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Old 23rd May 2013, 07:21 PM   #1231
Hikari1 is offline Hikari1  United States
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Quote:
Originally Posted by merlin2069er View Post
wow, those are big caps.
Yes, I was a bit surprised too. And they are only 8.2UF. They barely fit in the chassis I want to use.
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Old 25th May 2013, 07:33 AM   #1232
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Got it put together and...

It passes a signal but there's no gain...

I'll double check the schematic but something is not right. Bad jfets? They are BL grade left over from another project.
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Old 25th May 2013, 01:24 PM   #1233
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Any pics of the final build? A few angles, please.
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Old 25th May 2013, 06:48 PM   #1234
Hikari1 is offline Hikari1  United States
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Heres some pics, kind of a mess but you will get the idea.

All the RCA rounds and pot grounds are going to the copper "bus" between the caps.

Powered up, I only have .3V between D-G on the jfets. I've got 19V before the 2.2K V+ resistor and .3V after it.

Thanks for the help.
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Old 25th May 2013, 09:06 PM   #1235
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Putting the volt meter across the 2.2k, Pos. meter lead on the 19v side and the Neg. lead on the drain side, what's the voltage reading? Check the value of the 2.2k with unit powered off. What's value of the Source side resistor? Check orientation of jfets as well.

Do you have spare 2sk170 jfets?
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Old 25th May 2013, 10:08 PM   #1236
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looks like you have twisted the caddock resistor wire around the jfet middle leg

soldering that could be too much heat for the jfet

besides, there is no reason to twist the wires at all

thats said, I have not been able to destroy mine
tough devices
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Old 26th May 2013, 03:28 AM   #1237
Hikari1 is offline Hikari1  United States
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Quote:
Originally Posted by vdi_nenna View Post
Putting the volt meter across the 2.2k, Pos. meter lead on the 19v side and the Neg. lead on the drain side, what's the voltage reading? Check the value of the 2.2k with unit powered off. What's value of the Source side resistor? Check orientation of jfets as well.

Do you have spare 2sk170 jfets?
I've got 19V+ across the 2.2K. The 2.2K measures 1.2K with the unit powered off. Verified the source side resistor is 10ohm.

I am suspecting the jfets.
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Old 26th May 2013, 06:37 AM   #1238
Hikari1 is offline Hikari1  United States
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Oh man. I had made a stupid mistake.

I had just bought a thrift store DMM before assembling the jfet boz. I didnt realize the leads were plugged in backwards. I was delivering -19V NEGATIVE through the power supply. Stupid.

Well, I realized this, swapped the battery leads and...IT WORKS.

But it doesn't sound so good. It has lots of gain but it sounds a bit distorted and the soundstage is small. I will investigate further...
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Old 26th May 2013, 07:46 PM   #1239
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That's ok. Things happen.

Are the batts fresh?
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Old 26th May 2013, 08:35 PM   #1240
tinitus is offline tinitus  Europe
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I think original curcuit values were intended for much higher voltage

on a battery it might be under biased

but yeah, low battery sounds pretty bad too

at least you have a signal now
good step forward
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