SOLVED: HM-2 clone, high pitched shriek when Lo is dimed

[matopotato]

Note that the two opamps are "swapped" from the schematic and layout. In the Schematic the low gyrator uses pins 5,6,7, in the layout it's 1,2,3.

The components you should check if the lows gyrator is the problem:
1.5uf electro attached to low 2
330 ohm R between 1.5uf cap and IC pin 1 and 2
68nf cap between 330 ohm and pin 3
100k between pin 3 and VB.

And hey, you haven't posted voltages yet.
did you get the "cut" between that cap and the IC? It is hiding under that 100k R next to it. There are two cuts under that R but that's the treble control side...probably not your problem.

I forgot to mention: I could not find electrolyte 1.5uF so I got a tantalum polarized 1.5uF instead.

By check I assume you mean connectivity, glitch free etc. I feel I had done it during building. And seems none of them are not as they should be.

I had another problem fitting it in the box and the "Inpüt" and "Ütpüt" jacks just ran into some caps. Among them the 68nF you mentioned. So to fix that problem, I relocated them to the other side of the board. With a few cable plastics as protectors I got 4 of them relocated.
And lo and behold, the shriek is no longer there.
If I max some pots around I do get a shriekish noise but that seems very much more like feedback. It is a powerful circuit as far as boost goes.

So, all fingers and other things crossed, I now consider it solved enough to box it properly. In my experience some noise goes away when you finally put everything in place.
Should the problem pop up again, I have some good ideas where to check.

Many thanks!

[matopotato]

A huge thanks all who helped out with tips and ideas! I really appreciate it. 
I think my friend will get his present tomorrow if the coating will dry fast enough. 

[ElectricDruid]

A huge thanks all who helped out with tips and ideas! I really appreciate it. 
I think my friend will get his present tomorrow if the coating will dry fast enough. 

Don't rush it!

I once did a pedal in hurry like this for a friend's birthday, and it finished up having fingerprints in the clearcoat because it was still a bit soft!! I should have baked it or something! It would have been better to have waited a couple more days and done a better job.

[matopotato]

Thanks.
I usually wait a few hours after print. At least overnight and some after coating. Then at least half or a day for the water to get out. Cut holes and last coating overnight or a bit more.
I think I have previously rushed most stages at some point so I try leave it some time.
But thanks for the warning. Very valid point.

[matopotato]

I works! Not as chainsaw as I had hoped, but tons of output, and no shriek.



A bit tight, but I could improve planning for sure.

[duck_arse]

Those kind of high gain circuits on strip board with lots of wires are notoriously sensitive, but usually it is the treble pot that sets them shrieking. Have you tried moving the pots and wires, around, separating them from the board and each other?
Even the footswitch can be a site for mischief. Better to test before you wire those up!

Thanks, yes enough cable to keep them away from each other.
And yes I agree, it sparkles when you touch wires and move about so quite sensitive.

can I ask - whatchoo mean when you say sparkles? flashes of light or sound?

[iainpunk]

I used LM358s for ICs after recommendation on the blogsite.
...

My pre-studies suggest that these options should wotk ok at least. The ICs might even be better than M5216L as the original indicated.

my heart skipped a beat when i read this, for 99 out of 100 pedal designs, the LM358 is specifically awful, as it produces crossover distortion... but this pedal generates additional crossover distortion on purpose anyway, so adding more doesn't ''ruin'' the tone.

cheers

[matopotato]

Those kind of high gain circuits on strip board with lots of wires are notoriously sensitive, but usually it is the treble pot that sets them shrieking. Have you tried moving the pots and wires, around, separating them from the board and each other?
Even the footswitch can be a site for mischief. Better to test before you wire those up!

Thanks, yes enough cable to keep them away from each other.
And yes I agree, it sparkles when you touch wires and move about so quite sensitive.

can I ask - whatchoo mean when you say sparkles? flashes of light or sound?

Sound. Sorry, English not my mother tongue. Sometimes I sort of direct translate. And this happens

[matopotato]

I used LM358s for ICs after recommendation on the blogsite.
...

My pre-studies suggest that these options should wotk ok at least. The ICs might even be better than M5216L as the original indicated.

my heart skipped a beat when i read this, for 99 out of 100 pedal designs, the LM358 is specifically awful, as it produces crossover distortion... but this pedal generates additional crossover distortion on purpose anyway, so adding more doesn't ''ruin'' the tone.

cheers

Ok, I went by the discussion on the tagboard blog page where the LM solved problems of noise. At least that sounded as the consensus. I suppose TL072 would be more noisless, but the M5216L were considered the worse option.
Who knows, maybe even Metalheads have a distinction between chugg and noise? We'll have to ask Ola Englund 

[PRR]

...the LM358 is specifically awful, as it produces crossover distortion...

Not if the load is over maybe 50k.

