The Aleph Jango

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#101
IF you are using Aleoh J in SE mode, the negative input has to be shorted, correct. Nelson did this with pin in xlr.

As for transistor screw up. I had transistors in second position. This meant that the mosfet source was not attached to the bjt gate through 1K resistor. THe bjt gate was effectively connected to nothing.
 
#103
Zen Mod said:
for start-up testing/setting and measurements - both inputs need to be shorted to gnd

always , with all amps

My brain is really going in circles 😕😕😕 Can't remember if I shorted things when I set up "the 6"

looking forward to the Jango - found some 109s from a Borbely DAC - hopefully I didn't save non working Fets

Picking up a lot of tips from you guys - will double check everything and post the pix when back in Davis

Best

Bob
Click to expand...
 
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#104
Got it working. One caveat. The max bias I can get and still have zero offset is 560mv across Rs, about 1.2A. This is using 10k pot in parallel woth 470R resistor in tail of FE. If you want more and are using FQA Mosfet, you need 1k pot. 500 may do, but doesn't hurt to have extra. I may just pull pot and use whatever 470R resistor gives me. Thanks ZM. Will share impressions later.
 
#107
So, I dont think that the Jango will work with FQA as ACS. I can get the channels at zero offset when they are good and warm, but cold start up shows a nasty DC across the output of about 750mV. Perhaps I am doing something wrong, but I have pretty much eliminated all that i know to do including increasing LTP pot value and putting a pot as R27 for adjustablilty of the ACS. I can get zero offset when cold at lower bias, but not at 1A+. Apparently there different temperature coefficients make the case difficult. Probably wrong. I will tryagain later with IRF in top. Unless of course, there are other ideas.
 
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#109
Got them sitting at 1A bias and all is ok, but one SS is biased at about 1.7V and the other is about 1.9V for same current. One of the channels can be biased higher and still zeroed out at the offset, but the other channel is definitely limited to 1A. Odd thing is, I think it is do to the SS and not the FQA, as the offset is positive. IN other words, I have to drop the bias of the FQA in order for things to line up, as if the SS cant keep up or match it in terms of output. Kinda Bizarre! I might curve trace all the fets and make sure they are matched well. Perhaps that is the problem
 
#113
buzzforb said:
So what the deal ZM? DO i have a weak SS? IT just runs out of juice no matter how much gate voltage I throw at it.
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depends what you think with "how much"

1A is good in my book , if you're going to 2 pairs , so that'll be 2A overall

I'm cheapskate , so having just 2 outputs (both SJEPs) in my BJ2 , for 100W dissipation

I'm pretty sure that your SJEPs are good , so everything is just matter of LTP drain resistor , and base feed in A CCS
 
#114
6L6,
Will do. It sounds pretty good. Always liked the Aleph J. Dont have enough gain in current setup. Not quite as much as the F5t, which worked ok with passive volume control. Hope to habe more info on both the SS fets and their effect on the circuit, as well as the FQA. May take some time, but ill get to it all. Aleph is a smooth amp. Need to try F3:devil:
EDIT: Need to try doubling jfets in FE as well.
 
#115
Zen Mod said:
depends what you think with "how much"

1A is good in my book , if you're going to 2 pairs , so that'll be 2A overall

I'm cheapskate , so having just 2 outputs (both SJEPs) in my BJ2 , for 100W dissipation

I'm pretty sure that your SJEPs are good , so everything is just matter of LTP drain resistor , and base feed in A CCS
Click to expand...
Got to do further investigation as there is too much difference between channels with exact jfet FE. All are Idss of 10.6. Must be somthing about output fets that is different. Either FQA or SS, but i am leaning toward SS, because plenty of adjustability in bias of FQA, but SS runs out of steam. There has to be reason.
 
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