EDIT-FIXED PAS 3 with Phono Hum on phono and special inputs

EDIT 5-24-2020

The solution as suggested was to switch to a 3 prong power cord.  Buzz immediately fixed.

EDIT 5-11-2020
Definitely a grounding problem with my Empire TT.  I think somehow the tone arm itself is not grounded, as i can tap it and increase the buzz / hum.
Inerestingly, i can touch the the top of the tt and tap the the tone arm and i hear no increase in buzz, some how i am 'the path to ground'


Edit: 5-10-2020
So I swapped out my empire table  for my technics sl 1200 (which is internally grounded) and the Hum disappeared (but was humming yesterday * could have sworn*)
The technics seemed dead quiet, except i could hear a faint 'wind like rumble' out of one speaker barely, but i think that is just platter motor noise.
Fairly happy to find this out, however i like the sound of the empire far better. I think i need to focus on the Empire TT being the culprit.


EDIT: I have been able to eliminate the hum/buzz via testing by  turning all tone controls to the left (off?)  but when they are centered it sounds better. however tone controls on this unit are 'on' no matter what the switch does it seems.
       If i turn down Left / Right  Treble / Bass all the way the hum disappears!  Now i have to figure out if its the tone switch or the tone pots. Perhaps i should replace all those controls.
       I can sort of live with it now, knowing that i kind of isolated it. Perhaps someone can shoot me straight about how to proceed here?  I have also posted a pic to see if maybe someone can notice something in the wiring. I read on some other theads to move a ground from (1) to 8 on the line board or perhaps look for untwisted rca cables




Hi all ,

Just got my PAS 3 today, however i Has a hum on the phono input and also notice a louder hum on its neighbor 'special"
Unit does not have a ground lug, so i alligator clipped the TT ground to various places on the chassis



Things i have done / noticed:
* sprayed controls with deoxit.
* used an external phono pre and tried other jacks (quieter, but still a hum in one of my speakers.)
* tried different turntables in the phono jack and phono pre (still a hum)
* other sources like cd player play fine through spare, FM, etc
* hum is 'tolerable' below the 10 oclock volume position.  from 11 and up , its louder, not crazy loud, but noticeable standing 6 feet away, however you cant unhear it after you notice it.
* on spare with CD playing the volume knob seems to not scale the volume. There is alot of turn  from 9 oclock until you hit about 1 oclock and its noticeable louder. However on phono the volume knob scales up as it should.
* reseated all tubes.  tapped tubes and inputs / out puts to listen for noise.  did not look for bad solder joints yet.
* swapped tube positions, changing around the phono board tubes for the other 2 12ax7.
* Tried various combinations of amp / tt / pre in power strip plugged into variac at 117v, had only the amp in the variac, had turntable in different outlet, etc.

I knew buying this, though advertised as silent, probably wouldn't be. All things aside.. i love the sound.

Your first big issue is that your pre-amp appears to be completely original. You really, really need to replace the two bias supply electrolytics (the big green ones) and the selenium rectifier as step one (IMHO). Next I'd replace all the black caps on the two circuit boards and, test each resistor for drift in their values. The wires coming off the selector switch were not wound together very well by the original assembler (IMHO). I wonder if that is exacerbating hum in the unit? You might also want to make sure the RCA jacks for the phono section don't have a loose ground. By the way, when you turn the tone controls counter-clockwise, you aren't "turning them off". You are reducing the bass and treble. Think of the response curve looking like an upside down "U" when you do that. Positioning the controls at their center results in a flat response, not turning them "backwards". I'd also recommend you replace the quad electrolytic can as I'm sure it is at its end of life cycle. Look on this forum for lots of re-build info. It takes time but it is not too terribly difficult! Best of luck and ask questions on here any time you need to. Lots of resourceful individuals here who would be happy to help.

Midwestside wrote:EDIT 5-11-2020
Definitely a grounding problem with my Empire TT.  I think somehow the tone arm itself is not grounded, as i can tap it and increase the buzz / hum.
Inerestingly, i can touch the the top of the tt and tap the the tone arm and i hear no increase in buzz, some how i am 'the path to ground'


Edit: 5-10-2020
So I swapped out my empire table  for my technics sl 1200 (which is internally grounded) and the Hum disappeared (but was humming yesterday * could have sworn*)
The technics seemed dead quiet, except i could hear a faint 'wind like rumble' out of one speaker barely, but i think that is just platter motor noise.
Fairly happy to find this out, however i like the sound of the empire far better. I think i need to focus on the Empire TT being the culprit.


