Recomended voltage ratings for PAS 3 resistors and caps

PeterCapo wrote:350 VDC for the resistors should be fine, as the highest B+ to either board is 200 VDC.  Please note that most resistors in the PAS were originally 1/2-watt carbon composition, but there were some 1-watt precision resistors on PC6.  Most of the capacitors have their voltage rating marked right on them.

A 33pf is available in a Wima polypropylene from Mouser - try looking up Mouser #: 505-FKP2O100331D00JN.  You'll have to drill a small hole in the PC board to install it.  In other words, one lead will be soldered to one of the original solder pads but the other will go through the small hole you'd drill in the board, and then you'll have to run a wire from that lead to the other solder pad.  Worth the trouble, because this 33pf capacitor is in the line stage feedback loop, and I'd much rather have polypropylene here than ceramic or even mica.

I wouldn't be too anxious to replace the original 68pf and other original precision parts on PC 6.  I'd give it careful thought.  I'm not sure if you can get better parts to replace them with.  For the PCBs, I assume you are considering new production copies of PC5 and PC6.  If that is correct, have a look here: https://www.ebay.com/itm/Dynaco-Dyna-PAS-Preamp-NEW-BASIC-BARE-BOARD-SET-PC-5A-PC-6A-Made-In-USA/372987766390?hash=item56d7cda676:g:VYkAAOxySE9Q9LXA

With regard to your musings over aftermarket drop-in replacement circuits, I am sure you'd find enthusiastic responses from satisfied customers.  But, I would expect that the sonic character of the PAS would very likely be changed.  I'd think this is especially so, since some aftermarket circuits incorporate solid-state devices that I expect would shift the sonic character significantly closer to a solid-state sound.  I've run into this with some of my gear that uses tubes as well as solid-state devices.  It's really a question of what kind of sound you prefer.  A PAS rebuilt to the original Dynaco circuit design can have a clean, all tube sound, with a holographic sound-stage and other high-end sonic goodies that can compete with anything else in its price range and even beyond that.  The final arbiter is personal sonic taste.  That's the subjective parts of this.

On the objective side, the original Dynacos like the PAS have long since been vetted by independent labs and have been found to have solid performance all the way around.  If you have not seen them, have a look at the Audio Regenesis lab analysis of the original PAS, found along the left-hand side of the following webpage: http://www.audioregenesis.com/

PeterCapo wrote:I took a quick look through that thread.  Sounds like the recommendations changed some parts values?  Do you have an original PAS you are rebuilding, or are you cobbling one together by gathering parts?  I'd also cross-check part values, ratings and physical placement against the original Dynaco PC boards, the original Dynaco schematic, the original pictorial wiring diagrams and the photos in the original manual.  Do you have a copy of the PAS-3X manual WITH the pictorial wiring diagrams?  If not, PM me and I'll work on getting a copy to you.

For a 0.02µF have a look at Mouser #: 667-ECW-F6203HL

I'd have to look at an original PC6, but it has 1% capacitors, and I believe the one-watt resistors (brownish/reddish color) are something like 2%, they were sealed and are probably fine.  I'd just replace the six big, black tubular capacitors and the carbon composition resistors only.  Take care working on PC6, because there are wires going up to the selector switch, and that selector switch isn't very tolerant of being pushed and pulled.  IOW, the selector switch has open contacts that can lose good contact without a lot of provocation.

For tube sockets, I like the Japanese Azuma nine-pin ceramic sockets with either gold or silver contacts - but only their nine-pin sockets.  I am not crazy about their octal sockets.

20 gauge with Teflon insulation sounds fine.

For the power supply... cap boards have the potential to outperform the quad section capacitor.  But cap boards are also more difficult to implement.  I've read a number of reports of hum problems with cap boards.  I don't believe it's a problem with the cap boards.  Rather, I think it's a problem with integrating them into the PAS grounding scheme.  So, it can be challenging if you were to have hum problems.

