Fever 6j1 Preamp Measurements and Mods. How to measure a Preamp using the Audio Analyzer Suite.
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- Опубликовано: 29 сен 2024
- Detailed review and measurements and modifications of the $10-15 Fever 6J1 Tube Preamplifier using the Audio Analyzer Suite together with the Analog Discovery. Taking it from "not so good" to "much better" with a few cheap modifications.
Note: I'm using a new version of the Audio Analyzer Suite that will be released shortly.
Download the pdf document with my notes here:
dropbox.com/scl/fi/hokdvv2t55oxwh8x6ygll/Fever-6j1-Preamp-Measurements.pdf?rlkey=bfa94t1p8yh9ofn526au9pjek&dl=0
I have updated the description with the download link for the document with my measurement notes. Also note the new version of the Audio Analyzer Suite hasn't been released yet, still doing a bit of testing and some minor adjustments. Plus I want to make some plugin boards available for the various types of measurements.
Thanks! :)
Awesome!
Thanks!Awesome news:)
Thank you so much. So glad to see this project is still alive! Without doubt, AAS is the best and most practical software for audio testing. You deserve an award for services to the electronics industry.
Fascinating....cheers!
Thanks!
Outstanding work turning this preamp into something that performs so well for so little money! I just ordered one of the kits and will add all your mods.
Also, thanks so much for your continued work on the AAS program. Will the updates work with the Mk1 version of the Analog Discovery?
Thanks, yeah it's a fun little tube preamp. I still use my Analog Discovery 1, and the software will work with all 3 versions.
Cheers,
Jake
Wow your modifications have make this pre amp so much better. Amazing!
I look forward to the updated version of AAS . The current version is great and you've made it better. The AD2 combined with your software is a great tool.
Thank you so much for your effort.
Thanks, yeah I think is was a success modifying this little preamp. The new version will be released shortly.
Cheers,
Jake
Such an amazing video, congratulations. The Audio Analyzer Suite version that could be seen in the video looks very nice. Very promising the thd real time measurements in the Spectrum Analyser tab.
Thanks for sharing with the community this awesome software. Have a happy new year🎉!!
Thanks, happy new year to you too, well in a day or so :)
Olá bom dia, comprei dois kits e vou melhora-los com a sua sugestão, obrigado.
Amazing you've been still working on the suite. Do you have a donation link?
Nice. I can hardly wait for the update of the software and whatever accessory boards you make. I started designing tube amplifiers in the 60's as a teen and got shocking results! Just kidding 😀. My first "stereo amplifier" was a dual 20W chassis. I ended up spending over a dozen years with audio stuff, including various transistor and later OpAmp amplifiers, some low power, some high. Anyway, the tube stuff (using 12AX7s / 12AU7s / ECC83s @ 90 -110 VDC) tended to have a nice little white noise "hiss", the semiconductor stuff had some 60 / 120Hz hum. About 1/2 the hum was from poor shielding, the other half due to not enough capacitance for filtering (very few low voltage i.e.35-50V electrolytics with high capacitance values existed so I was stuck with using a large fistfuls of 40 uF / 350V caps).
To other viewers: Spoiler Alert: decades of experience reveal that tube amplifiers have a sound which is "smooth" and "soft", due to slow transient response and "soft clipping" / saturation resulting in even harmonic distortion. While this is pleasant to most, it is in fact a high level of distortion from the original audio signal. With low power output, using sensitive headphones, with a dynamic restricted Class A tube amp with a cathode follower output, they can sound very nice indeed. If you are going to use speakers, the distortion out of the power output tubes and output transformers is 100-1000 times greater than even inexpensive Transistor / IC amplifiers available everywhere today.
Excellent exploration of that circuit! With very practical experimentation!
Loving this channel. Any chance you might update the software to work with the Discovery 3? I just got one I tried the software but I'm not sure it's working right.
Hi, can you share more details on what errors you're getting? I don't have an AD3, but I have had several people confirming they got it running with the AD3.