EDIT: I have been able to eliminate the hum/buzz via testing by  turning all tone controls to the left (off?)  but when they are centered it sounds better. however tone controls on this unit are 'on' no matter what the switch does it seems.
       If i turn down Left / Right  Treble / Bass all the way the hum disappears!  Now i have to figure out if its the tone switch or the tone pots. Perhaps i should replace all those controls.
       I can sort of live with it now, knowing that i kind of isolated it. Perhaps someone can shoot me straight about how to proceed here?  I have also posted a pic to see if maybe someone can notice something in the wiring. I read on some other theads to move a ground from (1) to 8 on the line board or perhaps look for untwisted rca cables




Hi all ,

Just got my PAS 3 today, however i Has a hum on the phono input and also notice a louder hum on its neighbor 'special"
Unit does not have a ground lug, so i alligator clipped the TT ground to various places on the chassis



Things i have done / noticed:
* sprayed controls with deoxit.
* used an external phono pre and tried other jacks (quieter, but still a hum in one of my speakers.)
* tried different turntables in the phono jack and phono pre (still a hum)
* other sources like cd player play fine through spare, FM, etc
* hum is 'tolerable' below the 10 oclock volume position.  from 11 and up , its louder, not crazy loud, but noticeable standing 6 feet away, however you cant unhear it after you notice it.
* on spare with CD playing the volume knob seems to not scale the volume. There is alot of turn  from 9 oclock until you hit about 1 oclock and its noticeable louder. However on phono the volume knob scales up as it should.
* reseated all tubes.  tapped tubes and inputs / out puts to listen for noise.  did not look for bad solder joints yet.
* swapped tube positions, changing around the phono board tubes for the other 2 12ax7.
* Tried various combinations of amp / tt / pre in power strip plugged into variac at 117v, had only the amp in the variac, had turntable in different outlet, etc.

I knew buying this, though advertised as silent, probably wouldn't be. All things aside.. i love the sound.

Hum can have several sources.
bad filtering of the filament
bad filtering of B+
cable/grounding. But as what looks on the pictures all grounding seems
original
Start with checking the voltages according to the manual. Too low
filament indicated that the filament caps need replacement.( it's the 2
around the Se rectifier.)

The B+ can cap might have lost capacitance. To you have access to a scope
or feel confident that you can measure ripple on the B+ ?

Normally i recommend fixing all power issues by installing a dedicated
power board. It keeps the dynaco design but with modern component.
These boards replaces all power capacitors and the Se rectifier.
One such board is availabel at tride :
http://triodeelectronics.com/sdslacabofor1.html
another functionally equivalant from erhard audio :
https://www.ebay.com/itm/Dynaco-PAS-Z-PSU-Power-Supply-Upgrade-Kit-6/122728355713?hash=item1c932e1781:g:XowAAOSwstJZRtGi
or
https://www.erhard-audio.com/PAS-Upgrade-Kits.html
( the abay link is better defined, but it's the same board)

Note that the PAS will hum with covers off. Before anything started do a
calibration to know your starting point :
mount covers. Get 2 shorting plugs ( rca connectors with central connector soldered
the the outer metal. Install the plugs in the phono low connectors,
turn the selector to phono and turn upp the volume fully. You can then
measure with an voltmeter the AC voltage at left and right outputs. Note
the value. Cross check with PAS connected to your stereo to get a feel for
how much hum you have.

Then turn off and start replacing. But do wait with any suggestions of
"improving" or altering until you have got the hum and or voltage issue resolved.
When hum is fixed read http://www.audioregenesis.com/ and
peruse the articles about dynaco PAS. This will inoculate your mind
and prevent the worst mistakes.

Good luck, and don't hesitate to post here.

While I don't disagree with those who say you should replace the electrolytics (almost mandatory on a piece of this age), re-do the twisted pairs to the input jacks, etc. I think you should troubleshoot and address the problem at hand first. It is definitely not normal to get increased hum when you touch the tonearm.

First you should look below deck of the Empire and see if there is supposed to be a ground wire between the TT chassis and the tonearm, and that it is there.

Unfortunately, a more likely problem is the filamentary cable between the tonearm tube and the interface to the cable to the preamp. It's very delicate, and it's likely the shield has broken over decades of flexing. If the hum changes as you move the arm around on its pivot, or touch the little cable, it gives it away. If you don't have the means to repair this--it's delicate work and may require special tooling--you may have to send it away or find a local shop.

