Aion FX - Ares Echoplex Preamp - Has anyone built it? Question about 'Full' mode

[laundryman]

https://aionfx.com/project/ares-vintage-preamp/

Project documents: https://aionfx.com/app/files/docs/ares_documentation.pdf

Has anyone built one of these?  I finished one and I'm not sure that I did everything correctly as the 'Full' mode setting adds a considerable amount of gain and overdrive.

The project documents do say (Page 2) that the Fat mode: "is more full-range than the other two. It also increases the available gain", so maybe this is as intended, but mine is adding so much gain that it sounds like an overdrive pedal on the Full setting.  The Bright and Dark settings do not come close to that amount of gain.

Just wondering if anyone else has experience with this.  I tried finding a video demo and could not find any.

Thanks.

[Carlinb17]

We're you able to measure the jfets to find ones that came close to the ones referenced in the paperwork?

Also what type of Jfets did you use

I used smd j202 and smd 2n5457 it doesn't jump the distortion to the point your describing.

[laundryman]

We're you able to measure the jfets to find ones that came close to the ones referenced in the paperwork?

Also what type of Jfets did you use

I used smd j202 and smd 2n5457 it doesn't jump the distortion to the point your describing.

I used a 2N5484 and a 2N5485 (non-smd) that I ordered on eBay from someone in North America.  That could very well be the cause, I knew ordering off of eBay was a risk when I did it.  But I have them both socketed on the PCB so it's an easy substitution if so.

I'm not positive that I measured these voltages right, it's the first time I've tried to measure a JFET with a multimeter, but this is what I'm getting:

Q1 - 2N5484 - 2.4V
Q2 - 2N5485 - 2.6V

So it looks like I have Q2 pretty close (docs call for 2.66V), but the plans call for 1.27V for Q1.  I have a couple of extras of each so I'm gonna try swapping them out.

When measuring those voltage drops, is there a specific point that I should be placing the ground probe?  Or is any ground point the same?

Thanks

[Jarno]

So you didn't order a bunch and hand selected the best of them? That might be what is causing it, as outlined in the build doc, JFETs are pretty variable, so you need to select the right ones out of a batch.
I am building an Aion Ares myself, but am waiting on parts. With respect to FETs, I always order them with 20 or 50 at a time and then select the one which are best suited (come to think of it, I probable have a bunch of FETs so I could do this part already, waiting for the 1044 or 1045 IC which I do not have).

For the selection process you need something to measure the FET, I use a Peak Atlas DCA-75 transistor tester, if you want to use a multimeter, you'll need to make a test rig to be able to measure the parameters.

[iainpunk]

looking at the schematic, having overdrive on the fat mode isn't something out of the ordinary.
it basically overloads itself with bass, causing clipping.

what are your DC voltages on the Jfets?

cheers

[Big Monk]

I'm a little late to the party but I just built the Aion Ares as well.

Besides thinking there is an issue with the on board LED string (it didn't work no matter what I tried, so I had to jump in a separate LED and limiting resistor) the "Fat" mode (switch down) has an INCREDIBLE amount of gain as opposed to the two stock EP3 modes.

[bassrep]

Has anyone ever actually grokked this whole Gain issue? Best I can figure on the on off on, middle is not in the circuit, "up" is a bit brighter maybe but down is HAYWIRE! Crazy gain and low end?? Wassupwitdat?

[FiveseveN]

Has anyone ever actually grokked this whole Gain issue?

Yes, source degeneration and bypass caps are thoroughly understood. E.g. https://sound-au.com/articles/jfet-design.htm#s3

[mozz]

Yes the 47uf is way overkill.  Just built 2 of them and am going to pull the boards and lower that cap.  Probably 1uf. 

[antonis]

R5 & R6 could be omitted..
(no popping issues..)