| rman |
Hi all.
I just got my version of Richard Murdey's 6DJ8 phonostage
up and running, and it sounds just fine.
http://www.geocities.com/rjm003.geo...o/diy_pho3.html
I don't hear any real difference beetween it and my Hafler DH110
which by what I have read has an excellent phono section.
My turntable is nothing very special however.
Here are some pics. |
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| rman |
That's inside the psu. I haven't drilled vent holes in the lid yet.
this is the phonostge itself. |
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| rman |
Also, thank's to Tubewade and Hotbottle for their input when
I was planning this project. |
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| alexg |
Looks great.
I need to do a phonostage soon (am using a crappy SS phonostage) and I was looking at the hagtech's cornet octal (6sl7 and 6sn7) and this phonostage (6dj8) but since I have tons of 6n1p, I might do a 6n1p phonostage with slight modification of the circuit.
Great job on your 6dj8 phonostage. :) |
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| alexg |
BTW, how is the gain of the RJM phonostage?
I read in another thread that the estimated gain of this phonostage is around 35db.
My preamp does not have too much gain so I am a bit worried about the low gain of the phonostage.
Thanks. |
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| rman |
Hi.
Richard Murdy's page on this amp says 38db. Should be about
90x. 30x per stage with a 10 (20db) loss in the passive filter.
I am using a Hafler 110 preamp. the volume settings are about
the same as when using the built in phono section. The sound
is just as good too. The Hafler phono has a very good reputation.
So I didn't really need the tube phono but it was a fun project.
Watch out for hum. I just left the heaters floating and got alot of
hum. I have grounded one side of the heaters at the outboard
psu and the hum has dropped alot. I am going to ground them
in the amp instead and see how that works. I don't really want
to reference heater supply to a positive voltage because the
rectifier diode heater uses the same supply.
Since taking theese pictures I have fiished the lid for the psu.
Now I need to finish the case for the phonostage.
Rolf. |
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| mashaffer |
Are you using an IDH rectifier? If so then, I think, referencing the heater at a higher voltage (within reason) should not be a problem and I would think that it would make a world of difference. Tightly twisted heater wires is of course recommended as well. I did this on a high gain guitar amp and there was absolutely no audible hum.
just a newbie's opinion. |
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| alexg |
I gather that your heater supply does not have a center tap for ground. I don't think you need to reference the heater to a positive supply, the cathode voltage is very, very low.
If you don't have a center tap heater supply, try connecting each leg of the heater supply to ground with 100 ohm resistor. This seems to work for me.
I started drilling my chassis for this preamp, but I will be using 6n1p because I have tons of them. Thanks. :) |
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| rman |
Hi Mike.
Yes it is an indirectly heated diode a 6x4. I would't think it would be possible to share heater supply with the amp triodes otherwise.
Thank's for sending those plugs. I did go with a different
connector however.
alexg,
I think I will try you idea. good luck with your build!
ps. I did twist the heater wires.:) |
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| DaWoofer |
| Nice work Rman, I think my PAS 2 is my weak link in my system even though I've done a few simple mods. I still get slight hum out of it. What amplifier are you using with your phonostage? |
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| rman |
Hi Dawooffer.
I am using Hafler DH110 preamp and homemade 6EM7 series
single ended power amp. Phonostage sill hums a bit too
even after using alexg's idea. I don't hear the hum when
playing a record, only with volume up fairly loud.
here are some more pictures. |
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| alexg |
rman, how did you wire the ground of the whole phonostage?
I will be starting my build and am trying to get ideas. Thanks. |
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| rman |
Well,
What I did was put a large solid copper wire from a mains
wiring cable, the type that is used inside walls, around the
tube sockets in a U shape. The negative from the power supply
I attached to the bottom of the U. Then I made all my ground
connections to this ground buss. An earth ground wire was
brought from the power supply to the amps case. the only
connection beetween the negative supply rail and earth ground
is at the input jacks.
I don't know if it is the best way but I figured since it worked
in my poweramps quite nicely, I would try it in this project too. |
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| rman |
Another thing I have noticed, when volume is turned way up
with no record on, the wooffers were making large excursions
at a very low frequency, maybe 4 cps. I figured why not try
a little negative feedback? Rather unscientificaly, I put 30m ohms
between the output and the cathodes of the input stage. when I plugged it back in,
one channel had very low output. after a little messing around I
found I used the wrong resistors here, 600 ohms.:clown:
After fixing this, I think the woofers are not flailing about quite
so much. It may just be my imagination but the bass might be
a little tighter as well.
