• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Dynakit ST-35 - quiet static (popping noise) in one channel. Help!

TravAndAlex

TravAndAlex

Active Member
Hi. I'm hoping you can help me. I have a Dynakit ST-35 kit that I've used daily for a couple years. I love it! Unfortunately, today I noticed that one channel has an occasional static noise (quiet popping sort of noise). I tried disconnecting the pre-amp and I swapped tubes left to right, one at a time, to see if I could pinpoint the issue. No change. Static still in that one channel. Swapping the speaker wires, and the popping followed the channel, so the issue is definitely with the amp. Wondering if you can help me troubleshoot or suggest where I should start? Thank you!
 
Register to hide this ad
could it be capacitor leakage?
coupling cap failing?
I have 2 ST35s.
Really like those amps. not alot to them so mite be an easy fix.
U got a scope.?
 
I've got a old used scope... and absolutely no idea how to use it! :)

The kit is only 3 years old or so, so my first thought was it must be tubes...but swapping didn't do any good.

You are right though... doesn't appear to be many options to go bad. I bought it assembled, so I'm no expert. :P
 
In the channel that is making the noise, remove the 7247 and see if the noise is still present. If so, then the problem will be located in the output stage area. If the noise is gone, then the problem will be located around the circuits for the 7247.

Dave
 
OK... will do and report back! Thank you!

Sent an email to Dynakit as well tonight. Super fast response. Here's what they said:


I have encountered this type a issue before and suspect any one or more of the (3) Silver Mica capacitors.....Specifically (C2).....(C6).....(C7).
I would also not rule out a tube socket issue....
 
I have an ST-35 that I rebuilt about 2 years ago. I used new original-design audio boards from Dynakitparts and Dave Gillespie's EFB/power supply. It sounds fantastic, but has occasionally made the sounds you describe. One time one of the tubed red-plated for a few minutes. I shut it down and asked for advice on several forums. Based on the answers I cleaned all the tube sockets with alcohol and intradental brushes. The red-plating never occurred again, but later I wondered why I would have had to take such steps with relatively new tube sockets. And I still hear those popping and farting sounds now and then. My current thinking is that these newer tube sockets aren't up to snuff - I was thinking about looking into some of those expensive ceramic sockets for my next build.
 
Lightly tap on the chassis with a screwdriver handle or something like that, to see if you possibly have bad solder joint,if it causes the noise, use a plastic or wooden rod to lightly tap on some of the solder connections to narrow it down
 
Could be a bad contact in a tube. Got exactly the same symptoms you're describing once.
 
Of note too, I have found a number of the Russian small signal tubes that will emit a pop or two during warmup. The tubes that do this are not microphonic, and otherwise perform quite nicely. It's not a pin contact issue, or (in my case) circuit issues, but a tube issue -- the noise moves with the tube. Typically only occurs when things are expanding during warmup, but has occurred at other times as well.

Dave
 
Thanks guys! This is great. I'll see what I can do to narrow down the issue. If interested, I thought perhaps some photos would help...
 

Attachments

  • IMG_3765.jpg
    IMG_3765.jpg
    57.6 KB · Views: 74
  • IMG_3766.jpg
    IMG_3766.jpg
    58.2 KB · Views: 66
  • IMG_3761.jpg
    IMG_3761.jpg
    45.5 KB · Views: 68
  • IMG_3762.jpg
    IMG_3762.jpg
    56.9 KB · Views: 68
  • IMG_3763.jpg
    IMG_3763.jpg
    53.1 KB · Views: 68
  • IMG_3754.jpg
    IMG_3754.jpg
    78.2 KB · Views: 69
  • IMG_3755.jpg
    IMG_3755.jpg
    86.7 KB · Views: 69
  • IMG_3757.jpg
    IMG_3757.jpg
    89.7 KB · Views: 68
  • IMG_3758.jpg
    IMG_3758.jpg
    48.7 KB · Views: 67
  • IMG_3759.jpg
    IMG_3759.jpg
    41.1 KB · Views: 67
kinda tuff to see the noise thru the wire insulation.
O but wait. U can. On a scope.
seriously tho, I hope U get the prob resolved.
these amps are too good to be misbehaving.
funny noise is a stikler.
 
BTW - Absolutely outstanding and fast support from Dynakit. I'm betting you don't get this level or speed of support from most companies.

Here's the reply from Dynakit after they took a look at the pictures:


The (2) Z-565 output transformers are indeed Dynakit. The power transformer is by Triode.


A few things I see that are suspect. The (2) tubular silver colored coupling capacitors are Russian made. Many of these are un- insulated whereas there may be a voltage potential at the outer shell.

Be sure that these capacitors are not contacting the chassis.


Take a close look at the bottom side of the circuit board...Specifically Solder Pad # 10 where the Black lead is connected. Insure that the short solder trace is intact and not broken. This could be causing an intermittent problem. If it looks to be a possible issue...add a short jumper here...


The tube sockets appear to be good quality parts. Often you can detect a problem with the sockets by gently rocking the tube in the socket while the amplifier is operating. Keep in mind that the EL84 tubes will be hot. If you can replicate the distortion problem by rocking the tube then the socket is your problem. You can re-tension the socket pins with a small screw driver or dental pick.


Assuming the problem still persists..then I would replace all (3) of the Black Silver Mica caps on the circuit board. These values should be: 18pF......27pF......33pF. Typically, the value is marked on each of these capacitors.


We stock all of these value caps.
 
Last edited:
Have had similar "sounds" from loose pins sockets. Removed the tubes, tightened and cleaned the sockets and have not heard that since.
 
Ok. So here's what I've tried:

Ensured the Russian coupling capacitors are not contacting the chassis.
Replaced the solder trace with a jumper from Solder Pad 10.
Cleaned each pin socket with De-Oxit and a small dental brush.
Tightened each socket with a dental pick.
Traded around tubes and tried rocking them gently in place while on.

Unfortunately... no difference.

I think the next step for me is to replace the black silver mica caps on the board as suggested by Dynakit.
 
Have you done what Dave suggested in post #4? Just to locate the problem area? Could be those caps. I had a Heathkit 6BQ5 mono amp (Model MA12 here in the UK) which had to have a silver mica cap replaced before it worked.
 
You must log in or register to reply here.
Back
Top Bottom