Dyna PAS3X, SDS PSU Board and some Wine

104.244.105.51

Posted on July 12, 2015 at 04:20:44

I am sitting here scratching my head trying to figure out why.

About two years ago I purchased un un-built Dynaco PAS3X, a few missing parts but most of the Kit was intact, well apart from a soldering error on the Channel Selector Switch, was this Factory or deliberate not sure, as I think these parts came factory pre-assembled..

Okay here is my story.

Soon after getting the PAS3X built the Selenium Rectiifiers pooped out with a loud POP.

I decide to order an SDS PSU Board and replace it.

I did just that and decided to use the Diodes instead of the 12X4 Tube Rectifier for whatever reason, I thought to myself "less load on the Power Transformer".

So..... two years later, last night I decided to modify the PAS3X and re-install the stock Dynaco labeled 12X4 Rectifier Tube.

The sonic difference is HUGE. Apart from a loss of upper treble grain, the sound is totally relaxed, with air between the instruments and the voices are sublime.

Is there really that much of a difference between the 12X4 and a pair of Diodes?

Of is this a case of slightly lowered filament voltage on the 12AX7's now that the Tube Rectifier is loading the SDS board along with the filaments of the four tubes?

I have not had the chance to experience a Diode vs. Tube Rectifier thing in the past as normally it is one or the other, but this is a revelation.

I am not going back to the Diodes. The 12X4 stays in place and the sound is so much better I have to think Tube Rectifiers and Preamplifiers equal up to some type of synergy.

Thoughts?

Hide full thread outline!

use of SS diodes requires circuit changes IME&O

Timbo in Oz

19:10:49 07/15/15

3

RE: use of SS diodes requires circuit changes IME&O

Cleantimestream

09:56:43 07/16/15

RE: use of SS diodes requires circuit changes IME&O

TimeConstant

06:49:31 07/16/15

...

Show full thread outline!

use of SS diodes requires circuit changes IME&O

Timbo in Oz

19:10:49 07/15/15

3

RE: use of SS diodes requires circuit changes IME&O

Cleantimestream

09:56:43 07/16/15

RE: use of SS diodes requires circuit changes IME&O

TimeConstant

06:49:31 07/16/15

RE: use of SS diodes requires circuit changes IME&O

airtime

06:01:15 07/16/15

Is there really that much of a difference between the 12X4 and a pair of Diodes?"...

Cleantimestream

09:32:31 07/12/15

Well then you're pretty lucky

airtime

06:01:33 07/13/15

RE: Dyna PAS3X, SDS PSU Board and some Wine

airtime

08:12:53 07/12/15

If you didn't make other adjustments that isn't surprising

Timbo in Oz

19:19:19 07/15/15

RE: Dyna PAS3X, SDS PSU Board and some Wine

Eli Duttman

06:36:11 07/12/15

RE: Dyna PAS3X, SDS PSU Board and some Wine

TimeConstant

07:22:13 07/12/15

RE: Dyna PAS3X, SDS PSU Board and some Wine, posted on July 12, 2015 at 06:36:11
Eli Duttman Audiophile Posts: 10455 Location: Monroe Township, NJ Joined: March 31, 2000	The biggest factor is the large difference in forward drop between SS and vacuum diodes. Change the B+ rail voltage and the sound definitely changes too. A secondary factor is SS diode switching noise. Eli D.

RE: Dyna PAS3X, SDS PSU Board and some Wine, posted on July 12, 2015 at 07:22:13
TimeConstant	Nice. Eli its is quite an audible improvement, and change, I am had to play some Streisand, Sade and Eliane Elias as the vocals were spot on. The EL84 Dyna ST-35 clone was sounding also much better with the front end improvement. Making DC load changes to an un-regulated Power Supply can have a dramatic effect I now hear. Thanks.

RE: Dyna PAS3X, SDS PSU Board and some Wine, posted on July 12, 2015 at 08:12:53
airtime Audiophile Posts: 11287 Location: Arizona Joined: February 4, 2003	I don't know the technical "why's" but the tube rectifier sounds much better. Tried it and went back with NO regrets.

Is there really that much of a difference between the 12X4 and a pair of Diodes?"..., posted on July 12, 2015 at 09:32:31
Cleantimestream Audiophile Posts: 7551 Location: Kentucky Joined: June 30, 2005	Is very apparent to myself, others do not seem to hear it ... or care. I conjecture that substandard? speakers and or inefficient speakers is why. Another factor... when you change the voltage the whole circuit is changed ... the higher voltage definitely means more noise in the input stage. The Mind has No Firewall~ U.S. Army War College.

