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tony
Bronze Member
United Kingdom
142 Posts |
 Posted - 08/17/2008 : 16:57:25
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quote:
I picked up a good used Tektronix 2-trace CRO for $100 last year on ebay... Cheaper than a replacement delay pedal 
Particularly when that pedal is a "mint" DD 2
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 08/17/2008 : 17:09:24
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quote:
Originally posted by tony
Laurie, There's a lot of interference with the cable, also the room I'm doing this in is bad in general. I just got a bit of a "window" when the interference went very quiet and I tried all measurements again and found the following:
R44 - Clean signal, one clean repeat.
Both sides of C34 - the same.
Pin 10 - there is actually a signal - the single repeat, but it's very quiet - the same level as plugging in the pedal.
I guess what's happenig is that every time the repeat comes into the NE570 it's being crushed, so the delays disappear almost immediately- but it CAN'T be the chip now.
I feel we're really, really close. AAAArrggh!!!
The feedback "drive" comes from VR-2... which is driven (eventually) by pin 10 of the NE570. The output from the NE570 is fed back into the compressor side of the 570 (and thence to the digital circuitry - to create repeats) via VR-2. If there is no signal coming from pin 10 (or very little) then there is nothing being sent back through VR-2, so there are no repeats...
It all comes back to no/low output from pin 10 of the NE570. If the signal at pin 10 was at the same level as the signal going in at pin 14, then it should all work... I am seeking an epiphany, but it's not coming. There is nothing that tells me it is something other than the NE570 (or surrounding circuitry).
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tony
Bronze Member
United Kingdom
142 Posts |
Posted - 08/17/2008 : 17:27:42
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I definitely think we've (OK, mostly you've) isolated the problem. It can't be anything else.
However, everything around the NE570 on the expander side is dead in spec. I don't really know what the 2 - odd volts across C20 mean but I'm sure they're fine. I also get perfect readings from this new chip - exactly 9v in, etc. Was the 0v to ground out of pin 4 an issue or just a speculation about something? - because that is exactly zero volts now, whereas before it was about 1.5v
I've got a mind to order a couple of NE570's from Small Bear or Banzai effects in Germany and just try them out - for peace of mind. If I plan to do more of this in the future I'm sure they'll come in handy. |
Edited by - tony on 08/17/2008 17:29:13 |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 08/17/2008 : 17:32:27
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quote:
Originally posted by tony
I definitely think we've (OK, mostly you've) isolated the problem. It can't be anything else.
However, everything around the NE570 on the expander side is dead in spec. I don't really know what the 2 - odd volts across C20 mean but I'm sure they're fine. I also get perfect readings from this new chip - exactly 9v in, etc. Was the 0v to ground out of pin 4 an issue or just a speculation about something? - because that is exactly zero volts now, whereas before it was about 1.5v
I've got a mind to order a couple of NE570's from Small Bear or Banzai effects in Germany and just try them out - for peace of mind. If I plan to do more of this in the future I'm sure they'll come in handy.
You had me going for a second... it was actually 1.5 Ohms to the pedal case - which is comfortably close to 0. No problem. It should be 0V exactly, so it's all good.
I can't see that the new NE570 would have exactly the same failure mode as the old one (if it actually was faulty - which it doesn't appear to have been).
We are looking for something else... |
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tony
Bronze Member
United Kingdom
142 Posts |
Posted - 08/17/2008 : 18:22:56
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quote:
You had me going for a second... it was actually 1.5 Ohms to the pedal case - which is comfortably close to 0. No problem. It should be 0V exactly, so it's all good.
Sorry, I meant ohms. Maybe it's time to think about something else for a while!
I don't seriously think it is the NE570. It's just, the signal goes in good and comes out bad. With no indication of any failed components connected to it (at least thatI have the ability to test for).
