Archive for the ‘Boss’ Category

Boss HM-2 Heavy Metal

Wednesday, May 28th, 2014


What is it?
Boss HM-2 Heavy Metal distortion. Made in taiwan, early 1988. It has six number serial with leading zero, so that makes the unit one of the very first taiwan made HM-2s

If you have not heard anything about this distortion, you must have been living under a rock. It is one of the most desired Boss pedals ever, mainly due to swedish death metal frenzy back in the 90’s. The classic Daniel Ekeroth youtube video clip tells you everything you need to know about it. Due to it being in production from 1983 to 1991, the numbers are limited. There’s still plenty of them around, but since many death metal players try to get their hands on every single unit that they come across, the collectibility of these units is high. And the fact remains, it is the only pedal out there that gives you the authentic swedish death metal sound. Daniel is right about Metal Zone having nothing on this. They are very different designs. According to Effectsfreak, these should usually sell for less than $100, but i’ve seen units in good condition sell for a lot more. Well. It’s been over 20 years since Boss stopped making these, so some of the units must be dead and gone, others in use and some of them are in the hands of collectors. I smell prices rising r in the future.


Board is looking very appealing for a Boss design. Acidy styled strips with a crowded board always induce goose pumps. Apparently the board design has remained exactly the same when manufacturing moved from japan to taiwan.  If we take a look at the schematic (courtesy of, we see the distortion section after the input buffering/switching network to be quite unusual. Notice how the distortion control is wired – on the CCW end of the sweep it has maximum resistance between inverting input of the asymmetric clipping amp and ground (a similar method we’ll find on OD250/Dist+ gain control). While it’s doing that, it also tames the NPN/PNP transistor network that acts a pregain circuit. Once turned CW, the pregain has more effect – while the clipping amp is pushed to it’s potential. Ingeniously simple. After the asymmetric clipping amp we have two clipper pairs before there’s a buffer. After that buffer is the section which makes this a HM-2.


I bet the designer thought that simple clipping amp and the clippers after it weren’t enough for a design they were about to call Heavy Metal. Overall sound is fairly deformed at this point. The key ingredient is here – the three band active, Q boosting gyrator filters that offer up a big amount of boost for their selected frequencies. Low band is there to give out crushing lows and the upper two are controlled by Color Mix High control. This boosts mids and highs.

After that there’s a recovery stage, followed by standard level control and output switching/buffering. Rather complicated design, but successful in more ways than one. The gyrators mimicking EQ boosts are a thing of their own, but the pregain stage described above looks even more interesting.

On the negative side? Noticed the 330R resistor and D1 diode on the schem? Yup. This unit is meant to be used with idiotic Boss ACA power supply. Diode and resistor drop the unregulated 12V DC from ACA supplies to ~9V-ish. This unit cannot be used with standard regulated 9V supply. Or it can, but then you’ll need to daisy chain it with other pedals to counteract the effect of those components. If you are to try one with modern, standard pedal power supply, you’ll find the LED to light up dim and the sound being quiet octave up distortion. I know many people who have thought their units are broken due to this feature…

How does it sound?
Like swedish death metal from the 90’s. It is definitely not an overdrive, so don’t be surprised when you can’t get that bluesy tone out of it. It is a Heavy Metal distortion and very good one in what it does. The clipped frequencies stay consistent and the distortion is overwhelming and crushing – yet still defined. Color Mix is effective pair of controls, and with these the tone can be tweaked to match your guitar and your favourite frequencies. I still think you’ll want to max all the controls and learn a Entombed riff or two. I don’t blame you.

Here’s a quote from original marketing material: “Also, the HM-2 can be effectively used even with a single coil pickup guitar with low output level, because of its high gain.” – No disputing that.

Some of you know that i like MD-2 Mega Distortion a lot. This one could be considered as MD-2’s ancestor witth HM-3 Hyper metal on the on the same linear line of evolution. That would be a lot closer analogy than bringing MT-2 in to this equation. Super high gain usability. There’s a lot of crushing for this circuit to do yet.

