FX Audio 6j1 tube preamp - a $31 wonder

[Poultrygeist]

The transformers in a linear regulated are not unlike the transformers used in high end amps. To cut costs some companies have gone to SMPS but big iron still dominates.

Several of my 12v components have been using 13.8v linear regulated power supplies for over 5 years. I wonder if it's time to start worrying?

 

[50 Green]

The transformers in a linear regulated are not unlike the transformers used in high end amps. To cut costs some companies have gone to SMPS but big iron still dominates.

Several of my 12v components have been using 13.8v linear regulated power supplies for over 5 years. I wonder if it's time to start worrying?

If you are replying to my post, I'm not sure what you're trying to say.

If this is in response to my post, whether or not there is a transformer in the PS has absolutely nothing to do with the longevity issues I mention. It is simply a matter of whether the voltage put out by the PS is within the tolerance of the item being powered. Many items with a nominal 12V rating can tolerate 13.8V. The tubes I prefer to use, specifically can not. That is according to the manufacturer's engineers. (Which is why I posted the quote.)

A shortened lifespan for a vacuum tube doesn't necessarily mean it will die in the blink of an eye. It's quite possible that an overvolted tube will function acceptably for a time. Mullard's engineers say that will be a shortened time. That might be tolerable if the tubes were cheap and available. These have long been out of production.

If you were not replying to my post, my apologies for misunderstanding.

 

[petemcfc]

To be fair this is just speculation,I work in heavy engineering and the machinery made is tested to 125% of their load duty if it fails then it is inspected to find the cause of failiure,I cannot comment on other industries though I expect it to be the same,there is a possibility that Mullards' figures are there to protect the company from any come back if a product fails by being driven above their recommendations.
I think we will have to wait until a valve fails then if the user was to then report the valve details and the voltage we could all learn from that.
I'm using Mullards and a linear power supply by the way.

 

[Poultrygeist]

If you are replying to my post, I'm not sure what you're trying to say.

If this is in response to my post, whether or not there is a transformer in the PS has absolutely nothing to do with the longevity issues I mention. It is simply a matter of whether the voltage put out by the PS is within the tolerance of the item being powered. Many items with a nominal 12V rating can tolerate 13.8V. The tubes I prefer to use, specifically can not. That is according to the manufacturer's engineers. (Which is why I posted the quote.)

A shortened lifespan for a vacuum tube doesn't necessarily mean it will die in the blink of an eye. It's quite possible that an overvolted tube will function acceptably for a time. Mullard's engineers say that will be a shortened time. That might be tolerable if the tubes were cheap and available. These have long been out of production.

If you were not replying to my post, my apologies for misunderstanding.

I wasn't trying to say anything as I said what I wanted to say.

 

[50 Green]

Gentlemen, please feel free to run your equipment as you wish. I am merely speculating that any sonic difference perceived may be the result of increased voltage, and not anything at all to do with the type of PS used. Perhaps someone could do an A/B with 2 linear PS, one at 12.6V and the other at 13.8V, however even then the results would be largely subjective.

As I mentioned, I will be trying a linear PS, as I am curious whether it will make any difference in the sound quality, but it is my choice to remain w/in the published specs of the tubes I'm using. I choose to take the engineers at their word.

I doubt that running one set of tubes to failure would give much information of value, even if analyzed by an EE. Likely the only informative test results would come from running large enough sample groups to produce statistically valid results at various heater voltages, and analyzing and comparing the deterioration of the tubes within the groups. (I suspect this is very well what Mullard did in developing the specs for the M8100.)

Again, this is all my own preference. I'd personally put more weight in the carefully chosen words of factory engineers than a string of catch phrases that lacks logic and reads more like marketing hype from a bygone era of audio.

 

[Poultrygeist]

Gentlemen, please feel free to run your equipment as you wish. I am merely speculating that any sonic difference perceived may be the result of increased voltage, and not anything at all to do with the type of PS used. Perhaps someone could do an A/B with 2 linear PS, one at 12.6V and the other at 13.8V, however even then the results would be largely subjective.

As I mentioned, I will be trying a linear PS, as I am curious whether it will make any difference in the sound quality, but it is my choice to remain w/in the published specs of the tubes I'm using. I choose to take the engineers at their word.

