Dynamic Bass Envelope Filter Problems

niagra · Post by **niagra** » 26 Jul 2016, 14:45

Hi all,

I've just started building a couple of pedals and am hoping I can get some help with the problems with the current build. The schematic is here:http://pedalparts.co.uk/docs/BassBalls.pdf

I have followed the instructions carefully and assembled the pcb and wired up a battery. I tested it and it all worked fine. I then took out the battery and replaced it with a 9v DC connector, mounted it in the case and retested it. All I got was an electrical hum. So then, I swapped the DC connector back for the battery; now I have absolutely nothing - no sound at all!

I have the following voltages:
power 8.45
ground 0
IC1
1 1.0
2 1.1
3 4.1
4 0
5 0
6 0.8
7 0
8 8.45

IC2
1 4.2
2 4.4
3 4.2
4 0
5 4.2
6 4.2
7 4.2
8 8.45

I can't believe I had it working and then it all went wrong. Could the DC voltage/current have burned a component out?
Many thanks for any help given

Dario

deltafred · Post by **deltafred** » 26 Jul 2016, 15:40

Is your PSU definitely DC, some are AC, and if DC the correct polarity. If it is AC or incorrect polarity then it is almost certain that it was the cause of the damage as there is no reverse polarity protection on the circuit. Check (or substitute with known good) all transistors, opamps, and C14 and C15.

Is it stabilised, it may be marked as 9V but if unstabilsed that is under a certain output current, at lower current the output voltage can be appreciably higher (I have seen as high as 13V). If higher than 9v there is a possibility that this has damaged something.

I would suggest that you check the polarity and output voltage at no load with a multimeter then get back to us.

niagra · Post by **niagra** » 26 Jul 2016, 16:09

Thanks for the reply.

It says on the plug output DC 300mA and at the 9v setting (it has settings for 3; 4-5;6;9;12) it's putting out 15v. I changed the setting to the 12v and it now registers 20v. I tried all the other settings and it stays at 20v. I take it that the adapter is knackered? It is dated 1986!

What are opamps?

How can I check if the components are damaged?

Cheers,
Dario

deltafred · Post by **deltafred** » 26 Jul 2016, 16:51

niagra wrote:What are opamps?

IC1 and IC2.

20v is a bit high and the hum when you plugged it in is worrying. Best place for that is in the rubbish bin before it does any more damage.

Looking at your voltage readings I would guess that IC1 is faulty. (But as always fault finding over the net is difficult, there is no substitute for having the unit in front of you.)

Did you fit IC sockets, if not I would strongly advise it when you remove IC1, makes any future fault finding a lot easier.

niagra · Post by **niagra** » 26 Jul 2016, 16:57

Poo.

Better get myself a multiple power supply then. The kit included sockets, which are soldered to the board and the ICs piggy-back those - is that what you mean?

Thanks for your help,
Dario

deltafred · Post by **deltafred** » 27 Jul 2016, 08:03

Yes get a proper power supply, saves a lot of trouble.

Your ICs are already socketed, on reflection it would be stupid to sell a kit with the ICs soldered in directly.

niagra · Post by **niagra** » 29 Jul 2016, 17:30

Thanks for your help deltafred. Received some more bits today and swapped the IC with the low readings, and it now works fine.

deltafred · Post by **deltafred** » 29 Jul 2016, 17:57

Good to hear you got it fixed.