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4P1L preamp DIY

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Posted on March 17, 2017 at 06:07:19
Johno
Audiophile

Posts: 184
Joined: June 9, 2002






This preamp is designed by Radu Tarta he sells the two raw PCB's for $100 plus shipping you source the components, populate, test & house.

Radu has been great to deal with a true gentleman, he calls this preamp the***Shiny Eyes 4P1L Preamplifier***
He also sells this unit completed.
https://simplepleasuretubeamps.wordpress.com/products/

It's a very well thought out design based on Ale Moglia - Siberian Gen 3 (4P1L pre-amplifier)

My initial concern were reports of excessive noise using this valve but this has so far proven unfounded. Radu recommends both PSU & Audio board be mounted in the same enclosure but this assumes you have approx 450mm of available real estate regarding width, otherwise use a 2 box solution.

Upon completion I soak tested the unit for 3hrs then connected the pre to my main audio system, there were a few pings & mild bursts of noise as the valves bedded in but this disappeared after 10 hrs use. I suspect if you had a stash of 4P1L valves you could weed this out but the noise after warmup - 5 min disappears. Still shifting selector switch due to no physical decoupling with this chassis creates pings but who listens to selector switch switching ? Designer Ale Moglia has mentioned the 4P1L valve is a 'dancing lady' ultimately this unit will be installed into a wooden enclosure.

My N&D meter is not operational but output noise on CRO is non measureable. I hear a very small amount of noise & hum if I put my ear against the spkrs but who does that when listening ? !

The voltage gain is approx 2 giving a power gain of around 6-7db.

This design uses the Lundahl LL1671/30ma strapped in Alt Q (4-1 stepdown)

I used a TKD 2CP-2511 motorized volume control 50K ohm pot from 'hificollective' combined with there 'Glasshouse remote control module & remote'. These components have worked flawless they appear transparent to the pre-amp coupled via the superb Seiden's 2 pole 6 way switch. The pre-amp in question is worth spending money on front end parts.

I have been using a 15yr old British 'World Audio Design' - 6DJ8 trannie coupled pre-amp kit for sound comparison. There are similarities between the two where the gain of the 6DJ8 pre-amp in question was double that of the 4P1L which for my needs was excessive. But the difference in sound quality indicates to me the 4P1L pre-amp is superior. Cymbals, guitars, piano keys & voices are razor sharp more focused more immediate sounding. The 4P1L is a DHP but triode connected in this design and it has a toughness to its sound which blends nicely with DHT's downstream. The 4P1L has time / space decoding ability in spades. Thankfully there are no Blackgate or paper & oil caps in this design so no tonal shifts during break-in. The majority of the PCB components are affordable & of industrial quality.

I would heartily recommend this pre-amp for a front end feeding a 2 stage DHT amp. It has low output impedance approximately 150 ohm and runs thermally cool.

The only upgrade I would consider would be to substitute the 2 x 20 ohm Ohmite 10W kathode resistors for some MRA-12 non-inductive wirewound resistors. The cathode resistors are un-bypassed so quality is essential. Use 3 x 30 ohm Mills in // to get the 10 ohm rating. The design dissipates around 3.5W across these kathode resistors but they do get finger burning hot even though they are well de-rated. Have not fiddled with the Coleman regulators currently they are set at 6V. The anode current is set to 26ma by the cascaded DN2540 regulators. The B+ noise across Anodes is not measureable with a CRO & periodic monitoring has shown HT & LT regulators to be very stable.
Finally this preamp is a keeper, cheers Johno.

PS - Thanks to Radu Tarta, Rod Coleman, HiFi Collective & K&K Audio for supplying great designs & parts.

Regards Johno

 

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Can you post the schematic?, posted on March 17, 2017 at 06:28:56
Triode_Kingdom
Audiophile

Posts: 5986
Location: Texas
Joined: September 24, 2006
This is a DIY forum. I'd rather see the circuit than read a kit review.


--------------------------
Buy Chinese. Bury freedom.

 

RE: Can you post the schematic?, posted on March 17, 2017 at 07:02:26
Johno
Audiophile

Posts: 184
Joined: June 9, 2002
Contact the author if you have specific details !

