Small Clone Problem... Not Chorusing

[John Egerton]

Hi guys, have a slight problem...

I've had a completed small clone circuit for a month now with the exception of the MN3007 IC.

I was very excited to find the IC in the post from small bear (Great service ) and when testing the circuit I noticed that there was no chorus sound,it just sounded like its in bypass mode... When I alter the trim I hear something but other than that, it just sounds like its in bypass... On certain settings of the trim the clean sound kinda gets a little distorted...

Any help would be appreciated guys..

Thanks in advance

John

[Mark Hammer]

In principal, adjusting the trimpot should affect only the delay signal since you can see that there is a capacitor in between where the bias voltage is "inserted" and the point where the dry and wet split off in different directions.  That cap will block DC so trimpot adjustments should not make the straight signal change in any audible manner.

On the other hand, the trimpot DOES have the effect of bringing the DC voltage that the audio signal needs to ride on to make it through the BBD up to the appropriate level.  If it is off a bit, you will hear this as a distorted delay sound.

Which leads me to think the following, namely that your delay chip is essentially fine but is not being swept.  Perhaps the problem or stickingpoint is in your LFO.  So, with that inmind, you should take your meter, turn down the Rate so that it is slow, and measure the DC and AC voltage at pin 1 on that dual op-amp that makes up your LFO.  It should fluctuate appropriately in a manner that approximates the LFO change and be at least a couple of volts.

[John Egerton]

I don't have a multimeter yet...

Is there any chance of using an audio probe?

Thanks

[John Egerton]

The epdal still doesn't work however I think I'm closer to solving it than I was before...

I noticed that there were two small holes in my PCB where a part was supposed to go.. In the top right corner of the tonepad parts layout for the small clone there is a 150pf capacitor that is not indicated on the parts list!

anyway I didn't have one of these so i used some random capacitors in its place, i'mn not too good with capacitor markings however I used one with 153 marked on it...

Anyway, with nearly all the capacitors i got an ocilating noise which its rate increased with the rate pot (duh). Weird thing is that if a strum a pattern out on the guitar, about 3 seconds later a muffled distorted delay signal appears and matches the rhythm of the guitar, almost like a delay pedal with a  high delay time....

Any suggestions? Could it be the incorrect capacitor? Please could you give me the correct marking for the 150pf?

Thanks..

John

[Joep]

Hi,

You have to look for a cap marked 150 or 151 (where the last 1 indicates the number of zero's you have to add to 15)

If you don't have a 150p you can try 100p or 220p, to at least verify if the circuit works, in the end you can replace it with the proper value.

If I remember well this cap has influence on the depth of the effect....

Bye,

Joep

[John Egerton]

Thanks for that...

Also, on the parts list there is a 100pf cap and it is nowhere to be seen on the parts layout

So do you think that putting the correct value capacitor will solve the current problem?

Like I said, the effect still sounds like its in bypass, however there is also that occilating noise and the distorted 3 second delay, however the last two only happen if a capacitor is in there however I'm not sure on their values...

Thanks

John

[Joep]

I would try that 100p in place of the 150p, this will get the effect running....

[Mark Hammer]

Yikes!!!

That 150pf cap is absolutely essential to having a functioning clock, and a clock is absolutely essential to having the signal move from one stage/bucket to another in a BBD.  No wonder it wasn't working.

You can probably use anything between 82pf and 330pf but they will have different types of sounds because they will shift the delay time shorter (with smaller values) or longer (with higher values).

Joep is correct.  If the cap is not known to be in that range by virtue of packaging or what you requested at time of purchase, the third digit can often be relied on as a multiplier for the first 2 digits.  So "331" is 33 with a single '0' after it, or 330pf.  A cap of 332 will be 3300pf or .0033uf.

[John Egerton]

Ok, I put the 150pf cap in and the thing now works however I'm having trouble getting it to sound ok......

What does the trim do and how should i set it...

At the moment I get a kind of occilating/theremin type of sound which gets to a certain pitch and then cuts out, starting again a second later.... I can adjust the trim to stop the sound however when i switch the spst switch it starts again on the other setting...

Any suggestions???

Thanks

John

[John Egerton]

Does anyone have any suggestions for me? I'm literally sat here with my iron waiting for input...

[Joep]

Hi John,

Do you hear the chorus effect or do you only have the sound you describe above?

I looks like to have some bleedthrough of the clock signal driving the BBD.
Check your wiring (move it around a bit) or the PCB for solder bridges.

Hope this helps....

Joep

[John Egerton]

Funny how some things turn out.. It seems that my 9v battery was running out... I've plugged in a power supply and everything is fine...

I am still wondering how to set that trim though.. any suggestions???




John

[Joep]

If I rememeber well from my Small Clone the trim didn't do much so I set it in the middle position.

Good to hear it is working!

Joep

[John Egerton]

Thanks Mark and Joep

I'll make sure to post some pictures of the finished article once its done....

Thanks again...

John