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Boss DM-3 9v modification post/ DM-3 mod …FIX Yo Boss DM-3 right!


Vintage Boss DM-3 Analog Delay with upgraded 9v mod so it will run full power on standard pwr supplies (stock was 12v aca) see proper post on modding yours to 9v, below


I love my old yellow n black Arion!

Good luck with the sale!


What's the dif between the two?

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Apologies for the semi-related post. I have the same DM-3 and never really thought anything of hooking it into my pedal board. I use a one spot/daisy chain deal..the pedal seems to sound pretty I damaging it? What would be a symptom of the reduced voltage? Is the mod a loop back into the 9V battery feed? Thanks.


If the DM-3 is original and untouched, as Tavo said, it wanted to have 12v fed into it. If you're powering it with 9v, it's getting starved a bit due to a resistor on the power input jack, and the headroom is reduced as well as the LED not lighting up to proper brightness. UNLESS, you bypass this resistor on the power input jack (the mod) making the pedal run properly with the 9v. Done it myself with a Tavo tutorial and never looked back


BOSS DM-3 9v upgrade / mod for conversion from OEM 12v ACA to regulated 9 volt PSA pwr (culled from a few spots I posted about this, in addition to this mod I replace necessary Electrolytic caps that may have exceeded their 15 yr limit by year 2000..this isnt the case 85% of the time but has been the case for me with pedals I've bought from this era. Also the JRC 4558 can be damaged from overheating in the area of the resistor that isnt happy with modern power supplies. If you have a DM-2 or DM-3 with weak or dark repeats its time to replace the 4558 chip and a few E caps, then install the jumper mod)

the pedal in it original OEM state uses a 12vACA power supply, so to plug a 9V regulated power supply (ala boss PSA or onespot or ...) the pedal is being starved a little. If you plug it into a daisy chain with other regulated pwr supplied pedals running, it supposedly lets the pedal see the full 9v. I ran mine for yrs like that until I found a mod for older boss pedals like the CE-2 chorus.. Applying that mod to the DM-2/DM-3 and bypassing the resistor and diode, just insures a solid 9V regulated and low noise power supply (assuming you are not a nimnal using a non audio filtered regulated power supply like something from Radioshack/tandy).

The end result is a more defined slapback that is letting the DM-3s compander circuit perform its best as well as the proper voltage going to the delay chip. I get more headroom and less washed out repeats.. They are still warm and round. organic,yada yada but the pedal responds the way the designer intended.

  • worthy technical notes on the ACA - PSA conundrum D1 and R3 are in series between the power jack and the battery terminals - meaning the battery doesn't pass through D1 and R3 but the power supply does. T R3 must be dropping the current into the circuit when using an ACA PSU but unfortunately it's also doing it when a regulated is used, so bypass it and be able to use a regulated PSU.

Boss uses a diode and resistor to regulate the voltage in older boss pedals when powered by a power supply which is why a regulated 9v supply will not work. The resistor and diode drop the voltage to about 6.2 volts resulting in thin tone and a dim LED. When a battery is used the diode and resistor are bypassed, same is true when you daisy chain the power with other PSA effects.

Using a jumper is an easy and reversible mod but just be sure you don't use an unregulated 12v adapter after the mod. The first filter cap on the pedal is only rated for 16v and since all CE-2's are approaching 20 years old now those caps have to be pretty dry. If you are going to open the thing up and work on it it's not a bad idea to replace all the electrolytic caps and put a 100uf/25v cap for the filter cap for a little more headroom on the rated voltage.

Don't forget that the ACA adapter changed too in 1997. Earlier ACA adapters were 12 volts DC unregulated (to work with the ACA pedals of that time), while newer ACA adapters (produced after mid 1997) are 9 volts DC unregulated (to work with the ACA pedals produced after 1997).

...which more or less makes the modern ACA adapter useless. You can't use it to power your pre-1997 ACA pedal (which would need a different adapter, if powered alone), as it is only 9 volts DC instead of the 12 volts the pedal wants to see. And while it will work fine with the post-1997 ACA pedals, so will the regulated PSA adapter.

"ACA Adapter

The ACA is an unregulated 9V or 12V adapter. For a long time both the ACA and the regulated PSA adapter was available but in the later part of the 90s the ACA adapter was discontinued as all Boss pedals then was designed to run with the PSA adapter.

