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Old 9th March 2014, 09:38 PM   #1111
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According to the schematic you should see maybe 5V at D if connected to the single ended bias boards. What is your voltage across P201? Adjust it to bring your voltage from either end of R215 to to ground to about zero.
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Old 13th March 2014, 01:42 AM   #1112
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thanks for feedback

I set the D to gnd to 0V. I run 1K signal and thats the measurement I get at D.
My question now is:

can I connect this FE board to an F5 or F6 input using d and gnd signal?

is the out signal used in thios case?

thanks again for help
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Old 13th March 2014, 07:12 AM   #1113
Zen Mod is offline Zen Mod  Serbia
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post edited schematic with values what you set and where

D is node with cap in line , so there is always 0 Volts , so I'm puzzled how you "set" that;

set circuit exactly as Papa drew on sch , without measuring voltage at D node

if you put , say , 10 K resistor ( bleeder function , to prevent D from floating) from D to gnd , you'll see that's the case

however , D is proper out node of stage , while node marked out is connection for bootstrap potential , so using D node as out is normal

again , connect node marked Out to amp's out for best performance , or leave it unconnected for lesser performance , counting on fact that you anyway need lesser gain , so there is no such need for bootstrapping

anyway - you'll have too much gain for any power stage having own gain ( F5 and F6, too )

so , as Papa wrote in article , you can alter gain for your needs :

Quote:
The gain of this front end is set at about X 6, or 15 dB. You can have higher gain simply by changing R203 and R204 to higher values. You can double the gain (to about 20 dB) by increasing these to 100 Kohm, and you can push it to 150 Kohm (about 23 dB) without changing the compensation capacitors.
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Last edited by Zen Mod; 13th March 2014 at 07:15 AM.
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Old 13th March 2014, 09:37 PM   #1114
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Thanks Oh mighty ZM.

I adjusted the P201 until I got 0v offset at D.

Now, I connected to the F5 (without the output) and it works and I do get more gain. So now, I figure that I'm ok to connect the output to the output of the amp. (I'll probably try on the F6 since the F5 is all cased up)

I got that about the x 6 gain but conversely, If I need less gain, I can lower the values of r203,r204 to say, 22k.

Have I finally understood this circuit?

Other thing, can I power this FE with a salas shunt?

thanks again for your help.
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Old 13th March 2014, 09:56 PM   #1115
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Quote:
Originally Posted by necplusultra View Post
Thanks Oh mighty ZM.

I adjusted the P201 until I got 0v offset at D.
re-read what I wrote in previous post

see at picture : Click the image to open in full size.

you need to adjust P201 to get 0V at drain of Q203
......... node with R215 , to be more illustrative
what Pa wrote in article , mentioning output ....... is most probably addressed on biasing of output stage , not FE


Quote:
Originally Posted by necplusultra View Post

Now, I connected to the F5 (without the output) and it works and I do get more gain. So now, I figure that I'm ok to connect the output to the output of the amp. (I'll probably try on the F6 since the F5 is all cased up)
connect and listen ; choose what you like more - bootstrapped to output stage or not

Quote:
Originally Posted by necplusultra View Post
I got that about the x 6 gain but conversely, If I need less gain, I can lower the values of r203,r204 to say, 22k.

.
yes

Quote:
Originally Posted by necplusultra View Post

Other thing, can I power this FE with a salas shunt?
why not ?

Iq is in range of 25mA/rail/channel ; leave out (bridge) R210 and R211 , you can leave C205 and C206 in

programmed current for any shunt reg need to be at least 50mA/channel , each rail

max 75mA , no need for more
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Last edited by Zen Mod; 13th March 2014 at 10:00 PM.
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Old 14th March 2014, 02:27 AM   #1116
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Quote:
you need to adjust P201 to get 0V at drain of Q203
......... node with R215 , to be more illustrative
what Pa wrote in article , mentioning output ....... is most probably addressed on biasing of output stage , not FE
done

Quote:
Iq is in range of 25mA/rail/channel ; leave out (bridge) R210 and R211 , you can leave C205 and C206 in
will remove and use them to parallel r203/r204 to lower gain
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Old 14th March 2014, 09:18 AM   #1117
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Quote:
Originally Posted by necplusultra View Post
done

will remove and use them to parallel r203/r204 to lower gain
you're pulling my leg , yes ?

there is a slight difference in value ........ around 1000-fold ..........

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Old 14th March 2014, 11:26 AM   #1118
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Quote:
you're pulling my leg , yes ?

there is a slight difference in value ........ around 1000-fold ..........
my bad, I gotta get new glasses or get more sleep.

thanks again, next step is to try out with F6
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Old 28th June 2014, 09:08 PM   #1119
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I've been planning to use the BA-3 front end (now pushing SE outputs) for an upcoming complementary and/or balanced build. I bought the BA-GS V2.0 FE to use with the SE boards I have, but it appears the 2SJ109 is non stock and only only available on eBay.

I'm aware of this from the article: "Q201 is a dual matched pair of P channel Jfets, part 2SJ109. These are in scarce supply (although the recipients of Burning Amps will each get a pair). They can be substituted with matched 2SJ74 types, and a number of other parts will function with lesser performance."

Need a recommendation on the best approach, and if I use the matched pair is that just a simple side by side mounting. The pin pattern suggest that, but I've seen pairs strapped face to face in some cases.

Also not clear - is the bias board at the store considered universal now? I can see some version number differences but the photos look the same.
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Last edited by bcmbob; 28th June 2014 at 09:15 PM.
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Old 1st July 2014, 02:28 AM   #1120
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Quote:
Originally Posted by bcmbob View Post
Need a recommendation on the best approach, and if I use the matched pair is that just a simple side by side mounting. The pin pattern suggest that, but I've seen pairs strapped face to face in some cases.
A pair of matched J74 will do the job. I need to look at the pcb mounting to see exactly what the arrangement will be.

Any J109 from ebay is fake.

Quote:
Also not clear - is the bias board at the store considered universal now? I can see some version number differences but the photos look the same.
Most certainly no. The bias for the SE board is completely different than the Push-Pull.
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