Anyone think I should take it furthe to 15 megs? |
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| EC8010 |
| You have motorboating and it's due to HT supply problems. |
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| rman |
And here I thought I could never afford a motorboat!
But seriously, a breif search seems to sugest that lclc filters
are prone to this problem. I based my filter on Richard Murdey's
design as shown here. Rectifier is hybrid bridge with 6x4 tube.
filter components I ended up with are:
15H(1026 DCR), 22uf, 7H(340 DCR), 20uf.
The chokes are what I could find that were close to Richards
original plan. Maybe the first choke needs to be several times
the inductance of the second? I will need to do some research. |
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| EC8010 |
| Try using the step load function in PSUD2 to see if the problem is due to the LCLC power supply. If it isn't that, try decoupling the HT to the input stage of the pre-amplifier. |
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| SY |
If you are philosophically opposed to active regulation, C7 and C8 on the RLM schematic could easily be made much larger, 100u or more. That could help.
I haven't modeled your raw supply in PSUD2, but you may want to, and pay particular attention to the effect of a current step on the raw supply response. |
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| rman |
Thank's guy's
I played with PSU2. It seems a much bigger output capacitor
could be the answer.
Sy. Not opposed to active reglation. It might come to that yet.
I have never played with regulation yet. Changing those
decoupling capacitors in the phono circuit, not really an option.
I would likely make a big mess of that circuit board. It would be
much easier to do had I used point to point. Oh well.
Rolf. |
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| alexg |
I had a motorboating problem with an SE KT88 with an CLCLC filter on the driver tube, I took off the last choke and replace with 220R resistor, motorboating disappeared.
I am building this phonostage, and here is the PSU I am thinking of building:
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| rman |
Thank's for sharing your expierience Alex.
In the future I think I will leave two stage choke filters to the true gurus. I put 200uf of capacitance across the power supply output and the woofers stopped dancing. It is too big to put in the supply so I will try to jam it into the phonostage.
There is still more hum than I would like. I yhink it must be a
ground loop or hum pickup on the input wires. I used twisted
pair telephone wiring instead of shielded cable. I will try the
ground breaker I have been reding about on this forum. Two
back to back diodes across a resistor. If that doesn't work, then
it's shieled input cable.
I will let you know how it goes. How is your project coming along?
Let me know how your power supply works out.
Rolf. |
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| rman |
| I tried the groundbreaker. it still hums a bit and it turned into an am radio! |
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| alexg |
| I finished wiring one channel last night, one more to go, it should be singing tonight. |
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| Akita |
| Hi alexq, are you still using the 6n1p? I have some with me too. hope you get a good result. |
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| alexg |
| quote: | Originally posted by Akita
Hi alexq, are you still using the 6n1p? I have some with me too. hope you get a good result. |
Yes, am using the 6n1p, AC heaters (I was told that I need DC heaters), but I just want to listen to it.
If this sounds good, then I will tweak the circuit and get proper parts.
I will post my results late tonight (it's 1:00pm in Manila right now). |
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| alexg |
I finish my phonostage earlier than I expected.
With AC heating, it is quiet as a mouse! :cool:
And it sounds excellent too! I used the PSU schematic I posted earlier. I used 500ohm/20uf polypropylene for the last RC filter instead of the 1K/10uf that was used by RJM on his schematic.
My heaters are center tapped and I just twisted the wires tightly and connect the CT to ground. I use stargrounding on this phonostage. I was really expecting noise/hum, when I fired it up, I thought I did not turn on my preamp or amp, can't hear hum with my ear on the speakers using a 92db speakers. :bigeyes:
Pictures to follow as soon as I finish the plinth. |
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| zarniwoop |
38dB?!
very little gain. so are all you guys using additional preamps after the phonostage or what? My phono amp has about 58dB gain for a high-out MC cart. All my poweramps are passive attenuated and need 1.5-2Vrms for full output. Just seems backwards to have an additional preamp with gain for normal, 2V, line level sources. Keep seeing these phono stages with less than 50dB of gain and wondering why people do it this way. |
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| Akita |
| Great Job! I'm going to try it when I get my transformer.:smash: |
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| kevinkr |
| quote: | Originally posted by zarniwoop
38dB?!
