|
Dynaco-Doctor Forum Welcome! Need support, you got it. Or share your ideas and experiences. |
|
|
|
Dynaco-Doctor Forum Welcome! Need support, you got it. Or share your ideas and experiences. |
|
In Reply to: Cheap PAS 3 Upgrade posted by Kozzmo on October 24, 2003 at 12:04:36:
Hey David,Russ makes some good suggestions. I would like to add a little info and some of my experiences.
First, there are a couple of articles out there on the net that discuss PASS mods, one called "SPICE and the PASS" or something like that and an article by Audio by VanAlstine on the power supply. These gave me some good hints.
Second, I just redid a PASS power supply and phono section. I run this into my Foreplay line stage. I redid the power supply and filament supply as Russ57 suggested. However, I used two Angela (Solen) 60uF caps for first two caps and two 180uF electrlytics each bypassed with 10uF Angela caps for the next two caps. This got rid of all residual hum in the circuit (I modelled the supply first to get the values). In the phono section, I removed the positive feedback resistor. I replaced the plate resistors with metal film types. I then replaced the cathode resistor in the second stage with a diode (BEWARE- the tube manuals recomend that 12AX7's NOT be diode biased). Finally, I installed a 30pF "Miller" capacitor (grid to plate) on the input of the first stage.
These mods proved quite worthwhile. The bass is is well defined and articulate, but not overblown. Overall the sound is much cleaner and more airy. I like it allot and I think it is a better phono stage than my previous rebuilt Fisher 400C.
I have bee lucky enough to obtain a bunch of 12AX7s over the past few years. I would say the best in the phono section are "smooth plate" Telefunkens, "box anode" Mullards, and "bugle boy" Amperexes (never put in the "orange globes" so I can not comment). Anyway, in my setup the Amperexes are clear winners in the phono stage, yielding better detail and focus than the others. I have been using the Tele's in the line stage, BUT I have not rebuilt this stage so my preference could change. Moreover, in its current state, the PAS line stage is crushed by my actively loaded Foreplay. However, there is much room for improvement in the PASS line stage (Russ57 indicated some of the easier stuff), so I withhold my final judgement untill I finish up my mods.
Good luck,
Rodney
This post is made possible by the generous support of people like you and our sponsors:
Follow Ups
- a couple of comments, mods, tubes - rodney 12:50:42 10/30/03 (0)
Top of Page ]
[ Contact Us ]
[ Support/Wish List ]
[ Copyright © 2025, Audio Asylum, all rights reserved ]
