I am really enjoying my Dynakit Parts ST-35 Amp. I noticed that there is a choke available for it as a mod. What does the choke do to improve performance?
+3
petrnyc
Bob Latino
JimOfOakCreek
7 posters
Adding A choke To My ST-35 Kit Amp
JimOfOakCreek- Posts : 13
Join date : 2011-06-25
Location : Oak Creek, WI
Bob Latino- Admin
- Posts : 3262
Join date : 2008-11-26
Location : Massachusetts
Hi,
The choke won't really make the amp sound any "better" but it should remove the last vestiges of AC ripple that may be riding on the DC. You may notice the residual noise level of the amp drop a little. The nice thing is that there is a place for the choke on the top front of the amp. Just drill two 9/32" holes 2 3/8 inches apart and make another small hole behind the choke for the wires to enter the chassis. The choke replaces the 50 ohm resistor on the quad cap. See photo below.
Bob
The choke won't really make the amp sound any "better" but it should remove the last vestiges of AC ripple that may be riding on the DC. You may notice the residual noise level of the amp drop a little. The nice thing is that there is a place for the choke on the top front of the amp. Just drill two 9/32" holes 2 3/8 inches apart and make another small hole behind the choke for the wires to enter the chassis. The choke replaces the 50 ohm resistor on the quad cap. See photo below.
Bob
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JimOfOakCreek- Posts : 13
Join date : 2011-06-25
Location : Oak Creek, WI
Bob, thanks for your expert evaluation. I think I'm going to leave my ST-35 completly stock. It already sounds great and is very very quiet. I can barely hear an extremely faint hum with my ear 1/4" away from the speaker cone. My speakers are rated at 95db/watt@1meter.
Placement of the interconnects are critical since they will pick up EMF hum. I found that keeping the interconnects underneath, down the middle and tight to the chassis results in near zero hum.
I also made some standoffs for the tube cage. The cage tends to resonate slightly unless damped.
Thanks again....jim
Placement of the interconnects are critical since they will pick up EMF hum. I found that keeping the interconnects underneath, down the middle and tight to the chassis results in near zero hum.
I also made some standoffs for the tube cage. The cage tends to resonate slightly unless damped.
Thanks again....jim
petrnyc- Posts : 6
Join date : 2021-05-10
Question for Bob Latino, what choke is the one you used in your build?
Thank you
Thank you
Bob Latino- Admin
- Posts : 3262
Join date : 2008-11-26
Location : Massachusetts
petrnyc wrote:Question for Bob Latino, what choke is the one you used in your build?
Thank you
That choke is a Triad C-24X. You can get them at Mouser Electronics at the link below.
C-24X choke at Mouser Electronics
Bob
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petrnyc- Posts : 6
Join date : 2021-05-10
Thank you Bob
petrnyc- Posts : 6
Join date : 2021-05-10
Bob ,
Would you b any chance put two chokes one each on plus and minus rail?
Would you b any chance put two chokes one each on plus and minus rail?
Bob Latino- Admin
- Posts : 3262
Join date : 2008-11-26
Location : Massachusetts
petrnyc wrote:Bob ,
Would you b any chance put two chokes one each on plus and minus rail?
You don't really need two chokes on the ST-35. I do use two chokes on the VTA ST-120 and the VTA M-125's for dealing with the extra current draw that these two amps have but my feeling is that you don't need two chokes on the Dynaco ST-35. The C-24X choke is rated at 240 milliamps. The ST-35 doesn't use that much current.
Bob
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petrnyc- Posts : 6
Join date : 2021-05-10
Got it Bob thanks for your help.
daveshel- Posts : 169
Join date : 2011-11-06
Location : Tucson AZ USA
I have rebuilt two ST-35s, and I have not used a choke in either one. The key to getting the best sound out of the ST-35 is using Dave Gillespie's EFB board. Dynaco had to skimp a bit when they designed the ST-35, in order to make price point below the ST-70. The EFB board addresses these shortcomings by adding a regulated adjustable bias circuit and adding some capacitance to the power supply. The difference between even a rebuilt unit and one with EFB is astounding. The amp becomes more dynamic and the bass becomes punchy. I've owned an old school ST-70, a Van Alstine U-70, old school MK-IIIs, and a cool Admiral 7R1 console pull rebuild, and my ST-35 blows them all away.
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petrnyc- Posts : 6
Join date : 2021-05-10
Daveshel,
Would you by any chance have the whole schematic for that DG mod?
Would you by any chance have the whole schematic for that DG mod?
daveshel- Posts : 169
Join date : 2011-11-06
Location : Tucson AZ USA
I used his kits. There's one for the ST-35 that sits at the front of the chassis and another for the SCA-35. It doesn't look like either would work on the chassis pictured in your avatar. There are schematics available at http://tronola.com/html/daves_store.html where he sells the kits. (No affiliation, just a satisfied customer.) There are plenty articles on DIY versions at AK (where he has written much about it) and elsewhere on the interwebs.