Also note that the current grounding conventions--carrying the left and right signals over two wires each and a separate fifth wire to ground--hasn't always been followed. Most phono preamps today have isolated RCA input jacks, and a separate *signal* (not chassis) ground. The chassis is usually connected to the ground pin on the AC power cord (for electrical safety), and separate from the signal ground. Ideally you want one star ground point, usually the signal ground of the preamp. The cart may or may not have a shield tied to one of the signal pins, usually left low, which may interfere with this scheme.

In the Dynaco days, though, almost every audio component had a two prong AC plug and chassis ground *was* signal ground. Incidentally, in my experience with building two Dynaco kits nearly half a century ago--an SCA-35 integrated and a PAT-4 solid state preamp--there was a ground post on the chassis, but it was just a sheet metal screw. Perhaps it has gone missing.

The first TT I used with my Dynacos--an AR XA--had no hum issues. It had no separate ground wire, but carried the ground through the left cable shield. When I hooked up a Rabco SL8E on a Thorens TD125 (am I giving away my age?) I got hum between the L and R channels. It disappeared when I threw the mono switch. It was apparently a ground loop between the cable shields and the separate ground wire. I finally minimized this by soldering a piece of wire to each left RCA shell, hooking one end to the ground post on the Dynaco and hooking the other end to the ground post on the Rabco. When I replaced the PAT-4 with a Crown IC150 the hum problem disappeared altogether. The Crown did not have isolated RCA jacks but, rather, each jack grounded to the chassis and the signal carried to the electronics over one wire.

You may find a grounding scheme that works with your Empire (are the tonearm and cart also Empire?) But I believe you are right with your diagnosis that the tonearm is not currently grounded.

peterh wrote:

Midwestside wrote:EDIT 5-11-2020
Definitely a grounding problem with my Empire TT.  I think somehow the tone arm itself is not grounded, as i can tap it and increase the buzz / hum.
Inerestingly, i can touch the the top of the tt and tap the the tone arm and i hear no increase in buzz, some how i am 'the path to ground'


Edit: 5-10-2020
So I swapped out my empire table  for my technics sl 1200 (which is internally grounded) and the Hum disappeared (but was humming yesterday * could have sworn*)
The technics seemed dead quiet, except i could hear a faint 'wind like rumble' out of one speaker barely, but i think that is just platter motor noise.
Fairly happy to find this out, however i like the sound of the empire far better. I think i need to focus on the Empire TT being the culprit.


EDIT: I have been able to eliminate the hum/buzz via testing by  turning all tone controls to the left (off?)  but when they are centered it sounds better. however tone controls on this unit are 'on' no matter what the switch does it seems.
       If i turn down Left / Right  Treble / Bass all the way the hum disappears!  Now i have to figure out if its the tone switch or the tone pots. Perhaps i should replace all those controls.
       I can sort of live with it now, knowing that i kind of isolated it. Perhaps someone can shoot me straight about how to proceed here?  I have also posted a pic to see if maybe someone can notice something in the wiring. I read on some other theads to move a ground from (1) to 8 on the line board or perhaps look for untwisted rca cables




Hi all ,

Just got my PAS 3 today, however i Has a hum on the phono input and also notice a louder hum on its neighbor 'special"
Unit does not have a ground lug, so i alligator clipped the TT ground to various places on the chassis



Things i have done / noticed:
* sprayed controls with deoxit.
* used an external phono pre and tried other jacks (quieter, but still a hum in one of my speakers.)
* tried different turntables in the phono jack and phono pre (still a hum)
* other sources like cd player play fine through spare, FM, etc
* hum is 'tolerable' below the 10 oclock volume position.  from 11 and up , its louder, not crazy loud, but noticeable standing 6 feet away, however you cant unhear it after you notice it.
* on spare with CD playing the volume knob seems to not scale the volume. There is alot of turn  from 9 oclock until you hit about 1 oclock and its noticeable louder. However on phono the volume knob scales up as it should.
* reseated all tubes.  tapped tubes and inputs / out puts to listen for noise.  did not look for bad solder joints yet.
* swapped tube positions, changing around the phono board tubes for the other 2 12ax7.
* Tried various combinations of amp / tt / pre in power strip plugged into variac at 117v, had only the amp in the variac, had turntable in different outlet, etc.

I knew buying this, though advertised as silent, probably wouldn't be. All things aside.. i love the sound.

Hum can have several sources.
bad filtering of the filament
bad filtering of B+
cable/grounding. But as what looks on the pictures all grounding seems
original
Start with checking the voltages according to the manual. Too low
filament indicated that the filament caps need replacement.( it's the 2
around the Se rectifier.)

The B+ can cap might have lost capacitance. To you have access to a scope
or feel confident that you can measure ripple on the B+ ?