I’ve given it some thought recently, because I’ve been working with someone rebuilding his PAS.  I’ve suggested getting a new quad section capacitor and putting a 0.1µF polypropylene bypass capacitor in parallel with each of the four sections.  Also, put a 10µF polypropylene between E16 and ground on both PC boards.  I have not tried this, but it retains the original Dynaco power supply topology and could close the gap with a cap board.  Anyway, something to mull over.

For the filament supply, consider upping the electrolytics to something closer to 10,000µF apiece and using UF4008 ultra-fast diodes.

Now that I see you have a very nice original, factory assembled PAS-3, I'd like to float an ideas by you. But it's kind of past my bedtime, so maybe we can pick this up over the weekend. wrote:

Midwestside wrote:

Yes, my bed time too.  I read what you wrote,  I will start with the filament supply and then wait for the rest. Its in nice shape, i just want to do this thing justice and hear what it was designed to do sonically. obviously other have the expertise for that. Any suggestions welcome.

PeterCapo wrote:

Midwestside wrote:

Yes, my bed time too.  I read what you wrote,  I will start with the filament supply and then wait for the rest. Its in nice shape, i just want to do this thing justice and hear what it was designed to do sonically. obviously other have the expertise for that. Any suggestions welcome.

It might not be necessary to change all of its parts to arrive at a satisfying sound.  Maybe work in stages.  For instance, start with a refresh of the filament and B+ supplies and see how you like it.  Then you could try changing the volume control pot, which has often been reported as an improvement.  You could then non-destructively bypass the tone controls, meaning you'd perform the bypass procedure in such a way that it could be reversed.  By following the tone control bypass procedure, you'd also eliminate the DC offset at the main preamp outputs.  Finally, check the voltages at the test nodes given on the right-hand side of page 11 of the manual and correct any problems you might find.  These things alone can result in a significant cleanup of the sound that you may find satisfactory without changing all of the parts.

peterh wrote:

Midwestside wrote:

Yes, my bed time too.  I read what you wrote,  I will start with the filament supply and then wait for the rest. Its in nice shape, i just want to do this thing justice and hear what it was designed to do sonically. obviously other have the expertise for that. Any suggestions welcome.

One suggestion is to get a power supply board from, lets say erhard audio
See https://www.erhard-audio.com/Power_Supply_Kits.html  , the topmost board ( $42 )
replaces the filament caps and Se rectifier and also replaces the can cap, all this as
the price of teh can-cap.

Grounding is no pain, just follow the instructions that comes with the board. The result
will be an amp that can be serviced in the future using standard components ( board mounted
electrolytes, standards Si diodes etc)

Midwestside wrote:

peterh wrote:

Midwestside wrote:

Yes, my bed time too.  I read what you wrote,  I will start with the filament supply and then wait for the rest. Its in nice shape, i just want to do this thing justice and hear what it was designed to do sonically. obviously other have the expertise for that. Any suggestions welcome.

One suggestion is to get a power supply board from, lets say erhard audio
See https://www.erhard-audio.com/Power_Supply_Kits.html  , the topmost board ( $42 )
replaces the filament caps and Se rectifier and also replaces the can cap, all this as
the price of teh can-cap.

Grounding is no pain, just follow the instructions that comes with the board. The result
will be an amp that can be serviced in the future using standard components ( board mounted
electrolytes, standards Si diodes etc)

I went ahead and ordered one. The one rjpjnk recommended.  I just read the SDS ones were kind of confusing so i wrote off the idea entirely.
I also have volume , balance and tone control kit coming from dynaco designs as well as an LED light replacement.

So that will be phase one i suppose.

I want that original refreshed sound. I know i have a ground loop or some other hum  for the phono, and maybe a rewire and a new selector switch would help.
The turntable grounds to the chassis and gets quieter, but there is still faint buzzing in both speakers that you can 'sense' more than hear, but you can hear it.

I know im in the right place for help, so i can take it slow , just need to get the critical pieces refreshed first.

would an rca back panel upgrade be night and day with better contacts?

