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Arkless Electronics Transconductance Phono Stage

Putting it in the nice new cases would be a start.... ;-)

The few days to sort the valve amp SMPS I'd just started designing when I last saw you (I mentioned it in passing...) turned into 10 (now sorted) and several repairs have come in within the space of a few days... bills to pay etc so I have to put these first...
 
Yeh i noticed you'd picked up a bit of incoming business, excellent stuff.

Mark's dead keen top hear this. I think I've whipped him up into a bit of a frenzy. Well it's frenetic for Mark anyway.
 
The SMPS is working well and giving a smooth 280V DC from 24V in at about 82% efficiency (the type of SMPS I'm using doesn't reach the 90% + level at these voltages so that's pretty good) and can form the heart of a variety of budget valve products to come after the Transconductance stage, starting with a MM phono stage using the PCF802 telly valve;) It will be really cheap for the performance on offer (think £450 ish and "please compare SQ wise with £1K units" type VFM) but unashamedly in a naff looking case, hence it's so cheap. The money is spent on the innards not the appearance. That's the plan anyway but now I've "put to bed" the SMPS I'll not be going back to that for a few months... the phono stage itself is now designed at computer simulation level and looking good BTW.

Sony TC-377 R2R on bench at the minute, then a Quad 34 to do, then a Parasound power amp followed by a Musical Fidelity A100 and then I'll be putting the boards in the boxes... and it will be with you and Mark as first beta testers:) wish I could do things the other way round but the landlord and phone company aren't that understanding about hi fi:D... then that f'ing massive Musical Fidelity Nu-Vista on which the instructions have changed to complete rebuild using the finest parts around... plus Audio Research LS25 and MF phono stage for same customer. Then a custom build of a complete full function valve hybrid pre amp with valve transconductance MM phono stage, stepped attenuator vol control and both active and passive line outputs in a lovely Modushop case:) busy busy at the moment!
 
Can I go on the list for a listen to this phono stage. It looks interesting.
I’m close enough to Sheffield to maybe have a listen at sq225917’s place if he didn’t mind when he has it on test.
Cheers
 
Finally ready so should be going to first "beta testers" imminently.

Here's a teaser glimpse of rear panels of PS and PSU (snapped on a stool in my workshop... no attempt at being David Bailey here!)

jYJA1pp.jpg


Those are loading plugs just to the left of the earth binding post, inputs on right and outputs the remaining phono sockets.
It's dual mono and the leads on the far left of both PS and PSU are locking connectors for left and right channel power.
The three toggle switches give a variety of earthing options to cope with avoiding earth loops in various system dependent situations likely to be encountered in practice.
 
OK, as promised Jez's new stage was delivered to me last night and I have had a listen.... plugged it all in and everything worked exactly as it should - I didn't have to mess with the grounding options as there was no hum to eliminate. Hiss and gain levels were very similar to my regular Paradise (in other words, quite high gain and very low hiss). As to the sound - well very similar indeed to my Paradise - bloody fantastic! It has the same sort of poise, dynamic and vitality. I didn't have Si's adjustable loading plugs so couldn't experiment much with the loading. I did feel the native loading (I believe this is 600 Ohms) sounded just a bit more airy and focussed than the loading plugs supplied, but the difference was small. I'm finishing early today so will have another listen when I get home - but this is certainly one of the finest sounding stages I have heard.
 
Anyone interested in adding the RSL Phono-Stage to the bake? The final version is on its way to the UK as of about a week ago. I don't know when you were planning the bake but I could probably have the unit there in 10 days or so unless Customs gums up the works.
 
OK, as promised Jez's new stage was delivered to me last night and I have had a listen.... plugged it all in and everything worked exactly as it should - I didn't have to mess with the grounding options as there was no hum to eliminate. Hiss and gain levels were very similar to my regular Paradise (in other words, quite high gain and very low hiss). As to the sound - well very similar indeed to my Paradise - bloody fantastic! It has the same sort of poise, dynamic and vitality. I didn't have Si's adjustable loading plugs so couldn't experiment much with the loading. I did feel the native loading (I believe this is 600 Ohms) sounded just a bit more airy and focussed than the loading plugs supplied, but the difference was small. I'm finishing early today so will have another listen when I get home - but this is certainly one of the finest sounding stages I have heard.

Great stuff:) The loading plugs I left with it are 100R but for a precise figure the resistors in parallel equation should be used. Hence eg if 600R loading plugs were used the total would then be 300R, and the 100R loading plugs give an actual 85R. The Paradise also has a native loading of around 600-800R BTW. This is due to the type of circuitry employed which, although both are different, they both use bipolar transistors without negative feedback and so it's intrinsic to the device physics. This is why a MM version would need to be completely different and it's not possible to make a MM/MC switchable one. Both are transconductance stages and both use zero feedback. Both are extremely complicated in order to keep the actual signal path very simple... but mine makes it about half the path of the Paradise, with only 4 transistors in the signal path directly (the way they are used means they could be analysed as being only two), and eschews all capacitors other than those intrinsic to the RIAA EQ.

A valve hybrid MM only transconductance stage has been designed, prototyped and also sounding bloody marvelous BTW so those who have an up market MM or like SUT's will be able to share the joy of transconductance at some point in the future.
 


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