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Old 4th December 2011, 09:43 AM   #161
mogliaa is offline mogliaa  United Kingdom
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Copied the URL in a new browser window and worked. What is that piece of equipment for?
Looking forward to final tests today! Will report later
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Old 4th December 2011, 02:05 PM   #162
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MIG ?
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Old 4th December 2011, 02:45 PM   #163
mogliaa is offline mogliaa  United Kingdom
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Got the 4P1L "Siberian" preamp hooked in my 45 SE. Of course as expected something always goes wrong and I damage the Salas HV shunt regulator so had to remove it and power the pre-amp with the raw supply. Not ideal, but it's well filtered though. Will need to repair the Salas shunt regulator now.

The sad thing is that I can't do a side by side comparison against the 26, but let me tell you my first impressions of this preamp:

1) Ringing is not audible at all. With no signal I tap the table where the preamp sits and nothing. You need to tap the valves hardly enough to get them ringing. In my opinion, this has no contribution to my preamp performance or at least I can't notice it whilst listening to music.

2) Sound is really nice. Exceeded my expectations coming from a 26 preamp!. It has significantly more gain (Av=9). Played "Sonny Rollins' Way Out West" which has a lot of dynamics and superb bass phrases. Also played "Schumann's string quartets" which gave me the opportunity to appreciate the preamp in more detail. Overall the clarity is really good, great bass and warm tone.

3) Noise floor is very good, bearing in mind that the salas shunt regulator is not present. The 50 and 100Hz harmonics are below -100dB when the filament boards are running without HT applied. thanks to Rod Coleman's regulators! With HT noise comes up to over -90dB, which is not that bad

The quiescent point still is Ia=20mA and Va=91V. The THD is about 0.04% - fantastic if you compared to the rest of the DHTs I have been trying. You could get better THD if you run the 4P1L hotter!

Still need to play around to find the sweet spot of this preamp....


Now back to the workshop to fix the Salas Shunt Regulator and do the belated side by side test with the 26
Attached Images
File Type: jpg The Siberian 4P1L first test.jpg (123.5 KB, 849 views)
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Old 4th December 2011, 03:19 PM   #164
Charm is offline Charm  Russian Federation
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Quote:
Originally Posted by Wavebourn View Post
Looks quite similar.
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Originally Posted by nicoch58 View Post
MIG ?
No, the cruise missile.
http://www.audioportal.su/attachment...5&d=1231268158
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Old 4th December 2011, 04:27 PM   #165
mogliaa is offline mogliaa  United Kingdom
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Have been running for 30 min or so. Now playing Beethoven's violin sonatas. It's getting better now! Any idea of any burn in time for these valves?

They don't glow too much, especially if you run them at low filament current like in this case. A dim glow from the filaments. See attached
Attached Images
File Type: jpg 4P1L Siberian 2.jpg (43.7 KB, 782 views)
File Type: jpg 4P1L Siberian 3.jpg (47.4 KB, 742 views)
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Old 4th December 2011, 04:42 PM   #166
iko is offline iko  Canada
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Ale, is this still with the dn2540 gyrator plate load? What psu filtering are you using at the moment?
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Old 4th December 2011, 04:42 PM   #167
mogliaa is offline mogliaa  United Kingdom
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THD response and updated schematic attached.

Looking at increasing the value of R3 to improve the gyrator frequency response. Haven't updated the LTspice simulations, but before doing so, any recommendations around the practical value of this resistor? 1M or even higher? I've seen this to be around 4M7, but then Rod recommended a lower value. Bearing in mind the capacitor is already 1uF

Thanks for the help
Ale
Attached Images
File Type: png 4P1L stereo @20mA Va=91V.png (47.0 KB, 739 views)
File Type: png 4P1L Siberian DHT Preamp.png (65.7 KB, 814 views)
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Old 4th December 2011, 04:45 PM   #168
mogliaa is offline mogliaa  United Kingdom
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Quote:
Originally Posted by ikoflexer View Post
Ale, is this still with the dn2540 gyrator plate load? What psu filtering are you using at the moment?
Iko,
Yes. Gyrator loaded. See previous post. Added a 2uF capacitor on the preamp chassis. Blew up the salas HT shunt regulator so I'm using the HT raw supply. Is a CLCL stage using a hybrid AZ1 rectifier.
See attached
Attached Images
File Type: jpg 26 HT raw supply.jpg (268.1 KB, 654 views)
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Old 4th December 2011, 04:51 PM   #169
Charm is offline Charm  Russian Federation
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Alejandro, you liked the sound of Russian capacitors K72? How do you characterize their effect on the sound ?
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Old 4th December 2011, 05:00 PM   #170
regal is offline regal  United States
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Quote:
Originally Posted by mogliaa View Post
THD response and updated schematic attached.

Looking at increasing the value of R3 to improve the gyrator frequency response. Haven't updated the LTspice simulations, but before doing so, any recommendations around the practical value of this resistor? 1M or even higher? I've seen this to be around 4M7, but then Rod recommended a lower value. Bearing in mind the capacitor is already 1uF

Thanks for the help
Ale

Amazing FFT, is this without the Salas? Espect the 60hz hump will go away with the salas or is this a groundloop. You mentioned measuring without the B+ only the coleman supplies, can you post this FFT ?

Awesom job BTW, it sounds like the cord you found for suspension is doing the job. Only thing is you said average gain of 9, I thought that with a ccs/gyrator this tube should be close to a mu of 15 ?
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