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Old 10th March 2003, 03:18 PM   #1
Jay is offline Jay  Indonesia
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Default Best Tube 4 Solid State

Hi, I need info on a suitable tube pre-amp (with low output impedance).

I was about to build an Audio Note M7 LS10 pre-amp. It was posponed when I found out that it required an amp with very high input impedance.

I need the pre-amp to drive MOSFET class A. Could be Aleph, Zen, or if I had to, I will build push-pull class A from 2SK135/2SJ50 (I know that many hybrids use this transistor).

Thank's.
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Old 11th March 2003, 07:04 PM   #2
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I guess quite a few preamps would be suitable.

Personally...(beginner) I would just build a standard ECC99 amp transformer coupled. As far as I know that would guarantee a certain output impedance such as 600ohm. If you don't need the gain you could try a 6AS7 cathode follower. I believe there are a few on the web that would do that...Or if you have the bucks a (massive psu) you could build a 6C33C SRPP. :-) May also be found on the net.

Cheers,
Bas
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Old 12th March 2003, 11:38 AM   #3
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World Audio Design do a transformer coupled pre-amp kit.
I'm very pleased with mine. It's quite an easy build, it was the first kit I had built for a looong time and I had no real problems.
Cheers
Maxwell
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Old 12th March 2003, 12:10 PM   #4
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Default ...Thorsten's solution...

Hi Jay,

This is an excellent single valve low output impedance preamplifier that is very suitable for driving a solid state power amp.

Euridice

There are several valve options that this design can be simply adapted too if the 5842 doesn't suit you.

ciao

James
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Old 12th March 2003, 01:33 PM   #5
miguel2 is offline miguel2  Portugal
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Jay, do you have some tubes on hand like 12AX7, 12AU7, 6922 (ECC88), EF86? If you do have a pair of one of these laying around you can build quite easily a preamp with those, for very little money (your source is a CDP right?). Then, if you dont like it, just dismantle the thing and build something else. You can always keep the PSU if you do it with a pass tube to control the output voltage.

I made a very simple EF86 preamp and I am driving a ZenV4 with it. It has not enough guts to drive the Zen to clipping, but it just sounds wonderful and I am quite happy with it. I tried a beefier preamp with a low output impedance cathode follower after and the sound was worst. So I keep my high ouput impedance preamp driving my low input impedance Zen

Miguel
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Old 12th March 2003, 04:05 PM   #6
Jay is offline Jay  Indonesia
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Default Thanks for the answers!

Bas, Maxwell,

Transformer coupled! How couldnít I think about it? And now cathode follower!? Is this cathode follower also for the same reason as the coupling transformer? And what is SRPP? And what does ďmassive psuĒ mean? I will buy if I can do it with cash.

Miguel,

Yes I have several 12AX7 and several tubes which I think are equivalent with ECC88. For a simple pre-amp, I think a single 12AX7 will do for one channel (I think it is a twin triode, right?), Iím just not trying to build a pre-amp just to be dissatisfied with the result (You know, building 5 SS for fun is preferable than building 1 tube)

The output impedance, it is my first consideration. The second is the best sounding triode (millitary), and my target has been 6J5. The price is not my consideration, I will just build the best I can get.

Are you sure that the pre-amp drives Zen and the speaker happily? What is your speaker (the sensitivity)? Iím looking for a sensitive speaker also, my target is KEF Q35 (Iím using VIFA P17WJ and D27TG)

James,

Iím very impressed with the Euridice. I think I will do a survey on the tube, transformer, OT and power resistor availability (I donít use credit card; think I wonít make it with the transformer!).

I was just not expecting such a OT in a pre-amp. I wonder if the effect on small signal is much worse than in amplifier! But I think it is acceptable to me.
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Old 12th March 2003, 04:24 PM   #7
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I could be wrong here, but dosen't Zen V4 have an input buffer? Should be easy to drive.
-NS
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Old 12th March 2003, 04:50 PM   #8
Jay is offline Jay  Indonesia
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The Zen without input buffer is absolutely difficult to drive. So, the addition of an input buffer is not something special in my opinion. If Iím not mistaken, Zen4 input impedance is not more than 47k, which is still quite low for most tube pre-amps.
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Old 12th March 2003, 05:18 PM   #9
miguel2 is offline miguel2  Portugal
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Jay, if you have ECC88's I suggest you one of the RTP preamps. Never heard them but they have FET CCS for the tubes and seem to be very well regarded. Do a search on RTP preamp and you will find them.

Miguel
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Old 12th March 2003, 05:37 PM   #10
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Jay,

I drive an A4 or a Zen with or without input buffer.

Originaly I used a comon cathode 6922 (6DJ8) with somewhat good results somewhat loose bass though and not very good hi freq.

Reacently I finished a 417A (5842) which is way better, this one takes control of the amps in a commanding way with excellent lows and hi freq. Later I will add an OPT to get an Euridice type circuit.

This line amp (417A) has a lot of gain so the use of an OPT is recomended.

Have a look at some pictures on the thread I posted "417A Line Amp".

If you need a circuit for this L amp i will prepare one for you or for anyone for that matter.
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