|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
69.174.87.108
In Reply to: RE: pls recomend best upgrades for dyna pas 3x and st 35 posted by merdy on July 24, 2015 at 10:24:31
Check out the EFB modification for your ST-35. It only costs a few dollars in parts, and the measured as well as the subjective performance of the amp will improve. Not to mention that your output tubes will last a lot longer. Jim McShane didn't want to sell me a quad of Gold Lion EL84s for use in my SCA-35 until he found out I was doing the EFB mod. Then he was happy to, because the tubes see 27 mA of current after EFB, as opposed to 35 mA prior.
As for the PAS...I did the David Vorhis "Last PAS" mod on one of mine many years ago, and am still using it. At the very least, I'd follow the suggestions given by a few other posters, and upgrade the filament supply with schottky diodes and cram in as many µF as you can fit.
My first mod years ago was to a stock PAS, and I was quite disappointed. I added a couple of 1N4007s and two 7500 µF caps to the filament supply, and it sounded great. The reason I was disappointed was because it actually sounded better than my Audio Research SP3-A-1 which had, at one time been considered by some to be the best preamp made. I couldn't believe that a "lowly" Dyna PAS with a few dollars in parts could surpass it.
"You won't come back from Fletcher-Munson curve"-Jan and Dean
Follow Ups:
I did the full Curcio PAS upgrade / rebuild. It was quite good. I mean REAL nice sounding. However it did have one nasty problem. The power supply board would blow out the voltage regulator and take out a my very expensive and rare NIB 12AX7 tubes. You do know that now you can't get those tubes - GONE! This would happen about every three to four months. You could mark it on the calendar.
The pas can be upgraded into a very nice preamp. Search and ask and it will happen.
This is from memory but the 35 is a sweet little amp. Do it up nicely.
charles
...but the ST-35 with cathode bias is a sweet sounder. Some of that sweetness might be lost when converting to fixed bias. Converting to dual mono power supplies, requiring a larger chassis with two power trannies, plus independent bias for each channel could be a ticket toward sonic bliss...
The PAS has so much potential. First challenge is replacing that awful volume control. The tone controls, other than the PAS-3X versions, also leave something to be desired. As 1973shovel mentioned, an upgraded PAS can beat an upgraded ARC SP-3A. The simplicity of the four tube circuit in the PAS, plus no cathode followers in the PAS make the resto job well worthwhile. A sensibly upgraded PAS will trounce many "high end" preamps of any vintage...
If the OP can find the early 1980s Audio Dimensions lit, including the Trevor Lees cascode phono stage circuit, that one deserves mention; but it had no line stage. With some resourceful mods, including a more robust power supply, the PAS can fit a simple line stage.
One of the cool features about the PAS is that Blend Control; great with vintage discs. Unfortunately, there is no Stereo Reverse option built in. If the OP leaves out the tone controls, there are some interesting faceplates to be had for the PAS...
So I should mention that the PAS I referenced also had the tone controls disabled, so it wasn't just a filament supply upgrade which took it beyond my stock ARC SP3-A-1.Regarding the bias supply for the ST-35, you could be right regarding fixed vs. cathode biasing. I do a lot of searching of the Asylum archives, and there was a post on that very subject. I'll start by saying that I can't remember the member's moniker, so take this with the proverbial grain of salt. I will say that he had his own web site of tube history, schematics, etc. and seemed to be well thought of in the tube community. Gary somebody, maybe?
He posted that he converted a ST-35 from cathode to fixed bias, four individual pots, one for each tube. He stated that the sound got worse than with the cathode bias, but he wasn't sure why. Several years ago I read the David Gillespie article on EFB, which seemed to explain why the sound likely got worse after going to fixed bias. I sent a link to his email address at his web site, but he never responded.
As I have mentioned, my experience with the SCA-35 (same output stage and transformers as the ST-35) was positive after installing the EFB. A nice sonic upgrade for next to nothing, and increasing output tube life is a bonus.
Edited to insert omitted word.
"You won't come back from Fletcher-Munson curve"-Jan and Dean
Edits: 07/27/15
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: