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Somebody finally measured a 6j1 preamp

T

thirdicomplx

Member
I bought an FX Audio Tube 01 about two years ago because; I was a noob at hifi, I wanted to experience the "tube sound" and... I'm cheap :D. I wanted to like it but I could never get it to jive with my system. I knew it had too much gain but interesting now to see it's very low input sensitivity was also part of the problem. There's been a lot of talk on the interwebs about these 6j1 preamps. A lot of people like them. A lot of people scoff at them. But I've yet to see any measurements on them. Well, at least when I searched before(it's been a while). Just came across this

https://hackaday.com/2020/09/01/that-elusive-valve-amp-sound-for-not-a-lot-there-has-to-be-a-catch/

The author only quotes a few THD figures though. I don't understand their nonchalant attitude towards frequency response and phase either. Still interesting to see some kind of measurement on what these little 6j1 preamps are doing

Ps. I realize that page was posted a little over a year ago but I can't edit my title so deal with it :p
 
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There other versions using the 6J1's to drive a small amplifier chip for each channel. Usually single ended. I've seen a few like the one in the link you posted and there isn't much to them at all. And if you read the descriptions closely buried in them are things like "will drive mobile listening headphones". Meaning earbuds. And "headphone preamp / buffer". I have a small hybrid headphone Amp that uses 6J1's. I replaced them with 5654W's. Ut the one I bought has a small amplifier section that will drive headphones easily and can also has a set of line out jacks and can drive many of my amplifiers. It acually sounds pretty decent, and did cost more than the type in that link. You really have to look closely at these kits and read the descriptions carefully.
 
I've seen those around. I'd be surprised if the front end varied a lot from the basic 6j1 preamps though. While many people think there are different 6j1 preamps, I believe they are all the same gain stage. Well for all the low voltage versions anyway. I recently came across these two, operating the 6j1 at higher voltages. One is another preamp with gain and the other is a buffer

https://www.ebay.com/itm/6J1-Tube-P...2349624.m46890.l49286&mkrid=711-127632-2357-0


https://m.aliexpress.com/i/32814572662.html?gatewayAdapt=Pc2Msite
 
Both of those are much different than what I bought. I should have taken a picture of the inside when I cracked it open. It has a separate small amplifier circuit for the output. The 6J1's drive the small amp section and twice the parts count compared to those two. I bought it to use at my bench when testing amplifiers since it was small. I have it hooked up to a 5wpc spud amp I built at the moment. The front end is probably very similar to those though. But I have to crank it up pretty far before I notice any real distortion, even with headphones. The 6J1's themselves are pretty nasty sounding. The 5654's sound so much better.
 
I've used a CDP, Tuner, Turntables with an outboard phono preamp, cassette deck and a smartphone. Of course the smartphone can't drive it to full output.
 
Lavane said:
Both of those are much different than what I bought. I should have taken a picture of the inside when I cracked it open. It has a separate small amplifier circuit for the output. The 6J1's drive the small amp section and twice the parts count compared to those two. I bought it to use at my bench when testing amplifiers since it was small. I have it hooked up to a 5wpc spud amp I built at the moment. The front end is probably very similar to those though. But I have to crank it up pretty far before I notice any real distortion, even with headphones. The 6J1's themselves are pretty nasty sounding. The 5654's sound so much better.
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Yes they do and I know there are better tubes but these get you 90% of the way there for 20 bucks.

https://www.amazon.com/Riverstone-Audio-Matched-Fully-Tested-Platinum/dp/B01BFJDTW0

51ZIKUcs2sL._AC_SY1000_.jpg
 
According to the link I posted the simple 6j1 preamps would only be sensible with low output sources like a phone. And you can't get full output with your device using your phone. So it sounds like the one you have is indeed a different animal. Do you have a link?
 
I agree. I bought those 5654's when they were only a couple dollars. Now that they have become popular the prices have really shot up.
 
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