I doubt that running one set of tubes to failure would give much information of value, even if analyzed by an EE. Likely the only informative test results would come from running large enough sample groups to produce statistically valid results at various heater voltages, and analyzing and comparing the deterioration of the tubes within the groups. (I suspect this is very well what Mullard did in developing the specs for the M8100.)

Again, this is all my own preference. I'd personally put more weight in the carefully chosen words of factory engineers than a string of catch phrases that lacks logic and reads more like marketing hype from a bygone era of audio.

You might want to read through this thread and see how many feel the better power supply ( linear regulated ) made a huge improvement. If you can't believe the experience of others I'm glad you are willing to see for yourself.

This is what Parts Express says about one of their Pyramid 13.8v regulated power supply:

"This regulated power supply features binding posts for simple and secure hookup. It's perfect for powering 12V devices that draw up to 10 amp"

 

[mhardy6647]

On filament voltage and vacuum tube life:

A little high is (much) better than a little low.
Source: https://www.diyaudio.com/forums/tubes-valves/211731-heater-wiring-bad-ugly-3.html

RCA did a long comprehensive study and warned designers not to vary the heater voltage
from recommended values more than 4%: LOWER VOLTAGES especially KILL TUBES QUICKLY.
from https://www.diyaudio.com/forums/tubes-valves/211731-heater-wiring-bad-ugly-3.html#post3012333

Remember, though, that if the bias and plate voltages change, the operating point(s) for the tube(s) will also change, and may have sonic and/or tube (or other circuit components) lifespan consequences -- independent of the filament voltage.

 

[50 Green]

On filament voltage and vacuum tube life:

A little high is (much) better than a little low.
Source: https://www.diyaudio.com/forums/tubes-valves/211731-heater-wiring-bad-ugly-3.html



Remember, though, that if the bias and plate voltages change, the operating point(s) for the tube(s) will also change, and may have sonic and/or tube (or other circuit components) lifespan consequences -- independent of the filament voltage.

Thank you for that. Again insights based on studies performed by engineers. I'd always prefer to read the engineers own words, however the group on the other site tend to be guided by facts and analysis, with a number of EEs on board. Any misinformation is usually debunked rather quickly.

I agree w/ a previous post that it would be interesting to know the different bias and plate voltages w/ 12.6V and 13.8V PSs. As others and I previously alluded, any differences in sonic character may very well be due to these being different, rather than anything to do with the type of PS being used. If this is indeed the case, and if the sound is indeed improved, one might be able to tweak the amp design to achieve the changes w/o increasing heater voltage beyond spec... but that really defeats the cheap and easy aspects of these little amps, doesn't it?

It's my own choice to run my tubes w/in spec. Others can certainly do as they please, and may get what they consider to be an adequate period of use from them, even if overvolted.

BTW, I read this thread in its entirety, long before posting.

 

[50 Green]

Quick measurements of the stock SMPS and ifi PS show 12.33V for stock and 12.21/12.22 for the ifi. The heater circuit w/o tubes or any load measures at 12.01V w/ the stock SMPS. 12.00 would be at the absolute low end of the +/-5% tolerance, so there's a decent chance that w/ tubes installed and the stock SMPS, the heater voltage is running a little below spec. (Possibly even more likely w/ the ifi.)

This may be another indication that increased voltage could be the cause of any perceived sonic differences, rather than type of PS used.

I don't have time right now, but if I get a chance, I'll pop one open and take some measurements at various PS voltages w/ the Shuguang tubes that came w/ it installed. (IMO, they're useless for anything other than testing, when I don't want to risk a good tube. I certainly don't like the sound of them.)

 

[50 Green]

As I mentioned, I have a pair of these amps. I picked up the first one at the end of 2017, when I was using a tablet as a source for a little while, and was looking for a bit of extra gain. They were cheap and the idea of a tube stage was intriguing, so I gave one a try. I was surprised at how quiet it was and the sound quality.

Of course I opened it up to see what they put inside. I was astounded to find that all the through-hole components were name-brand stuff: Nichicon, United Chemicon, etc. Seemed almost impossible to put something like that together with name components at that price. Could they be counterfeits? I started looking up part numbers and quickly discovered the secret: every last through-hole component on that board was an obsolete part number. Stale stock!

