Real World All Tube LCR Phono for MC Without SUT

the road not taken.
fvale
Posts: 9
Joined: Fri May 13, 2011 9:34 am

Post by fvale »

Hello Naz, I will initially (and hopefully definitively) use the 5687 through all power supply. Would you suggest a 3 or a 4.1V shunt regulator? ... or to listen/measure both....

I'm curious to know if you've preferences about resistors - type and makers - to use both in the PS (are 1/2W enough?) and in gain stages.

Last question, did you measure the output impedance with your 6DJ8 output tube?

Thank you.
Naz
Posts: 71
Joined: Wed Aug 06, 2008 4:27 am
Location: Sydney Australia

Post by Naz »

Hi Fabio,

Technically a 5687 will not be as good as a 6H30P in terms of ripple rejection and OP impedance. If you want to try it, instead of reducing the ref voltage, stick with the LM139 and increase the value of R2 (47K) to around 150K then fine tune to get approx 250V OP. You can use this method for other tubes as well.

I tend to use reasonable quality metal films almost everywhere but different resistors can definitely be used to fine tune the sound, eg Mills for a Warmth, Holco or Vishay for more detail etc. 0.5W is enough everywhere except for plate Rs in the Phono where I prefer to use 2 - 3W to keep the temp down. Just make sure that the resistors have adequate voltage rating.

The OP impedance of the 6DJ8 family is a little over 3K in this configuration. I used to think this was way too high but it really isn't provided you aren't running very long ICs. You can dramatically reduce the impedance by taking drive from the cathode of the upper tube (classic mu follower) but it sounds too Hi Fi for my taste.

Cheers,
Naz
fvale
Posts: 9
Joined: Fri May 13, 2011 9:34 am

Post by fvale »

Hi Naz,

idea was to use all 12V heaters, lowering currents around, on the tubes in the PS, not a wise one if I've to loose OP impedance... I will use 6N6 in place of 6H30P initially.

R8, R15, R22 only need to be 2 or 3W? Or R2, 5, and 6 also?

I'd pay to know if 3K could be enough with my setup! My preamp is a passive autotransformer only (enormous nanocristalline double c-core from Promitheusaudio) and I believe it should be driven with low impedance sources. Possibly a 6N6P on last stage could be ok. I will try to see if I'm able to calculate OP impedance with this tube.


Thanks
Fabio
Naz
Posts: 71
Joined: Wed Aug 06, 2008 4:27 am
Location: Sydney Australia

Post by Naz »

Hey Fabio,

12V heaters is a good but since you have 3 stages a better option is to run all top tube heaters in series or parallel and elevate to 100V or so (a simple resistor divider connected to the neg terminal will do) and run all bottom tubes from a separate heater supply tied to ground.

R8, 15 & 22 all dissipate less than a watt but I like to use 2-3W. 0.5W is more than enough for R2, 5 & 6.

Not sure what you need to drive your autoformers with. Your options are to take drive from the cathode of the upper tube (I don't like it but some do) or go with a tube with lower rp such as 6H30P, 12B4, 6BX7. A 6N6P will not be much better than a 6DJ8/6922. At a little over 2K OP impedance a 5687 will give you about 30% improvement over a 6DJ8.

You could simply choose a tube and compare between drive taken from the plate of lower tube to cathode of top. If there is an appreciable difference at high frequencies you'll know the OP impedance is too high (assuming you don't have the equipment to measure this).

This brings me to another important point. Ideally, you really need a reverse RIAA filter if you want to test for final RIAA accuracy. Remember that Dave puts taps on his coils for fine-tuning.

Naz
fvale
Posts: 9
Joined: Fri May 13, 2011 9:34 am

Post by fvale »

Hello Naz,

what about "connecting" the 6.3V DC heaters power supplies to ground via a 0.1uF cap? I used this (Broskie's suggested) method with perfect results in a stacked triode stage (Aikido at 150V B+).

In my mind a 2K output impedance isn't a high value, I will try the 5687. The only equipment I have is a signal generator and a 20MHz oscilloscope.
It should be a good idea to get a PC based real time audio spectrum analyzer software that will be very useful, also, to get a perfectly flat response with the reverse RIAA.

Do you have a commercial reverse RIAA filter, or a schematic to suggest?

Thank you for your super support!


Fabio
Naz
Posts: 71
Joined: Wed Aug 06, 2008 4:27 am
Location: Sydney Australia

Post by Naz »

Hey again Fabio,

Connecting the bottom tube heaters to ground as you suggest is fine but it would still concern me a little having floating heaters (DC wise) on the top tubes using this method. I haven't tried it although in theory it should be OK. This is where the 6H30P excels with a whopping 400V HC max so you don't need to elevate the top tube's heaters at all.

