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Old 22nd January 2014, 07:04 PM   #1
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Default F5 with 2sj162 2sk1058 ?

any one built a pass F5 with 2sj162?

possible? any modification to the circuit?
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Old 22nd January 2014, 07:11 PM   #2
Zen Mod is offline Zen Mod  Serbia
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already done with laterals

however - their Xconductance is lower , comparing to verticals;

less OLG , so less feedback , different THD spectra

'cause I didn't compared it with original , can't say what's difference in sound
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Old 22nd January 2014, 09:16 PM   #3
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could you post any schema or bias resistor mod for it?
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Old 22nd January 2014, 10:21 PM   #4
juma is offline juma  Germany
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Quote:
Originally Posted by marconi118 View Post
could you post any schema or bias resistor mod for it?
Use the Ohm's Law - if your JFETs work at Id of, say, 5mA and you need 2V of Vgs to bias the LATFETs at about 1A you'll need JFETs' drain resistors to be around 400 R (use 1k multi-turn pots and omit LATFETs' Rs, NTC and the rest of parts HEXFETs need for thermal compensation). Since LATFETs have lower parasitic capacitance meaning that they need less gate drive than HEXFETs it would be beneficial to use GR grade JFETs (lower ID) since that way their drain resistors will be higher and the OLG won't drop (maybe a little since the GR grade parts have lower gm).
I got good results by using the BJTs in the input stage at the Ic of about 3mA. I proposed that solution few years ago and can't search for those posts now but you can see it in Lazy Cat's thread about VSSA - that's F5 gone BJT with LATFET Source Follower output stage added.

Last edited by juma; 22nd January 2014 at 10:24 PM.
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Old 27th January 2014, 07:52 AM   #5
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to avoid one extra stage, going only with J74GR the gain will be too low?
I could reduce the feedback resistor, but then distortion will be higher?

how will it sound?

found one schema of a sort of it but with even less gain and no feedback:
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Old 27th January 2014, 10:14 AM   #6
juma is offline juma  Germany
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Quote:
Originally Posted by marconi118 View Post
to avoid one extra stage, going only with J74GR the gain will be too low?
Not clear what do you mean - can't make F5 with j74 only, what extra stage?...

Quote:
Originally Posted by marconi118 View Post
I could reduce the feedback resistor, but then distortion will be higher?
Feedback net usually employs 2 resistors. Reducing one of them will increase the gain and distortion (and the Id in the input stage too). Again, it's not clear what you really mean ?

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Originally Posted by marconi118 View Post
how will it sound?
What ? Few ideas are already mentioned and each will sound different...

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Originally Posted by marconi118 View Post
found one schema of a sort of it but with even less gain and no feedback:
It's a transconductance amp, like BA-3. Its gain is determined as G=1A/V and the voltage on the speaker will largely depend on its impedance, so voltage gain cannot be declared as high or low since it depends on the speaker.
Absence of feedback makes it what it is. Insert a feedback loop and you'll get pretty standard amp.


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Old 13th February 2014, 10:13 AM   #7
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Sorry I was too fast in writing last time...

I would like to keep the original F5 2 stage design. Avoid to add a transistor stage to drive the 2sj162 2sk1058


Will the OLG be too low with laterals?
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Old 13th February 2014, 10:54 AM   #8
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Quote:
Originally Posted by marconi118 View Post
Avoid to add a transistor stage to drive the 2sj162 2sk1058
indra's suggestion to use the LSK pre to drive the laterals

LSK pre - BAF 2013 (post#76)
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Old 13th February 2014, 01:18 PM   #9
juma is offline juma  Germany
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Quote:
Originally Posted by marconi118 View Post
...I would like to keep the original F5 2 stage design. Avoid to add a transistor stage to drive the 2sj162 2sk1058
Nobody mentioned additional stage to drive LATFETs. Just put them in circuit instead of HEXFETs and do as written in post #4.

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Will the OLG be too low with laterals?
No. Maybe lower (depending on input stage parts choice) but not too low.
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Old 21st April 2014, 11:21 AM   #10
juma is offline juma  Germany
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As it usually happens, looking for something else, today I found my F5 version with Lateral MOSFETs that I mentioned in post #4.
Laterals here need no source resistors and no thermal compensation.
3.5mA runs through the each of the input BJTs - BC550C/560C work here great too (matching is beneficial but not mandatory).
Biasing procedure is the same as for the standard version - the only thing different is that you can bias LATFETs somewhat lower (1A is OK) since the absence of source resistors and the specific curvature of MOSFETs' transfer characteristic enables much later (in terms of load current) switching to AB class regime.
Oh, and 4.7mF means 4700uF.
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