I can't seem to find Q2 and Q3 anywhere (a 2SC2240 2SA970, respectively). Would a 2N5088 and 2N5087 work as substitutes for those?
Re: Boss - HM-2 Heavy Metal
Posted: 17 Jan 2018, 02:23
by Victor Nery
Greetings,
I was looking into Brian Wampler's "How to modify effect pedals for maximum tone" book and got into a weird stuff (just the info, not the result) about the HM-2 mods.
The frequency he states for the gyrators are tottaly out of the values I've got when I threw them into the amz calculator:
According to the calculator (link above) the stock center frequency would be 86,79Hz for bass control and 958,47Hz/1278,6Hz for treble control.
He suggests inhis mods to change C26, C27 and C30 for 2.2nF, 500pF and 47nF respectively and although the sound is pretty awesome, what he states is too confusing.
Here is what he says about C26 and C27: Stock is around 3kHz and after the mods would be around 7kHz. What I got in the AMZ calculator was 1868,84Hz (C26 - 2.2nF) and 3534,65Hz (C27 - 500pF).
And here is what he says about C30: He says 22nF will give 250Hz, 56nF 100Hz and in the end recomends 47nF but... when I throw in these values in the calculator, the results are tottaly different:
22nF - 152,59Hz
56nF - 95,64Hz
47nF - 104,4Hz
I'd like to understand how he got these results. By the way, here is how my HM-2 sounds after the mods he suggested in his book and some I mods I did on my own (It's an Oliver HM-20, they have the same circuit, though):
Thanks in advance.
Re: Boss - HM-2 Heavy Metal
Posted: 17 Jan 2018, 08:38
by Manfred
I'd like to understand how he got these results.
Re: Boss - HM-2 Heavy Metal
Posted: 17 Jan 2018, 11:46
by Victor Nery
The equation you posted above works exactly as AMZ's. What confuses me are the numbers he mentioned in his book and how he got them. Was that a mistake?
Re: Boss - HM-2 Heavy Metal
Posted: 17 Jan 2018, 23:22
by Manfred
Victor Nery wrote:The equation you posted above works exactly as AMZ's. What confuses me are the numbers he mentioned in his book and how he got them. Was that a mistake?
I cannot give you an answer because I do not read the book.
Re: Boss - HM-2 Heavy Metal
Posted: 19 Jun 2018, 12:49
by Kukuruzo
Can you please share the book?
Re: Boss - HM-2 Heavy Metal
Posted: 28 Apr 2020, 09:32
by pervyinthepark
Just comparing this to the HM-3 and wondering... am I tired and/or blind, or is the only real difference a capacitor in the clipping stage??!
Re: Boss - HM-2 Heavy Metal
Posted: 13 May 2020, 11:05
by Pruttelherrie
That's not the HM-3 schematic.
This is.
Re: Boss - HM-2 Heavy Metal
Posted: 15 Oct 2020, 21:13
by FrodeK
Hi!
I got this old hm-2 and when I opened it up it looks like this.
The material is quite hard and seems difficult to remove.
The stuff seems similar to this material used to glue the broad cable between the fx circuit and the pot circuit.
Since I am quite new in the world of stompbox mods and repairs; is this residue from a broken cap or diode? Or is it just glue or some substance from outer space?
Re: Boss - HM-2 Heavy Metal
Posted: 15 Oct 2020, 21:21
by FrodeK
One more thing:
It seems to work fine driven on battery, but not with power connected.
Re: Boss - HM-2 Heavy Metal
Posted: 16 Oct 2020, 09:13
by Fender3D
FrodeK wrote: ↑15 Oct 2020, 21:21
It seems to work fine driven on battery, but not with power connected.
Since this pedal has not the usual resistor + diode cell, the only way to achieve this issue is having a broken DC connector, assuming you're connecting a correct power supply of course....
The goo in above pics is glue to keep stuff still
Re: Boss - HM-2 Heavy Metal
Posted: 16 Oct 2020, 23:02
by FrodeK
After some google searching i found that the problem relates to the ACA/PSA issue. This pedal needs ACA power. One suggested solution is to remove and jump D1 and R2 to make it PSA compatible.
Another solution i found suggested online is to jump the blue cable (hole 4) from the power and the yellow input jack cable (hole 5). I tested it and the PSA-power works. Does anyone know if this will cause any damage to the D1 and R2? I left them in there.
I got this old hm-2 and when I opened it up it looks like this.
IMG_3216.jpg
Awesome you got great Photos of the PCB!
One kind of larger question: could you or somebody here possibly measure the forward voltage of the germanium diodes (D6 & D7 according to the "official" schematic, should be those glass-tubey, offstanding ones)? Please include measurement current, as I have a multimeter that does Vf measurements with 1mA and another one that uses 2mA, and the results do differ.
I did my own hm2 clone using exchangeable schottkys(250mV@1mA) and 1n60, apparently "true" Germanium with around 340mv@1mA. The charge varies between 340mV to almost 1V with lots of them dead, however.
I'd really love to know the specs of the original ones, as there's literally no data on those Japanese germaniums.