very little gain. so are all you guys using additional preamps after the phonostage or what? My phono amp has about 58dB gain for a high-out MC cart. All my poweramps are passive attenuated and need 1.5-2Vrms for full output. Just seems backwards to have an additional preamp with gain for normal, 2V, line level sources. Keep seeing these phono stages with less than 50dB of gain and wondering why people do it this way. |
I use a low gain transformer coupled dht line stage (4dB)because I have so many sources and several amplifiers I swap back and forth - too much wiring to disturb every time I want to make a minor change or repair. I use stepped attenuators, high end rca jacks and the transformers are permalloy so replicating even the stepped attenuators and jacks in multiple amplifiers would be far too costly.
My phono stage like yours does have quite a lot of gain at around 50dB with a Grado Platinum Reference..
Your comments are well taken, but there are still a lot of people running line stages with >20dB of gain and with those phono stages having gains of 40dB or so work well. People with old analog sources need the additional gain in some instances as well. Everything in my system is generally 2V output, but none of my tuners are - fortunately there is adequate gain available to get loud even with these sources. I am about to get a reel to reel, and most of these will have maximum output levels of less than 1Vrms. |
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| alexg |
| quote: | Originally posted by zarniwoop
38dB?!
very little gain. so are all you guys using additional preamps after the phonostage or what? My phono amp has about 58dB gain for a high-out MC cart. All my poweramps are passive attenuated and need 1.5-2Vrms for full output. Just seems backwards to have an additional preamp with gain for normal, 2V, line level sources. Keep seeing these phono stages with less than 50dB of gain and wondering why people do it this way. |
This phonostage is my first attempt of making a phonostage.
Anyway, am using a high gain linestage so the lowish gain of my new phonostage is not really too much of an issue.
Next phonostage will be a higher gain phonostage, next time I think I am more proficient of dealing with hum and noise issues of high gain phonostage. :) |
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| Sander'Z |
| Sorry. My english is so bad... I maked this phonostage about year ago. In begin, it used a 6n1p, but now it used a 6n23p (russian 6dj8). Sound of this phonostage is nice. In PSU I used a HFA06TB1200 rectifiers and IRF840 regulater. Case is plywood? no screening? but no hum. |
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| Akita |
Look nice...........Ohh....white AC Cap?
I saw quite lot of people using ac cap in their amp. Any comments on this kind of capacitor? |
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| alexg |
Sander'z, nice job!
Neat layout, beautiful work. Am sure it sounds excellent.
;) |
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| Sander'Z |
Thanks! Yes, it's a AC cap, it used in 1st stage as plate cap. I change some types of caps in this position and stoped on it. Because sound with it is better than with others.
Another pic. |
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| alexg |
Here are the pictures of my RJM phonostage using 6n1p instead of 6dj8/6922:
The RJM phonostage with 6n1p tubes.
On the left is my 12au7 VA/CF preamp, on the right (black chassis) is my RJM phonostage and below is my EL84 driven EL84 parafeed amp. |
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| mashaffer |
| Very pretty Alex! I have a pair of Sovtek 6N1Ps that are begging to be put to just such use. Did you end up modifying any of the circuit beside the power supply? |
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| alexg |
| quote: | Originally posted by mashaffer
Very pretty Alex! I have a pair of Sovtek 6N1Ps that are begging to be put to just such use. Did you end up modifying any of the circuit beside the power supply? |
I did not modify the circuit, I checked the loadline of the 6dj8 and checked if it is optimal with the 6n1p, it does seem optimal. I have not tweaked the circuit yet, but I used polyester caps on the RIAA and I want to replace them with silver mica. The resistors used on the RIAA are carbon and I want to replace them with metal film.
This phonostage is quite a good performer. |
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| mashaffer |
| Thanks Alex, please keep us posted on your progress as you continue to tinker. |
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| alexg |
I started tweaking the circuit, first I used red LEDs to bias, sounded too harsh for me.
I also tried to bias the 6n1p hotter, replaced the bias resistor with 470R and then 330R, went back to 500R, the sound is much better with the 500R cathode resistor.
Since the gain is a bit on the low side, am thinking of using 12at7 for the first stage and then 6n1p for the second stage. Passive RIAA equalization in between the two stages.
Does anybody knows to compute for the resistors and capacitors of the RIAA if I replace the 6n1p with 12at7? Thanks. |
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