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Old 24th May 2012, 03:45 PM   #2181
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I have 16 (per channel.) Sounds like four would be the way to go. I might be able to parallel two on top and two on bottom of the board. Any comments on the source resistance? I also noticed the input (AC) coupling is different compared to my schematic. Is that a requirement based on a JFET vs MOSFET front end?
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Old 25th May 2012, 03:42 AM   #2182
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What is the limiting factor on the jfets? It looks like the 74s are rated for twice as much power dissipation at 400mW than the 109s. As such, perhaps using two vs four might be ok?
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Old 25th May 2012, 07:02 AM   #2183
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If you have J74's with higher Idss.
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Old 25th May 2012, 07:03 AM   #2184
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Hi,

the limiting factor is the current they can deliver. With only 10mA total bias this is only half the current the standard 9610´s can deliver.
This will cause bandwith limiting.

There are a few more reasons why two pairs is better. You can find them in the thread I posted somewhere above.

William
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Old 25th May 2012, 09:14 PM   #2185
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If I can get two pairs, would I stick with the 15R source resistors as well or eliminate as Graeme has done?
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Old 25th May 2012, 09:42 PM   #2186
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Hi,

I only used the source resistors (in form of a pot) to get my relative DC offset low enough. I had not enough 2SJ74 to find good enough matches.

William
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Old 25th May 2012, 09:50 PM   #2187
gl is offline gl  United States
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I removed the 15 ohm resistors years ago. I consider them unnecessary.

Graeme
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Old 25th May 2012, 11:46 PM   #2188
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Mine are matched with with 0.5mA. I think I will try the MOSFETS from Graeme (thanks again Graeme) since I know that will work fine and then consider upgrading to JFETs later. Besides, that will give me a chance to hear for myself what the difference is.

Plus, tinkering is fun!
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Old 30th May 2012, 06:14 AM   #2189
mace_be is offline mace_be  Belgium
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Does anyone have alpeh-X boards for sale ?

I have bought a guys big monoblock DIY Alpeh X amps, but his pcb is a little confusing, it goes not use the component numbers on the original schematic and the track width is somewhat narrow. it's easier for me to do debugging when i can easily correlate the components on the pcb with the schematic.
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Old 7th June 2012, 03:16 PM   #2190
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Default PCB's?

Hi there,

I am also looking for a couple of PCB's for the "low" powered version of Grey!

Anybody able to help me out here?

Cheers!
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