Out of curiosity (and just because I can) I picked up a second unit and replaced all the through-hole components. Didn't bother touching the SMD stuff. (The second amp was to pull apart and experiment with. I liked the first one so much, I didn't want to take a chance on killing it,) I used Nichicon and Panasonic for the 'lytics, replaced the polyester input and output coupling caps with polypropylene, and the two little polyester bypass caps w/ polyphenylene sulfide. Went as far as to replace the resistors w/ 1% RN metal films.

Had the parts on hand, so when the second amp worked out OK, I swapped out everything in the first one. I should have A/B'd them to see if I could hear any slight difference, but I didn't. However I really didn't notice any audible difference, listening from memory.

Two changes did make a difference, though. I tossed the linear, indexed pots, and replaced them w/ logs. It's much more pleasant adjusting volume w/ the audio taper and w/o the detents. (I didn't find any snap-in w/ fluted shafts, and the case grounds through the pot, so I just soldered in some clipped leads to the snap-in holes, and brought them around to the front where they can make contact between the face of the pot and the case.)

The one change that did make an audible difference was to up the capacitance of the output coupling caps to match the impedance of the receiver I'm running these through. That resulted in fuller bass.

The choice of tubes of course does make a big difference in sonic signature. Maybe I'll post my takes on those at some other time.

 

[Wally1955]

Aloha
after reading some days this forum decided to order 2 off this cute preamps and now after couple days listing this setup must say its double worth the money sounds improve in my ears works fine with Elekit TU-898/WE300
gorgeous AK Forums with friendly ppl
cheers

View attachment 1580659
sounds also good with Victor M-7070 and JBLs
View attachment 1581138

Aloha
today paired first time the Victor P-3030 with the M-7070 and Elekit TU-879s in my ears it's sounds more clearer and detailed now as in the earlier setup
well it's great fun to play around with different hardware
Cheers

 

[ejman]

Wondering if the volume control taper has been changed on the latest units? I just got another one from Amazon today to play with and I noticed that the volume control had to be set up considerable higher for same loudness and it seemed to increase much more gradually than my older unit.

 

[50 Green]

Wondering if the volume control taper has been changed on the latest units? I just got another one from Amazon today to play with and I noticed that the volume control had to be set up considerable higher for same loudness and it seemed to increase much more gradually than my older unit.

If it increases gradually it's probably linear, rather than log / audio taper. Do both have detents?

I doubt parts are spec'ed for these things. More likely it's what ever they can get a lot of for cheap, that will work.

 

[hifix]

I tossed the linear, indexed pots, and replaced them w/ logs.

Wondering if the volume control taper has been changed on the latest units?

This is what is needed for my setup.
50 Green, do you have a part # / reference for the replacement pot ?

Ejman, are there any markings / ratings on the new item ?

 

[ejman]

If it increases gradually it's probably linear, rather than log / audio taper. Do both have detents?

I doubt parts are spec'ed for these things. More likely it's what ever they can get a lot of for cheap, that will work.

Yes, they both have detents.

 

[ejman]

This is what is needed for my setup.
50 Green, do you have a part # / reference for the replacement pot ?

Ejman, are there any markings / ratings on the new item ?

I don't see any differences externally. Haven't opened it yet

 

[Pio1980]

Detents don't necessarily mean stepped switchpoint pots, which are generally a better pot than carbon track, but some users find the steps too broad for preference.

 

[50 Green]

This is what is needed for my setup.
50 Green, do you have a part # / reference for the replacement pot ?

I used Bourns PTD902-2015K-A503. Again note that since they are not snap-in, you'll lose the case ground unless you make a provision for it. (With the original pots, the case grounds through the pot, via the snap-in lugs.)

...some users find the steps too broad for preference.

Yes, that is my experience. I prefer finer control ...and also just prefer the smoother feel of pots w/o detents.

(BTW, not sure what part of Eastern Bamalama you're in, but I may have just been in your neighborhood, visiting a fellow AKer.)

 

[hifix]

Thanks Ejman & 50 Green.

 

[Pio1980]

I used Bourns PTD902-2015K-A503. Again note that since they are not snap-in, you'll lose the case ground unless you make a provision for it. (With the original pots, the case grounds through the pot, via the snap-in lugs.)


Yes, that is my experience. I prefer finer control ...and also just prefer the smoother feel of pots w/o detents.

(BTW, not sure what part of Eastern Bamalama you're in, but I may have just been in your neighborhood, visiting a fellow AKer.)

West of Jacksonville, Al. in the woods.