Someone asked about the tubes  i think it came with 2x chinese 12ax7 and 2x 12ax7 sovtek (which are in the phono section)

peterh wrote:

Midwestside wrote:

peterh wrote:

Midwestside wrote:

Yes, my bed time too.  I read what you wrote,  I will start with the filament supply and then wait for the rest. Its in nice shape, i just want to do this thing justice and hear what it was designed to do sonically. obviously other have the expertise for that. Any suggestions welcome.

One suggestion is to get a power supply board from, lets say erhard audio
See https://www.erhard-audio.com/Power_Supply_Kits.html  , the topmost board ( $42 )
replaces the filament caps and Se rectifier and also replaces the can cap, all this as
the price of teh can-cap.

Grounding is no pain, just follow the instructions that comes with the board. The result
will be an amp that can be serviced in the future using standard components ( board mounted
electrolytes, standards Si diodes etc)

I went ahead and ordered one. The one rjpjnk recommended.  I just read the SDS ones were kind of confusing so i wrote off the idea entirely.
I also have volume , balance and tone control kit coming from dynaco designs as well as an LED light replacement.

So that will be phase one i suppose.

I want that original refreshed sound. I know i have a ground loop or some other hum  for the phono, and maybe a rewire and a new selector switch would help.
The turntable grounds to the chassis and gets quieter, but there is still faint buzzing in both speakers that you can 'sense' more than hear, but you can hear it.

I know im in the right place for help, so i can take it slow , just need to get the critical pieces refreshed first.

would an rca back panel upgrade be night and day with better contacts?

Someone asked about the tubes  i think it came with 2x chinese 12ax7 and 2x 12ax7 sovtek (which are in the phono section)

changing selector won't cure hum problems, in fact is must be a last resort to be done
if the selector breaks down.
The dynaco selector has a big feature - it shorts unused inputs to prevent them from
blleding over. As an example: a tuner might be on all the time, if one listens to
phono ( or CD ) then you don't want radio ads or anything else bleed over to the
phono music. Dynaco selector prevents this, the other i have seen does not.

For debugging phono hum :
get a pair of shorting plugs. Install them in the phono inputs, select phono and
turn up volume. The expected AC signal  at the pre output should be 2-3 mV . If
you measure this the amp is fine, the hum problem is to be fixed elsewhere.
A ground connector between PAS and record player, make sure this is electrically
connected to the tonearm outside.
Connect the record player to the phono inputs, connect power amps and speakers.
Move the cables between record player and PAS while listening at the speakers. Often
cheap cables will pick up electromagnetic disturbances in the room, changes in
volume while moving cables will confirm this. Bad contact a tthe backplace rca  connectors will
be hearabe if rotating the contacts , a cleaning with a glassfiber brush usually fixes this.
There is new backplanes to bye, but this are big jobs with lots off opportunities
of problems. Like selector, avoid these if possible.


Does any of the above actions work out ?

PeterCapo wrote:

Midwestside wrote: ... I also have volume , balance and tone control kit coming from dynaco designs as well as an LED light replacement. ... I want that original refreshed sound. ...

Don't shoot the messenger, but last time I looked it appeared to me as if the DD tone control kit is not an exact replacement for the original tone control circuit; looked to me like it is something different from the original.

Midwestside wrote:

peterh wrote:

Midwestside wrote:

peterh wrote:

Midwestside wrote:

Yes, my bed time too.  I read what you wrote,  I will start with the filament supply and then wait for the rest. Its in nice shape, i just want to do this thing justice and hear what it was designed to do sonically. obviously other have the expertise for that. Any suggestions welcome.

One suggestion is to get a power supply board from, lets say erhard audio
See https://www.erhard-audio.com/Power_Supply_Kits.html  , the topmost board ( $42 )
replaces the filament caps and Se rectifier and also replaces the can cap, all this as
the price of teh can-cap.

Grounding is no pain, just follow the instructions that comes with the board. The result
will be an amp that can be serviced in the future using standard components ( board mounted
electrolytes, standards Si diodes etc)

I went ahead and ordered one. The one rjpjnk recommended.  I just read the SDS ones were kind of confusing so i wrote off the idea entirely.
I also have volume , balance and tone control kit coming from dynaco designs as well as an LED light replacement.

