ThermalTrak+TMC amp

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#343
18mA IDSS is too high to be BL; see attached.

Might be V instead ... or maybe a different device altogether ...
😕 😱

mlloyd1
 

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  • 2SK170_IDSS_range.png
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#346
I have used these same JFETs in a few other amps without issue.

Did you look at the voltages around them in the schematic I posted? They are in line with the spice file. I think the problem is with the layout. You have said you used a two sided layout. The one I am using was the most recent one posted at the time you suggested I try this amp. After I etched the boards you posted a different one. To my knowledge, that one hasn't been tested either. You said the only error on the one I used was that P1 and R35 were reversed so I swapped them. I am attaching a pic of how I did that. I suppose it is possible that that may have something to do with it but to me it looks like it is correct per schematic. Please look over the layout and schematic and see if you find any more errors. You know how hard it is on etched board when you keep replacing parts. So far every part I have pulled has measured fine.

Thanks, Terry
 

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  • DADO-TT-TMC-7-2-g-2.LAY] VBE correction.jpg
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#349
still4given said:
Did you look at the voltages around the jfets?
Click to expand...

Terry, this is not 2SK170BL as Idss is to high, max Idss for BL type is 12mA. There is not only Idss, but Vgs(off). 2SK170BL has very low Vgs(off) lower then -1V.
The fake fet could work in some applications. If this one has higher Vgs(off) then it could work with higher voltage than 3.5V as it's here. Try to replace one LED with 10V zener, cathode the pointing to the + side.
2SK170 or LSK389 is low noise, low Vgs(off) fet and with other type here the sound could be worse.
I could not find any layout fault. If you want I can send you the double side layout gerbers I use in my amps, but again there is question of the fet.
BR Damir
 
#351
To be honest the fets I installed were from a different supplier than the one pictured. I don't actually remember the ldss numbers. They were wrapped together in foiI with a sticker. I bought a few matched pairs a year ago from someone here at DIYA. These were the last two pair. The ones in the picture are from some I bought on eBay. They mostly measure 12ma except for 4 pieces. I should have stopped when I found that this amp was designed around a part I could not buy. I hoped it would work with the alternate parts but evidently not. I now feel like I have burned up a lot of parts for nothing. I'm not experienced enough to troubleshoot this issue.

Sorry, Terry
 
#352
still4given said:
To be honest the fets I installed were from a different supplier than the one pictured. I don't actually remember the ldss numbers. They were wrapped together in foiI with a sticker. I bought a few matched pairs a year ago from someone here at DIYA. These were the last two pair. The ones in the picture are from some I bought on eBay. They mostly measure 12ma except for 4 pieces. I should have stopped when I found that this amp was designed around a part I could not buy. I hoped it would work with the alternate parts but evidently not. I now feel like I have burned up a lot of parts for nothing. I'm not experienced enough to troubleshoot this issue.

Sorry, Terry
Click to expand...

Sorry Terry for that. You where to fast with your build, I could not worn you about the layout. I have built 10 boards of this amp, all double sides layout with no problem except that change in Vbe multiplier.
By the way LSK389 is still produced by Linear Systems Linear Systems || JFET Amplifiers - Duals
BR Damir
 
#353
I am very sorry that Terry lost interest.
I someone wants to build this amp here are the gerbers for the double side PCB I used in my amps and all of them with no problem. This layout has corrected part around the Vbe multiplier, P1 and R35.
This is excellent sounding VFA.
BR Damir
 

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  • TT-amp-TMC-7-4-f-double.jpg
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  • gerbers-f-double.zip
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#356
dadod said:
Long time no hear, and it's all my fault. How is going with the square law amp? I have somewhere the original article from WW but I have to find it.
Click to expand...

Hi Damir,

All is well. I've been busy designing, building, and marketing Tribus Drive. The square law amp is coming along, but slowly - too busy playing my guitar and spending time with my two-year old.

Do you have any new designs in the works?

Regards,
Mason
 
#357
I will get back to this one eventually. A lot of parts invested. I just needed to get away from it for a while so I could come back with fresh eyes. I have 4 other amps that were incomplete waiting for parts. The parts have come in so I have been busy finishing them. I'll be back here looking for more help before long. 😀

Blessings, Terry
 
#358
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