Aleph-X builder's thread. - Page 219

oneplustwo · 24th May 2012, 03:45 PM

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?

oneplustwo · 25th May 2012, 03:42 AM

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?

jacco vermeulen · 25th May 2012, 07:02 AM

If you have J74's with higher Idss.

wuffwaff · 25th May 2012, 07:03 AM

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

oneplustwo · 25th May 2012, 09:14 PM

If I can get two pairs, would I stick with the 15R source resistors as well or eliminate as Graeme has done?

wuffwaff · 25th May 2012, 09:42 PM

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

gl · 25th May 2012, 09:50 PM

I removed the 15 ohm resistors years ago. I consider them unnecessary.

Graeme

oneplustwo · 25th May 2012, 11:46 PM

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!

mace_be · 30th May 2012, 06:14 AM

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.

jeekee · 7th June 2012, 03:16 PM

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!

24th May 2012, 03:45 PM	#2181
oneplustwo 1.21 Gigawatts?! diyAudio Member Join Date: Apr 2009 Location: San Francisco	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? __________________ My Projects

25th May 2012, 03:42 AM	#2182
oneplustwo 1.21 Gigawatts?! diyAudio Member Join Date: Apr 2009 Location: San Francisco	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? __________________ My Projects

25th May 2012, 07:02 AM	#2183
jacco vermeulen diyAudio Member Join Date: Oct 2004 Location: At the sea front, Rotterdam or Curaçao	If you have J74's with higher Idss. __________________ Not so much,.......if it says "ZM" in the corner.

25th May 2012, 07:03 AM	#2184
wuffwaff diyAudio Member Join Date: Aug 2001 Location: Ingolstadt Germany	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 __________________ een ooievaar is geen konijn want zijn oren zijn te klein!

25th May 2012, 09:14 PM	#2185
oneplustwo 1.21 Gigawatts?! diyAudio Member Join Date: Apr 2009 Location: San Francisco	If I can get two pairs, would I stick with the 15R source resistors as well or eliminate as Graeme has done? __________________ My Projects


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25th May 2012, 09:42 PM	#2186
wuffwaff diyAudio Member Join Date: Aug 2001 Location: Ingolstadt Germany	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 __________________ een ooievaar is geen konijn want zijn oren zijn te klein!

25th May 2012, 09:50 PM	#2187
gl diyAudio Member Join Date: Dec 2003 Location: Sierra Foothills - California	I removed the 15 ohm resistors years ago. I consider them unnecessary. Graeme

25th May 2012, 11:46 PM	#2188
oneplustwo 1.21 Gigawatts?! diyAudio Member Join Date: Apr 2009 Location: San Francisco	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! __________________ My Projects

30th May 2012, 06:14 AM	#2189
mace_be diyAudio Member Join Date: Jan 2008 Location: Belguim	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.

7th June 2012, 03:16 PM	#2190
jeekee diyAudio Member Join Date: Jun 2012	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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