So that will be phase one i suppose.

I want that original refreshed sound. I know i have a ground loop or some other hum  for the phono, and maybe a rewire and a new selector switch would help.
The turntable grounds to the chassis and gets quieter, but there is still faint buzzing in both speakers that you can 'sense' more than hear, but you can hear it.

I know im in the right place for help, so i can take it slow , just need to get the critical pieces refreshed first.

would an rca back panel upgrade be night and day with better contacts?

Someone asked about the tubes  i think it came with 2x chinese 12ax7 and 2x 12ax7 sovtek (which are in the phono section)

changing selector won't cure hum problems, in fact is must be a last resort to be done
if the selector breaks down.
The dynaco selector has a big feature - it shorts unused inputs to prevent them from
blleding over. As an example: a tuner might be on all the time, if one listens to
phono ( or CD ) then you don't want radio ads or anything else bleed over to the
phono music. Dynaco selector prevents this, the other i have seen does not.

For debugging phono hum :
get a pair of shorting plugs. Install them in the phono inputs, select phono and
turn up volume. The expected AC signal  at the pre output should be 2-3 mV . If
you measure this the amp is fine, the hum problem is to be fixed elsewhere.
A ground connector between PAS and record player, make sure this is electrically
connected to the tonearm outside.
Connect the record player to the phono inputs, connect power amps and speakers.
Move the cables between record player and PAS while listening at the speakers. Often
cheap cables will pick up electromagnetic disturbances in the room, changes in
volume while moving cables will confirm this. Bad contact a tthe backplace rca  connectors will
be hearabe if rotating the contacts , a cleaning with a glassfiber brush usually fixes this.
There is new backplanes to bye, but this are big jobs with lots off opportunities
of problems. Like selector, avoid these if possible.


Does any of the above actions work out ?

Put in shorting plugs, phono selected, volume up  got a reading of about .002v AC  which i assume is Mv.
There is no 'noise' twisting around the rca inputs.  So i will try hooking a wire directly to the tone arm and moving around to the amp and the pas.
Perhaps a new volume knob will help, i have to turn it to around 12 oclock to get good listenable sound for phono.  with a cd player it can be around 10 oclock.
I can turn the volume on phono to around 9 oclock and the buzz is amost non existent, but it is too low for listening.

using another pre and a phono stage with the turntable grounded to the phono stage, i get no hum. so it must be a ground loop i suppose.

Your PAS seems to have no internal generated hum, it's externally you find the source of hum. A new volume pot ( not knob) won't change anything here. It will help if tracking is bad. Now back to hum: Ground loop is unlikely as the PAS has no ground connection with it's 2 prong cable. Connecting the PAS case to ground might change things. The proper way is to install a 3 prong mains cable , but before that a ground cable connected to any of the backside screws will do. Reversing the power cord might also make a difference. Mine PAS is grounded with a copper cable to my outlet ground, as are the rest of my equipment. The volume differences of various sources comes by the sources, there is no standard (or rather many conflicting standards) for "line level" sources. Some preamps has adjusting pots for each input, PAS lacks this. wrote:

Best not lack focus, do one thing at a time ; hum is one set of actions , then if any of the pots needs changing do that. But don't dig everywhere at once ! Volume pot is available ( you need a 250k w/loudness which is available at ebay). The tonecontrol pots differs for PAS3 and PAS3X. The PAS3X is special and has as far as i know no source other then used from scrapped amps. PAS bass pot is 750k, the treble pot 400k both rather unusual but not impossible to find. wrote:

peterh wrote:

Midwestside wrote:

peterh wrote:

Midwestside wrote:

peterh wrote:

Midwestside wrote:

Yes, my bed time too.  I read what you wrote,  I will start with the filament supply and then wait for the rest. Its in nice shape, i just want to do this thing justice and hear what it was designed to do sonically. obviously other have the expertise for that. Any suggestions welcome.

One suggestion is to get a power supply board from, lets say erhard audio
See https://www.erhard-audio.com/Power_Supply_Kits.html  , the topmost board ( $42 )
replaces the filament caps and Se rectifier and also replaces the can cap, all this as
the price of teh can-cap.

