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Old 15th December 2009, 02:56 AM   #211
ra7 is offline ra7  United States
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Salas,
I was trying more configurations with the load resistors etc. I found one with 16V first stage and 24V second stage. The distortion dropped to 0.08%. I built it and it sounds better in every way except it has become very hot... in the sense that it is picking up the clicks and pops too strongly and there is some electrical noise as well. I put 520uF caps before the load resistors and ground and the noise went away for a while, but its back again now.

I tried changing the input resistor and it changes the sound, for good and bad depending on value, but i couldn't get rid of the noise. Apart from the noise, this is a winner. What gives?
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Old 15th December 2009, 03:33 AM   #212
Salas is online now Salas  Greece
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The second stage is the main THD contributor in such a circuit because it handles some appreciable level. You gave it better swing and degeneration now. That is well. You have two floating psus (batteries) as I understand on it now? One 16V and one 24V? Use just the 24V one, put a large electrolytic across it, right on its poles. Then from the B+ node on the circuit use 2 resistors towards the stages drains. 100R for the second stage, 2k2 for the first stage. Leave the local drain to earth caps you used there. See that your 1st stage drain voltage is around 15-16V or change that 2k2 a little (you did not give me bias current data but it should be around 4mA?). That experiment may save the you the susceptibility problems, else its something else.
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Old 15th December 2009, 03:41 AM   #213
Salas is online now Salas  Greece
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Quote:
Originally Posted by LucasAdamson View Post
ok, so could I trial and error it, starting with 27R? I don't have a test disc, or a good enough knowledge of test procedures to really trust myself without a guiding hand looking over my shoulder. If the spice suggests 27R, then I'd be happy to go with that. I'd only raise the alarm if it sounded awful I guess.

Many thanks
Lucas
I can't suggest more than a simple trial and error test given the limitations you sincerely admitted for performing adequate technical procedures. Wishing success then. Cheers.
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Old 15th December 2009, 01:24 PM   #214
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Yes the current draw per stage is about 5mA. About 20-22mA total for both channels.

I will try it this evening. thanks again!!
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Old 15th December 2009, 02:07 PM   #215
Salas is online now Salas  Greece
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5mA, OK. Use 3k3//3k3 instead of a 2k2 Rdrop from +24 towards the first stage then.
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Old 15th December 2009, 02:42 PM   #216
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I was looking at your simplistic njfet riaa and you commented at the start that this type of circuit should not be used for mm. You recommended cascoding the input jfet. Can you please post a schematic of such a circuit? All the ones in that thread appear as black bkgnd with blue lines... :|
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Old 15th December 2009, 03:05 PM   #217
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After some time all 3 sensitivity versions adopted that feature. Go at post 2706 there. A download link has a pdf overview made by member psgr and kindly hosted by Ikoflexer.
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Old 16th December 2009, 11:39 PM   #218
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Discounting batteries, as I imagine them to be inconvenient, what kind of power supply should I use for this circuit? I am currently looking for a 2x 24-28v regulated supply, as i assume this is the best thing. I imagine that the current draw is quite tiny on this circuit. I would like something physically small, yet effective. Can anybody suggest a design, or kit from eBay, or whatever please.

Many thanks
Lucas
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Old 17th December 2009, 11:02 AM   #219
RCruz is offline RCruz  Switzerland
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Hi Lucas

Try this one: Simplistic NJFET RIAA

Ricardo
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Old 17th December 2009, 08:17 PM   #220
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Quote:
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Hi Lucas

Try this one: Simplistic NJFET RIAA

Ricardo
Wow! Even more K170s! How many can one cram into a hifi? I have 2 in the phono stage and 4 in the buffer already. It looks a touch complex. Is it? Is there a layout plan for p2p or a PCB anywhere? Have you built one?

Many thanks
Lucas
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