Boss - OD-1 Overdrive  [schematic]

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Boss - OD-1 Overdrive

Postby seniorLoco » 17 Jan 2008, 02:25

This OD-1 clone using a single chip ...just wanted to post it here 8)
The brief history of differant version from Boss.
OD-1A
Serial: 6400 - 6500
Marking of PCB: 052-281a
Switch: Transparent
Silver screw
OP-AMP: RC3403ADB

OD-1B
Serial 6600-8800
Marking of PCB: 052-281b
Switch: Up to 8400 transparency, from 8600 black
Silver screw
OP-AMP: Up to 8400 RC3403ADB, from 8600 uPC4741C (NEC)

OD-1D
Serial 8900- , 6 digit sticker
Marking of PCB: 052-281d
Switch: Black
Screw: 8900-0300, silver screw, 0500- black screw
OP-AMP: 9900 - NJM4558D (JRC)
9300,0300 - uPC4558C (NEC)
0000 TL4558P (Texas Instruments)

OD-1E
Serial: 6 digit sticker
Marking of PCB: 052-281e
Switch: Black
black screw
OP-AMPs: uPC4558C (NEC)
JRC4558D (JRC)
JRC4558DD (JRC)
JRC4558DX (JRC)
C4558C (NEC)



Like this...
Schematics and build report at Matsumins ... 8)
Here

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Postby seniorLoco » 17 Jan 2008, 02:58

Gut shot
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Boss - OD-1 ( Overdrive )

Postby MWichni » 22 Feb 2009, 09:38

I also have the OD-1 original board from bossarea.com.

So here it is:
http://odsiebie.com/pokaz/1638012---1d87.html

I know that in pdf is permission refuse to other site than bossarea.com but the links are broken and I got it via e-mail so I uploaded it on the server.

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Boss - OD-1

Postby thyx » 05 Feb 2011, 08:08

Hello folks...I've been working on trying to get the flip-flop circuit working on a used pedal I picked up for cheap, but I can't seem to get it to work. It's an OD-1 with the quad op-amp chip. The transistors are all good, and the circuit flips when I ground out the base of each conducting transistor, but when I ground out the 220p caps that lead to the foot-switch, I get nothing...no change. Everything appears to be working, but it just won't flip at the switch!!! Are there any obscure peculiarities to this circuit?

Please help...mental visions of a sledge-hammer are beginning to creap in...
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Re: Boss Flip flop circuit  [schematic]

Postby blackbunny » 05 Feb 2011, 11:11

There are a couple of things to be aware of with the quad op-amp OD1's.

Firstly, even when the flip-flop is working properly the red indicator LED flashes on briefly during the changover period and then turns off again. Later Dual op-amp OD-1's have a different flip-flop circuit where the LED stays on when the effect is on, as per all other modern Boss pedals. See the attached schematic to modify the flip-flop.

Secondly, these pedals were designed to operate on a 12VDC plugpack or a 9v battery, and the flip-flop does not operate reliably at less than about 8.7VDC from the battery. Check to make sure your battery is at least 9v and/or your plugpack is 12VDC.

The pedal can be modified to work from a 9v plugpack by changing R30 from 470 ohm to 47 ohm.
Replacing D4 with a 1n5818 or 1n5819 schottky diode helps as well.
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Re: Boss -OD1

Postby RnFR » 05 Feb 2011, 14:00

I turned the valuable info in this thread into a proper od1 thread, since it was absent from the forum.
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Re: Boss - OD-1

Postby thyx » 05 Feb 2011, 22:40

Thanks black...I'll try the R30 mod and see if it makes a difference.
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Re: Boss - OD-1

Postby blackbunny » 06 Feb 2011, 02:51

Here's an image showing the location of R30 and D4.
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Re: Boss - OD-1

Postby thyx » 06 Feb 2011, 22:57

Tried the mod...no dice. Also verified no traces are broken. Any other ideas?
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Re: Boss - OD-1

Postby blackbunny » 07 Feb 2011, 11:11

Using the schematic and pcb image attached, you can carry out basic troubleshooting.

Firstly, check the mod you did against the pcb component markings.
Second, check the pcb for signs of burning, especially dark discoloration around D1, D2 or D4.
This would indicate that the power supply diodes and electro caps have been hit with reverse polarity, which would be a good reason to replace them.
Before plugging in / not powered up: Use a diode tester or the diode test function on a DMM to test all the diodes for forward conductance, black probe to yellow or black bar side of each diode. Readings of 500-550mV are good, a very low reading points to a shorted diode or something close to it in the circuit. If all looks OK, reverse the probes and test for reverse conductance. You should get high or open circuit readings for each diode.
Using the diode tester or DMM, test the diode junctions in Q3 qnd Q4, the switching transistors. The pinouts are E-C-B with the flat side facing you, pins down. You should get readings of around 525-560mV B-E and B-C.
If all the diodes and transistors test OK, plug in / power up and test the DC voltage across D1. If this is 8.5 volts or more,
measure the voltage across C18, which filters the bias supply and should be half of the voltage across D1.
If this all looks good, you can try replacing the indicator LED with a high efficiency 3mm in the colour of your choice, check for full supply voltage between pins 11 and 4 of the 14-pin IC, check for bias voltage (around half supply voltage) between ground and pins 3, 5, 10 nd 12 of the IC.
If none of that looks faulty, and it still won't switch, take DC voltage readings from ground to each pin of the IC, also each leg of Q3 and Q4, and post them in your reply.
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Re: Boss - OD-1

