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FX Audio 6j1 tube preamp - a $31 wonder
- Thread starter Poultrygeist
- Start date
FlaCharlie
Super Member
Thanks, I thought they looked pretty small.
I'm still amazed at how large his cap banks are considering that they're only 10uf and 400v. In my most recent amp build and my current breadboard amp I'm using all polypropylene film caps (Panasonic and Kemet) in the power supply. The largest are 100uf 600v and one of those is less than half the size of one of his 10uf banks and only cost ~$25. The 10uf versions (Panasonic, Kemet, Wima, TDK, Vishay) are all $6 or less and smaller still. Not small enough to fit inside an FX, though.
It's always nice when junkbox parts suffice and you don't need to buy anything new. Experimenting is fun, too. For me it's usually more fun than just going out and buying something new and sometimes I even learn something in the process.
lazylistener
Member
I managed to find one on Lazada – tomorrow's 11.11 (basically the Singaporean version of Black Friday) so I'll hold out to see if there's a good price on this.
No worries about the list, feel free to share it if you do come across it one day.
All I can say is that I've had a lot of fun using this. I'd say that it doesn't make a huge sonic difference in the tape loop on my NAD 3020i – IMO speaks to the sonic signature of the 3020i that it's warm and tube-y for a vintage SS amp – but it helps a lot when it comes to accommodating different kinds of music with wildly different mastering. The difference is instead more apparent via headphones (Grado SR225e) vs speakers (Elac B5.2 in a near-field desktop arrangement) – genuinely amazed at how it transforms the soundstage over headphones. This is my first time using tone knobs for vinyl too (Schiit Mani w/ Swagman LPS) and it's amazing how better certain records can sound, especially when I've gone for years believing good-sounding records don't need any further EQ tweaking.
I've been using the Voskhod 6J1P-EVs and they've been terrific, but I'm definitely keen on rolling tubes just to play around. So far, over the thread, I've read that the standout picks for many have been the Tesla EF93s, RCA 6AK5s, Mullard 8100s. I'd love to hear out from anyone who recommends tubes that aren't spoken about here as often!
Also, this is a question for those experienced with SS amps – I usually feed my Tube-03 through the tape loop, achieving unity gain with the NAD at 11 o'clock on the tube amp. I noticed that there's a warmer sound when I push the tubes to 3 o'clock and dialing back the NAD, but I wanted to ask if there's any danger in doing this!
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Tech question about Tube-03 ... does anyone have the tone control specs ?? Just curious what the frequencies are and db +/- ... the high freqs really seem to improve with a slight adjustment ... I have installed improved op-amps, (I can't recall which ones I finally decided on .) and not sure if these affect the tone controls ... it still sounds great ...
FlaCharlie
Super Member
I don't know about the specs but supposedly one of the op amps runs the tone controls - I think it may be a dual opamp - and other one runs the volume control. So it makes sense that the control responds differently after an opamp swap. Some people have removed them and this defeats their function but the preamp section still works. So it seems like it functionally converts the -03 into an -01.
THX for post - I have the recommended Muses 8920 - a dual op-amp ... looks like it is now EOL - glad I got it back in May ... as usual, I would never have known about this w/out this great thread and AK community..
drjohnnyfeva
Well-Known Member
I have rolled several opamps already. I don't know the finer details of the specs, but from listening, some have more "gain," just as the different tubes do. I never change settings before the opamps or tubes. I want to hear something different or no change at all and go from there. With each of the rolls - tubes or opamps - there have been changes in the sound. I'm using the opa626's that I found on ebays with a pair of Phillips EF95's. Before this I had a pair of LME49720's in with the same tubes. There was no additional gain, but the clarity was improved. I really like this combo, 627's and EF95's, altho I have been wanting to try different opamp combos. So I think I'm going to experiment with flipping the 627's and the MUSES8920's into each of the slots. I also want to try the LME49720's and a pair I have yet to hear, the LM4562's, in the same fashion.
edit- To clarify my intention... I want to have one opa627 in the Tone and a MUSES in the Volume and vice versa to see if this is something worth pursuing more. I have read that people have done it with some improvement for their listening, but I am not aware of manufacturers using different opamp chips in a unit in that manner. At least, I haven't read anything along those lines that I recall.
There are also members who have used different tube brands in the unit. I don't remember the pages, but there was experimentation with some apparent success. Some of this seems too far down the rabbit hole.
But it is fun to play around with if you can simply reverse path to what you liked most. It's a rainy day project and lower on the to do than trying the different opamps in the controls.
edit- To clarify my intention... I want to have one opa627 in the Tone and a MUSES in the Volume and vice versa to see if this is something worth pursuing more. I have read that people have done it with some improvement for their listening, but I am not aware of manufacturers using different opamp chips in a unit in that manner. At least, I haven't read anything along those lines that I recall.
There are also members who have used different tube brands in the unit. I don't remember the pages, but there was experimentation with some apparent success. Some of this seems too far down the rabbit hole.
But it is fun to play around with if you can simply reverse path to what you liked most. It's a rainy day project and lower on the to do than trying the different opamps in the controls.
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They are essentially the same op amp.
You might want to try some of the discrete FET plug in options from Burson and Sparkos. I'm quite happy with Burson V5s in a Music Hall 25.3 DAC.
drjohnnyfeva
Well-Known Member
It's funny, a bunch of us had this discussion in this thread maybe a year ago - a little more, perhaps. I would love to try the Bursons and Sparkos and some others, but when the cost for one of those opamps is double the cost of the unit itself, it almost makes a mockery of the thread itself - $31 Wonder.