Cheers,
Jake
Absolutely wonderful software, please keep up the good work it is appreciated. I know that the AD2 has differential inputs. I think the signal generator is unbalanced. It would not be difficult to build a low distortion balanced sig. generator from the AD2. Would this setup work for balanced audio equipment measurements and would your great software give the correct measurements. Thanks again.
Thanks, yes you can use a couple of opamps to make the outputs balanced, but you will probably end up with double the output voltage, so either just keep that in mind or add some attenuation. Otherwise it should be fine, just make sure not to use the BNC board as it shorts the negative inputs to ground.
Cheers,
Jake
Thanks Jake I will give it a go. Steve
Excellent video!
Is there a new version of the audio analyser suite? The video shows version 1.5. Great software.
Thanks, yes this is a new version, I haven't released it yet, still doing a few minor changes and bit of testing/debugging. However it's nearly ready for release.
Cheers,
Jake
Thank you for the great video! I’m glad you keep this project going.
Hello and thank you very much for the excellent review
I have the preamp being tested which I purchased after reading very positive opinions on its sound especially in relation to its price
After this video I'm really perplexed.
How is it possible that measurements and listening differ so much?
I am referring in particular to the high noise and distortion and the high output impedance which makes this preamp difficult to pair with solid state power amps
I'm very puzzled
Could you recommend a preamp that isn't too expensive but has better performance?
thanks again and best regards
gino
Very interesting stuff, thank you! There are probably products on the market which already have the modifications and only cost slightly more, like the "FX-AUDIO TUBE-01 Valve 6J1 Stereo preamplifier", which is 30€. Seems to have film coupling capacitors and even comes with a case ;)
I doubt it will have the same modifications, film capacitors, sure, but 90% of engineers would spot that terrible mistake, the rest of the modifications will not be included and you'd be wasting a lot of money.
Cheers,
Jake
Thank you so much for the thoroughness and the opportunity for learning!!!
✌️🙌🙏
Great work as usual! Looking forward to the new version of the app and the plug-in boards. BTW would it be possible to get schematics files of the plug-in boards to make the PCB?
Looks like a lot of trouble with 12V AC and a voltage doublers instead of using a switching boost converter to convert 12V DC on the supply to 250V.
Hi , thanks for a very intersting video. I have one of these kits I have not built yet, and as you say, it seems an interesting little project to have a play with. You mention in the video that your notes will be available for download with a link in the description - it does not seem to be there as yet, could you supply the link please? Thanks in advance.
Thanks, you're correct, I have updated the description with the download link.
Cheers,
Jake
Thanks Jake, for the guide I have the preamp and wanted to mod it.
thank you so much for sharing your knowledge and your software! it will certainly ensure some well spended time on my weekends ahead.
Thanks, much appreciated. 👍
excellent video, I decided not to buy the preamp :p You pretty much solved the 99% of the issues people claim about on internet, It looked like a nice project but now I don't really see any good use for it, specially since I live on a remote area and do not have the proper capacitors for the mods (it will cost me too much just to buy all the extra components on line to fix this little circuit). Have you ever think about selling your own version of a tube preamp kit?
hi dear, is there possible to preamplifier a dynamic mic ou a guitar adapting a plug or respective cable? if yes, can wee add tube distortion?
Outstanding video! Always learning from you to get the most out of AD2. Very interested in your plug-in boards so pls notify when ready.
Great to see your work again so thank you so much. I have a few NOS army surplus solder-in vacuum tubes rescued from being thrown out that are rough equivalents to the 6J1 (EF95) so when i have a quiet moment i will put a couple to work & see what sorts of results i can achieve thanks to your SW for the Analog Discovery 2 .
Thanks, yeah these little pentodes can perform surprisingly well at "low" voltage when used as triodes.
Cheers,
Jake
Thank you so much🎉🎉🎉Best mod and test of this little preamp🎉🎉🎉 I just bought a 12v dc version of this. Very eager to try out the mod.🎉🎉🎉
Thanks, good luck with the mods.