Grounding is no pain, just follow the instructions that comes with the board. The result
will be an amp that can be serviced in the future using standard components ( board mounted
electrolytes, standards Si diodes etc)

I went ahead and ordered one. The one rjpjnk recommended.  I just read the SDS ones were kind of confusing so i wrote off the idea entirely.
I also have volume , balance and tone control kit coming from dynaco designs as well as an LED light replacement.

So that will be phase one i suppose.

I want that original refreshed sound. I know i have a ground loop or some other hum  for the phono, and maybe a rewire and a new selector switch would help.
The turntable grounds to the chassis and gets quieter, but there is still faint buzzing in both speakers that you can 'sense' more than hear, but you can hear it.

I know im in the right place for help, so i can take it slow , just need to get the critical pieces refreshed first.

would an rca back panel upgrade be night and day with better contacts?

Someone asked about the tubes  i think it came with 2x chinese 12ax7 and 2x 12ax7 sovtek (which are in the phono section)

changing selector won't cure hum problems, in fact is must be a last resort to be done
if the selector breaks down.
The dynaco selector has a big feature - it shorts unused inputs to prevent them from
blleding over. As an example: a tuner might be on all the time, if one listens to
phono ( or CD ) then you don't want radio ads or anything else bleed over to the
phono music. Dynaco selector prevents this, the other i have seen does not.

For debugging phono hum :
get a pair of shorting plugs. Install them in the phono inputs, select phono and
turn up volume. The expected AC signal  at the pre output should be 2-3 mV . If
you measure this the amp is fine, the hum problem is to be fixed elsewhere.
A ground connector between PAS and record player, make sure this is electrically
connected to the tonearm outside.
Connect the record player to the phono inputs, connect power amps and speakers.
Move the cables between record player and PAS while listening at the speakers. Often
cheap cables will pick up electromagnetic disturbances in the room, changes in
volume while moving cables will confirm this. Bad contact a tthe backplace rca  connectors will
be hearabe if rotating the contacts , a cleaning with a glassfiber brush usually fixes this.
There is new backplanes to bye, but this are big jobs with lots off opportunities
of problems. Like selector, avoid these if possible.


Does any of the above actions work out ?

Put in shorting plugs, phono selected, volume up  got a reading of about .002v AC  which i assume is Mv.
There is no 'noise' twisting around the rca inputs.  So i will try hooking a wire directly to the tone arm and moving around to the amp and the pas.
Perhaps a new volume knob will help, i have to turn it to around 12 oclock to get good listenable sound for phono.  with a cd player it can be around 10 oclock.
I can turn the volume on phono to around 9 oclock and the buzz is amost non existent, but it is too low for listening.

using another pre and a phono stage with the turntable grounded to the phono stage, i get no hum. so it must be a ground loop i suppose.

Your PAS seems to have no internal generated hum, it's externally  you find the source of hum.
A new volume pot ( not knob) won't change anything here. It will help if tracking is bad.
Now back to hum:
Ground loop is unlikely as the PAS has no ground connection with it's 2 prong cable.
Connecting the PAS case to ground might change things. The proper way is to install
a 3 prong mains cable , but before that a ground cable connected to any of the backside screws
will do. Reversing the power cord might also make a difference.
Mine PAS is grounded with a copper cable to my outlet ground, as are the rest of
my equipment.
The volume differences of various sources comes by the sources, there is no standard
(or rather many conflicting standards) for "line level" sources. Some preamps has
adjusting pots for each input, PAS lacks this.

I've read a number of posts where folks have reported a significant improvement in sound quality by replacing the volume pot with a "better" pot or stepped attenuator. My own PAS improved when I went to a better volume pot. The nice thing about this is that you get an improvement in the sound quality while keeping the circuit design original. Lacking more details about the pots in the DD kit, IMO they do not look like anything of standout quality. Audiophile-preferred upgrades to the original volume pot include Blue Alps, or a stepped attentuator, or something like the Noble brand pots (if you can still find them). wrote: