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Old 30th January 2009, 10:26 AM   #11
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Quote:
Originally posted by oshifis
I have another idea for buiding a MC amplifier. The idea is that an MC cartridge needs low load impedance. This is why a step-up transformer is used, but what about this topology:

Laszlo's Valve Output Stage with Lundahl transformer

I tried it with a current-output DAC, but haven't tried with an MC cartridge yet. Also the turns ratio must be figured out.

Hi Laszlo,

very interesting argument here!

Mine friend have experimentated various loads on his Asaka( re=5 ohm).
With great surprise, the Asaka sounds natural and full ONLY with low loads, to say 10 ohm or less
(With 470 ohm as suggested by Linn, the sound is fragile, anemic, near digital! No bass, only mid-high !!! Incredible.)

IMO, in this scenario the cartridge start to operate near in power mode instead in voltage mode.
In particular at 5 ohm we have perfect power mode, but the insertion loss is 6dB, no?
I am speculating this is the manner that Dynavector PHA100 and 200 works. Exerpt they claims current mode operation.
But PHA's has a input selector at 3/4 ohm - 10/12 ohm and 35/40 ohm, if I well remember.

Thus I am confused: to work in true current mode, your load have to be zero ohm, am I right? Equal for alls............

Thus, what really makes that selector?
IMO they work in power mode, not current mode, but this is obyovsly only my speculation

Cheers,
Paolo
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Old 30th January 2009, 10:33 AM   #12
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Default Re: Re: Re: Commitment

Quote:
Originally posted by bambo
Hi Paolo and Laszlo (and all other phono-lovers),




Hope I did not scare anyone, and: you are welcome! Further, I completely agree with Laszlo: the best (simplest) way forward for you, Paolo is to include a step-up. My recommendations:

1) Sowter 8055 1:10 with OCC wire (goood!) @ 80,= approx
2) Lundahl LL1681 1:13 @ 85,= approx
3) Lundahl LL1931 (real high end! ) 1:8 @ 155,= approx

The lundahls could be used parallel: parallel to better match the very low output resistance of the asaka cartridge. This is normally not rcommended practise, because of the limited magnetic coupling. At very low inputlevels though, it's useable with fine effect: wired parallel to parallel, the 1681 would be low noise (noise figure 2.4 dB) while the the 1931 would be stellar (noise figure 1.3). Of course one would need two transformers per stereo pre-pre

Cheers,
Mark
Indeed, mine friend need only 6-9 dB gain, not 20!
Because his A. Loesch gain jet 1500 times !
Unfortunately he is totally unreasonable about transformers, he has fear to try ( purchase) and reject it because bad sound...
I am sure a good Lundhal could be the way to go, but I repeat this man is very ostinate!!

Thanks for very good suggestions, Mark


Cheers,
Paolo
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Old 30th January 2009, 04:27 PM   #13
MRupp is offline MRupp  Germany
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Default MC headamp

Hello Paolo,

You may want to look at this MC headamp of Frank de Groove, supposedly pretty quiet: http://www.diyaudio.com/forums/showt...333#post485333
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Old 30th January 2009, 04:40 PM   #14
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Thanks Martin,
Those is very interesting to my inexpert eyes

Have to study it a bit just to understand how it ...works!

very appreciated, thanks again

Cheers,
Paolo
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Old 8th March 2009, 10:53 AM   #15
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Default Ping Mark

Hello,

I would like to ask Mark/Bambo about his RTP3c but the email button is off. Mark, would you mind to activate it, of drop an empty mail to: vrhff04_at_xs4all_dot_nl

Best, Arjen.
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Old 8th March 2009, 07:35 PM   #16
waltube is offline waltube  Italy
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Hi Inertial,

here you can find a mc step up made with a 417A tube; it is working very good .
With an accurate dc supply it is quite. The reostat in input is to trim the value for mc cartridge.
http://www.multitask.it/step-up/mc-tube.bmp
http://www.multitask.it/step-up/mc-tubepower.bmp power supply

Hiere is the circuit at 1KHz, 3mV input, gain is about 20.
http://www.multitask.it/step-up/tube-1KHz-3mv-in.jpg

Here with 1KZ, 10mV in
http://www.multitask.it/step-up/tube-1KHz-10mv-in.jpg

Here the square wave at 10KHz
http://www.multitask.it/step-up/tube-10KHz.jpg

Bye

Walter Gentilucci
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Old 8th March 2009, 08:05 PM   #17
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waltube

This PS seems extremely marginal. I would not consider it seriously for a high quality preamp, especially not one working at uV level.
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Old 8th March 2009, 09:07 PM   #18
waltube is offline waltube  Italy
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Please, try to build it and and listen.
If you look on spectrum you can see where is a noise floor;
my test set is not very sophisticated but I can check the performances of any circuit I build.
Regarding the filaments they must be in dc by a LM317 or similar.
The C-L-C I used is efficent and the results are good for ripple.
I tried also with a tube rectifier, 6X4, with always a good results; the ripple is also low.
If you think that this is not enough, you can use a TL783C, high voltage regulator; with a simply resitor network you can manage until 125 Vdc with 700ma max. of current.

Here is another choice with a very good fet for this job:
http://www.multitask.it/step-up/mc-fet.bmp
The supply is a battery at 9 V

this is a spectrum at 3 mV in:
http://www.multitask.it/step-up/3mVin-63mVout-1KHz.jpg


Bye

Walter
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Old 8th March 2009, 09:28 PM   #19
waltube is offline waltube  Italy
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I forgot to say that normally I use transformers (from Sowter mainly).
The 8055 OCC (1:10) is one of the best I ever heard.
Also the 9990 OCC (1:20) is very good.
Regarding the matching with cartridge, with 1:20 (a good ratio for Asak) we have a Zload reflected on primary (if secondary is connected with the standard 47k) of 117 ohm, if we put in parallel another 47kohm we reach 58 ohm that can be good for a low impedance one.

Ciao

Walter
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