To your point, tho. The opamp I have in there now was a single channel that only recently - 6 months, or so, became available as a dual channel. I bought my dual on the bay. The OPA627 was part of a ratings comparison with the above mentioned FET and the MUSES1 and 2. They were all similarly priced. If memory serves, they were all single channel in the comparison and all had similar price tags - all over $50 each, with some being still more pricey. The single channel at the time were in that neighborhood - maybe $35/each, but I could only find kits where you could follow directions to solder the two OPA627's to an 8-pin adapter to fit the FX's socket. This is the same way the OPA1656 was adapted, but that was a single dual chip. I can't solder to save my life.
So finding the pre-made OPA627's at the whopping price of $5/ dual, I jumped at giving them a try and I'm glad I did.Everything the guy who wrote that article said turned out to be true. I posted the link to the article in this thread someplace. It was another forum site, but I can't recall off the top of my head. It is linked in this thread someplace tho. I really liked both the MUSES8920 and the LME49720, more than the OPA1656's. But I really, really like the OPA627's. The comparison concluded with the guy really digging both the Burson and the OPA627 calling it basically a dead heat with his slight preference toward the OPA627. So when I saw them for $10 for a pair of duals, I jumped at it, not really worrying about potential counterfeits. I figured they either sound great or shitty and I could part with $10 to experiment. Glad I did.
Maybe I'll try the Burson's one day. But I'm a big believer in the law of diminishing returns too, tho. I learned the hard way that there are tubes that sound great at the sub $20/matched pair price point. Some of the more expensive pairs I tried left me really disappointed; but that's to my ear and I certainly don't begrudge others and their tastes or favorites.
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I look at it as a comparatively cheap way to truly elevate the performance.
I did effectively the same thing with my Raspberry Pi players. I found that using a nicely made starquad DC cord from Ghent Audio improved dynamics.
RPi4-$40
Case-$15
Battery power supply-$20
Cord-$29
drjohnnyfeva
Well-Known Member
https://www.head-fi.org/threads/opa...-muses8820-and-8920-burson-v6-classic.870832/
Here's that article I posted awhile back on a bunch of opamps that a guy test drove. These were not tested in a Tube 03. I just used the info as a reference. The only thing I have no way of proving is whether the opamp627's I have are real or not. There is some discussion on page 112 of this thread that basically designates the opa627 from ebay to be fake, but this was a couple years ago. I'm almost certain the ones from the Philippines were not available back then because when I looked originally about a year ago they were no results on dual 627's. Either way, as Rob43 suggests, just give them a go for the $10/pair and decide for your self. There is a high likelihood that they are fake, but they sound great nevertheless.
Here's that article I posted awhile back on a bunch of opamps that a guy test drove. These were not tested in a Tube 03. I just used the info as a reference. The only thing I have no way of proving is whether the opamp627's I have are real or not. There is some discussion on page 112 of this thread that basically designates the opa627 from ebay to be fake, but this was a couple years ago. I'm almost certain the ones from the Philippines were not available back then because when I looked originally about a year ago they were no results on dual 627's. Either way, as Rob43 suggests, just give them a go for the $10/pair and decide for your self. There is a high likelihood that they are fake, but they sound great nevertheless.
FlaCharlie
Super Member
It just attenuates (reduces) the incoming signal by 6 db. Unless you have your volume control turned up all the way, you're also reducing the level of the incoming signal.
Modern amps don't need any gain in order to produce full power output when driven by a modern source's line level output. That's why many people use so-called "passive preamps", which are just a volume control and, often, also provide switching between different sources.
The tubes in the FX provide quite a bit of gain, though. As I recall they have a mu (amplification factor) of ~35. As a result some people find that the volume control can be very touchy, meaning that it's hard to make very small adjustments in level, and that the range of the control is severely limited as a result.
Using the -6 db switch should give you more adjustment range and make it easier to make minor changes to the volume.
Most commercially sold preamps do have way too much gain which doesn't make any sense at all from a technical standpoint but they are limited in the sense that they need to use tubes that are widely available and often still being produced.
As a DIY builder I'm not constrained by such considerations. So, when I built a preamp, I only considered tubes that have a mu of less than 10. My Boogie Factor preamp uses the 1626, which is a transmitting triode with a mu of 5. So I have "tube sound" and a bit of gain if I need it but with none of the problems created by the use of higher gain tubes. It's output impedance also matches better with SS and Class D amps than the tubes used in the FX, although I mostly use it with tube amps.
https://www.audiokarma.org/forums/index.php?threads/1626-preamp-build.931276/
FlaCharlie
Super Member
Sure, tube amps are typically a better impedance match for these than SS or Class D amps.
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FlaCharlie
Super Member
FlaCharlie
Super Member
I thought it might be a Chinese amp but I've never seen one that uses 6L6GCs. I'm sure the one you're buying will be much better since the Chinese amps (the more modestly priced ones, anyway) require some mods for reliable operation.
I've never heard of PJL Electronics. When your amp arrives please start a thread over on the Tube Forum about it with pics and all. I'm sure a lot of people would be interested in seeing it.
Yeah . . . that is someone poking a badger with a spoon.
I saw that years ago and got a kick out of it. I later looked up the saying . . .
It's a quote taken from a stand-up comedy routine by British comedian Eddie Izzard about the Catholic idea of original sin. He talks about a guy going to confession and saying "Forgive me Father, for I have sinned . . . I poked a badger with a spoon. In response, the priest says "that truly is an original sin".