Regards Johno

 

RE: Can you post the schematic?, posted on March 17, 2017 at 07:12:42
Johno
Audiophile

Posts: 184
Joined: June 9, 2002
https://simplepleasuretubeamps.wordpress.com/products/

 

RE: 4P1L preamp DIY, posted on March 17, 2017 at 07:50:25
GeorgePope
Audiophile

Posts: 17
Location: Havant , UK
Joined: March 15, 2017
Not much gain in there but very nice :) The issue with the PCB is that you are tied into someone elses design with not a lot of leeway for mods. There are advantages to the PCB as hanging unsupported components and wires from a chassis-mount 4P1L socket can accentuate the microphony that is inherent with this tube . A PCB mount loctal socket does help , even better if it's mounted on a heavy brass subchassis :)

I can see you have Coleman regs in there . A good way of squeezing out the maximum is to use a choke input filament supply with a separate filament transformer for each channel . Hardly anything in it measurement wise (a few tens of uV ripple/noise) but to me , it does sound better

Also look for some Chinese 4P1S . In some applications , these sound even better than the Russian 4P1L

George

 

RE: Can you post the schematic?, posted on March 17, 2017 at 10:44:10
sideliner
Audiophile

Posts: 100
Location: NYC
Joined: August 22, 2013



Here's the schematic. The Salas shunt regs SSHV2, the Rod Coleman CCS boards for filament biasing as well as the Lundahl line-out transformers, can all be obtained from K&K AudiO.

PS. TK, having previously stated your aversion to incorporating SS devices within tube circuits, this pre is probably not for you, but the above info might be of use to others.

 

RE: 4P1L preamp DIY, posted on March 17, 2017 at 11:30:20
sideliner
Audiophile

Posts: 100
Location: NYC
Joined: August 22, 2013
I can see you have Coleman regs in there . A good way of squeezing out the maximum is to use a choke input filament supply with a separate filament transformer for each channel . Hardly anything in it measurement wise (a few tens of uV ripple/noise) but to me , it does sound better

The reason for the better sonic results with the choke, probably stems from the reduction in the upper harmonics, from say the 20th and beyond. This is something that a basic DVM measurement will not reveal, but the scope will. Look at the following two reports on DHT DC filament supplies.


http://www.clarisonus.com/Research%20Reports/RR002-DCFilterTest/RR002-DCFilSupplyTest.html

http://web.archive.org/web/20130201030256/http://www.clarisonus.com/blog/?p=169


Here's a quote from Lynn Olson's conclusion at the end of the second linked article above:

Now, maybe you have a lot of faith in an expensive active voltage regulator, but I wonder if it would really deliver a 55 dB improvement at 3kHz? Remember, regulators use feedback to do their magic, and the feedback is most effective at DC, and decreases at 6 dB/octave as frequency goes up. By contrast, the choke filter gets better as frequency increases, up to the point where stray capacitance makes the choke resonant.

Considering that elsewhere in a power amp we'd be struggling for a 6 dB improvement in noise (especially buzz and hash levels), hand-selecting tubes, careful wiring layout, etc. etc., how can anyone dismiss a 55 dB improvement?

If you were really hard-core, there would be four chokes: a pair on the high and low-side between the bridge and first cap, and a second pair on the high and low-side between the first and second cap. The first pair, since it emits magnetic noise, would be physically isolated from the audio circuit (on the far side of the chassis, close to the dedicated filament transformer), and the second pair would be close to the DHT, since it is part of a LC filter circuit. Another improvement would be to insert an RF common-mode choke of the type seen in the input of computer power supplies. This would reduce the common-mode RF noise that can sneak through the large power-frequency chokes.

 

RE: 4P1L preamp DIY, posted on March 17, 2017 at 16:45:28
Johno
Audiophile

Posts: 184
Joined: June 9, 2002






Hi George,

The designer...Radu has balanced the size / performance / cost relationship pretty well. For example the PSU board in the LV supplies use dual 0.33 ohm Welwyn resistors in the CRC filter. The resistors could be substituted with suitable off-board filament choke's. Lundahl current choke LL2751 in serial / balanced mode would work fine.

The Kathode resistors could be mounted off board with fly leads because they get hot approx 3.5W is dissipated across them.

