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Steady state buzz in Dyna PAS.

24.20.10.236
Posted on December 12, 2021 at 19:14:57
viridian
 I have a factory assembled Dyna PAS. When I acquired it, there was a steady state buzz in both channels. Thought it might be in the power supply, so replaced the whole power supply with the Gearhart board, which replaces the quad cap and selenium rectifiers and filters. The buzz is the same and has not been changed at all. Interestingly, the preamp sounds much better.

So the preamp is completely stock other than the power supply board. The buzz is not super loud but is steady state and present on both line and phono. Any suggestions on the next place to look would be appreciated. Thanks in advance for your time.

 

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I know you know your way around, posted on December 14, 2021 at 08:08:24
1973shovel
Audiophile

Posts: 10183
Location: Greenville SC
Joined: February 25, 2007
 ...but since you don't mention the usual troubleshooting methods:

Have you cleaned the tube sockets, or at least removed and re-seated tubes?

Have you swapped in other 12AX7s?

Have you cleaned the selector switch?

Have you tried adding a ground wire, either to your tonearm, or to the AC outlet ground?

Have you tried reversing the PAS's non-polarized plug and seeing which way gives you the lowest AC leakage measured at the chassis?

Have you tried different interconnects between your source(s), preamp to amp, or both?

There's more, but you see my point. If you haven't, I'd start there before you start replacing parts.

Also, I'd compare your voltages to those in the PAS manual, and also check the coupling caps on the board to make sure you have no DC leakage.

Good luck with it.

 

Thank you! You give me far too much credit, much appreciated., posted on December 14, 2021 at 08:28:44
viridian
 I am about half way through the list, but there are plenty of things you mention yet to be done. Will work through the rest. The guidance is great, and thank you. And happy holidays!

 

Wow, posted on December 15, 2021 at 08:36:15
1973shovel
Audiophile

Posts: 10183
Location: Greenville SC
Joined: February 25, 2007
 That's a much better reply than, "Thanks for the useless comment"! What a dipshit that guy was.

Meanwhile, good luck tracking down the buzz, and please post your results. It helps keep the tumbleweeds outta this place.

 

I think the pandemic has a lot of folks wound up. , posted on December 15, 2021 at 14:49:56
viridian
 I will give ol' Jaynemo the benefit of the doubt. Perhaps I should've put a smiley face after my comment.

Now, back to our regularly scheduled program. I have three days off both Christmas and New Years weekends and the week in between will be pretty slow, so I am really looking forward to working through the rest of your suggestions. I truly appreciate the support and encouragement. Have a great holiday and don't forget to over eat and over drink, just the later not while driving.

 

Ain't that the truth?, posted on December 17, 2021 at 06:45:53
1973shovel
Audiophile

Posts: 10183
Location: Greenville SC
Joined: February 25, 2007
 Last week I was behind a car in the acceleration lane, getting on a highway. The car in front of me was doing about 50 MPH, while the posted speed limit was 65 MPH, so this person was not merging correctly.

The guy behind me sped up, safely changed into the far left lane and got up to the speed limit. This wouldn't have prevented the slow driver's merging in any way. But the under-speed car apparently took exception to being passed, and cut across two lanes in an attempt to drive the other car into the concrete barrier which divides the lanes from oncoming traffic. The two cars continued to play enraged games, now doing about 45 MPH.

The car that was nearly wrecked finally got around the car who was intending to play Demolition Derby, by passing them in the right lane. They were apparently so enraged (I don't blame them for being angry) that they then swung a hard left, and attempted to drive the first car into the same concrete barrier. Then they continued to chase each other up the highway. I was doing 70 MPH, and they left me like I was standing still.

It was the worst case of road rage I've ever seen, by a long shot, and I attribute it to people being "wound up", as you said. It made the rest of my motorcycle ride a bit more unnerving than usual, to put it mildly.

Meanwhile, back at the Dynaco ranch, I hope you're able to track down your PAS issue without much problem. Oh, and I wasn't able to find any information about your "Gearhart board". Does it remove the 12X4 rectifier? If you can't solve the buzz, you might want to try finding the Gearhart's schematic ahead of time.

A healthy, happy Christmas to you too.


 

That's why I sold my bike many years ago. Link to board. , posted on December 17, 2021 at 16:56:56
viridian
 My mistake Erhard Audio. It's basically just like Sheldon's board, replaces the selenium and the quad cap with discrete caps. Retains the 12X4.

Though that it might take care of the buzz, but no dice. Was way worth it though as the preamp just sounds a whole lot better. Sorry to send you on the wild goose chase, after you apparently watched the wild goose chase on the highway, LOL.

Link below:

 

Ahh, the Erhard, posted on December 20, 2021 at 05:00:51
1973shovel
Audiophile

Posts: 10183
Location: Greenville SC
Joined: February 25, 2007
 That one I've heard of! A quick Duck Duck Go search hardly qualifies as a "wild goose chase" though, although I did keep it in the waterfowl family.

It would be interesting to know whether the improvement in sound you noticed with the Erhard was due to the replacement of the can cap, the increase in filament voltage due to the elimination of the selenium rectifier, or both.

After you've got your hum issue sorted out, if you're in the mood to experiment, I'd suggest adding additional capacitance to the filament supply. You can try it temporarily by using two caps with as much capacitance as you can find, of the proper voltage rating, of course.

Clip-lead the caps into the circuit, then power up the PAS. Listen for a while, then carefully disconnect one of the leads, and listen again. The improvement for me was always very easy to hear when the extra capacitance was added. You can connect and disconnect the caps multiple times during the trial, once the caps have received the initial charge.

That's a moot point though, at least until you find the cause of the buzz you're experiencing. Good luck with it.

 

Epic fail., posted on January 2, 2022 at 13:26:27
viridian
 No luck and I ran out of road. Did it all and reflowed some solder joints, rerouted wires. Nada. Flipping the polarity of the plug in the receptacle was the only thing that helped. Just not enough. I'm going to box it up and put it in the closet until I am ready for another go.

 

That's too bad, posted on January 8, 2022 at 03:29:28
1973shovel
Audiophile

Posts: 10183
Location: Greenville SC
Joined: February 25, 2007
 I was hoping you'd find the source of your buzz and been done with it. I don't blame you for taking a break from it though.

Although I do enjoy seeing the cobwebs being brushed away from this forum on occasion, if and when you do get back to your PAS, I might suggest posting on the DIY Tubes Asylum. I have the distinct impression that those who could help you the most rarely, if ever, click on this ghost town.

That said, I thank Rod on occasion for not closing this place up, since I think it's a good bet that it's no longer a sponsored forum. I say that because there's a wealth of Dynaco information buried in the archives, stuff I've never found anywhere else.

Take care.

 

Thank you. Much appreciated., posted on January 20, 2022 at 15:00:38
viridian
 Oh, it will get solved, one way or the other.;^)

I have quite a few projects going, but when I get back to Mr. PAS I think that I will hook him up to a headphone amp and listen while carefully rerouting the interior cables. Maybe I will find something.

 

RE: Steady state buzz in Dyna PAS., posted on January 17, 2023 at 12:01:59
xaudiomanx
Audiophile

Posts: 3663
Joined: August 16, 2004
 Sounds like a 120 cycle grounding issue. There is a guy in New York that can find any buzz or low frequency hum. He totally fixed my Arthur Loesch preamp from any audible noise. His name is Da-Hong See-Too and he is fabulous. He is a 6 time Grammy winner for classical music and his work is second to none.

Look him up!

Try him out! You can send it to him from where you live. Or send it to me and I'll give it to him to fix.

 

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