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Old 21st December 2009, 06:07 PM   #471
syn08 is offline syn08  Canada
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Quote:
Originally Posted by Allen Wright View Post
Joachim, Holgar,
If you are getting to hear a Vacuum State RTP3C/D, a word of advice.

Please do NOT listen to it until it's been on for AT LEAST 24 hours. For whatever reason, it sounds quite ugly until it has really warmed up - and once it's on, leave it on please. It's intended to run constantly, 24/7/365.

That does NOT burn out the tubes - in fact they last much longer if never turned off!

Second point: it's a conventional voltage input on the phonostage which has provision for loading Rs. I strongly suggest you use 47k, and nothing lower.

The RTP has enough input overload headroom as to not be affected by any ultrasonic cartridge resonances - and 47k loading allows the full dynanics of the cartridge to shine through.

Attached is a schema of the phono section, it feds a balanced selector and attenuator, and a simple/complex line stage.

If you send me your mailing address, I'll send you a Xmas present.

Very interested in your opinions.

Regards, Allen
No pun intended Allen, but I would be really curious what are the advantages (or secret ingredients for performance) in this schematic. That's because by all engineering standards, it has poor performance (noise, input impedance, offset, etc...). I also miss the purpose and advantage of cascoding bipolars with tubes.

Was it designed following "subjective sound" criteria only? That would explain some of the decisions...
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Old 21st December 2009, 06:12 PM   #472
SY is offline SY  United States
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syn, you have me scratching my head. Noise is very good (0.8nV/rt Hz), the tubes give very large and linear swing, input impedance well high enough to not bother a cartridge. No output offset, it's cap-coupled. What's the objection?
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Old 21st December 2009, 06:46 PM   #473
syn08 is offline syn08  Canada
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syn, you have me scratching my head. Noise is very good (0.8nV/rt Hz), the tubes give very large and linear swing, input impedance well high enough to not bother a cartridge. No output offset, it's cap-coupled. What's the objection?
Stu, I am scratching my head as well. For example, 2x22ohm in parallel with the input makes 11 ohm, or about 0.4nV/rtHz noise by itself. And this is before considering half of the emitter resistor.

I would understand tubes in a gain stage, but what's the advantage of a tube as cascode? A high voltage mosfet will do exactly the same, while the cascode noise doesn't matter anyway.

Using the SSM pairs, what's the current noise of this amp?

And why feeding the RIAA network from a finite impedance, while a (e.g.) folded cascode (like in the Vendetta) will provide a very high impedance?

Last edited by syn08; 21st December 2009 at 06:58 PM.
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Old 21st December 2009, 06:58 PM   #474
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Originally Posted by syn08 View Post
Stu, I am scratching my head as well. For example, 2x22ohm in parallel with the input makes 11 ohm, or about 0.4nV/rtHz noise by itself. And this is before considering half of the emitter resistor.

I would understand tubes in a gain stage, but what's the advantage of a tube as cascode? A high voltage mosfet will do exactly the same, while the cascode noise doesn't matter anyway.
Well, yeah, there's that. One more reason to use transformers at the input.

I haven't looked at the distortion spectra for MOSFETs on top- I have seen Allen's results with FETs on the bottom, tubes on top, and they're quite good.
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Old 21st December 2009, 07:01 PM   #475
syn08 is offline syn08  Canada
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Well, yeah, there's that. One more reason to use transformers at the input.
Yuk, transformers
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Old 21st December 2009, 07:02 PM   #476
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Oh my, you'll have fun with my RIAA article.

Transformers are terrific in this application, though I certainly understand the prejudice against them.
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Old 21st December 2009, 07:05 PM   #477
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[QUOTE=syn08;
but I would be really curious what are the advantages (or secret ingredients for performance) in this schematic. That's because by all engineering standards, it has poor performance (noise, input impedance, offset, etc...). <<<

Can you please explain why it has poor noise, poor inpt impedance, poor offset - and why these, other than noise, and to a very small degree, offset, are important in a MC phonostage?

>>I also miss the purpose and advantage of cascoding bipolars with tubes.

Was it designed following "subjective sound" criteria only? That would explain some of the decisions...<<<

I'm happyto amswer your questions after I'm clear as toyour complaints.

Regards, Allen
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Old 21st December 2009, 07:38 PM   #478
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Syn, I believe you are focussing on engineering princlpals without regard to anything else, especially practicallitiy and sonic results.

We all have our preferences, you say "Transformers -yuk" and I agree with you. But you suggest a HV MOSFET and i say YUK. You use huge amounts of NFB to get distortions way below anything a human can sense - i personally HATE using NFB and have developed my circuits over 30 years without it.

The 22R input Rs are there to stop the whole mess oscillating at 30MHz or so.

The cascode bipolars/tubes were a R&D development when atube/tube casode was way too noisy for MC, and jfet/tube didn't have the 72dB gain in one stage (before RIAA eq) I needed. The MAT02 does the job and is VERY quiet in practice, Maybe not as quiet a 10 of them in parallel but more than enough for all cartridges I own, including a 100uV IKEDA.

The people who own this preamp love it, and most have owned serious commercial units before. It's going up against Joachim's best, how about sending one of yours over and there can be a real shootout?

I'm game!

Regards, Allen
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Old 21st December 2009, 10:34 PM   #479
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Hello all !
I do not know where to start. Well, letīs say i learned it the hard way building the Hiraga Optime that a circuit with a serious technical flaw can sound excellent. It is not that bad if you look more closely. Itīs low noise in my system and it is wide band. The input impedance works with my 5.5 Ohm Titan i without audible treble loss. It has quite high distortion. 0.32 % @ 1V RMS after the RIAA but ONLY 2nd montonic. It does not sound distorted to my and other trained ears. Quite the opposite. It sounds clean and dynamic. If you apply feedback you always end up with lower but more complex distortion. If i trust Geddes who spend his half life searching for correlation between subjective sound and distortion measurements the human ear is very tolerant to 2nd but higher order harmonics should be weighted much more aggressively. A simple THD reading says nothing so listening is required. That does not say that a circuit sounds poor with feedback. My Goldstandard Pre-Pre uses feedback but not the NFB parallel kind and has distortion below the -145dB noisefloor. In speed and precision it beats the Hiraga and needs so sorting, tuning or matching. High Z and low Z versions can be made. I would only condemn a product if it failed in my listening room. I will have a chance to listen to the Vacuum State and i am very interested to hear the latest Synaesthesia too.
It is technically brilliant and why should it sound bad ? There is still so much to learn until we reach perfection.
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Old 21st December 2009, 10:53 PM   #480
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Today i build another PSK buffer this time with LSK389C. The C version has higher IDss and that brought a well come gain in bandwidth (from 3.5MHz -3dB to 6.5MHz -3dB) and more class a. This time i am using the Alps K faders from studio consoles. I used 2 x 10kOhm log and put them in parallel. Balance can be adjusted easy that way. i already told you that i stole that trick from a Curl pre. Frequency response is now 2Mhz -3dB in the worst position of the faders, this time at around 3/4 full. The sound is now very transparent and open in the treble. The slightly dark character is gone. It sounds close to my reference with the exception of slam and extension in the bass. I attribute that to my primitive power supply. Just 4 9V alcaline cells plus 4 x 10.000uF Nichcon bypassed with 1uF MKC. It has a bit more DC offset, 6mV in both channels. No problem in my system. I use a safety cap in front of my power amp. This is really a great fun project, easy and cheep to build. Great sound and measurements.
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File Type: pdf PSG Buffer.TSC - TINA.pdf (29.7 KB, 149 views)
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