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Old 9th January 2011, 05:45 PM   #1
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Default Low voltage tube pre-amp for T-amp

I'm planning to build power amp based on dual TK2050 (STA517B) Hifimediy|Hifimediy T3 300W@4ohm Amplifier set and I'm looking for a cheap (below $150) low voltage tube pre-amp (build or kit).
So far I found two models:
Arjen Helder tube pre-amp -- NEW tube pre-amp MKIII 12AU7 fully assembled - eBay (item 260710287509 end time Jan-18-11 18:14:35 PST)
and Indeed Hi Fi Lab one -- Hybrid Headphone Tube Pre Amplifier 6N23P G2 Class A - eBay (item 250748620802 end time Jan-27-11 11:20:12 PST)
Headphone jack is nice to have but not must to have requirement.
Any feedback on aforementioned pre-amps or other suggestions are highly appreciated.
Thank you in advance.
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Old 9th January 2011, 06:07 PM   #2
mwiebe is offline mwiebe  United States
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There is also the $99 Bottlehead "Quickie battery powered directly heated tube preamplifier" which is low voltage. There is a lot of support on the Bottlehead forum if you are new to building.
Matt

Quickie battery powered directly heated tube preamplifier
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Old 9th January 2011, 06:15 PM   #3
mwiebe is offline mwiebe  United States
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There are also a few low voltage Oatley Electronics "kits" that you will have to provide switching, volume and a housing for. There have been a few threads on these preamps here that should turn up in a search for the tube used "6418".
Matt

Oatley Electronics
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Old 10th January 2011, 02:21 AM   #4
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Quote:
Originally Posted by mwiebe View Post
There are also a few low voltage Oatley Electronics "kits" that you will have to provide switching, volume and a housing for. There have been a few threads on these preamps here that should turn up in a search for the tube used "6418".
Matt

Oatley Electronics
Thank you for new options.
I have read somewhere that life time of JAN6418 tubes is kind of short. Please correct me if I'm wrong.
With Quickie I didn't understand what I'm buying -- they have neither schematics nor list of parts. Also, I'd like to have a power supply instead of batteries.
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Old 10th January 2011, 02:46 AM   #5
erin is offline erin  Australia
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I have the Oatley ( 6418 valve) phono pre amp. And whilst it has outstanding soundstage and instrument seperation, those darn valves like to ring and feedback like crazy if the music is turned up to a decent listenable level. I have tried everything to stop them from ringing even hot glued them to the board and have the PCB firmly screwed to thick MDF and kept on a solid concrete floor, and still the ringing persists. If the valves did not ring I would say this is a contender for one of the best souning phono pre amps at any price. But with the ringing, its unuseable in real life so can really not recomend it, or any kit using the 6418 tube. they are just far too microphonic, but they sound really nice. its such a shame. Dang it!

I also read on the thread about these Oatley kits that many other people seem to have problems with high levels of microphincs with these valves, and I think some people did not have too much of a problem.
Perhaps I have been unlucky?

Last edited by erin; 10th January 2011 at 02:50 AM.
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Old 10th January 2011, 03:06 AM   #6
erin is offline erin  Australia
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I have not actually heard it but the B1 Buffer is meant to be a good sounding and cheap discreet solid state pre-amp, and going off the reviews of other forum members who's oppinions I trust to be true, this is the one I would recommend for you to match with your amp.

Myself, I have a valve pre amp, and love it, and use it exclusively, as my one and only pre, but It is an expensive pre-made one that uses 5687 valves. I dont personally think all valves sound as good as others.
I have also bought used, and since sold one of those Chineese "marantz 7" clone amps off ebay, that one used the 12AU7 and AX7 Chineese equivalent valves and this amp did not sound very good to me. I even did some mucking around with it but could never get it to sound any good. so in my opinnion not all valves are good for audio, and I put the 12AX7 in this category. And this is my personal oppinion so feel free to ignore me. I know someone I going to say their 12AX7 or AT7 or AU7 amp sounds great.
And thats cool. I personally have never heard one that I liked very much. I would happily change my oppinion if I heard one I liked.
I also suspect those ebay kits you mentioned operate off too low a voltage to actually sound good (my oppinion here only).
I'm worried that these kits are just cashing-in on people who want valve sound at a very modest price, but I am concerned that the results will be far from what can be achieved with a well designed valve amp biased correctly.
Valves run off high voltage to operate in their linear region. The 6418 is designed for low voltage, the 12AU7 is not!
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Old 10th January 2011, 03:10 AM   #7
erin is offline erin  Australia
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Class A matched SE J-FET stereo buffer kit ! - eBay (item 220717805395 end time Jan-31-11 08:14:27 PST)

B1 buffer kit on ebay.... $29 + shipping.
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Old 10th January 2011, 03:14 AM   #8
erin is offline erin  Australia
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Current boosted diamond buffer preamplifier stereo kit - eBay (item 320636258667 end time Jan-28-11 08:11:33 PST)

Same seller different kit. Looks interesting. Has onobard power supply, just add the transformers. A bit easier than the B1, but I have no idea how it would sound....
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Old 10th January 2011, 04:48 AM   #9
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Quote:
Originally Posted by erin View Post
Valves run off high voltage to operate in their linear region. The 6418 is designed for low voltage, the 12AU7 is not!
According to Arjen Helder 40V is enough for 12AU7 but 12AX7 needs at least 80V. I was thinking about Indeed board because of 24V requirement.
Pass B1 was first in my list but then I switched to tube preamp for more unique setup. Maybe I should buy/build both (B1 and tube) and compare.
Thank you for your feedback.
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Old 10th January 2011, 07:27 AM   #10
erin is offline erin  Australia
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No problems. I think I rambled on a bit though.. Let me ramble some more.

As Arjen designed a number of well regarded circuits perhaps he is correct about this one sounding good with only 40V? I guess you can tell us if you build it.

I like a valve pre amp sound (as long as the pre amp is a good one) but even I will say that even valve pre-amps are a little fiddly. They take a short amount of time to warm up, and this is just the least of their fiddlyness.

If you go for a transistor option, just turn it on and off you go....

I like my valve amp because to me it sounds quite neutral, and smooth, however there is no reason that a transistor pre cant also sound neutral and smooth. The B1 seems to be regarded to sound like this and hence would be my preference.

You want to do something unique, build a valve rectifier power supply for the B1?
I think that would be interesting. No diode switching noise? And still some valves in the circuit. Nice!
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