It’s from AliExpress.
Online Shop 2PCS / Permalloy 600: 15K/20K audio frequency step-up isolation transformer single ended conversion transformer | Aliexpress Mobile
It’s worked well.
I posted this in the M2x thread, but it was suggested that I post it here instead.
I’m going to build the ISHIKAWA daughter boards (the same design as the M2 with the Toshiba JFETs) and have match JFETs of 10.82 idss. I read somewhere a recommendation to increase the resistors to 15ohms with an idss that high. Should I do that or keep the resistors at 10ohms?
Thanks in advance for the help.
I’m going to build the ISHIKAWA daughter boards (the same design as the M2 with the Toshiba JFETs) and have match JFETs of 10.82 idss. I read somewhere a recommendation to increase the resistors to 15ohms with an idss that high. Should I do that or keep the resistors at 10ohms?
Thanks in advance for the help.
I have an F6 with SemiSouth outputs and I used
JFETS with an idss of 10+ . What are the negatives
if I use the normal 10 ohm resistors as
used for 8ma idss JFETS?
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measure voltage across 10R resistors and write here , so we can tell are they on verge , dissipation wise
with TO99 , I'm always nervous past 150mW , 160mW slightly more but on 200mW already hysteric
Arrg!
You would have to ask! Last week I pulled the F6 pcbs out for F5c pcbs. I don't know what the idss is of the jfets in the F5c, but measured it anyway.
They drop 50mV across 9.3 Ohms. Supply voltage is 21.9 V.
Is the only concern the disapation of the jfets?
Is there a sonic penalty?
I see that the idss of the jfets in the F5c is 5.3 mA !
Is that a concern as to sound quality, current drive to
the output mosfets, which there are two per power rail,
i.e. two pairs per channel?
-Thanks
Ok, I have ordered infrared temperature meter. One with higher D:S ratios, so I can measure each particular spot. They have wide selection with reasonable prices.
I figured this will be useful in the future to know exactly the surface temp. No more burned fingers
Infrared Non-Contact Thermometers Archives - Calright
Ok, the infrared meter arrived, it works great. Nice thing is that it has quite a small spot it measures.
Theses are measurements I just obtained after amp has been working for half an hour. I got two fans on half the speed to force the air around big heatsinks.
So I measured the output transistor itself, then the board temperature itself, and the heatsink nearby.
Left channel (where a little smell is coming from) in degC.
46.5 94.4 37.1
41.2 55.8 39.2
Right channel
39.8 61.6 37.0
42.0 61.0 36.8
As you can see, one spot on the board is hot, but the transistor is not. This hot spot is very close to input transistors, so I am starting to suspect that smell (light smell, nothing burning) is coming from input jfets.
They are slightly hot to touch.
They are linear system jfets from the diystore.
What should I do next? Voltages are ok on both sides.
Should I put small heatsink on input jfet, or just replace it?
if pcb itself is hot , there is bad solder joint -
measure part itself to decide how big dissipation issue is
anyway , try to clarify a little where and how you're getting 94C measurement ....... problem with IR+laser LED meters is that you can' be sure that laser point and measurement focus area is the same , so trouble is when you need to localize something ...... for these things contact meter with physically small sensor is the best
measure part itself to decide how big dissipation issue is
anyway , try to clarify a little where and how you're getting 94C measurement ....... problem with IR+laser LED meters is that you can' be sure that laser point and measurement focus area is the same , so trouble is when you need to localize something ...... for these things contact meter with physically small sensor is the best
I like this infrared thermometer...it shows a circle by laser where it measures.
Ok, it was not easy, because they are small and close to each other, but I got temp of each...three of them are ~43degC, one is over 70degC.
I think this one needs to be replaced. Btw, amp measures and sounds good.
Board is hottest right under this jfet.
Ok, it was not easy, because they are small and close to each other, but I got temp of each...three of them are ~43degC, one is over 70degC.
I think this one needs to be replaced. Btw, amp measures and sounds good.
Board is hottest right under this jfet.
ZEN
Ok, after much jiggery pookery I jury rigged one F6 pcb to a scabbed PS from the F5c. Wanted to post porn but wouldn't you know the battery was pffth!
