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-   -   Arjen Helder's old version valve pre amp (http://www.diyaudio.com/forums/class-d/227860-arjen-helders-old-version-valve-pre-amp.html)

captain pugwash 15th January 2013 11:25 AM

Arjen Helder's old version valve pre amp
 
I've been sitting on an old version of an Arjen Helder valve pre amp board ( v1.3 2009 is printed on the board) for a few years now but lost the instructions and it is no longer listed in the shop. Did anyone ever pair one of these up with his 2020 amp? If so is it any good and can you recommend a good valve? (I contacted Helder himself about the instructions but he hasn't been any help)

Johnny2Bad 15th January 2013 12:43 PM

Works fine. As for instructions it's pretty straightforward ... needs about 350mA at 12V, has no problem with unregulated voltage up to perhaps 16V.

Replacing the supplied tube yields rewards. I was able to get a pair of Hammond-branded (Raytheon NOS 60's mfg; Organ manufacturers like Hammond had close-tolerance hand-insptected contracts so they are almost always excellent examples) which is probably overkill but it's what I have so I run it. Found 'em local for $10. Life on these tubes runs into the 10,000+ hours so I probably will never need the spare, but it's there anyway.

It is not much of a distortion-generator if you are looking to add some "tube warmth" to a sterile digital system. These small-signal tubes are known for outstanding low distortion and extremely high headroom. Not the ideal unit if you want "Unplugged" to sound like "Live At Leeds".

On the other hand if you want a tube for a small-signal buffer they are an excellent choice. They are still used today in mic preamps in the studio, where clean headroom is King Spec.

If you do some careful level matching you will end up with a Source -> Tube Buffer -> Chipamp system that won't clip easily if at all. Or, if you need a lot of drive ... say running RCAs to a remote amp ... it does a very good job.

Its quiet, no issues there.

I replaced the "Audiophilter" caps on mine, it helped. I used some lower-tier Mundorfs, not sure if I would choose them a second time as there was a tendency towards sibilance but I killed that by bypassing them with some Russian teflons. It sounds good now but if I were to do it again I would try different caps than the Mundorfs.

I also replaced the yellow caps (near the tube) with some WIMA MKP-10's (because I had them laying around in the right values) but due to a lack of listening tests I can't say what effect that had. Maybe just leave them.

I also replaced the pot with some decent eBay-China sourced SMD resistor switch attenuators ... cost me a (very) few dollars and when I tested them they were very tight L-R and overall. The supplied pot can't be described that way.

I used it with some TA2020's (6 channels worth).

I'm currently not running the buffer but it's slated to go into a car stereo build I'm working on in the next few months.

captain pugwash 15th January 2013 01:58 PM

Thanks for the reply Johnny, interesting stuff. I think, however that preamp you have (supplied tube and yellow caps) is the latest mk4 version. The one I have did not come with a tube and has no yellow caps, it says v1.3 2009 on the board but that's all I know about it. I got it about 3 years ago but lost all the paperwork

Johnny2Bad 15th January 2013 02:15 PM

Quote:

Originally Posted by captain pugwash (Post 3326932)
Thanks for the reply Johnny, interesting stuff. I think, however that preamp you have (supplied tube and yellow caps) is the latest mk4 version. The one I have did not come with a tube and has no yellow caps, it says v1.3 2009 on the board but that's all I know about it. I got it about 3 years ago but lost all the paperwork

Well, I must have been in my Time Machine when I bought it then. Mine is at the latest Dec 2009 production. It is the version you cannot change tube types (much). Arjen sells his wares with and without tubes, with paid and with free shipping, prices adjusted accordingly, and different options depending on which eBay site they're listed (UK, USA, etc).

captain pugwash 15th January 2013 02:33 PM

1 Attachment(s)
The attached photo is the one I have and I can't see it anywhere in the Helder shop that's why I assumed it to be an old version.

Johnny2Bad 17th January 2013 05:01 AM

You have the Mk 1 version (not called Mk 1 because it was, well, Mk 1).

I have the Mk II version. For a time you could buy either. Neither of us has the Mk IV version, which allows for wide tube substitutions.

The Mk 1 board is a somewhat different design, but oveall I say "run her".

Issues addressed with Mk II deal with DC offset.

Most chipamp powered devices have some DC offset at the output. This includes your typical mp3 player. So a cap at the input helps there.

Arjen's TA2020 and TA2024 boards have input caps also to stop DC offset issues. The Mk II buffer has output caps. In all cases these are the large orange "audiophiler" caps. See if your Tripath boards have them; if so all good.

You don not need BOTH output caps on the buffer and input caps on the Tripath boards, but you do need them at one of those boards. Or at least you should ... the "no cap is a good cap" camp run without, but then again they blow up a lot of boards.

When I ordered mine from Arjen, I had him build the board with no output caps or volume control, which made it easier to mod it for me (avoids having to remove parts).

In any case, I think as far as instructions go, see if you can determine the tube type and the rest is just hooking stuff up.

captain pugwash 17th January 2013 08:20 AM

Cheers Johnny you've been really helpfull, much appreciated

tubesteve 11th February 2013 12:43 AM

12AU7 Buffer
 
1 Attachment(s)
Attached the schematic of the buffer amp. The mentioned gain is the "unloaded gain", means, no load (or better: very high impedance ) attached.

Ronj 19th October 2014 02:09 PM

Reviving an old thread. I also have a so called MK1(the first version) of Arjen's tube buffer, I want to use it in a vintage amplifier re-build. Where the amp works on a single 50V DC rail. So can I skip the 555 pulsed Dickson charge pump/multiplier(well it looks like one, but I can't see two out of phase pulses. Instead a single pulse) and feed my 50VDC directly to Anode Triode 1 and anode 2 using same anode resistors as in the circuit? I can skip all those 4.7uF cheap Chinese caps also in the process. That means feeding the 50V directly to those 10K anode resistors... Yes I do have another 12V line in the system to, the heater. I can see Arjen uses 12V line for heating, which I will use my 12V line...


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