Hi guys,
Regarding the bom and schematics, I can fairly easy provide that (need to clean up a few values). However the real work is in providing component recommendations for the bom and documenting the optional components - when to populate what.
I have basically no time and a pile of projects in the pipeline, so it is difficult for me to provide a lot of support for the layouts.
Christian
Regarding the bom and schematics, I can fairly easy provide that (need to clean up a few values). However the real work is in providing component recommendations for the bom and documenting the optional components - when to populate what.
I have basically no time and a pile of projects in the pipeline, so it is difficult for me to provide a lot of support for the layouts.
Christian
Hi Steve/Christian,
Thanks for the info Steve and the offer of some help Christian, I think I should be Ok with what I now have the proble is mainly the various changes made from the start to the end of the projest many "tweeks" are made and these can be spread and descused over an on many threads and for a newcommer like me its an almost imposible task to find the info required without trolling through hundreds of posts and I dont find the search engine on the forum that helpful.
That said I thank you for your support and if i need further assistance I will ask.
Kind Regards
Ian
Thanks for the info Steve and the offer of some help Christian, I think I should be Ok with what I now have the proble is mainly the various changes made from the start to the end of the projest many "tweeks" are made and these can be spread and descused over an on many threads and for a newcommer like me its an almost imposible task to find the info required without trolling through hundreds of posts and I dont find the search engine on the forum that helpful.
That said I thank you for your support and if i need further assistance I will ask.
Kind Regards
Ian
Bias problem
Hi Guys just fired up my first F5C and all is working apart from the fact I can't get it to draw enough bias current I have adjusted the P1 & P2 pots alternately and I can achieve only 0.134mv across the source resistors.
The amp is obviously working and is stable and I am able to adjust P1 & P2 to achieve 0.00 MVP offset at the output, I have had the amp on for a few hours just to see if she's stable and the sinks have warmed up nicely to 36deg C I'm guessing some resistors will need adjustment so any ideas where I should look.
Ian
Hi Guys just fired up my first F5C and all is working apart from the fact I can't get it to draw enough bias current I have adjusted the P1 & P2 pots alternately and I can achieve only 0.134mv across the source resistors.
The amp is obviously working and is stable and I am able to adjust P1 & P2 to achieve 0.00 MVP offset at the output, I have had the amp on for a few hours just to see if she's stable and the sinks have warmed up nicely to 36deg C I'm guessing some resistors will need adjustment so any ideas where I should look.
Ian
oh. i miss read. it says 0.134mV. i read 134mV. here there is somthng else thats wrong. is it both ch? or just one?
So it's a cascoded 2 pair version? Wich rail voltage do you have? And whats the value of the resistors in the cascode circut?
okei.
Also. Whats the idss of the J-fets? And are you sure they are the real deal?
okei.
Also. Whats the idss of the J-fets? And are you sure they are the real deal?
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Rail volts are 34v cascode resistors are R101.102,103,104 are all 10k R106,107 are 150r cascode volts is 16.3v
Not sure about the JFET's I purchased them some time ago from an eBay seller in Israel (alweit) allegedly matched quads they were marked 4.45 ?? But what measurement is god only knows.
I have ordered some new JFETS from the DIY audio shop I will swap them out and see if they cure the problem, I think you may be right as the amp is basically working.
I have ordered some new JFETS from the DIY audio shop I will swap them out and see if they cure the problem, I think you may be right as the amp is basically working.
Earthquake -
Increase the resistance across the bias pots - add another 2.2K in series or swap for a 4.7 or something in that range - it seems like your Jfet are low Idss and just need more resistance in the bias circuit to turn on. Easy, simple fix.
And just to verify, the max bias you can get, with zero offset, is 0.13V?
Increase the resistance across the bias pots - add another 2.2K in series or swap for a 4.7 or something in that range - it seems like your Jfet are low Idss and just need more resistance in the bias circuit to turn on. Easy, simple fix.
And just to verify, the max bias you can get, with zero offset, is 0.13V?
4.45? is it GR grade?
6L6. i think i need 6.8Kohm. or maybe more. it depends on how much bias he wants of course🙂
however. i'n not sure that a single pair J-fets with 4.45mA IDSS is up for the task of driving 2 output pairs.
6L6. i think i need 6.8Kohm. or maybe more. it depends on how much bias he wants of course🙂
however. i'n not sure that a single pair J-fets with 4.45mA IDSS is up for the task of driving 2 output pairs.
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Hi guys (6L6 & Audiosan) your both right it is almost certainly a bias issue the devises are GR's and not BL's so that's most likely cause I am expecting some Jfets from the DIY audio shop any day now but in the mean time I'll play with the 2K2 resistor value. Thanks for the pointers.
Ian
Ian
I'm glad someone is following this thread and answering questions! Just catching up. Ian, if you need some matched BLs, email me directly.
Steve
Steve
Thanks Steve I have ordered some from Spencer and from the DIY store one question I do have is the Jfets for sale in the DIY audio store are available in 4 different IDSS values A,B,C & D as most of the Pass amps seem to use the same "front end" why do we need so many choices??
The choices in grade are due to LS's limited supply - that said, some of the designs are very tolerant of Idss in the circuit, and usually it's only a resistor change to make them work.
lsk170a = 2sk170gr
lsk170b = 2sk170bl
lsk170c = 2sk170v
Some of the lsk170c I bought in the years ago Group Buy came in @ >20mA Idss. I called them C+.
lsk170b = 2sk170bl
lsk170c = 2sk170v
Some of the lsk170c I bought in the years ago Group Buy came in @ >20mA Idss. I called them C+.
Thanks Steve & Andrew for your informative replys one other question the Jfets for sale in the DIY audio shop are not matched does this matter in this F5 cascode if not I will change my GR's this weekend as mine have arrived.
If it doesn't matter to much in this design which ones of NP amps do require close matched Jfets.
If it doesn't matter to much in this design which ones of NP amps do require close matched Jfets.
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