Postby thyx » 07 Feb 2011, 16:04

Hey man...thanks a heep for posting this. I'll try this out when I get home today...but to be honest, I've already covered most of what you've posted. I'm wondering if I should start fooling around with the value of the resistors going from the base to ground on the switching transistors. It almost seems as if they're not quite sensitive enough, or something.

BTW, I think there are some problems with your schematic. I think the LED ends up at the collector of one of the switching transistors. And don't the 56k resistors go from transistor base to ground...not bias voltage? (Probably just a slip, that last one.)
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Re: Boss - OD-1

Postby thyx » 07 Feb 2011, 18:03

thyx wrote:BTW, I think there are some problems with your schematic. I think the LED ends up at the collector of one of the switching transistors.


Wait...my bad...I think your schematic is the "momentary switch" version.
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Re: Boss - OD-1

Postby blackbunny » 08 Feb 2011, 00:27

Yep, I tried to draw the original OD-1 Rev A or B circuit, so it would correspond directly to what's on the pc board, but you are right - the 56k transistor base resistors go to ground, not vbias.

I will check for other errors against my pc boards and post an amended schematic.

That said, the switching is a flawed design. I think maybe driving the LED puts too much load on Q3's collector, which lead to the extra driver/buffer transistor Q5 in later models.

For more sensitivity you could try reducing the value of the 56k collector resistors a la Ibanez flip flops, which usually have 22k or 10k resistors from collectors to +9v. 33k or 39k might be a good starting point?

You can also play around with the timing capacitors. Assuming you have replaced C13 and C14 with 220pf capacitors and jumpered across D3, you can play around with C10.

One of my OD-1B's had a diabolical intermittent switching fault which I fixed by replacing C10 with a .047 mylar capacitor, replacing the LED with a new high output diffused LED, and replacing D4 with a 1N60 Ge diode (for less voltage drop from the 9v regulated plugpack).

Let me know if any of this helps.

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Re: Boss - OD-1

Postby thyx » 09 Feb 2011, 16:58

blackbunny wrote:Yep, I tried to draw the original OD-1 Rev A or B circuit, so it would correspond directly to what's on the pc board, but you are right - the 56k transistor base resistors go to ground, not vbias.

I will check for other errors against my pc boards and post an amended schematic.

That said, the switching is a flawed design. I think maybe driving the LED puts too much load on Q3's collector, which lead to the extra driver/buffer transistor Q5 in later models.

For more sensitivity you could try reducing the value of the 56k collector resistors a la Ibanez flip flops, which usually have 22k or 10k resistors from collectors to +9v. 33k or 39k might be a good starting point?

You can also play around with the timing capacitors. Assuming you have replaced C13 and C14 with 220pf capacitors and jumpered across D3, you can play around with C10.

One of my OD-1B's had a diabolical intermittent switching fault which I fixed by replacing C10 with a .047 mylar capacitor, replacing the LED with a new high output diffused LED, and replacing D4 with a 1N60 Ge diode (for less voltage drop from the 9v regulated plugpack).

Let me know if any of this helps.


Well, I lowered the collector resistors at Q3 & Q4 to 27k and 33k. At those values, the LED comes on, when powered by external power (higher voltage than battery), when you plug into the input jack...but won't do this when powered by battery. On battery, Collector voltage is 7.39v and 7.38v...can't get much closer than that. Base voltage on battery (with D3 still present) is 1.25v and 1.19v. Voltage across D3 is 0.56v. I'll try jumpering across D3 and playing with the timing...but at this point I'm wondering if the switching transistors are at fault. They don't look original. Could swapping them out change things around?
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Re: Boss - OD-1

Postby blackbunny » 10 Feb 2011, 04:04

Definitely worth trying a change of switching transistors. Higher-current types such as 2SC1815 would be ideal, but many GP NPN transistors will work fine.

Have you changed the indicator LED circuit yet? I think this is an essential part of the "factory" mod; an efficient high-brightness 3mm LED will allow you to increase the value of LED current-limiting resistor R29 to 3.3k, 3.9k or 4.7k.

The reduction in the load on Q3's collector can really improve footswitching performance.

