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Posted

I have checked the wiring and there aren´t problems but since I am doing things, I have a XLR 4 pin output conector and a TRS. What is the most appropriate way to connect the TRS ground?

From the TRS to ground of any Sigma22 or join the cold outputs into TRS ground.  ¿?

Posted

Don't quite understand your question? At any rate, the ground lug from the TRS jack should go straight to PSU ground (sigma22?)

Posted (edited)
On ‎21‎/‎10‎/‎2017 at 2:44 AM, Pars said:

Don't quite understand your question? At any rate, the ground lug from the TRS jack should go straight to PSU ground (sigma22?)

Sorry Pars, I have dismantled the channel and I am checking the solders but for the moment I have not found anything strange.

I asked you about TRS gorund because with this ampli I worked hard to avoid the ground loops. 

 

Edited by jose
Posted

I have been reviewing the entire pcb and I have not encountered any problems. Solder is OK, resistors, sand seemed intact too.

So I installed the board and decided to change the THAT340 as it´s the easiest component to replace and the most prone to make noises and ... Bingo! Totally silent. :rolleyes:

Fortunately, I placed these components on the bases. 

This is the third THAT340 that I change by different noises. Has anyone else had problems with them?

I've bought it at Mouser so they are original. 
:(

Posted

that definitely does suck, I had one noisy one out of a batch of 10.

birgir is making a little mini board, and Justin bought a pile of dual transistors, might be a better solution

the layout of the amp is such that you can replace the that340 with jfets if you can get them

Posted

Thanks Dr. Gilmore.

My ampli sounds amazing in both SE and Balanced, but as I can change the THAT by another solution.

 

I have several Jfets in my "warehouse" so I'm tempted to make a small mini-plate for them.

 

 

Posted

If you have the THAT socketed, you can just plug the JFETs in there, assuming they are thru-hole TO92 packages (that is what I did on my SS Dynalo). Make sure they are good machined pin sockets though (Mill-Max, etc.) and not those crap leaf sprung ones.

Posted
3 hours ago, jose said:

I have been reviewing the entire pcb and I have not encountered any problems. Solder is OK, resistors, sand seemed intact too.

So I installed the board and decided to change the THAT340 as it´s the easiest component to replace and the most prone to make noises and ... Bingo! Totally silent. :rolleyes:

Fortunately, I placed these components on the bases. 

This is the third THAT340 that I change by different noises. Has anyone else had problems with them?

I've bought it at Mouser so they are original. 
:(

Did you try re-inserting the noisy THAT340 to verify if it's a contact problem instead of a defect BJT? 

Posted (edited)

well then my Jfets are exactly backwards for K170 J74

but those are K246 J103 so OK (if it matters)

they did work fine here but not so in Dynahi, used K170 J74

the silk is marked so

Emitter – (E)     >>     Source – (S)
Base – (B)     >>     Gate – (G)
Collector – (C)     >>     Drain – (D)
Edited by congo5
  • Like 1
Posted

good to hear that you amps is working again jose.

i had also 1 noisy out of 6 that340 from mouser, would be nice to test some single jfets or have them as alternatives.

Posted (edited)

Any drawbacks if I use resistors rated at higher power? For instance the 50Ω resistor at 1/8W costs 4X higher than the 1W counterpart.

Also, just a thought. How bad is it to have long flying leads to the front panel for the feedback resistors so I can make a gain switch? Or is it just better to not do it.

Edited by penmarker
added the gain question
Posted

Thanks for the answers and photos guys.

 

I also use Mill-Max sockets so I discard a connection problem... but yesterday I was thinking of soldering a THAT with noise to a socket and try this again. I have nothing to lose.

 

Maybe I bought a lot with some kind of problems :huh: I bought 6 units I had 3 with issues.

 

However, now I like the idea of using two set of 2SK170/2SJ74GR.

This is a more expensive solution but I have units for this.

 

Those who have tried this, what do you prefer? I mean use a THAT or JFETS.

 

Thanks

 

 

Posted
Any drawbacks if I use resistors rated at higher power? For instance the 50Ω resistor at 1/8W costs 4X higher than the 1W counterpart.


1/8w? Do you have the BOM? You should use 1/4w
Posted
9 minutes ago, jose said:

 


1/8w? Do you have the BOM? You should use 1/4w

 

Wewlad. Glad I didn't get them yet. Thanks a lot.
I got some BOMs but I didn't check the power rating.
So would it be ok to use resistors at higher rating?

Posted
4 hours ago, jose said:

Those who have tried this, what do you prefer?

The THAT340 is a sub for jfets,  because they are hard to find and costly
  I changed mine because offset would move 100mv over the range of pot.

in hindsight might be just wiring, or solvable with a couple resistors to ground.

that pot /bjt input interaction could also cause noise

sounds very good both ways

Posted (edited)

it would be nice to come up with some universal layout that would take all the available options

that340, 4 x single jfet,2 x dual jfet,2 x dual bipolar...

yes pars posted the picture I was thinking of, I even found the board

 

Edited by kevin gilmore
  • Like 2
Posted

That's a very neat idea! :wub: 

Would allow for a bit of experimentation to see how the JFETs change the sound of an existing amp I guess. Would you mind sharing artwork or schematics?

//UFN

Posted
6 hours ago, kevin gilmore said:

it would be nice to come up with some universal layout that would take all the available options

that340, 4 x single jfet,2 x dual jfet,2 x dual bipolar...

yes pars posted the picture I was thinking of, I even found the board

 

I would  like to experiment with something like that.

 

Posted (edited)
20 hours ago, UFN said:

That's a very neat idea! :wub: 

Would allow for a bit of experimentation to see how the JFETs change the sound of an existing amp I guess. Would you mind sharing artwork or schematics?

//UFN

sure,there it is

https://drive.google.com/open?id=0B9gzuIhmVOLcVmFnWUFXYUQxQ2s

It works fine on dynalo,but need to trim down PCB outline a little on current susy dynahi releases due to trimpots are close to THAT340 Socket .

and check transistor pinout before soldering :)

Edited by ang728
Posted
On ‎25‎/‎10‎/‎2017 at 3:13 PM, kevin gilmore said:

it would be nice to come up with some universal layout that would take all the available options

that340, 4 x single jfet,2 x dual jfet,2 x dual bipolar...

yes pars posted the picture I was thinking of, I even found the board

 

Any recommendations for dual Jet or dual bipolar?

soon I will start my Dynalobal and I want to buying for components to test in both amps. 

 

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