Fever 6j1 Preamp Measurements and Mods. How to measure a Preamp using the Audio Analyzer Suite.
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- Опубліковано 26 жов 2023
- 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.
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.
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…
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.
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?
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 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.
After modding them to lower the output impedance, can I connect two of them in series and make it into a valve distorter?
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 .
What did you do to reduce the bad ac hum?
Thank you so much for the thoroughness and the opportunity for learning!!!
Wow your modifications have make this pre amp so much better. Amazing!
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.
Excellent exploration of that circuit! With very practical experimentation!
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).
Great news, looking forward to the new version of AAS!
thank you so much for sharing your knowledge and your software! it will certainly ensure some well spended time on my weekends ahead.
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.
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.
Thanks Jake, for the guide I have the preamp and wanted to mod it.