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Re: Boss - OD-1

Postby thyx » 12 Feb 2011, 09:45

Diode mod is done, emitter diode D3 bypassed, replaced Q3 and Q4, and played with values for the timing cap from .01uf to 1uf. No dice. I do appreciate all the effort, but this one is a complete mystery to me...the kind that gnaws at my gut. Sometimes the LED comes on when I stick the jack into the input, and sometimes it doesn't...even though the circuit is always alive. Appreciate all the effort, but unless you're a magician I don't think this pedal is ever going to work. A shame, really.
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Re: Boss - OD-1

Postby blackbunny » 12 Feb 2011, 16:25

thyx wrote:Diode mod is done, emitter diode D3 bypassed, replaced Q3 and Q4, and played with values for the timing cap from .01uf to 1uf. No dice. I do appreciate all the effort, but this one is a complete mystery to me...the kind that gnaws at my gut. Sometimes the LED comes on when I stick the jack into the input, and sometimes it doesn't...even though the circuit is always alive.


What type of transistors did you replace Q3 and Q4 with?

I didn't get a clear picture of the current fault(s) from your post.
When you say the circuit is always alive, do you mean it passes signal but won't switch from bypass to overdrive? Or do you mean that it will switch between overdrive and bypass, but the LED won't light?
Is it the same fault you started with before attempting the repair?
Did you change the LED, current limiting resistor R29, or zener diode D2 (ZD2)? If so, what values did you use?

thyx wrote:Appreciate all the effort, but unless you're a magician I don't think this pedal is ever going to work. A shame, really.


Try not to lose heart, everybody has a pedal repair or build that seems to be jinxed every now and then.

I have fixed about 10 of these things over the years, and a couple of them have been very hard going.

I like the old quad op-amp OD-1's so much, I would buy it off you and fix it myself if you don't want to do it any more.
But I would feel better about it if you could get it working properly, and get to enjoy the results of your efforts.

I'm happy to keep at it if you are. Cheers.
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Re: Boss - OD-1

Postby thyx » 12 Feb 2011, 22:41

Remember I said it looks like somebody had changed Q3 and Q4? Well...here's the chain of events:

- Replaced Q3/Q4 C1815Y with pair of C1685R out of working Boss pedal
- Checked that new 220p caps across the base of Q3/Q4 were in spec
- Made sure D3 was successfully jumped (by ohm-meter)
- Went back to 56k at the collectors, Q3/Q4
- Installed new LED out of modern working Boss pedal
- Went to look at R19 and....

.......!

...oh, no...I can't believe I didn't see it before. It's so dumb, yet so obvious. It seems the person who installed new transistors also installed some other components. R26 and R27 are supposed to be brown/black/green (1M)...but...it's hideous...what was in their place was green/brown/black! 51 freaking ohms!!!! Popped a pair of 1M resistors in there and all is well.

I already gave you a thumbs up, but were it within my power I'd give you ten. You stuck with this even more than I did. I knew I was missing something stupid..but I couldn't figure out what it was to save my life. Thanks again. 8)
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Re: Boss - OD-1

Postby thyx » 12 Feb 2011, 22:50

...forgot to ask one more thing. With a fresh battery, I get about 9.5 volts at the 100uf cap. I did the mod to R30 that you suggested...going from 470 ohms to 47 ohms. Using the correct ACA-120, I now get 13.1 volts at the 100uf cap. Is this going to hurt anything? How does it affect the tone (I haven't tried it yet...wife is sleeping)? I'm thinking I should go back to the 470...?

Thanks again.
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Re: Boss - OD-1

Postby blackbunny » 13 Feb 2011, 02:47

thyx wrote:I knew I was missing something stupid..but I couldn't figure out what it was to save my life. Thanks again.


Yay! I knew you would find it if you kept at it.
I'm sure everyone at FSB has had at least one experience like this. I know I have had....er, more than one.

Of course, I'm a little sad that I didn't get to own another one of these great pedals, after you sold it to me cheap.
I already have 3 quad op-amp OD-1's; could use a couple more though.

thyx wrote:...forgot to ask one more thing. With a fresh battery, I get about 9.5 volts at the 100uf cap. I did the mod to R30 that you suggested...going from 470 ohms to 47 ohms. Using the correct ACA-120, I now get 13.1 volts at the 100uf cap. Is this going to hurt anything? How does it affect the tone (I haven't tried it yet...wife is sleeping)? I'm thinking I should go back to the 470...?

Thanks again.


Looks like the power supply Zener, D1 / ZD1 is faulty, or not the correct value
With the ACA-120 connected and input plugged in you should have around 11vDC across this Zener and the 100uF filter cap, if it is working properly. While 13v is not immediately damaging to the pedal, I would replace this zener with a fresh 11v / 1 watt zener as soon as you can if it is higher than 11.5 volts or so.

However, if you intend only using the ACA-120 and don't chain the OD-1 up with other pedals off a common 9vDC supply, I would definitely change the 47 ohm resistor back to 470 ohm, along with the new 11v zener diode.

The 470 ohm resistor shouldn't affect the circuit voltage when running from a battery - it's only in the plugpack circuit.

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