Along with a Rev RIAA a sig gen and a scope is all you need. Haggerman has a great little unit that you could once buy in kit form (maybe still can). It is engineered to provide Rev correction for the Enhanced curve so you would have to compensate by 0.6db at 20KHz and 3db at 50KHz if you are shooting for a standard RIAA curve but that's easy. You could build your own filter but it's a pain gathering the fine tolerance components so I'd go with the Haggerman.

Cheers
Naz
Posts: 71
Joined: Wed Aug 06, 2008 4:27 am
Location: Sydney Australia

Post by Naz »

Not sure whether it was Bravi or Fabio who suggested trying 6S15P in lieu of 6C45P but I tried a couple and must say I was impressed and worth reporting on.

Specs are the same but the pair I tried sounded a tad different. Perhaps not as quiet but VERY little in it. They are slightly more open, airy and less forward than all but the best 6C45P, very detailed but leaner. These might suit many systems better.

Naz
opus64
Posts: 2
Joined: Fri Sep 30, 2011 2:29 am

Post by opus64 »

Hi Naz,

Delighted to come across your LCR phono design, both because of all the raves I've read about them, and because it'd be a perfect use of the stash
of 6c45p's & 6n6p's I have that I wound up not using in another project.
Thanks for sharing it :)

I'm curious about the 2nd & 3rd stage dual triodes. Are they paralleled individual tubes for each position, or 1/2 for top & 1/2 for bottom tier ?

With the UPSC600's unavailable, can I assume any 600V, 1A Schottky SiC with the same 1.6 Vf is OK to use? How does the 1.6 Vf determine the cathodes 0.8 V bias, or does it ?

Is there any significance to the schematic showing 6200, 7500, & 1600 ohms instead of 6K19, 7K49, & 1K62 ohms in LCR ?

Finally, what is min. volt. rating for the 1000uF cap in your tube reg PSU ?

Hope that wasn't too many questions & again, thanks.
Peter
Naz
Posts: 71
Joined: Wed Aug 06, 2008 4:27 am
Location: Sydney Australia

Post by Naz »

Hi Peter,

Happy you are considering taking the trek, I'm sure you won't be disappointed.

2nd & 3rd stage triodes are individual halves. Using one tube for both bottoms and one for the tops makes it easier to elevate the top triode heaters but of course they either have to be the same tube type or you could share between L & R channels. You can get away without elevation but safer to do it. Alternatively you could elevate to about 50V if you use one tube per stage.

Any SiC Schottky will do as all are around 0.8V at these low currents.

The LCR is finely tuned for correct RIAA and therefore each value is critical. In reality you would be hard pressed hearing a difference as long as the values are within a % or so but remember that errors are additive.

I'm happy to answer any further questions so don't hesitate to ask.

Cheers,
Naz
fvale
Posts: 9
Joined: Fri May 13, 2011 9:34 am

a quick for opus64... and all the DIYers

Post by fvale »

I'm almost at the end on the building of this incredible phono stage. I'm now listening to it and it performs excellently (at least), even if it's not 100% tweaked.

On LCR stage resistor tolerances: Partsconnexion sells 1/2W Shinkoh tantalum resistor, that apart being well sounding, have exactly the required values. You can also ask for matched pairs. BUT first test frequency response with cheap resistors, values might require little adjustments.

As I didn't see any note on this here I want to "warn" about HUM. Any phono stage is critical in this regard, but this one has a fully tubes MC stage AND big inductors on signal! So high voltage power transformer and power supply filtering inductors (I use 20H) have to be installed in a SEPARATED BOX! And I don't believe two stacked boxes are enough, I suggest to build a little cabinet with tube rectifiers, HV transformer and inductors with a 1meter (about 4 feet) cord to leave on the ground.
If you do like this you don't even need to shield inductors (which is VERY DIFFICULT and expensive) and you will get a silent and almost hum free phono stage!
I used EI transformers, things should be much easier with toroidal transformers and that way a single box should be possible. BUT perform carefull listening tests with test wiring before definitively boxing parts!

Last little tip: if you choose the 6N6 tube for the voltage regulator R5 resistor has to be lowered (on Naz suggestion to about 300K, if I recall correctly) to get the required 250V.

Eye candy attached!

Happy listening and a BIG thank you to NAZ for publishing such a great project.
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opus64
Posts: 2
Joined: Fri Sep 30, 2011 2:29 am

Post by opus64 »

:shock: Man that looks cool !!!