So, could we be looking for something that would affect the gain of the NE570? Could those tanatalum caps going into what is on the datasheet as "rectifier cap in" (pins 1 and 16 have any effect on that? Or is this just wild speculation? |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 08/17/2008 : 18:35:38
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It cant hurt to change C33.
EDIT: just had ANOTHER look at the data sheet. It doesn't say anywhere what the measured averaged voltage should be on pin 16, but it's clear if it is too low, the gain will be lowered. Change C33 and see if something magical happens. |
Edited by - Laurie on 08/17/2008 20:11:08 |
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tony
Bronze Member
United Kingdom
142 Posts |
Posted - 08/17/2008 : 20:22:25
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Am definitely going to do that. Unfortunately .68uf caps seem to be pretty hard to come by. RS components, the best place in the UK to order stuff from, is the only place I can find them and they have them listed as a special order with a minumum buy of 1000 pieces, which might exceed my requirements slightly!
Banzai effects in Germany are really good, sort of the European Small Bear. Takes about a week to get stuff though. They've got small Panasonic film caps in that value.
Not after any odd value caps, etc. that you can't be bothered to special order and not in a rush for are you? Adding them to the order and sending them on to you would be the least I could do.
Now we play the waiting game(!)......
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Edited by - tony on 08/17/2008 20:26:44 |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 08/17/2008 : 20:46:45
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Use a 1uF cap (an old electrolytic or even a polyester is fine - at least for testing), or you could swap C33 and C32 and see what happens.
Nah... dont need any caps. Just buy me a beer next time I'm in the UK 
The last time I needed a 0.68uF cap I found it in an old dead AIWA stereo in the junk box. I find that if you go to the local thrift store, they just throw out or recycle electronic stuff that's donated if it doesnt work immediately when they turn it on - and they will usually give it to you if you ask nicely. I think I snagged the AIWA I mentioned above out of a skip somewhere...
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Edited by - Laurie on 08/17/2008 20:52:45 |
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tony
Bronze Member
United Kingdom
142 Posts |
Posted - 08/18/2008 : 15:58:16
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quote:
[ Just buy me a beer next time I'm in the UK
If you ever come down to the London area or the South East, I will gladly do that.
I've ordered the caps from Banzai as I needed some other stuff anyway. Besides, I want to be able to put them in and leave them there without doubting them.
Amazingly, they've already shipped the order which is really weird for them.
We shall see...... |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 08/18/2008 : 16:03:55
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quote:
Originally posted by tony
quote:
[ Just buy me a beer next time I'm in the UK
If you ever come down to the London area or the South East, I will gladly do that.
I've ordered the caps from Banzai as I needed some other stuff anyway. Besides, I want to be able to put them in and leave them there without doubting them.
Amazingly, they've already shipped the order which is really weird for them.
We shall see......
Been thinking about it some more, and the voltage on C33 seems right. So I'm not holding out much hope 
Will think some more... plus I PMed Dr. Bob and he might get a chance to look at the problem too.
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tony
Bronze Member
United Kingdom
142 Posts |
Posted - 08/18/2008 : 16:33:34
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quote:
[
Will think some more... plus I PMed Dr. Bob and he might get a chance to look at the problem too.
Much obliged, as ever.
I was going mad over it before but I feel quite relaxed about it now. After all, it produces echoes just fine. There's just something dragging them down around the NE570. |
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tony
Bronze Member
United Kingdom
142 Posts |
Posted - 08/19/2008 : 00:33:04
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I don't think it's those caps either really. I've just tested all the voltages around pin 16 when plucking strings - pin 16 to ground, perfect, pin 16 to c33, perfect, c33 to ground, perfect.
With the delay time at maximum, I pluck the string, wait .8 of a second and get a lovely line level leap which fades exactly according to the decay of the strings - if I mute them, it drops instantly, just like it should.
Sitting here with the NE570 datasheet, the first diagram on pg 1. is pretty much how BOSS have it set up on the expander (and compressor) side. I can go round all the pin inputs and tick them off as good. Except the output. And it's not the chip.
