out of
the circuit. So, I decided to remove them.  Of the various instructions that I found online, I decided to go with the Audio Regenesis mod, since it
includes using 1µF caps in order to prevent DC voltage at the outputs.  I just finished the mod and I'm stunned by the improvement
in clarity and imaging. Moreover, both trebel and bass reproduction are greatly improved, and I now have more usable volume below 12:00 It's as if a veil has been removed from in front of my speakers. This mod is truly a no-brainer.

PeterCapo wrote:Having followed along in Dynaco-related forum discussions for about twenty years, I can say that your experience of bypassing the PAS tone controls is not uncommon.

For anyone in a similar situation, I think it's worth mentioning that getting the tone controls "flat" in the non-X PAS means orienting the knobs as instructed in the manual.  Specifically, flat response for the non-X tone controls is achieved when the knobs are installed so that there is a certain asymmetrical rotation relative to the center mark on the face-plate.

The improvement in sound you hear is probably largely a result of bypassing what are old, worn-out electronic parts in the circuit.  It is doubtful that the PAS with tone controls in-circuit sounded that bad when it came off of the assembly line in the 1960s.  But if there are problems with the tone control pots presently, given their age and irreplaceability, bypassing the entire tone control circuit is probably the best option.

Don't recall what you have for a power amplifier, but with your tone controls now bypassed, you should be able to drive low input impedance power amplifiers.  Just a few days ago I hooked my PAS (tone controls bypassed) back up to my Parasound Halo A21 with input impedance of 33KΩ.  They sound great together, and there's no problem with bass roll-off.

PeterCapo wrote:Some thoughts...

I would think that replacing the Black Cats with polypropylenes could make a significant difference, depending on the condition of the pots.

PeterCapo wrote:

billinrio wrote:Here in Brazil, there's a Parasound Halo A21 (black) being offered at an online auction site for US$2,500 + shipping.  Worth it?

Uhh... well I guess that seems like it's a little high for a used A21.  Then again, I have no idea what the market is in Brazil for used audio gear.  You might also inquire about the shipping cost, because the A21 is pretty heavy.  But, before jumping on it, I'd explore other options, if you want to go the solid-state route in a power amp.  For example, do you need the kind of power the A21 produces?  What else is available for less money and would it be sonically synergistic with a PAS?  One of the most important things I can think of would be to have return privileges if you don't end up liking the way it sounds with your PAS - cannot stress this enough.

peterh wrote:
Another buffer sold as kit on ebay : https://www.ebay.com/itm/6N3-5670-Tube-buffer-Audio-Preamplifier-Pre-AMP-board-For-DIY-Amplifier-board/132249408707?hash=item1ecaadd4c3:g:isEAAOSwvflZWyGX

Another kit that seems ok : https://www.ebay.com/itm/JSDZ-DIY-Kit-6N3-Tube-Buffer-Amp-Audio-PreAmp-Amplifier-Board/362869932971?hash=item547cbbc3ab:g:EE0AAOSwW89eDrL6