Boss RV-2 Digital Reverb

Friday, March 7th, 2014


What is it?
Boss RV-2 Digital Reverb. Made in japan, 1987.

Got the unit in a bag of crap i bought from one local guy. The unit was missing a bottom plate altogether and it was not in working condition. Checked the insides around for a while and there were just couple of loose wires coming from the jacks to the board. Soldered those back to their places and got it running. The missing bottom plate was another issue. Where was i to acquire a grey label Boss bottom plate? Nowhere. But i had an old japanese DD-3 with burned chip in a  spare parts box, so i scavenged the plate from that one. It is with blue label and from around 1988, so it’s not the closest possible match, but it’ll have to suffice.

This is likely to be the very first digital reverb in a compact pedal form ever. With all the features of professional rack mount units included, it’s bound to be quite complex design.


I may have written about filled boards before, but this one takes the grand price. The boards are made with tiniest SMD-components and the design still had no  chance of fitting in a standard Boss enclosure. Didn’t notice it at first. But yes. The box is slightly taller than the standard boxes. Apparently, the taller box is used only in PSM-5 and RV-2. PSM-5 needs the taller box because of the jacks at where the knobs normally are. This one however.. Needs all the possible space to house the boards. All the other designs fit in the standard one.

These pictures do not cover the detail of two stacked boards too well, but that’s how it’s made. With two massively crowded, two-sided boards bonded together. More as a detail, even the digital chips are Boss-branded. This must have been pretty expensive thing to manufacture…


Quick googling around didn’t give out a schematic, but i’d like to see one – just to see if i could understand anything of it.. All in all, this is the most complex design in such a small enclosure i’ve ever seen. The board design has more components on it than your 90’s PC motherboard. And it’s still nothing more than a reverb unit, mimicking a full fledged rack mount monster. The features easily trump most of the modern table top units. Six modes from plate to gate, to room, to hall and panned reverbs. All with adjustable time from 0.2 to 10 seconds. Then there’s the pre-EQ control for tuning the frequency range that we want to reverberate. And mix control, of course. Overall, very controllable.


It does surprise me that the current market value of these units is not higher. First of all, these were only made in japan for less than a year and a half, from 1987 to 1988. Second, the engineering is more than just respectable. Third…

How does it sound?
It doesn’t sound bad at all. Sure, it may not last too many rounds in the same cage with high-end brand rack mounted studio reverbs.. But then again. This is just a tiny pedal from Boss’ compact series and it’s meant to be used with a guitar. As a guitar effect? Just beautiful from small ambient plate to massive, wettter-than-ever surf reverberation. Good controls, good overall feel and sound. Where some (or be exact, most) Boss compact pedals leave me with no feelings at all, this one is not one of them. It’s versatile and usable pedal. And on top of that it is an important piece of stompbox history. So.. If you have a grey label bottom plate laying around without a pedal, drop me a line…

Boss GE-7 Graphic Equalizer

Wednesday, January 29th, 2014


What is it?
Boss GE-7 Equalizer, made in taiwan in may 2002. Otherwise in fair condition, but missing a few slider knobs (which seem to very hard to source as spares).

Schematic is online, courtesy of There are three DIP-8 and two SIP-9 opamps plus a transistor based output buffer that make up the circuit. There’s also standard Boss-style electronic JFET switching. All seven frequency ranges from 200 Hz to 6.4KHz are active filters that are able to boost or cut the desired frequency while keeping other frequencies well in tact. Plus the gain slider sets allover level and offers a reasonable amount of boost for all individual bands.


The board is your standard modern taiwanese specimen. Dull, ground/trace-filled, autorouted touch, which doesn’t raise much feelings. The (a)symmetry is more pleasing than most of the modern designs, but still quite boring.


Didn’t expect to see SIP opamps so this was one quite interesting things about this pedal. But now that i’ve been inside of various Boss boxes, the surprise isn’t that big. Other thing that in reality is interesting is definitely the board fastening. All the sliders have their own board, which is fastened to the main board and the enclosure with a single screw. With these few peculiarities boosting the otherwise low interest, this is not a bad tool to have.