The scary thing is, I don't even have to look at the expander section of the schematic anymore - I know it off by heart.
EDITED:
Here's a chart showing all the DC voltages on the expander side (can never decide if I should spell that with an "e" or and "o"....).
Make of them what you will.....
pin 9 - 1.8v
pin 10 - 4.87v
pin 11 - 1.8v
pin 12 - 1.8v
pin 13 - 9v
pin 14 - 1.8v
pin 15 - 1.8v
pin 16 - Delayed Guitar signal
Don't understand how that works with the voltages on 14 and 15 because I get clear signal from them. Whatever.
Hold on, 4.87v on pin 10? Isn't that a bit high? Or not?
Might be worth adding that plucking the strings didn't effect any voltage change on pins 14 and 15, where I heard a clear signal with the probe, or any change on pin 10.
That DD7 gets more appealing every minute.
EDITED AGAIN:
Looking at how the expander works (you learn something new every day) C33 is definitely quite important as it controls the average voltage for the rectifier. Definitely gonna give it a go anyway. Read some funny things about tantalum caps. |
Edited by - tony on 08/19/2008 01:21:44 |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 08/19/2008 : 01:30:13
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quote:
Originally posted by tony
I don't think it's those caps either really. I've just tested all the voltages around pin 16 when plucking strings - pin 16 to ground, perfect, pin 16 to c33, perfect, c33 to ground, perfect.
With the delay time at maximum, I pluck the string, wait .8 of a second and get a lovely line level leap which fades exactly according to the decay of the strings - if I mute them, it drops instantly, just like it should.
Sitting here with the NE570 datasheet, the first diagram on pg 1. is pretty much how BOSS have it set up on the expander (and compressor) side. I can go round all the pin inputs and tick them off as good. Except the output. And it's not the chip.
The scary thing is, I don't even have to look at the expander section of the schematic anymore - I know it off by heart.
EDITED:
Here's a chart showing all the DC voltages on the expander side (can never decide if I should spell that with an "e" or and "o"....).
Make of them what you will.....
pin 9 - 1.8v
pin 10 - 4.87v
pin 11 - 1.8v
pin 12 - 1.8v
pin 13 - 9v
pin 14 - 1.8v
pin 15 - 1.8v
pin 16 - Delayed Guitar signal
Don't understand how that works with the voltages on 14 and 15 because I get clear signal from them. Whatever.
Hold on, 4.87v on pin 10? Isn't that a bit high? Or not?
Might be worth adding that plucking the strings didn't effect any voltage change on pins 14 and 15, where I heard a clear signal with the probe, or any change on pin 10.
That DD7 gets more appealing every minute.
EDITED AGAIN:
Looking at how the expander works (you learn something new every day) C33 is definitely quite important as it controls the average voltage for the rectifier. Definitely gonna give it a go anyway. Read some funny things about tantalum caps.
It all looks good to me too. 4.87V on pin 10 is fine - it's there because of the the pull-up resister R37.
Change C33... that's the next logical thing.
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starr36
Platinum Member
Canada
1172 Posts |
Posted - 08/19/2008 : 05:06:42
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i am flabberghasted.
when this is done, we can talk about my DD-2 that 'can't tell you've turned the feeback knob down"
no, really, we should be taking a collection for starbucks gift cards for something....
fascinating read. |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 08/19/2008 : 14:50:31
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quote:
Originally posted by starr36
i am flabberghasted.
when this is done, we can talk about my DD-2 that 'can't tell you've turned the feeback knob down"
no, really, we should be taking a collection for starbucks gift cards for something....
fascinating read.
No problem starr36! But based on our success with tony's DD-2 it might take a while to figure yours out 
Where in Canada are you? If you are in Calgary, bring it around and I can have a look at it on the scope... |
Edited by - Laurie on 08/19/2008 14:51:12 |
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Topic |
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DD 2 problems