The LV transformers used is a dual bobbin design made by Triad something which Rod Coleman has proven reduces capacitive coupling ie noise between primary & secondary.

There is a '555' timer on the PSU board that delays the HT for 30 seconds a nice feature.

And yes the Lundahl LL1671 very cost effective but could be substituted with the Amorphous core (AM) but this all comes at a price $

Yep I'm pretty weary of valve amps & pcb's so time will tell.

PS - Kevin Carter of K&K Audio sells a number of discrete DIY boards for the 4P1L pre-amp, similar design to this one.

Cheers Johno

 

RE: Pics of populated boards, posted on March 17, 2017 at 17:02:10
Johno
Audiophile

Posts: 184
Joined: June 9, 2002






(nt)

 

Looks like transistor amplifier, posted on March 17, 2017 at 17:22:53
sser2
Audiophile

Posts: 2227
Location: Pittsburgh USA
Joined: July 30, 2003
Just kiddin'

 

RE: Looks like transistor amplifier, posted on March 17, 2017 at 21:30:08
Johno
Audiophile

Posts: 184
Joined: June 9, 2002
Hi mate,
yep there are plenty of SS devices in there.
I'm pretty wary of valve amps & pcb's so time will tell.
But all the active SS devices run cool which is a good start.

Cheers Johno

 

RE: 4P1L preamp DIY, posted on March 17, 2017 at 21:42:48
Johno
Audiophile

Posts: 184
Joined: June 9, 2002
Hi George,
thanks for the heads up regarding Chinese 4P1S, was not aware.
Yep some LV Lundahl filament chokes are very doable in this design.
Can honestly say though this pre-amp is quiet as a church mouse.

Cheers Johno

 

RE: 4P1L preamp DIY, posted on March 18, 2017 at 06:28:21
drlowmu
Manufacturer

Posts: 9706
Location: East of Kansas City
Joined: January 10, 2005
With 98 dB speakers or higher, I need NO active preamp at all, into a two stage DC amp, with a mu of 100 input tube. Just a VERY high quality passive volume control, ALTEC VOTT A7-800s.

The switch system in your box is a source of sonic degrade, needs to be a really good Shallco.

Have fun.

Jeff Medwin

 

RE: 4P1L preamp DIY, posted on March 18, 2017 at 08:49:07
xaudiomanx
Audiophile

Posts: 2947
Joined: August 16, 2004
Hi,

I tried copying the email address off the website and it comes up as an error. I was wondering if anyone has his email address or a phone number to call him.

Thank you,
Paul

 

RE: 4P1L preamp DIY, posted on March 18, 2017 at 14:35:50
xaudiomanx
Audiophile

Posts: 2947
Joined: August 16, 2004
Jeff,

I know that others say adding another stage isn't the best way to go but with my 26 tube preamp I do like the coloring it gives. Might not be the most natural way to go but I think everything we do to amps, preamps, speakers(crossovers), etc. is coloring. That is why I personally like single driver speakers but a lot of times I do use a tone control so that kills what a single driver full range speaker does.

 

RE: 4P1L preamp DIY, posted on March 18, 2017 at 17:00:31
drlowmu
Manufacturer

Posts: 9706
Location: East of Kansas City
Joined: January 10, 2005
Speak for yourself. Color your own hi fi, not mine please.

Fact is, no single driver ever has cut it for me. in audio. I prefer as neutral and as honest to the recorded event as I can obtain.

I prefer a two way ( simple ) speaker, sometimes even a point source co-axial, no active preamp, and only a two stage amp, which uses a mu of 100 driver tube. This specific topology, properly executed, " does it " for me.

YMMV.

Jeff Medwin

 

RE: 4P1L preamp DIY, posted on March 19, 2017 at 09:47:15
xaudiomanx
Audiophile

Posts: 2947
Joined: August 16, 2004
You know Jeff,

You really have social issues. I have been nothing less than a friend and in most cases I stuck up for you against all odds. The best thing that has happened to this site is when you get iced from using it but then you reappear, like ion a Schwartzenegger movie or Chuckie. One of these days we will meet in person and you might not like the end result. I might seem like a gentle no nothing in audio person but I can assure you I can handle most situations to my benefit, even if it compromises others and itr seems to be that you need a real compromise. Your good buddy never gets nasty or maybe you are there to do it for him. I never challenged what you do or hear even though those with much higher qualifications that I trust almost always do. You jam things down others throats.

If you read what I said about your likes I never implied you like anything. I said I do. In fact! You don't unless it is built by you and yours. Then it is the end all and be all. And who is to say what's natural or honest? 18K amps? 40K speakers? 1 inch piece of wire?

You are a sick and mentally disturbed person.

I hope for your sake that your hangover leaves because the one you are on sure makes for an ugly character. You don't suggest or have an opinion. You jam things down others throats like a past president I also disliked. I am almost sad to think I am one of the lonsmen as long as you are. You are not fun.

 

RE: 4P1L preamp DIY, posted on March 20, 2017 at 07:58:53
Jim D.
Audiophile

Posts: 726
Joined: October 26, 2000
Contributor
  Since:
April 6, 2002
I built this line stage recently and really like it. I use it between my SACD player/DAC and my S&B 102 TVC. It only has 6 to 7 db of gain with the Lundahl 4.5:1 step down so it works nicely with my system. I used the schematic posted by Kevin Carter on his forum and I used his filament regulator and shunt regulator boards. The signal path is pretty simple really. It requires Rod Colemans regulator boards. I'm not much for adjectives but the sound is larger and deeper and more dynamic.

Jim

 

RE: 4P1L preamp DIY, posted on March 20, 2017 at 08:01:39
GeorgePope
Audiophile

Posts: 17
Location: Havant , UK
Joined: March 15, 2017
'The reason for the better sonic results with the choke, probably stems from the reduction in the upper harmonics, from say the 20th and beyond.'

I really have no idea how you come to that conclusion regarding high order harmonics although I can take measurements using a wave analyser or FFT if need be . In terms of measurement , I do not posses a DVM with the sort of resolution to take such measurements so an HP mV meter was used

As for the rest in cut and paste format . There is no feedback in the filament supply . This consists of LCRC to a Coleman reg (buffered CCS) taking the cathode connection from the 4P1L filament centre tap

George

 

RE: 4P1L preamp DIY, posted on March 20, 2017 at 08:46:52
LinuxGuru
Audiophile

Posts: 539
Location: European Union
Joined: November 11, 2008
Hi, Johno,


Very nice and accurate build !

BTW, have you tried to move PCB located on the top of the choke and mount it in vertical position nearby ?

 

RE: 4P1L preamp DIY, posted on March 20, 2017 at 11:58:06
sideliner
Audiophile

Posts: 100
Location: NYC
Joined: August 22, 2013
You stated that you heard a sonic improvement with a choke in place preceding the Coleman regulator. I took that at face value and my response was an attempt to explain why you heard such an improvement - that's all.

The reduced upper harmonics, is obviously a conjecture or an educated guess on my part with no concrete proof offered and the language I used reflects that. Having said that, I still think that the quite drastic reduction in the upper harmonic content put out by the choke supply, is responsible for the sonic improvement you hear, irrespective of the filament regulator. On my part I don't understand why you would think that it'd be that big of a leap to even entertain such a hypothesis. It's been common knowledge for decades now that upper harmonic distortion even at very low levels is quite detrimental.

As far as the regulator comment is concerned, I haven't seen Rod Coleman's circuit, but do you know of any regulator, be it either of the voltage or current reg variety, where the core working principle is not based on feedback? Olson's comment as quoted, is very much on the money IMO.

Maybe you misunderstood me, I don't know, but if you haven't taken a close look at the filament supply test that I linked to earlier, I would give it another shot.

 

RE: 4P1L preamp DIY, posted on March 21, 2017 at 04:41:08
GeorgePope
Audiophile

Posts: 17
Location: Havant , UK
Joined: March 15, 2017
The point I am making is that a Coleman reg presents a high impedence and hence a very large degree of isolation from the downstream PSU circuitry . It feeds the filament with a ring of two CCS one side and a gyrator/buffer the other . By using choke input , the measured noise at the filament pins drops by an insignificant amount . In terms of harmonics measured on the FFT , I can't see a difference in comparison to cap or resistor input but there is an unexplained improvement in sonics . Maybe I need better equipment to measure this but as far as I'm concerned , it's not worth it

George

 

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