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Old 23rd September 2010, 07:49 AM   #4981
kenev is offline kenev  Greece
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Hi there,

I have decided to build this RIAA preamp, but there seems too much to read already written in this thread.

I know there is a pdf file published by psgr, but the two links I found searching in this thread are dead. Can anyone direct me to a valid link for this pdf file or re-uoload the file?

Thank you
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Old 23rd September 2010, 07:56 AM   #4982
Salas is offline Salas  Greece
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That's the updated circuits link you can click below. What cart, and what is the gain of line and main amp, speakers SPL? The PDF has good general instructions but prefer the polished circuits in the link. I am not sure if the pdf is hosted still. PM me to send you if you can't find it.

Simplistic NJFET RIAA
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Old 23rd September 2010, 09:55 AM   #4983
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It had very low voltage headroom in the cascode and on second stage your numbers show me. That is why you got sound when you added B+. Your leds appear strong, maybe at 8.1V, take one out from each quad, short its pads. You should be left with 3 glowing leds per channel. Your 2nd stage fets are stronger, or your R6 is 22R. 1k1 is a good R7 value. If with stronger fets its not bad, but make R6s into 100R trimmers (middle leg connected to ground leg, top leg to source pin). Don't throw away your old R6s, recycle them as in the picture so they are helpful with Q6's dissipation. Set trimmers at 33R, connect to the 37V (exactly set) shunt, turn the R6 trimmers for 8V at Q2's drain to ground. Should be doing OK with those numbers hopefully. Also tell me the new numbers on Q1 & Q5's drain to ground after that. Use coaxial shielded cable for input. What is your test cartridge and what load did you use for Rload? Also is your C3 a combination of polysterenes and what is the value of its main component?

My cartridge is a Goldring eroica lx. 0.5mV 100ohm load recommended.
I saw you suggested 1k instead of 100R for load earlier and i will try it with the next bunch of resistor i will order. Yes those are Remix polysterens or stiroflex. 47n, 15n+1n,100n. I don't know how it sounds correlating to russian pio or silver micas but i will when occasion offers. I have a lot so the simplest way was to use theese stiros.
Getting back to my shunt problem my TX is a 20VA 2x15V toroidal, so can its weakness in current cause some deviation to normal playing?
Relevant modification will be place when i get home again.


Karesz
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Old 23rd September 2010, 10:07 AM   #4984
Salas is offline Salas  Greece
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Depends on each cart and system. You gotta listen to some loads because subjective tone has to do with TT set up, speakers HF in room etc. 100R looks OK electrically for an 8 Ohm coil cart like yours. A DL-160 would sound good from 1k to 8k2 for instance when a DL-103R from 150-180R. Try 15.4n instead of 16.1n C3 in total also before you lighten its load to 1k. I hope all it will work OK first with those changes. Having 20VA must still be OK since you consume 8.4W. Is your Vin to reg 42V when working?
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Old 23rd September 2010, 10:24 AM   #4985
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Originally Posted by Salas View Post
Depends on each cart and system. You gotta listen to some loads because subjective tone has to do with TT set up, speakers HF in room etc. 100R looks OK electrically for an 8 Ohm coil cart like yours. A DL-160 would sound good from 1k to 8k2 for instance when a DL-103R from 150-180R. Try 15.4n instead of 16.1n C3 in total also before you lighten its load to 1k. I hope all it will work OK first with those changes. Having 20VA must still be OK since you consume 8.4W. Is your Vin to reg 42V when working?
Without load it was 41V if i remember well but i will check the accurate value.
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Old 23rd September 2010, 10:43 AM   #4986
Salas is offline Salas  Greece
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A bit marginal for a 37V Mosfet reg with 4V Vgs in series CCS. I would find it better with a 2x17V Tx in series for 34VAC.
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Old 23rd September 2010, 11:07 AM   #4987
RCruz is offline RCruz  Switzerland
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[QUOTE=The Space Egg Corp;2311405]Hi thanks for recommending ARMAGEDDON to me.
QUOTE]

Hi Simon

I built a Geddon and basically it is a 500VA toroid reducing from 220Vac to 110Vac.

The reduction in voltage also brings lower torque to the motor but it also reduces noise so you can hear better detail.

Check what type of motor is installed in your TT before building this rig because it does not work with all motors. (Both my TT (Rega and Ariston) use a premotec 24 pole AC motor)

Last edited by RCruz; 23rd September 2010 at 11:09 AM.
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Old 23rd September 2010, 02:55 PM   #4988
kenev is offline kenev  Greece
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Quote:
Originally Posted by Salas View Post
That's the updated circuits link you can click below. What cart, and what is the gain of line and main amp, speakers SPL? The PDF has good general instructions but prefer the polished circuits in the link. I am not sure if the pdf is hosted still. PM me to send you if you can't find it.

Simplistic NJFET RIAA
Thanks Salas,

I was already aware of the quoted, link but a friend told me that (as you also state) that the pdf is a good general paper.

My cart is VdH MC10 Super (0.65 mV), preamp has 15 dB of gain, I play with a couple of (mainly sensitive) amps and my speakers are horn loaded at 96 dB/W/m.
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Old 23rd September 2010, 03:04 PM   #4989
Salas is offline Salas  Greece
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The normal MC circuit will do fine. Good luck with the build, and don't hesitate to ask if stumbling. Are you the guy you came asking for birch plywood sources years ago when I was working for that pro sound company by the way?
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Old 23rd September 2010, 04:54 PM   #4990
kenev is offline kenev  Greece
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...Are you the guy you came asking for birch plywood sources years ago when I was working for that pro sound company by the way?
Correct!
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