Well then you're pretty lucky, posted on July 13, 2015 at 06:01:33
airtime Audiophile Posts: 11287 Location: Arizona Joined: February 4, 2003	Go with what is more practical and suites your taste. Audio is a very personal thing. With virtually no two people liking the same thing. The corner stone of sales in audio.

use of SS diodes requires circuit changes IME&O, posted on July 15, 2015 at 19:10:49

Timbo in Oz
Audiophile

Posts: 23221
Location: Canberra - in the ACT - SE Australia
Joined: January 30, 2002

Soft recovery (SR) SS diodes - that don't have switching noise problems - do exist and can be used. Because they don't have voltage drop and PIV limitations at switch off, they allow for much stiffer power supplies, which IME is always a good thing.

Switching noise might have been a problem for you but needn't have been.

Higher voltages can be adjusted for, but also don't seem to have been here, and extra volts too can have some significant advantages. Valve amps run on supplies of several hundred volts and storage is 1/2 the capacitance times the square of the volts.

The difference in PSU stiffness between 240 volts and even 280 volts is not small. 240X240 = 57600, 280 V (17% more v) sq'd gives a factor of 78,400 (36% more storage) and ripple would be very low.

There is one other advantage, you have just freed up the heater/filament supply to the VR and it can be used, yep even the 5V ones?, to boost your heater supply headroom and even use higher Gm valves. These almost always sound better so less loop NFB is needed, which is a good thing. Still with the logic of this?

A PP amplifier I came to like and even sold on weekends at the shop years ago was a Quicksilver 8417 type using two 5AR4 VRs. Where two ought to have been adequate - from a VR-design-era perspective - and a choke/cap ladder supply.

So, I don't think VRs are a bad idea, I simply know that SR SS diodes can be better. I don't think QS still use VRs.

Any circuit is a system, in any given state it has dependencies, which are state dependent.

I listen at least once a week to live acoustic music performed to a high standard. At home I find that the audible advantages of valves, in reproducing such music for me, lie in their instantaneous headroom, basic linearity, and low amounts of loop NFB, all making timbre distinct.

None of these valvey features depend on the use of VRs and indeed could be restricted by them.

LBNL Valve Rectifier PSUs have 'sag' which IMO does not belong in a hi-fi amplifier.

Warmest

Tim Bailey

Skeptical Measurer & Audio Scrounger

If you didn't make other adjustments that isn't surprising, posted on July 15, 2015 at 19:19:19
Timbo in Oz Audiophile Posts: 23221 Location: Canberra - in the ACT - SE Australia Joined: January 30, 2002	In circuits where the adjustments have been made the advantages of higher headroom, lower PSU and circuit noise, are quite audible, as we might expect. Warmest Tim Bailey Skeptical Measurer & Audio Scrounger

RE: use of SS diodes requires circuit changes IME&O, posted on July 16, 2015 at 06:01:15
airtime Audiophile Posts: 11287 Location: Arizona Joined: February 4, 2003	I think this may be the reason why "I" prefer tubes for classical and solid state for rock-ish type music. Solid state amps can and do have a wonderful sound, when done right. However, in the end it is a "taste" issue. For me - tubes. Thanks for that excellent explanation. charles

RE: use of SS diodes requires circuit changes IME&O, posted on July 16, 2015 at 06:49:31
TimeConstant	Great... So with a few changes to the Power Supply to account for the offloading of the stock PAS transformer, a pair of high quality FR low noise diodes, the quiescent voltages should park themselves properly for an objective comparison. All good points, all well taken. Appreciate you taking the time to post.

RE: use of SS diodes requires circuit changes IME&O, posted on July 16, 2015 at 09:56:43
Cleantimestream Audiophile Posts: 7551 Location: Kentucky Joined: June 30, 2005	I don't think QS still use VRs." Yes, Mike Sanders still uses them in the re-issue of his full function pre-amp. I hear increased definition and detailed nuance with valve rectifiers. I do not believe this can ONLY be heard through Khorns, although the difference is not as apparent with my Quad ESL 63's. The Mind has No Firewall~ U.S. Army War College.

Vintage Asylum

Dyna PAS3X, SDS PSU Board and some Wine

104.244.105.51