Anyway, jfets from Weitzman in Israel, real Toshiba 74/170s, marked as 9.12 and 11.72 idss. PRP resistors measured exactly 10R each on a Fluke 8060A.
Voltages across them is 70.36 & 71.75 after a 10 minute warm up.
What say you? Increase resistors to 15 ohms?
Is the only concern disapation? Does linearity suffer?
Ok, after much jiggery pookery I jury rigged one F6 pcb to a scabbed PS from the F5c. Wanted to post porn but wouldn't you know the battery was pffth!
Anyway, jfets from Weitzman in Israel, real Toshiba 74/170s, marked as 9.12 and 11.72 idss. PRP resistors measured exactly 10R each on a Fluke 8060A.
Voltages across them is 70.36 & 71.75 after a 10 minute warm up.
What say you? Increase resistors to 15 ohms?
Is the only concern disapation? Does linearity suffer?
we are ignorant about linearity and all other issues left for more clever ones 
70-ish (hopefully mV) means you have 7mA through JFets , and with usual rails voltage of 22V5 that means each JFet is having 22V5 x 7mA=157mW of dissipation ..... right where Papa wants them to be
so no worries
70-ish (hopefully mV) means you have 7mA through JFets , and with usual rails voltage of 22V5 that means each JFet is having 22V5 x 7mA=157mW of dissipation ..... right where Papa wants them to be
so no worries
we are ignorant about linearity and all other issues left for more clever ones
70-ish (hopefully mV) means you have 7mA through JFets , and with usual rails voltage of 22V5 that means each JFet is having 22V5 x 7mA=157mW of dissipation ..... right where Papa wants them to be
so no worries
Ok!
Not sure I agree with bad solder joint. Two of you suggested that.
My soldering is ok, I have been doing it for quite some time. Besides, bad solder would introduce resistance, that means lower current, less heat. So I do not see the logic there. I retouched the solder, that was not it.
Good news is, I know that is it...
Well, I realized that ZM is right, the closer you put infrared meter to the object, more apart are two beams, so to speak. Laser pointer and measuring spot are coinciding about 20 cm from the reader. I used soldering iron tip to optimize. Anyway, long story short, one power transistor was the culprit.
I replaced one irfp9240 and all is good. Well, I first replaced input jfet, lsk170, but that did not help. I even put it back, since it was matched.
Interestingly, the replaced mosfet still measures ok outside. It was playing nice music and all the voltages were ok, so not sure why it over heated. It sure is original, as I bought these as big batch 20+ years ago from digikey when I was building sun of zen.
Thanks for help everyone.
After fine tuning the exact measuring spot, power transistors are between 68 and 72 degC. Jfets are around 41degC and heatsink is 37degC. No smell.
That spot on the board, which was hot, is now 65degC, and due to recalibrating the measuring spot, is not under jfets, but right under formerly overheated output mosfet.
That spot on the board, which was hot, is now 65degC, and due to recalibrating the measuring spot, is not under jfets, but right under formerly overheated output mosfet.
Hi all,
I surly made the mistake to build up the M2 before , testing The cards separately !
But I carefully check everything while building!
I tried to power it up today!
It seems that I have a problem with the transformer toroidy 500w 18vx2
No power can be seen from 1 st secondary and 2nd secondary
The transformer is brand new , and does not seem to have short ciurcuit!
Any idea where to dig whitout unsoldering and taking parts out!
Thanks in advance!
I surly made the mistake to build up the M2 before , testing The cards separately !
But I carefully check everything while building!
I tried to power it up today!
It seems that I have a problem with the transformer toroidy 500w 18vx2
No power can be seen from 1 st secondary and 2nd secondary
The transformer is brand new , and does not seem to have short ciurcuit!
Any idea where to dig whitout unsoldering and taking parts out!
Thanks in advance!
An externally hosted image should be here but it was not working when we last tested it.
<a href="https://www.casimages.com/i/190324080125675167.jpg.html" title="1210B6A1-1221-421F-AEE7-9CB36F9EB612.">Lien vers mon image</a>
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