My first project with the quad LM324 worked fine into a hi-Z input, obviously nasty into a 500 Ohm equalizer. I hacked a fix on tight deadline and moved on. But later I saw other people using the LM324 without complaint. I realized that many of these were real lightly loaded. (The others were, as you say, distortion boxes.)

[matopotato]

...the LM358 is specifically awful, as it produces crossover distortion...

Not if the load is over maybe 50k.

My first project with the quad LM324 worked fine into a hi-Z input, obviously nasty into a 500 Ohm equalizer. I hacked a fix on tight deadline and moved on. But later I saw other people using the LM324 without complaint. I realized that many of these were real lightly loaded. (The others were, as you say, distortion boxes.)

Is there some way to measure the actual input and oitput impedance of a pedal. I have a DMM pretty standard, and I think impedance and resistance are possibly 2 different things. Impedance relate to AC and resistance to DC roughly. And more than resistors have influence in AC.

[antonis]

I think impedance and resistance are possibly 2 different things. Impedance relate to AC and resistance to DC roughly. And more than resistors have influence in AC.

Resistors exhibit the same constant resistance both for DC and AC..
(at least, for frequencies where not modeled as series inductor and parallel capascitor besides their natural resistance..)
https://resources.system-analysis.cadence.com/blog/msa2021-understanding-resistor-behavior-at-high-frequencies

Is there some way to measure the actual input and oitput impedance of a pedal. I have a DMM pretty standard

A brute (but easy and convenient) way is to place a high value pot, wired as variable resistor) between signal source and impedance for measurement..
When signal's amplitude is halved, take pot out of circuit and measure its resistance..
The result reflects input impedance at question..
Of course, you can obtain the same with just a single series resistor of value about equal to estimated impedance (or any other value) but you'll have to deal with voltage divider Thevenin equivalent calculation..

[matopotato]

I think impedance and resistance are possibly 2 different things. Impedance relate to AC and resistance to DC roughly. And more than resistors have influence in AC.

Resistors exhibit the same constant resistance both for DC and AC..
(at least, for frequencies where not modeled as series inductor and parallel capascitor besides their natural resistance..)
https://resources.system-analysis.cadence.com/blog/msa2021-understanding-resistor-behavior-at-high-frequencies

Is there some way to measure the actual input and oitput impedance of a pedal. I have a DMM pretty standard

A brute (but easy and convenient) way is to place a high value pot, wired as variable resistor) between signal source and impedance for measurement..
When signal's amplitude is halved, take pot out of circuit and measure its resistance..
The result reflects input impedance at question..
Of course, you can obtain the same with just a single series resistor of value about equal to estimated impedance (or any other value) but you'll have to deal with voltage divider Thevenin equivalent calculation..

Thanks, I think I  will have a problem knowing "half"volume. Especially since I thought it being logarithmic.

[antonis]

Thanks, I think I  will have a problem knowing "half"volume. Especially since I thought it being logarithmic.

Volume is considered signal's amplitude (voltage..!!)
You don't have to "translate" it at dBs 'cause you don't address to engineers..

Just measure AC voltage at signal source output and effect input..

[matopotato]

Thanks, I think I  will have a problem knowing "half"volume. Especially since I thought it being logarithmic.

Volume is considered signal's amplitude (voltage..!!)
You don't have to "translate" it at dBs 'cause you don't address to engineers..

Just measure AC voltage at signal source output and effect input..

Ok, I have a tonegenerator. So I can measure AC voltage from that machine?
And measure at pedal input. But with cable, so open box I guess. And then I  an calculate impedance?
I actually have a strobe, but only 1 channel.
Sorry for my ignorance. I could probably ha e googled as well...

[matopotato]

I found this link which should be useful for the details
https://www.diystompboxes.com/smfforum/index.php?topic=57305.0

[antonis]

I found this link which should be useful for the details
https://www.diystompboxes.com/smfforum/index.php?topic=57305.0

Just do what R.G. says in his 1^st post..

[PRR]

....I think I  will have a problem knowing "half"volume. ....

Trust your ears. There's two main zones: >90% of volume, and <10% of volume. "Down a little, not a lot." You never need to know with great accuracy. It WILL be different bass and treble so your musical brain is needed to judge the effect.

[matopotato]

I found this link which should be useful for the details
https://www.diystompboxes.com/smfforum/index.php?topic=57305.0

Just do what R.G. says in his 1^st post..

Is Vs AC i.e. tonegenerator signal
Or DC, like 9V?
I thought Vin would be 9V with +/- and the Vs be an AC signal of sorts with varying frequencies to get some spectral view.

[antonis]

Forget all about DC here..
Impedance hates DC 'cause it neutralizes reactive components..
(caps turn into open circuit and inductors to short circuit.. - resistors, frankly, don't give a damn..)

Vs is signal amplitude and Vin is a portion of Vs, according to above mentioned formula..

About spectral view: IMHO, 3 measuremets at lower, higher and mid-band frequencies of interest should be adequate..