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Old 24th April 2003, 09:06 PM   #1
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Default fet-riaa with LCR?

Hi,
glanced at LCR with tubes
I have an existing breadborddesign of le pacific, and I'm wondering how to integrate a LCR-RIAA as a try-out.

I want to avoid 1) interstage transformer, 2) large coupling cap's.
So I guess I need an additional stage to drive the 600Ohm load of the LCR. I'm not a smart designer, so maybe someone has a few hints?

have fun,
Rudiger
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Old 24th April 2003, 11:02 PM   #2
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Default LCR

Hi Rudiger,

This was done with FETs before by some Japanese audio guys...maybe even Kaneda.

I must have details on that somewhere in my library, the only trouble is the FETs will likely be obsolete or tough to come by.

The good news is it shouldn't be too hard to accomplish a 600 Ohm Zo with FETs.

The bad news is...I don't know enoogh about them to help you.

Surely some members should though.
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Old 25th April 2003, 07:32 AM   #3
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Just curious if you already have the LCR modules or not. If not you'll be free to use other impedances than 600ohms. A simple way to drive the LCR modules will be through bipolar cathode followers after the fets in your riaa.


cheers

peter
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Old 25th April 2003, 07:48 AM   #4
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Hi Peter,
I'm only testing; I bought cheap cores and made my own coils. (1.8H and 45mH). The parts are here, so I'd like to use them...
Rüdiger
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Old 25th April 2003, 08:11 AM   #5
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Hi onvinyl,
yes you have to put in an impedance converter with bipolar or with fet to drive the lcr riaa.But you need a big cap after the follower to get the right 20 Hz
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Old 25th April 2003, 08:44 AM   #6
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Hi hsort,
well, ok. But how? I have +24V U, fets handy are 2sk170.
It should not be though to make, but I have no idea

It seems, Hiraga described a circuit in L'Audiophile No. 39, but all I can find in the net concerns the LCR-circuit only.

Rüdiger
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Old 25th April 2003, 09:23 AM   #7
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Have alook at this circuit which drives part of the split riaa through an emitter follower. I am pretty sure it will drive 600ohms with ease.


cheers

peter
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File Type: jpg cr-eq3circuit.jpg (62.6 KB, 799 views)
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Old 25th April 2003, 09:26 AM   #8
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Hi Rüdiger,
with sk 170: g to d(first amp),d to vcc,s in series with 600 Ohm to Ground,to couple to the lrc stage with 47 U from s ok ?
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Old 25th April 2003, 11:53 AM   #9
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Hi,
Quote:
with sk 170: g to d(first amp),d to vcc,s in series with 600 Ohm to Ground,to couple to the lrc stage with 47 U from s ok ?
easy enough :-)
I'll try and report later. May take some days...
thanx a lot!
Rüdiger
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Old 30th April 2003, 12:15 PM   #10
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Hi,
made a first test yesterday. Just opened the existing circuit, connected to the suggested impedance converter, through the LCR and back to existing circuit.
Partly, it works. But it seems like i get too much treble/not enough dampening of trebles. If I change the original 0.12uF cap to 0.270uF, tonality comes back, but still too much treble (i can tell cause i just changed one channel).

I'm not able to calculate the LCR, which choke(s) may be wrong? I cannot measure the inductance, with DC the 1.8H ones have 70 Ohms, the small ones 4-5 OHms.

Any hints?
Rüdiger
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