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Official M2 schematic
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Old 9th March 2019, 08:57 AM   #3261
KweeSong Lim is offline KweeSong Lim  Singapore
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Official M2 schematic
Quote:
Originally Posted by Stanislav View Post
Hey Kwee,
What transformer is that?
Looks interesting, maybe a good substitute for the Edcor.
Itís from AliExpress.

Online Shop 2PCS / Permalloy 600: 15K/20K audio frequency step-up isolation transformer single ended conversion transformer | Aliexpress Mobile

Itís worked well.
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Old 13th March 2019, 09:25 PM   #3262
BRN is offline BRN  United States
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I posted this in the M2x thread, but it was suggested that I post it here instead.

Iím 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.
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Old 13th March 2019, 09:32 PM   #3263
Zen Mod is offline Zen Mod  Serbia
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go for 15
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Old 13th March 2019, 09:33 PM   #3264
BRN is offline BRN  United States
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ZM,

Thank you. I will
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Old 14th March 2019, 12:15 AM   #3265
ichiban is offline ichiban  United States
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Quote:
Originally Posted by Zen Mod View Post
go for 15

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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Last edited by ichiban; 14th March 2019 at 12:17 AM.
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Old 14th March 2019, 12:30 AM   #3266
brianco is offline brianco  Ireland
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Old 14th March 2019, 07:34 AM   #3267
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally Posted by ichiban View Post
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?
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
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Old 14th March 2019, 03:47 PM   #3268
ichiban is offline ichiban  United States
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Quote:
Originally Posted by Zen Mod View Post
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
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Old 16th March 2019, 02:46 PM   #3269
adason is offline adason  United States
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Quote:
Originally Posted by adason View Post
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?
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Old 16th March 2019, 03:05 PM   #3270
JeffYoung is offline JeffYoung  Ireland
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@adason, that much heat from the board but not the output transistors suggests a cold solder joint. (It's making electrical contact but at high resistance so dropping a lot of voltage and generating a lot of heat.)

What temp do you measure on your JFETs?
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