Dr. Ears
Super Member
Make it four 6J5-G's or L 63's and I'm with you.
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FX Audio 6j1 tube preamp - a $31 wonder
- Thread starter Poultrygeist
- Start date
Make it four 6J5-G's or L 63's and I'm with you.
Hi ! thanks a lot for the very helpful advice. I will do at least this I have to find something that fits in nicely
Given the measured voltages i guess 100V parts can be fine as well. I would like to increase the out cap a little I am using solid state amps
I will look in mouser catalog
Thank you very much again. I am very beginner ... the voltages look very low for tubes in general. I read somewhere they could not be optimal for these tubes ? that they should be used instead, like most of tubes, with higher plate voltages ? but i really out of my safe understanding area
Tubes voltages have always scared me Maybe i should look for something solid state but tubey sounding, if something like that exists. I am scared to operate with so high voltages.
By the way i looked around for some noise and distortion tests but found nothing
One day i would like to try some testing with a decent sound card. Just to get an idea of the electrical performances, if those mean anything.
I like what this unit provides to the overall sound. I prefer the sound of my system with it in place. And i do not find it too warm sounding at all. Maybe transparency is not the ultimate. But i should work on it. The parts on the signal path are of unknown quality. Unfortunately the board is very small. I would much prefer a 10"x10" board with more space to work.
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Poultrygeist
Lunatic Member
Tube preamps are pretty safe.
Poultrygeist
Lunatic Member
I read somewhere that the FX can add as much as 10 dbs.
No doubt the reason it helps my flea watt tube amps drive some inefficient speakers.
No doubt the reason it helps my flea watt tube amps drive some inefficient speakers.
you mean that the high plate voltage is not lethal ?
If i am not wrong a voltage gain of about 3 times ? thanks a lot. This is a very important information. I really would like to replace the pot. I am sure it is holding back the performance. I do not remember if you or another poster he is using it at full volume with a quality passive attenuator in front of it. I cannot find the listening impressions
I will be trying something
Poultrygeist
Lunatic Member
Tube amps are where you find lethal voltages.
FlaCharlie
Super Member
That was probably me.
Devices like the FX and others that run "normal" tubes at very low voltages work but the tubes are not being operated as they were designed. The only advantage of running them at such low voltages is cost.
Not sure if you saw it but I posted comments about working with voltages on the thread you posted on DIY Audio. Here's an edited version:
Being afraid of high voltages is a good thing. It will just make you more careful. The only thing you do with a powered circuit is measure things and as long as the only thing you touch is the insulated handle of the meter probes there is no danger. And after you power down you need to drain the voltage from charged caps.
My breadboarded 6AK5 circuit(s), which are posted earlier in this thread, used a power supply voltage (B+) of about 240v and just over 100v on the plates. That's about the same as your wall voltage in Italy, right? Yet you probably don't get scared every time you plug or unplug anything from the wall.
Low voltage tubes do exist. They are known a "space charge" tubes and were designed to be used in car radios (and perhaps for other uses as well). I don't know much about them but it would be interesting to see if some of them could be used in the FX. Actually, the plate voltage in the FX might have to be lowered to use some of them, which run with 12.6v heaters and 12.6v on the plates.
I expect someone must have built a preamp with them. You might want to do some research.
Earlier, you said you might try to replace the pot. Here's a very nice, relatively inexpensive, stepped attenuator. I've used them and they work well, sound clear and are perfectly balanced.
https://www.ebay.com/itm/DACT-Type-...839183?hash=item2ef390a78f:g:HXkAAOSwawpXwSSM
I like to have some room to work too. I usually experiment with a circuit on a breadboard first since it allows you to easily substitute parts, usually without having to solder anything. After you get it to your liking, you can build it in some sort of enclosure.
I build using point to point wiring and use parts that can be assembled easily by hand, not those tiny SMD parts found on boards that are assembled by machines.
Rob43
Active Member
First, with a switching PS like my Meanwell 36v unit, using a bigger smoothing capacitor like roughly a 2200 uF is more suited. On the other hand, a regulated linear PS likes a Much Smaller smoothing cap. My pictured 1000 uF on the front of my Pyramid PS is overkill, if I were doing it again I'd buy a 470* Uf 16v instead.
To answer your question about the tiny cap: Look up and research "Bypass Capacitors".
Rob43
* I already provided you a link for two appropriate 470 uF caps assuming you buy a Pyramid PS.
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50 Green
Well-Known Member
As I mentioned earlier in this thread, good quality linear, regulated power supplies can be found barely used (or even NOS) on that auction site for very little money.
