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Old 8th January 2003, 05:22 PM   #1
Mad_K is offline Mad_K  Norway
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Lightbulb ultrasimple mm/mc riaa preamp

Have anyone tried this?

(I'm going to

http://www.users.nac.net/markowitzgd/phonopre.html
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Old 8th January 2003, 07:42 PM   #2
halojoy is offline halojoy  Sweden
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Arrow "EL CHEAPO" mm/mc riaa preamp

The Analog Addicts Phono Preamp
By Thorsten Loesch

It is also called "El Cheapo" (low price)

Hope noone will hang me, if I provide a schematic.
I have changed the size a bit, to fit DiyAudio.com.

Best is to read the whole article, that Thorsten Loesch have written.
See Link in post above!


/halo
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Old 8th January 2003, 09:03 PM   #3
Mad_K is offline Mad_K  Norway
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BB OPA 637 is not 'cheapo in my book...

(But the design is 'cheapo in comparison to other Loesch riaa designs)
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Old 8th January 2003, 09:23 PM   #4
Optical is offline Optical  New Zealand
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Default Re: ultrasimple mm/mc riaa preamp

Quote:
Originally posted by Mad_K
Have anyone tried this?

(I'm going to

http://www.users.nac.net/markowitzgd/phonopre.html
i'll be keen to hear what you think of it when its done!
Ive been meaning to build all of these simple phono circuits and do a comparison of each to mark the differences for future reference..
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Old 8th January 2003, 09:37 PM   #5
lohk is offline lohk  Europe
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Have you ever ordered an OPA627/637 ?

Must be one of the most expensive opamps available...

Klaus
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Old 8th January 2003, 09:40 PM   #6
lohk is offline lohk  Europe
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and please ask Kuei Yang Wang about that design
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Old 8th January 2003, 11:00 PM   #7
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Hi,

Quote:
and please ask Kuei Yang Wang about that design
Speak of the Evil one....

Not much to say about this thing really. I started fafelling about with Selfs "Precision Preamp" Phonocircuit. It sounded BAD. So I messed about a lot and tried many things.

Doing this circuit with lead acid battery power, OPA637A and a 10k Pot (later an unusual active linestage with a FET Buffered LM6181 and Volume control with a 1k Shunt Pot and a 150 Ohm output resistor) sounded rather decent for solid state. Acrylic case BTW, mixture of hardwiring and PCB.

Still, I like valves and transformers better. Butafter you put don the long green for a pair of S&B TX-103 MC Steups and the same amount for the LCR RIAA EQ Module and shelled out the green for a PSU using 8pcs 10H chokes and 6pcs 120uF Film Capacitors you appreciate just how good this little job is for the money, how simple to build.

And the price of a pair of OPA637 plus a pair of 2SK147 and four 12V/2.1AH Lead acid batteries is not THAT outrageous. Hell, my current RIAA Stage clocks in at near 1,000 in materials uses near unobtanium NOS Valves and it is NOT ten times better than the little ugly duckling solid state stepchild. In wood, netal and all it looks a lot better though.

Sayonara
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Old 9th January 2003, 12:33 AM   #8
Mad_K is offline Mad_K  Norway
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Quote:
Originally posted by lohk
Have you ever ordered an OPA627/637 ?

Must be one of the most expensive opamps available...

Klaus
I have them in a little box, along with some other goodies TI was kind enough to send me

And, yes I have yet to see an opamp with a higher price...
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Old 20th January 2003, 08:42 PM   #9
Mad_K is offline Mad_K  Norway
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Default And here's how it turned out...

As I've changed the circuit somewhat I'm not allowed to say it's Thorsten's, but I think it is close enough.
Changes:
1. Only MM stage.
2. Not rechargeable batteries.
3. None of the specified components (brands) are used, except for the OPA637BP.
3. Supply filtering changed: Elna RJH 1000uF + 100nF Rifa MMK.
4. RIAA caps are WIMA FKP2, 2,5% but matched to exact value.
5. Outputcaps are Elna RJH 330uf (arranged as descibed) bypassed with 0,47uF SCR.

So, here comes the pics; board:
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Old 20th January 2003, 08:45 PM   #10
Mad_K is offline Mad_K  Norway
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Hardwired my usual way. You can see that it was put together with a little haste. I know this is not the best way to build a circuit like this (PCB with ground-plane and p2p combo should be best), but it's my way..

backside:
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