Morning Glory V3 Clone JFET Issue

[adbernal]

Hi all,

I'm building a dual OD with Klon and Morning Glory following the layouts from Effectslayout (http://effectslayouts.blogspot.com/search?q=morning+glory). KLON is working great but the MG is giving a glitchy, low output with knobs up all the way. Here are my voltages (+/- a 1/4 of a volt):

IC (LM833N)
1-4.25
2-4.25
3-4.25
4-0
5-4.25
6-4.25
7-4.25
8-9

Q1 (1N5458, no 2N5457's on hand):
G- 0
S- 2
D- 6

I went in with the Audioprobe and the weird glitchy signal starts before the second opamp stage once I cross the 10k resistor after the drive pot and 100nF capacitor which confuses me because otherwise I would think this is a JFET biasing issue. I cracked open my real deal MG v4 and the 2n5457 in there reads:

G-0
S-1.5
D-7

Soooo... I only have a handful of 1N5458's and SMD J201's and they are all reading roughly the same and Im making this for a buddy who wants it soon. Would it be possible to change the resistor values to properly bias the 1N5458's that I have? Or because the audioprobe showed the weird signal starting before the second opamp stage that something is awry there?

Im really confused and I hope that you can give me a good lecturing here Perhaps its a combination of a cold solder joint causes the buzzing and the misbiased JFET causing the low output? Picture attached although im already a full day into messing with this board so I apologize for the ugliness.

[PRR]

> Morning Glory

https://i.postimg.cc/dJ92gXZZ/JHS-Morning-Glory-Schematic.png

[anotherjim]

I don't think you should worry about the JFET you started with. Getting 6v on the drain is good going for this type of device. The ideal would be closer to 4.5v.

The opamp voltages are ideal. It could be an open circuit from the drive pot to the second opamp input. There can be just enough stray capacitive coupling across an open circuit for strong signal peaks (and only the peaks) to get through. You only have C8, R8 and the solder/traces to check.

[iainpunk]

that circuit board looks to have some shorts, but it could also be excessive flux, you might want to clean that off with cleaning alcohol and an old toothbrush, so you and the members here can see the board a bit clearer and maybe spot a few mistakes/bad connections.

cheers

[duck_arse]

if we could see the top of the board, we could comment on the components, wrong, backwards, missing.

[adbernal]

Thanks for your comments, you all rock! So I have:

-Brushed the board with alcohol
-Driilled a new hole for pin 2 of the B100K Drive Pot because the trace had lifted.
-Replaced C8 and R8 with tested components of the same value
-Replaced the IC--just to make sure that the IC wasn't the culprit.

And the result:

Same thing. I Audioprobed and I'm still getting that glitchy sound once I pass R8. Now , something else I noticed is that I get no signal with the Drive pot all the way down, and then loud signal when the drive pot is all the way up. Is that typical with these sorts of circuits? Just want to make sure that the issue isnt actually before the drive pot and just getting "observed" once its to that 2nd clipping stage.

I'll include more pictures, reluctantly  . I made a mistake etching this board and didn't flip the etch horizontally. So as a result I have to put my IC "upside down" by bending the legs the other way and then the JFET I put opposit. Does that make sense? It will make sense if you see the layout of it--Haha! Interested in your thoughts and once again so sorry for the mess!

[anotherjim]

Could be misleading here. When an opamp inverting amplifier is working properly, you should not find a good signal on the inverting input pin, even though it appears that is the one pin the signal is feeding! Every time signal voltage appears at the input, the amplifier reacts by moving the output pin voltage so the negative feedback (R9 primarily) counters the signal voltage. It tries to maintain the inverting pin at the same voltage as Vb on the non-inverting pin. So audio probe should find the signal on the C8 side of R8 and the amp output pin7.

"Glitchy" sound on pin6 might just mean something is wrong with the feedback path which has a lot of parts to go wrong or the output is clipping and can't produce enough negative feedback signal to keep pin6 silent.
You might temporarily simplify the second amplifier by tacking on a 10k resistor between pins 6 & 7 which makes it a unity gain inverter and see if the audio is clear at its output.

!

[antonis]

I get no signal with the Drive pot all the way down, and then loud signal when the drive pot is all the way up. Is that typical with these sorts of circuits?

With Drive pot all the way down, you should get unity gain signal, 'cause IC1A works a a unity voltage follower..
(even if Drive pot wiper can travel down to zero ohms..)

Could you please check R4 value..??
('cause  it seems to me like IC1A works as subtractor)..

[duck_arse]

like I always say - those russian germanium diodes are backwards. they mark the A with a band, so in effect, all your diodes are pointing in the same direction. unless I've misread your board.

and extra bonus points, it's very rare indeed that the unreversed etch is ever noticed, let alone the inverted opamp trick is employed.

[adbernal]

Thanks to your help, this pedal is fixed! Duck_Arse has to take the Gold, even though everyone here had some great insight. I had forgot that those Russian germaniams have the band over the anode. So that glitchy sound must because only half the waveform was being clipped as all 4 of my diodes were facing the same direction. The phenomena with the drive control may just amount to what anotherjim was mentioning with the inverting opamp? (which is fascinating... there's so much more I need to learn!).

Very grateful for you all!

[anotherjim]

Yes, the diodes limit the gain when the output signal gets big enough to make them conduct and place a stronger negative feedback to the input. The original idea of doubled LED's (if ordinary red) would limit around 6v peak to peak (LED Vf about 1.5v, 2 in series Vf=3v each half cycle for total 6v). This would reduce the chances of the opamp output clipping - it can't give stronger feedback if the output has swung to its positive or negative limit which for LM833 is about 1v away from the positive or negative supply which with 9v supply is about 7v.

[duck_arse]

I'll include more pictures, reluctantly  . I made a mistake etching this board and didn't flip the etch horizontally. So as a result I have to put my IC "upside down" by bending the legs the other way and then the JFET I put opposit. Does that make sense? It will make sense if you see the layout of it--Haha! Interested in your thoughts and once again so sorry for the mess!

was thinking bout this today. when you do an east-west non-reversal, the north-south aligned in-line parts, as is your jfet, don't need any change. so - check you datasheet for your jfet for pinout, and then check the board traces, see if you've backwarded it or not.