The International Power IHN12-5.1, linear, regulated PS that I use to power Tube-01 units, came from the factory with a 23,000 uF filter cap. It was something like $27.
Similar models, in a variety of voltages, are commonly available. The PS I have is US made and the components used are far more robust than those used in Pyramid PSs, for example. With quality, linear PSs available so inexpensively, I don't see a need to bother with trying to get better performance from a cheap PS or a SMPS.
The International Power IHN12-5.1, linear, regulated PS that I use to power Tube-01 units, came from the factory with a 23,000 uF filter cap. It was something like $27.
Similar models, in a variety of voltages, are commonly available. The PS I have is US made and the components used are far more robust than those used in Pyramid PSs, for example. With quality, linear PSs available so inexpensively, I don't see a need to bother with trying to get better performance from a cheap PS or a SMPS.
Rob43
Active Member
I just looked on Ebay, I'm seeing this model at about double the price (or more) of my Pyramid PS.
Do you see any at roughly ~$30 shipped that are in great condition ?
Rob43
50 Green
Well-Known Member
Do I see any now? You'll really need to do your own search. This type of PS is very commonly listed on that site. (You can check from time to time if you are actually interested.) Your own search will determine what shipping to you will be. I took a quick look just now and saw the same model from another manufacturer for a little less than $30 (shipped to me) and a NOS unit from that same manufacturer for a little more.
Not sure why you're asking about $30 including shipping, when the comparable Pyramid model is closer to $40 plus shipping - although I'd really only consider it comparable in terms of voltage and amperage ratings. For example, output ripple spec on the Pyramid is 150mV vs 5mV for the International unit. (Also compare the components used in each.)
Pyramid is a hobbyist PS. International (and similar PS from other mfrs.) are used in industrial and medical applications, where reliability and consistent performance are far more critical. The only caveat is that they are not "plug and play." They need to be wired properly and will need to be put into some sort of housing. (I saw a post on here by someone who did a clean job w/ a $2 card file from a thrift store.)
AS WITH ANYTHING INVOLVING MAINS WIRING, CORRECT WIRING AND A SAFE HOUSING ARE CRITICAL FOR THE USE OF THESE DEVICES. ONLY PERSONS COMPETENT AND COMFORTABLE WITH WORKING WITH MAINS WIRING SHOULD ATTEMPT TO USE DEVICES OF THIS NATURE.
Rob43
Active Member
I WILL STICK WITH MY ~$31 DOLLAR PYRAMID REGULATED LINEAR POWER SUPPLY.
MY PYRAMID POWER SUPPLY HAS BEEN WORKING GREAT FROM THE DAY I PLUGGED IT IN.
+
= A GREAT WORKING REGULATED LINEAR POWER SUPPLY.
Rob43
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Poultrygeist
Lunatic Member
I'm not sure there are any sonic advantage that this $150 linear regulated Astron might have over the $30 Pyramid.
50 Green
Well-Known Member
Good for you, for finding the unit on sale. Enjoy the music.
Can’t wait my tube 01 to arrive from China, so I ordered another tube-03 from Amazon along with the ps7kx power supply. Arrived today.
Hook it up normally without the polarity reversed, the first thing I notice is seems half of the low is gone, Switch the speaker cables at the power amp. It sounds about the same. The high and mid are more clear but seems missing low. Did not hook up the power supply yet. Use I gotta the wall wart comes with the tube03. This is my setup, DAC to tube 03 to main in of a vintage Onkyo A 7022 to a pair of DCM TF600.
One more problem is at certain point of time, the right channel is totally out and the has lower volume, it might be my power amp but can’t tell. Swap left and right tube the problem seems still there. There is no balance for me to adjust that. Need to keep playing.
Hook it up normally without the polarity reversed, the first thing I notice is seems half of the low is gone, Switch the speaker cables at the power amp. It sounds about the same. The high and mid are more clear but seems missing low. Did not hook up the power supply yet. Use I gotta the wall wart comes with the tube03. This is my setup, DAC to tube 03 to main in of a vintage Onkyo A 7022 to a pair of DCM TF600.
One more problem is at certain point of time, the right channel is totally out and the has lower volume, it might be my power amp but can’t tell. Swap left and right tube the problem seems still there. There is no balance for me to adjust that. Need to keep playing.
NZVinylFan
Member
Nice!!
Regarding low output problem on the one channel, have you checked and maybe swapped the RCA audio in or out cable? Swap the left and right rca plugs around and see if it follows to the left or stays same. It could be a faulty input or output cable. Also, try and switch the input selector on the amp a couple of times - could be a bit of dirt on the selector switch contacts. These suggestions seem so obvious, but sometimes the issue may be as simple as that. Just a thought.
All the best.