I'm envious that someone can do a build like that in just a few months. Usually takes me at least that long just to gather parts. Thanks for posting this Fabio, I'm going to use it as motivation.

I have couple questions related to output imp. and gain. I have an integrated linestage/active xover designed for my dac and speakers. Its unity gain and has a ladder attenuator at the input w/ variable input imp. w/ a min. @ 22K ohms. Its fine with the dac's >2V output & 200 ohm output imp. so I omitted a buffer ahead of vol. control.

If I can have the cable from the phono as short as 9-12 inches, would Naz's phono be OK into 22K or do I need the buffer back in?

With apology for sucking at math, what is the expected RMS Vout from a 70dB gain phono using a 0.27 mV cartridge. My tube amp needs ~ 1.2V at the driver to reach full output & I'm wondering if this phono into my linestage would reach that. The linestage could be modded to provide a little gain if needed.

Thanks
Peter
fvale
Posts: 9
Joined: Fri May 13, 2011 9:34 am

Post by fvale »

Hello Peter,

I'm not expert enough to answer all questions anyway here's my experience. My system has a passive preamp, autoformer based with no gain, so for me too output impedance and good gain are very important. With a 0.9mV cart it sounds much louder than my digital sources (TDA1541 dac, unfiltered, followed by a Aikido 12AX7/12SX7). About output impedance I used a 5687 tube at last stage, in place of the shown 6DJ8, to get a output impedance of about 2Kohm. I believe it should be ok with your 22K..... otherwise you could use a 6H30 there too.... to get a much lower one (few hundreds ohms).

Find attached a pic of the external part of power supply.
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maymymay
Posts: 6
Joined: Mon Sep 08, 2008 2:07 pm

Post by maymymay »

Hi Fabio,

Can you please post the schematics of the last stage in use of the 5687 tubes? I really hope to try this phono lcr for my main phono amp, hope you can help, thanks.

Ngan
fvale
Posts: 9
Joined: Fri May 13, 2011 9:34 am

Post by fvale »

Hello Ngan,

there is no need for any change! The silicon carbide diode - Cree 1A 600V in TO-220 case - bias 5687 tube fine. And I can confirm unit measure and sounds excellent. There is people that uses it in setup costing as much as a nice house (no joke).
This is a compelling, expensive (if build with right parts) and time consuming project but efforts are well worth in my opinion. It's also exclusive and I really believe you DON'T need to upgrade anymore! That's a lot for me.

Once again thank you to NAZ, the beautiful mind behind it.
Brettee
Posts: 1
Joined: Wed Nov 02, 2011 5:31 pm

Post by Brettee »

Hey Naz, I am quite impressed from replies, and i thought you have great knowledge of it.
Naz
Posts: 71
Joined: Wed Aug 06, 2008 4:27 am
Location: Sydney Australia

Post by Naz »

Much appreciated. I've spent more time on Phono than anything else in recent years because I love Vinyl and found that there is more to be gained at the front end than anywhere else. Besides, I have been extremely happy that I'm getting near enough as much as I can out of my PSE 845s, having spent years in that area of design.

FWIW, I have tried everything from Feedback and RC RIAA to LCR and many types of front ends including FET/tube hybrids and SUT. All tube LCR is my personal favourite although with careful tweaking and the right tubes it's amazing what you can get out of any topology.

Naz
PET-240
Posts: 23
Joined: Sun Jan 29, 2012 1:30 pm
Location: BrisVegas, Austalia

Fellow Ocker

Post by PET-240 »

Hello Mr Naz,

I see you are a fellow ocker, good to see,

Wondering if we can have a yarn on the terrorphone at some point soon? I'm young enough to have missed vinyl and silly enough to want to have a go!
Would like an all tube rig, SS is great for bass, but so far in my exp kills the emotion. Hence the attempt at vinyl. Also just learning about SE amps and the like.
Be great to have a chat.

Thanks,

Drew.
Naz
Posts: 71
Joined: Wed Aug 06, 2008 4:27 am
Location: Sydney Australia

Post by Naz »

Hey Drew (mate),

Just found the notification for this post in my Junk Mail, (went looking for it after receiving your PM).

As you can see up above Fabio has done a great job of his. So many options and suggestions ... a call is best to discuss, see PM.

Naz
Maturin
Posts: 22
Joined: Thu Jul 19, 2012 5:36 am

Post by Maturin »

Naz, truly nice work, both versions, the all-tube mu-stages and the using the cascoded DN2540's...

....I couldn't help wonder if going to all the trouble of using either design but in a fully differential manner might be a useful way to go cancel noise, power supply noise, and so on.