When a power supply is unregulated, it means that the voltage level will drop as the load is increased. The ACA adapter may give out a full 12 volt when it is powering one or two pedals but if it is hooked up to a long row of pedals the voltage will drop. The ACA adapter is capable of supplying as much current as 250mA but problems keeping the voltage up may occur before the load reaches that level.

The early compact pedals was designed to run on either a 9V DC battery or 12V DC adapter. Because of this the ACA adapter was a 12V adapter. The voltage was reduced to 9V internally by using a 470 Ohm resistor and 1S2473 diode between the minus input on the power jack and ground. The resistor diode pair was later removed and at the same time the ACA adpater was redesigned to output 9V instead.

Powering ACA pedals with a PSA power supply Powering the older pedals designed for 12V DC input with either a newer ACA or PSA adapter will not work very well. The voltage drop over the resistor and diode will prevent the pedal from getting enough power and its LED will usually only glow faintly. The solution is to use a daisy chain and plug in another pedal designed for the newer ACA or PSA adapter. The lead between the two pedals will short the resistor diode pair and the pedal will receive full power.

Depending on the mains voltage there are 4 were versions of the ACA adapter. ACA-100, ACA-120, ACA-220 and ACA-240. The number denotes the mains voltage that the adpapter should be plugged into. The 9V version of the ACA adapter has a G appended at the end of its name. Pictured is the ACA-120G which is the version sold in the USA."

"PSA Adapter

The PSA adapter is a regulated power supply that outputs 9V DC and can supply up to 200mA current. Regulated means that the power supply contains a circuit that helps stabilise the voltage at 9V even when the load is increasing. The earlier ACA adapters did not have this feature and when many pedals were connected, the voltage would drop.

Like the ACA adapter, the PSA adapter is available as PSA-100, PSA-120, PSA-220 and PSA-240. The number reprsents the input mains voltage it is designed for.

Powering ACA pedals with a PSA power supply Powering the older pedals designed for the 12V DC ACA adapter PSA adapter will not work very well. The older pedals contains a resistor and diode that will lower the internal voltage voltage supplied to the rest of the circuit. This will prevent the pedal from beeing fully powered and its LED will often fail to light up properly. The solution is to use a daisy chain and plug in another pedal designed for the newer PSA adapter. The lead between the two pedals will short the resistor diode pair and the pedal will receive full power."

* DM-3 Delay The DM-3 was last analog delay pedal produced by Boss. The circuitry is similar to the DM-2's but it isn't identical. The DM-3 has a built in high speed noise reduction circuit and an additional filter. It's also got a direct output that can be used to create a stereo effect. The delay time is variable between 20ms and 300ms just as the DM-2 and the control layout is also identical. The knobs on the DM-3 stands out when comparing to other Boss pedals. They only featured on the DM-3 and early versions of the CE-2B.


Controls: Repeat Rate, Echo, Intensity Connectors: Input, Output, AC Adaptor Current Draw: 18 mA (DC 9V, D.Time control at center) Weight: 450 g (0.99 lb.) Input Impedance: 1Mohm (FET Input) Residual Noise Level: -100dBm (IHF-A) Recommended Load Impedance: 10kOhm or greater Delay Time: 20ms to 300ms Recommended AC Adaptor: ACA Series Labels

Green - Made In Japan The DM-3 was sold from May 1984 to May 1988.***[/QUOTE]


Thank you Tavo for the post, and for cluttering your sale post


Bump to this thread as I just had a nocturne customer ask about the 9v mod to get the proper response from an early ACA powered 12v Boss DM-3. Check Post #7 cheers ,tv


Is this the same for the CE-2?


Is this the same for the CE-2?

– Mark G

yes indeed. that is jumpering the resistor to the power supply. I first found out about this the hard way believing the lump heads innernets back in the 90s that " mehh any 9v volt supply is fine, dont worry". So i didnt worry until that resistor burned up and charred part of the PCB. Not really sure why it was so dramatic but at least it tuned me into what was going on for real.


Help! Back when this thread was started I jumpered R3 but left D1 intact.. is this bad?


This place seems to be one of the most dm3 discussed places... so I´ll try here.

Got myself and old DM3 and am noticing some artifacts on the repeats. Hard to describe but ringing/pinging/scratching or the like is the best I can put it into words...

Is this how the DM3 should sound? It's not super audible, but it's there if you listen carefully. And once you hear it, it can't be ignored and is quite annoying. It's particularly audible with max delay time and max repeats.

Would changing the caps remedy this noise?


Nature of the beast.

Unless, previous owners adjusted internally the delay time.

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