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Old 6th June 2012, 07:12 PM   #201
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Quote:
Originally Posted by juma View Post
We already did it here.
Now we can take it one step further by avoiding the output cap (just C1 stays as a small coupling cap between stages, so it can be of high quality and still not expensive).
Four PSs seems a lot but it's two actually: we start with +24V(V2) and -12V(V5). Then we regulate them down: +24V to +12V(V4) and -12V to -3.3V(V1).
Gain is 10dB (since you like it LOUD).
For clarity, schematic doesn't show bypass/decoupling caps - 10uF Low ESR on every rail will do the job, but depending on PS type,you can try whatever you like (RC combos, small caps in parallel, etc...).
The pot/volume control at input is not shown but 10 to 20K log device is recommended.
Yup. I remember it. IF i can solder the little farts without frying 50% of them, I will try a couple different iterations. Schematic above added to the queue. THanks Juma for the ideas.
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Old 8th June 2012, 03:06 PM   #202
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Juma,
This seems a bit back to front but I wondered if there is a simple way to make this idea work well ...

I want to drive both F3 and F5 in parallel out of the Aikido preamp ( O/P Z of about 500R) and if use the BF862 gain stage to raise the gain of the F5 to exceed the gain of the F3, where would it be possible to fit a volume trimmer - the F3 feeds a 97dB/W FR driver and the F5 into a 96dB/W bass driver (speaker uses a biamp or split passive Xover)
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Old 8th June 2012, 10:44 PM   #203
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Aikido has enough gain to drive your amps, but the Zout is too high for F3, so you'll need a buffer and the way to independently lower the F3 volume.
If I were you, I'd do it like this:
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Old 9th June 2012, 01:19 AM   #204
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Thanks Juma, my other idea just too cute!

Now, a simple jfet totally transparent buffer, hmm? Maybe the ones ZM used on his Lightspeed, rather than the DCB1?
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Old 11th June 2012, 05:27 PM   #205
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Juma,
Got parts coming for two different versions of an integrated F5 for the PC desk. Will try cascode bf862 with lm337/317 regulators stepping down the voltage and one with Jfet, Bipolar combo. All SMD Parts. Hope to keep it small and tight. Well see. Haven't decide on output devices. Being for nearfield, I may use either TO220 Toshibas or standard FQA. What do you think about possibility of lateral output? I know gain is low, but I do love that lateral sound.
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Old 11th June 2012, 09:03 PM   #206
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Originally Posted by buzzforb View Post
...What do you think about possibility of lateral output? ...
Not the best idea. Output devices in F5 work in common Source mode i.e. as voltage amplifier. Laterals don't have enough gm for that job. I tried it and wasn't satisfied. IMHO 2sk2013/2sj313 are the best option.
If you want Laterals in smal PC desk amp, use them as Source Followers - I like the one in attachment. R4 sets the BS170's Id at about 15mA and R6 will set the Laterals' Id - 0.5A was OK for me. The gain equals R8/R10. This little amp gives 9V_peak of clean swing at 4 Ohm load.

EDIT:
you can leave the R5 out if you plan to drive it with B1 in the same case. B1's output cap is not needed too.
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File Type: gif Lovely1.gif (5.8 KB, 684 views)

Last edited by juma; 11th June 2012 at 09:10 PM.
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Old 11th June 2012, 09:10 PM   #207
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Quote:
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Not the best idea. Output devices in F5 work in common Source mode i.e. as voltage amplifier. Laterals don't have enough gm for that job. I tried it and wasn't satisfied. IMHO 2sk2013/2sj313 are the best option.
If you want Laterals in smal PC desk amp, use them as Source Followers - I like the one in attachment. R4 sets the BS170's Id at about 15mA and R6 will set the Laterals' Id - 0.5A was OK for me. The gain equals R8/R10. This little amp gives 9V_peak of clean swing at 4 Ohm load.
SRPP FE. I like it. Can swing big voltage into high impedance load, correct. Missing gate resistors for input fets? I need to stop talking to you. Can't keep up. Thanks.
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Last edited by buzzforb; 11th June 2012 at 09:13 PM.
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Old 11th June 2012, 09:23 PM   #208
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Originally Posted by buzzforb View Post
... Missing gate resistors for input fets? ...
Never.
Behold the R3 and R10 - they are gate resistors too, although you are used to smaller values...
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Old 11th June 2012, 09:49 PM   #209
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Your right. Does such large resistors pose noise issues?
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Old 11th June 2012, 09:53 PM   #210
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Look at them again and read the about the thermal noise again
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