Great news, looking forward to the new version of AAS!
Hi, my PC needs the DWF.DLL, where can I get the file please.? Thanks. David.
You have to install latest version of the Waveforms (64 bit) software from Digilent.
Cheers,
Jake
I just built up this kit using your upgrades. Works ok, but not much change to the sound of my capacitor coupled amp. Looking forward to trying it with other amps that have direct outputs. Also changed R1 from 2.2 ohms to a 3 watt 3.9 ohm. This lowered to the heater voltage to 12.6 and dropped the resistor temperature from 150f to a more acceptable 115f. Added a 220uF cap to the heater circuit and this lowered the ripple to 1.0vac from 2.25. Thanks for posting your upgrades & measurements, these seem to be the best ones I could find for the 6j1.
Update: Increased heater cap to 3300uF. Ripple voltage dropped to .24vac. Also added 470uF caps to R5/9. This lowered the 60cycle hum substantially.
Channel separation is cumulative - meaning if a record has bad separation a poor amp separation will add to that, making it even more important for sources with poorer separation performance to be matched with high precision amps. 25db channel separation means about 5.62% from each channel can bleed into the other at the source already, then if the amp stage is also 25db separation we are talking about another 5.62% bleed from each channel already now mixed with 5.62% from the previous stage. At 90db channel separation, we are talking 0.00316% channel bleed in, so a significant difference. At least that is my logic…
I'd encourage you to do a listening test and see if you can hear any difference. Perhaps use something like the Depeche Mode Black Celebration album, it's got a lot of electronic sound effects going from channel to channel, then listen to a vinyl copy, maybe using an AT95e cartridge, it's got channel separation as low as 15dB, and compare it to a digital copy.
@@TheStuffMade I have an Art 9 installed currently, but my stereo is in boxes right now, so it won't be until later this year that I can do the listening.
What an excellent video, just acquired one of these amps so I’ll have fun playing and modding! Be interested in the software suit too! God bless
Hello, can you use this as a headphone amplifier? I currently have hd560s (which by many sound very good with tube amps), a k361 which is rarely being used and an apple dongle, only point in getting this would be trying tubes on the 560s, otherwise might get the 47 classic
I have the hd560s and this unit. It barly raises volume and for me it aint loud enough without another preamp. You have to try. If you dac can run your headphones well this would add some nice harmonic flavor.
@@Pe721 yes my da can easily run them, I'm maxed on audio output on tidal, always about 40% on windows which means it can drive them with ease
@@Pe721 How does it change the sound?
After modding them to lower the output impedance, can I connect two of them in series and make it into a valve distorter?
That should work fine, but the output from the second board will be at pretty high level once you drive it into distortion, you will probably need to attenuate it.
Cheers,
Jake
@@TheStuffMade of course. So adding another volume control/pot before the pot of the power amp or audio interface?
A eq module/tone stack chould also be added in between the two stages? If I remove the input DC blocking caps, chould I use an op amp circuit to include a DC offset in the input?
I suspect running them in series without the output impedance mod is not a good idea sience I would get a lot of low frequency attenuation.
@@misterinfinity4076 Yes, I'd add a 10k volume pot on the output of the 2nd board before going into mixer/amp/audio interface. And any tone stack and equalizer either before the first board or after the 2nd board, not between. You can't remove the coupling capacitors, they are required for the tubes to operate.
Cheers,
Jake
@@TheStuffMade thank you so much for the tips and video.
I mean converting the output of the AD2 from unbalanced to balanced.
What did you do to reduce the bad ac hum?
Thanks for the test data. I have a formal background in engineering, got through all the fundamentals in the tube family in school, but bought the kit to finally have some first hand experience before getting into designing my own from the ground up.
*The 2nd transistor in that particular architecture is for voltage regulation BTW.*
It's used in solid-state schemes as well. It's collector is tied into the base of TR1 so it shifts it's input base bias current with the constantly changing input signal swing.