I think that's where I'm going to go; perhaps a fully differential CCS'd or mu-staged phono preamp might work well for mc's as well as mm's without the SUT (not a big fan of using any transformers or capacitors except when you just can't get around it).
Naz
Posts: 71
Joined: Wed Aug 06, 2008 4:27 am
Location: Sydney Australia

Post by Naz »

Thanks Maturin,

I personally haven’t bothered with differential Phono so can’t comment on the real vs perceived benefits except to say that for me, the added cost and complication of differential in general for other applications has not been worthwhile.

I’m sure that it can provide an advantage in certain circumstances (noise rejection with long ICs perhaps) but common mode rejection from PSU noise should not be one of them. For Phono, you need a good regulated supply and that should be enough, especially with the additional PSRR afforded through the implementation of tube or SS CCS. Other sources of noise, namely earth loops and the proximity of susceptible components to magnetic fields (particularly coils and tubes) are by far the biggest challenges. Some may disagree but this has been my experience and I’ve spent countless hours on Phono design, build and rework.

If you’d like to give any element of this Phono a try, (even in differential) I’m happy to help. Maybe I might learn something :)

Naz
Maturin
Posts: 22
Joined: Thu Jul 19, 2012 5:36 am

Post by Maturin »

LOL, I rather doubt I would learn something from you, Naz, but I appreciate the gracious gesture.

Oh, good points - yes, the only thing the differential design does is eliminate common mode noise, my bad, I was being fast and sloppy.

I first learned audio electronics in the 60's in radio, where a 600 ohm balanced line was religion...a lot of us were not happy when the idea of an unbalanced line was introduced, shortly after the idea of bridging inputs, which are now commonplace, but then we thought it was heresy. But it sure saved on copper LOL.

Still, to go from mc to input stage without a transformer, in your experience the common mode noise rejection of a differential input stage is not worth it? Interesting.

I have a thought for a circuit...I'll post it. :idea: :P
bluesman
Posts: 7
Joined: Sun Dec 25, 2011 3:34 am

Post by bluesman »

Hello Naz or fvale,

Can this phono be built with balanced output? All phono cartridge is balanced by nature, so I am wondering if this is possible.
TonyB
Posts: 30
Joined: Mon Feb 14, 2005 7:11 pm
Location: Toronto, Canada

Post by TonyB »

Hi Naz,

You mentioned a more complicated regulated power supply for your
Ref phono a while ago. Would you mind sharing its schematic?

I use RC tubed phono and am on 4th or 5th power supply. I always
want to try more.

Tony
Naz
Posts: 71
Joined: Wed Aug 06, 2008 4:27 am
Location: Sydney Australia

Post by Naz »

bluesman wrote:Hello Naz or fvale,

Can this phono be built with balanced output? All phono cartridge is balanced by nature, so I am wondering if this is possible.
Naz
Posts: 71
Joined: Wed Aug 06, 2008 4:27 am
Location: Sydney Australia

Post by Naz »

TonyB wrote:Hi Naz,

You mentioned a more complicated regulated power supply for your
Ref phono a while ago. Would you mind sharing its schematic?

I use RC tubed phono and am on 4th or 5th power supply. I always
want to try more.

Tony
TonyB
Posts: 30
Joined: Mon Feb 14, 2005 7:11 pm
Location: Toronto, Canada

Post by TonyB »

I do not see any reply, Naz.

TonyB
Naz wrote:
TonyB wrote:Hi Naz,

You mentioned a more complicated regulated power supply for your
Ref phono a while ago. Would you mind sharing its schematic?

I use RC tubed phono and am on 4th or 5th power supply. I always
want to try more.

Tony
Naz
Posts: 71
Joined: Wed Aug 06, 2008 4:27 am
Location: Sydney Australia

Post by Naz »

Sorry Tony,

It's been a long while since I posted and must have done something stupid in haste, happens as you get older :(

I only have old schematics and will need to find the latest update but I'm happy to dig them up, scan and share with you. You are obviously much like me and always curious enough to try everything for yourself and push the boundaries if something looks promising.

I had meant to draw the PSU up in Spice; perhaps I should just get it done. I can tell you that the voltage is rock solid, I'm talking about to the mV at all times, under all conditions and with immeasurable ripple.

Naz
TonyB
Posts: 30
Joined: Mon Feb 14, 2005 7:11 pm
Location: Toronto, Canada

Post by TonyB »

Thanks, Naz.

TonyB
roger
Posts: 1
Joined: Fri Jul 12, 2013 11:09 pm

Problems with e-mail, can't order inductors

Post by roger »

Hi

I've tried to send E-mails to Dave, but my mails are returned. Does anybody else have the same problem?
Roger
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