Normally i recommend fixing all power issues by installing a dedicated
power board. It keeps the dynaco design but with modern component.
These boards replaces all power capacitors and the Se rectifier.
One such board is availabel at tride :
http://triodeelectronics.com/sdslacabofor1.html
another functionally equivalant from erhard audio :
https://www.ebay.com/itm/Dynaco-PAS-Z-PSU-Power-Supply-Upgrade-Kit-6/122728355713?hash=item1c932e1781:g:XowAAOSwstJZRtGi
or
https://www.erhard-audio.com/PAS-Upgrade-Kits.html
( the abay link is better defined, but it's the same board)

Note that the PAS will hum with covers off. Before anything started do a
calibration to know your starting point :
mount covers. Get 2 shorting plugs ( rca connectors with central connector soldered
the the outer metal. Install the plugs in the phono low connectors,
turn the selector to phono and turn upp the volume fully. You can then
measure with an voltmeter the AC voltage at left and right outputs. Note
the value. Cross check with PAS connected to your stereo to get a feel for
how much hum you have.

Then turn off and start replacing. But do wait with any suggestions of
"improving" or altering until you have got the hum and or voltage issue resolved.
When hum is fixed read http://www.audioregenesis.com/ and
peruse the articles about dynaco PAS. This will inoculate your mind
and prevent the worst mistakes.

Good luck, and don't hesitate to post here.

While I don't disagree with those who say you should replace the electrolytics (almost mandatory on a piece of this age), re-do the twisted pairs to the input jacks, etc. I think you should troubleshoot and address the problem at hand first. It is definitely not normal to get increased hum when you touch the tonearm. First you should look below deck of the Empire and see if there is supposed to be a ground wire between the TT chassis and the tonearm, and that it is there. Unfortunately, a more likely problem is the filamentary cable between the tonearm tube and the interface to the cable to the preamp. It's very delicate, and it's likely the shield has broken over decades of flexing. If the hum changes as you move the arm around on its pivot, or touch the little cable, it gives it away. If you don't have the means to repair this--it's delicate work and may require special tooling--you may have to send it away or find a local shop. Also note that the current grounding conventions--carrying the left and right signals over two wires each and a separate fifth wire to ground--hasn't always been followed. Most phono preamps today have isolated RCA input jacks, and a separate *signal* (not chassis) ground. The chassis is usually connected to the ground pin on the AC power cord (for electrical safety), and separate from the signal ground. Ideally you want one star ground point, usually the signal ground of the preamp. The cart may or may not have a shield tied to one of the signal pins, usually left low, which may interfere with this scheme. In the Dynaco days, though, almost every audio component had a two prong AC plug and chassis ground *was* signal ground. Incidentally, in my experience with building two Dynaco kits nearly half a century ago--an SCA-35 integrated and a PAT-4 solid state preamp--there was a ground post on the chassis, but it was just a sheet metal screw. Perhaps it has gone missing. The first TT I used with my Dynacos--an AR XA--had no hum issues. It had no separate ground wire, but carried the ground through the left cable shield. When I hooked up a Rabco SL8E on a Thorens TD125 (am I giving away my age?) I got hum between the L and R channels. It disappeared when I threw the mono switch. It was apparently a ground loop between the cable shields and the separate ground wire. I finally minimized this by soldering a piece of wire to each left RCA shell, hooking one end to the ground post on the Dynaco and hooking the other end to the ground post on the Rabco. When I replaced the PAT-4 with a Crown IC150 the hum problem disappeared altogether. The Crown did not have isolated RCA jacks but, rather, each jack grounded to the chassis and the signal carried to the electronics over one wire. You may find a grounding scheme that works with your Empire (are the tonearm and cart also Empire?) But I believe you are right with your diagnosis that the tonearm is not currently grounded. wrote:

This makes a lot of sense. Since my first post, i have tested a different modern 3 prong preamp and external phono pre . NO HUM not even touching the tone arm.

My PAS does not have a grounding post. I was thinking about installing one.
I have tried multiple grounding schemes. I have been able to minimize considerably. You can only really hear it a foot infront of the speaker, but its always in you mind that the hum is 'there'.

I do think i need to replace components. Filament caps, diodes, maybe a new can cap.
I did mess around with disconnecting the loudness switch , which gave me better volumes at the lower end of the volume taper. Meaning i didn't have to turn the volume knob wide open to 12 oclock on phono where i would hear hum. but rather played at the same volume nicely at 9 oclock with the volume knob less wide open. There may be a grounding issue, but it could also just be replacing caps and such as everyone mentions.