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Old 18th September 2011, 11:55 PM   #321
njepitt is offline njepitt  United Kingdom
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Quote:
Originally Posted by Zen Mod View Post
....but - I'm not expecting that you are going to hear too much difference
Nor am I, if I'm honest, but it should be fun, and it won't cost much, so why not give it a go? And if it only shows that there's no difference between PRP and the cheapo Brazilian no-names I'm using then that's better still, right?

And I've already learned something from you and juma this evening, so that's good too...

Regards

Nigel
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Old 3rd February 2013, 12:30 AM   #322
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Originally Posted by juma View Post
Those who have already built B1 and just need some additional gain, can add just the gain stage (and the PSU) in the existing box. Coupling cap (C3) is not needed if your B1 already has one at the input.
Hello

Does this gain stage would change the sound of the B1 ?

Thank

Gaetan
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Last edited by gaetan8888; 3rd February 2013 at 12:33 AM.
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Old 3rd February 2013, 12:39 PM   #323
juma is offline juma  Germany
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It's very easy to test it.
I like BF862 better than 2SK170 - you might have different preferences...

Last edited by juma; 3rd February 2013 at 12:42 PM.
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Old 31st October 2014, 08:07 AM   #324
OllBoll is offline OllBoll  Sweden
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I found this thread interesting...

But of course I have a question! =)

I am in need of a few buffers, and I don't have enough 2SK170s to make normal B1s but the BF862 are infinitely more available. I, however, only have a positive rail 24V PSU in my amps:

Would the buffer part of the preamp work without the negative PSU? Here you say that the gain part absolutely needs negative supply but not if the same is true for the buffer part.

EDIT: Not sure if it makes a difference but I don't need the full 6V output, 2V would be enough for me.

Last edited by OllBoll; 31st October 2014 at 08:16 AM.
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Old 31st October 2014, 11:50 AM   #325
juma is offline juma  Germany
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Originally Posted by OllBoll View Post
...Would the buffer part of the preamp work without the negative PSU?..
Yes
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Old 31st October 2014, 07:05 PM   #326
OllBoll is offline OllBoll  Sweden
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Quote:
Originally Posted by juma View Post
Yes
Nice!

So I have a bunch of more questions:

First about Idss, is there a specific Idss range this circuit is optimized for?

And lets see if I've understood this:

First I chop off the gain stage. The output I want to buffer is that from a Jensen JT-11P-1 with ideal load of 10k. So I set R1 to 11k and R3 to 100k for 10k input impedance.

The next step I'm not sure about but I think I want 1/2 vcc => 12V at the upper Jfet gate so I set R2 to 100k too.

And then after the Jfets, do I just chop off the negative supply part like this or do I need to do something more?

And I think R16 controls output impedance, my amp has 10k input impedance so I don't need as low as 33. I might as well throw on 100 as I have lots of those lying around =)
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Old 31st October 2014, 08:01 PM   #327
juma is offline juma  Germany
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Idss = 10 - 20 mA
Sch OK
R16 = 15 - 33 R
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Old 31st October 2014, 09:09 PM   #328
OllBoll is offline OllBoll  Sweden
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Quote:
Originally Posted by juma View Post
Idss = 10 - 20 mA
Sch OK
R16 = 15 - 33 R
Nice, and 33R on R16 it is.

Thanks for the help!

Now I just need to buy a few matched BF862s or say 50 and match myself
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Old 1st November 2014, 12:17 AM   #329
juma is offline juma  Germany
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Yes, just take care that your 24V power supply is perfectly clean because it's connected directly to JFETs gate. Otherwise, you'd better use B1 schematic...
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Old 1st November 2014, 01:21 AM   #330
OllBoll is offline OllBoll  Sweden
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Originally Posted by juma View Post
Yes, just take care that your 24V power supply is perfectly clean because it's connected directly to JFETs gate. Otherwise, you'd better use B1 schematic...
Yup, in the actual circuit i'll probably clean the rail a bit before I connect it to the buffers.

Also, if I understand correctly the buffer will have a bias current of ~ 15-20mA?

My rails should be pretty clean, I'm using a SMPS with extra CRCRC filtering. I'll probably chuck at least a local cap close to the Jfets on each buffer board or I'll go all out and build another small CRCRC on it. With the SMPS I can get away with small caps and I need to burn 2V to get my rails to 24V anyway. But considering that my main power is clean enough that the ripple is below the noise of my scope it's probably enough to just add a cap =)
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Last edited by OllBoll; 1st November 2014 at 01:25 AM.
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