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petrnyc- Posts : 6
Join date : 2021-05-10
Thank you Daveshel.
did nit know about this site, amazing!
did nit know about this site, amazing!
corndog71- Posts : 840
Join date : 2013-03-19
Location : It can get windy here
I built a couple of custom versions of this amp with EFB. Nice little amps!
daveshel- Posts : 169
Join date : 2011-11-06
Location : Tucson AZ USA
Beautiful.
What's that joystick-looking thing sticking up from behind the PT?
What's that joystick-looking thing sticking up from behind the PT?
corndog71- Posts : 840
Join date : 2013-03-19
Location : It can get windy here
That’s just the power cord. I think it was one that used a big ferrite. Always experimenting.
I built it for my brother. He wanted all connections on top so he could drop it into a wood box of his own creation.
I built it for my brother. He wanted all connections on top so he could drop it into a wood box of his own creation.
csgod- Posts : 2
Join date : 2021-11-15
Hi all - I'm a new owner of a Dynakit ST-35 with EFB. From first firing it up, with no EFB but with a choke in the PS, there has been just enough hum and buzz to be noticeable. Through various tube changes, lifting the AC ground, then the EFB mod, I have 5.2 mV noise with no input, 7.4 mV with inputs connected to an unused input selected. This is with a TVC passive volume control, but it's about the same with a dead quiet active preamp. This noise does not change with volume control changes.
I've concluded at this point that this level is this amp's inherent noise. Even if that's true I'd really like to make it decrease below audibility at my listening position.
The little amp sounds very, very good with the 89dB/W speakers I bought specifically for it - Triangle BR02 bookshelfs (highly recommended!) The EFB really put it into the outstanding zone, and with these relatively efficient speakers it competes well with my other, much more powerful amps.
Any ideas on what to do next to quiet this gem down?
I've concluded at this point that this level is this amp's inherent noise. Even if that's true I'd really like to make it decrease below audibility at my listening position.
The little amp sounds very, very good with the 89dB/W speakers I bought specifically for it - Triangle BR02 bookshelfs (highly recommended!) The EFB really put it into the outstanding zone, and with these relatively efficient speakers it competes well with my other, much more powerful amps.
Any ideas on what to do next to quiet this gem down?
peterh- Posts : 1832
Join date : 2012-12-25
Location : gothenburg, sweden
Do you have a matched quad of EL84 tubes ? This is a starting point to get a quiet ST35csgod wrote:Hi all - I'm a new owner of a Dynakit ST-35 with EFB. From first firing it up, with no EFB but with a choke in the PS, there has been just enough hum and buzz to be noticeable. Through various tube changes, lifting the AC ground, then the EFB mod, I have 5.2 mV noise with no input, 7.4 mV with inputs connected to an unused input selected. This is with a TVC passive volume control, but it's about the same with a dead quiet active preamp. This noise does not change with volume control changes.
I've concluded at this point that this level is this amp's inherent noise. Even if that's true I'd really like to make it decrease below audibility at my listening position.
The little amp sounds very, very good with the 89dB/W speakers I bought specifically for it - Triangle BR02 bookshelfs (highly recommended!) The EFB really put it into the outstanding zone, and with these relatively efficient speakers it competes well with my other, much more powerful amps.
Any ideas on what to do next to quiet this gem down?
csgod- Posts : 2
Join date : 2021-11-15
Thanks for your reply, Peter. I think I should have started a new thread?
I'm using a seemingly matched quad of NOS 6P14P-K, but it might be better defined as 2 matched pairs. With EFB I believe that should be adequate. I've tried other matched pairs of JJs and Sovteks with the same result.
Anyone with an ST-35 measure your inherent noise? Is 5.2 mV on par?
Cam
I'm using a seemingly matched quad of NOS 6P14P-K, but it might be better defined as 2 matched pairs. With EFB I believe that should be adequate. I've tried other matched pairs of JJs and Sovteks with the same result.
Anyone with an ST-35 measure your inherent noise? Is 5.2 mV on par?
Cam
daveshel- Posts : 169
Join date : 2011-11-06
Location : Tucson AZ USA
My ST-35 is dead quiet. But everything is new except for the transformers - new audio boards and EFB from Dave, even a new chassis. I didn't use a choke - the way the EFB board mounts there isn't any place to mount one. (There is also an article on the site about how to implement EFB without the full board, but the full board also replaces all the power supply caps.)
peterh- Posts : 1832
Join date : 2012-12-25
Location : gothenburg, sweden
No, it's not adquate with 2 matched pair. You must have a matched quad. This as all cathodescsgod wrote:Thanks for your reply, Peter. I think I should have started a new thread?
I'm using a seemingly matched quad of NOS 6P14P-K, but it might be better defined as 2 matched pairs. With EFB I believe that should be adequate. I've tried other matched pairs of JJs and Sovteks with the same result.
Anyone with an ST-35 measure your inherent noise? Is 5.2 mV on par?
Cam
are interconnected and all bias voltages will be the same, if tubes differ the current
through the output transformer will differ.
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