• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

4P1L DHT Line Stage

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#524
beardman said:
Hello
If i buy a Lundahl 1660 40ma trafo for the 4p1l preamp,,can i then use this trafo for the 26tube pre as well ??

how long will the 4p1l tube live with 35ma ?

best Bjarne
Click to expand...

The tubes are very different. The 26 with an anode resistance close to 8 needs much more inductance. I would start at 100H (18MA) but 130H (10mA) is better and more, like using a 5mA version, is better still. You get some inductance back with step-down.

If you really want to use both tubes I suppose 18mA is the compromise - it's what I use for the 4P1L but only because I had some. 25mA would be better. 4P1L can certainly live with 35mA - just depends what anode dissipation you have. 9W is the maximum in triode, so that's 250v anode to cathode.

But it's best to choose one tube or the other. If you have around 2v in you can use 4P1L without microphonics problems. If you have 0.5v you're safer with a 26.
 
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#526
Hello
will like to know, what value the volume pot need to have in the Gen 3 4p1l pre

the diagram shows 100k,,,i have a Dantimax relay 5k volume..is this very wrong ?

if this low value is wrong i must buy a new...but how low can one go for the 4p1l ?

best Bjarne
 
#527
A low value isn't "wrong" - it will work. It depends what you are putting into the line stage. If it's only the DAC you are using, tell us what the output resistance is. If it's 1K or under you won't be too far wrong. The advantage of 100K or indeed 50K is that it gives you the option of a higher output resistance for your source.
 
#529
Great Interest in 4P1L from danish site hifi4all.dk

Hi mogliaa.

I put up my 4P1L experience, on the danish hifi4all forum, and
after a while I meet "beardman" who is building the Gen3 4P1L.

After a while "a few people started to send me PM" regards building
a 4p1L for them.

I said I could not help them, due to the fact that you have the copyright
on you schematic, which I respect.

My question to you is the following.

Are we who actually has managed to build your lovely 4P1L allowed to help
other in getting this great amp to their own stereo.

I'm in no way interested in doing commercial benefit of this amp.

Just thinking of doing a workshop, which could help people...

/thanks Michael.
 
#530
First 3 month with my 4P1L "little siberian gen1".

Today it's 3 month ago i managed to get sound through
from my belowed 4P1L.

In the meanwhile I have made my own PBC Board, so it's
now "finished" If it ever will be 🙂

I have now a (Clarity MR and a V-Cap CuFt both 0.1 uF) for decoupling
Caps so it's now a little lower 0.2 uF instead of the 0.33 uF Clarity in the
first place.

When I did this for about 10 days ago, The sound improved a lot.

I can now "hear" the difference if I'm running the 4P1L at 21mA or 25mA.

The V-Cap "Teflon" adds a lot of details, but at 25mA it sound someway "cold"
and I considered to remove it from the Amp.

But when I run the amp at 21mA/100Volt it's another story.

I have plenty of Details and The sound is even "warmer" than it was with the
0.33 uF Clarity Mr.

So combining the V-Cap "teflon" CuFt 0.1uF and Clarity MR 0.1uF was exactly what
makes me 10 times happier.

I have ordered some russian PIO K75-10 caps 0.22 instead of the Clarity MR, just to
see how they works out.

Too all the People who describes the 4P1L having a "cold" sound, Try run it at different
operation points mA, And maybe mix the decoupling Caps, This did the tricks for me.

Again Great thanks to all your guys who make it possible..

/Michael.
 
#531
Hi Michael,

Glad to hear your project is working nicely!

If you buy Russian capacitors, please consider the Teflon ФT-2 (FT-2) or ФT-3 (FT-3) Фтоуропласт (Ftouroplast = Teflon dielectric) types. These are excellent, especially for low signal levels.

Are you using filament bias?
 
#532
Hi Rod...

Heard a lot of the russian Teflons, I was just using my V-Cap CuFT i had in my
old pre-amp..

Are you using filament bias?

Yes with your boards. And I'm so happy 🙂

The really sweet thing, in my ears, was the mixing of Teflon and the Clarity MR.

I'm still on the Gen1, but as long as I haven't heard the Gen3 from Beardman, I'll
stay with it. Music is more important too me than all the tech stuff...

Have you tried the russian teflons, as standalone in a DHT amp ??

/Michael
 
#533
Hi Michael,

In my #26 preamp (filament bias -R.C. regulators-, cascode CCS, SSHV2 HV supply) I use 0.22uF FT-3 with parallel 0.1uF tin folie V-Cap (the output volume control is S&B TVC).

FT-3 is the superb coupling capacitor.... after 300-400 hour burn in period.
V-Cap -mainly the copper version- is better, but the price....
 
#536
Still waiting for my Lundahl trafo and socket to arrive--The Lundahl 2745 40ma is made for me
my Rod Coleman regulator i have testet with a 15ohm resistor,,give me 10.34vdc

next is to prepaire my Maida hi volt regulator,to give 210vdc out

so i think in a few weeks time i can get it to play-

Normally the Gen3 version use 34ma...is it ok to use lower ma , if i like the sound better ,..or is there something in the construction who need the 34ma ???

Best Bjarne

Ps .i heard michaelvv 4P1L preamp,,,it is really nice
 
#537
Hi Michael,
Glad to read you like the sound. As said many times before, 4P1L needs at least 20mA or more to run nicely. I'd run it at 25-30mA at least. Haven't found significant change in sound above 30mA. It is only a question of headroom given grid bias point as well to ensure you can drive it without entering into grid current when you use a high output DAC or CD player.

Unfortunately my gyrator-based preamp got dismantled and can't so a side by side comparison with the transformer coupled one am currently using. Both are great but tend to like the OT a bit. The mu-follower configuration version ( aka gyrator) is great value for money and if you use the Russian caps as Rod suggested, you get a great preamp.
I found an improvement in sound with a choke input LT supply. Split bobbin transformers, quality chokes and capacitors is all you need before the filament boards!

Keep us posted on your sonic impressions!
Ale
 
#538
Hi Mogliaa.

I would like to help my neighbour make a 4P1L, if it's okay with you.

People here in little Denmark, like it so much.

Tomorrow we'll do a test on my 4P1L on a more expensive setup,
I'll try too describe how it turns out.

The microphonics is not an issue anymore, using the "silent Blocks".

/Michael
 
#539
Pleased to hear that the Microphonics is fixed, excellent! And I'm glad that the Coleman Regulators are giving good performance.

Yes, I have used FT-2 and other Russian teflon caps in standalone positions. It's most obvious improvement (compared to other caps, like polypropylene) appears in my low signal-level Moving-Coil Phono amplifier, as first-stage to second-stage coupling.
 
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