Morning glory volume issue

[pingponggwen]

Hello guys,

New on that forum and I see great things to learn!

I need help to debug a morning glory. The pedal worked well, since I changed a cracking jack the volume goes very weak.

I checked with the audio probe and the sound is good through the circuit until Q1.

Firstly I changed Q1 but same thing: the volume is dropping, very weak but still present.

I removed Q1 and in fact the volume is dropping between R14 and R15. (Volume is ok between C12 and R14).

First time I'm facing sort of problem, I'm wondering if the ground is the cause.

What's need to be checked now?

Big thanks.

[antonis]

Hi & Welcome..

I'm wondering if the ground is the cause.

On the contrary..
(in case of R15 not grounded, you should experience no volume drop on R14/R15 junction..)

Could you check volume difference between Q1 Gate and Drain..??
(Drain volume should be higher than that on Gate..)

P.S.1
Are you sure about R15 proper value..??
(there is strong possibility for "something" dominating its actual value..)

P.S.2
Those, residual from tube amps, blocking distortion resistors do more harm than good (sometimes)..

[pingponggwen]

Hi,

I checked R14 and R15, the values are correct.

There is no volume difference between gate and drain, that's why I was thinking JFET was the issue.

Nevertheless without the transistor, I should'nt have volume drop. Or I need to have a look between the tone pot and R14... (a voltage maybe?)

[antonis]

I checked with the audio probe and the sound is good through the circuit until Q1.

Does the above stand or not..??

[pingponggwen]

Yes the sound is the same from LM833 output to R14 

[antonis]

Then focus on R14/R15 junction..

Short R14 and probe on R15 upper leg..

[pingponggwen]

It's a SMD board I'll see how to short it (any advice?).

Just a question before welding: R14 is right at 68k, is it possible for a resistor to fail and keep its correct value?

[duck_arse]

The pedal worked well, since I changed a cracking jack the volume goes very weak.

also welcome. show us photos, please. I rekon the problem might be your jack or rewiring.

[pingponggwen]

When changing the jack I only cut wires and resolder.

Here are photos of the board

[Matthew Sanford]

Not much after Q1, but I'm wondering which jack was cracking? Was it the output jack, or the dc jack? Is the VCC at the top end of the drain resistor showing full VCC? If it was the output jack, is the shield connected to ground? I would look for continuity issues around those parts at the output end...

[pingponggwen]

I checked ground/shield and everything is ok.

VCC is at 9v on Drain, other voltages are good (Vd 4.5V)

I will replace the tone pot because there are some "blocking points" into it, it's used. Even though its resitance is correct do you think that pot can cause that problem?

I was wondering the role of Q1 in that circuit (I think the small attenuation before it souhld be normal if this transistor amplify the signal)?

[antonis]

I was wondering the role of Q1 in that circuit

It pretends to be Tonestack loss recovery CS amp..