| Author |
 Topic  |
|
|
funkyjunky
Copper Member
Brazil
8 Posts |
 Posted - 02/26/2010 : 01:33:45
|
Cheers from Brasil! =) Old forum reader, but new member here! 
Need some help! Searched all the forum and couldn�t find anything like this! Just got an old DD-3, with the long Roland IC, rev.1, and with a very unusual problem. It works just fine, but when it�s in off position, and you hit a string a little harder, some wet (delay) signal leaks and gets mixed with the dry signal. Maybe some FETs? Leaky or dry caps?
Thank you! Keep up the good work! |
Edited by - funkyjunky on 02/26/2010 01:36:45 |
|
|
Dr. Bob
Moderator
Australia
6593 Posts |
Posted - 02/26/2010 : 08:38:37
|
Hi funkyjunky
Welcome to the forum form Australia.
Regards Dr. Bob  |
 |
|
|
Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 02/26/2010 : 14:31:56
|
quote:
Originally posted by funkyjunky
Cheers from Brasil! =) Old forum reader, but new member here!
Need some help! Searched all the forum and couldn�t find anything like this! Just got an old DD-3, with the long Roland IC, rev.1, and with a very unusual problem. It works just fine, but when it�s in off position, and you hit a string a little harder, some wet (delay) signal leaks and gets mixed with the dry signal. Maybe some FETs? Leaky or dry caps?
Thank you! Keep up the good work!
Welcome!
The effected sound is all passed through Q8. Disconnect wire #13 and try it - does it still happen? |
|
|
|
funkyjunky
Copper Member
Brazil
8 Posts |
Posted - 02/26/2010 : 16:26:13
|
Thank you Dr.Bob, Laurie! 
Ok Laurie, thanks for the reply.
Just disconnected wire #13 (E.Level middle lug). No delay effect when is on, which I suppose it�s OK, since there is no wet signal coming through from wire #13 to output. The good news is that the "leaky" delayed signal, stoped. It makes me wonder...bad pot? maybe C13 (1uf)?
|
|
|
|
Dr. Bob
Moderator
Australia
6593 Posts |
Posted - 02/26/2010 : 16:46:17
|
Hi funkyjunky & Guys
Do you have a schematic to work from?
You can find one here for the DD2 ... (Plus many others)
http://www.freeinfosociety.com/electronics/schempage.php?cat=1
The DD-3 long chip is almost identical to the DD-2,
with the addition of the extra output,
& some simple opamp buffering to support the extra output.
Do you have any, & what type of test gear?
Regards Dr. Bob |
Edited by - Dr. Bob on 02/26/2010 16:47:46 |
|
|
|
funkyjunky
Copper Member
Brazil
8 Posts |
Posted - 02/26/2010 : 17:00:24
|
Hello Dr.Bob!
Working with DD-2/DD-3 schematic. Using a digital multimeter, pc audio card signal generator.
Just replaced C13, and nothing. Working on Q8/D4 "neighborhood" right now. Q8 is K118 (2SK118?) and not 2SK30A, like the schematic. More updates soon!
Thank you guys! |
|
|
|
funkyjunky
Copper Member
Brazil
8 Posts |
Posted - 02/26/2010 : 18:22:13
|
OK...some updates...
Checked Q8 and everything around. (C28, C29, R37, R38, D4) all in shape. Changed Q8 with another K118 and a 2SK30A.
With 2SK30A, things got weird, more leakin delayed signal. With K118, same as the original transistor, leakin, but not so much.
Going down to Q5 and 5218 IC.  , but first, try a new E.Level pot. Who knows!? |
|
|
|
funkyjunky
Copper Member
Brazil
8 Posts |
Posted - 02/28/2010 : 03:45:18
|
I got nothing
Any suggestions? |
|
|
|
Dirk_Hendrik
Copper Member
Netherlands
28 Posts |
Posted - 03/03/2010 : 16:46:06
|
| Check the voltage levels on the drain ad source of Q8. They should be half VCC. What you describe suggests thes voltages are off spec, causing the FET not to close completely. |
|
|
|
funkyjunky
Copper Member
Brazil
8 Posts |
Posted - 03/03/2010 : 23:26:52
|
Hello Dirk! Thanks for the reply!
Just checked Q8 Drain and Source.
With a 8,90V power supply, I�m getting half VCC on D and S. Looks good to me.
I�m starting to think that, maybe there�s a problem with the electronic switching parts. Around diodes, fets and BA634. Since I get this "leakin" with delayed signal when effect is OFF, I noticed that, when the effect is switched ON and then OFF, the wet (delayed) signal goes on, fading away until it stops. It just doesn�t stops immediately.
What do you guys think?
Cheers!  |
|
|
|
Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 03/04/2010 : 00:14:53
|
Wet signal will go away over time - is it "soft switched". There is an RC network and a time constant around (IIRC) 100ms.
If you can actually hear it fading, there might be a problem with the RC network driving the gate.
|
|
|
|
funkyjunky
Copper Member
Brazil
8 Posts |
Posted - 03/04/2010 : 00:27:02
|
Hello Laurie,
You mean the gate of Q8? |
|
|
|
Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 03/04/2010 : 02:29:43
|
| Yes. R36 and C27 for an RC network with a time constant of about 50ms... definitely too fast to hear. So if you hear the echos fade after switching, maybe there is a problem with the gate drive to Q8. |
|
|
|
funkyjunky
Copper Member
Brazil
8 Posts |
Posted - 03/04/2010 : 20:58:21
|
Hello!!
Laurie, thanks for the advice.
Just checked R36 and C27, the RC network. All good, no problem at all!
This thing is driving me crazy!!
Another thing... can I use 1N4148 in place of the ISS133-T77 diodes? They�re both switching diodes.
Cheers! |
|
|
|
Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 03/04/2010 : 21:22:53
|
quote:
Originally posted by funkyjunky
Hello!!
can I use 1N4148 in place of the ISS133-T77 diodes? They�re both switching diodes.
I've successfully done this. |
|
|
|
Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 03/04/2010 : 21:27:24
|
Measuring the DC bias voltage at the gate of Q8 is tricky. Most mulitmeters have too low an input impedance, so you get a material drop across the meter itself giving an incorrect reading. This happens because the meter is connected to the drive voltage through the 1M gate resistor and it will act as a voltage divider with low impedance meters.
You will need to use a very high quality meter for this measurement - I have three meters but the only one that gives the correct bias reading of the FET gates is a Fluke 73.
|
|
|
| |
Topic |
|
Unusual DD-3 problem