How does it sound?
Loudish. Can be used as a clean boost in addition to frequency tweaking. Versatile 7 band eq. Doesn’t sound like “Wohoo”, but rather like “Yey.” One can definitely use this to pre- or post-eq other pedals  in addition to boosting one’s cleans. And distortions.

Boss BD-2 Blues Driver

Wednesday, January 22nd, 2014


What is it?
Boss BD-2 Blues Driver. Made in Taiwan. Unit has nice road worn on the casing. Manufactured in april, 2004.

Although i’m not deeply in love with Boss boxes, there are a few designs that i find interesting and usable at the same time. This is one of those. Discrete opamp  and well designed JFET sound in compact box. There are a lot of these milder overdrives available from various manufacturers, but still only couple of really good ones come from big names. Boutiquers and few high end brands offer similar JFET-based vacuum tube analogy, but practically none of the mass producers do it.

For those interested, Gauss Markov has the redrawn schematic up on his site, so check it out. There’s factory schem available at Free Info Society too.


Under the hood shows the reason why most of the Boss boxes give me a severe case of meh. Autorouted, neat and clinical. These are made to last, but not to please the eye of an aesthetic electronics freak like me.


There’s a lot of spare room on the board, even though the discrete opamp stage is at least as complicated as using a standard opamp. That’s the key to the sound.

I really don’t get it why this pedal is listed high on big name modding lists. In my opinion a pedal should not be fixed if it’s not broken. And the Blues Driver is definitely not.

How does it sound?
Like one of the greatest low gain overdrive/distortions. It nearly captures the feel of overdriven old Fender tweed or Gibson amp. Quite edgy, articulate and dynamic. With low gain settings this is shining as one of those always on effects. Reacts quite dynamically to the way you play. It simply sounds great, even for someone who isn’t a fan of Bosses.

Boss MD-2 Mega Distortion

Sunday, January 12th, 2014


What is it?
Boss MD-2 Mega Distortion, made in Taiwan in february 2009.

Got the unit in very good condition for a fair price – without a box and papers, but still nice. Actually i got this on the same day as the Morley Crystal Chorus. So, of course, i hooked them both up for testing at the same time. Oh boy. Let’s return to that in a bit.


Modern looking traces on a filled board. This time, a space well used. The amount of gain the two SIP opamps and a handful of transistors deliver is respectable. The design that has basically five stages amplifying and/or driving the signal, with no diode clippers and manages to keep the massive noise content away is quite respectable too. Aside the buffering and standard Boss electronic switching, there’s a discrete JFET opamp acting as first gain stage. This stage offers the Gain Boost control too. Which is followed two standard gain stages. After that there’s very peculiar looking differential stage, followed by active tone control leading to standard level control. Not simple in any way. You can check the schematic out at FreeInfoSociety‘s page.


That peculiar differential stage i mentioned.. I’ve not seen that configuration exactly like that before. If it is something standard i’ve missed, please let me know. I may dig deeper in to the idea at some point to satisfy my curiosity. Anyway. This is standard Boss box that would normally, even with one interesting stage on the signal path, raise not much more than meh. But this time…

How does it sound?
Like a very pleasant surprise. I don’t think i’ve heard distortion as thick and saw waved before. Massive amount of gain with sufficiently low noise levels. The amount of sheer distortion is so high, that the sound is no more distorted in traditional sense. It reminds me a lot more of a tight and thick saw wave synth sound. And as i previously didn’t know where or when to use chorus effects to get something decent out of them.. This box solved it. Place a soft analog chorus in front of this one and be prepared for total angry synth mayhem. So far, this is the greatest distortion to me in all of Boss’ lineup. So. I’d sum this one up as so over the top distortion, that it isn’t one in the vast number of normal distortions. Quite nice to run into something like this instead of thousands of standard distortions.

Boss MT-2 Metal Zone

Monday, December 30th, 2013


What is it?
Boss MT-2 Metal Zone Distortion. Made in Taiwan in january 1999.

While the design seems to be quite a standard for metal players, it doesn’t move me that much. The eq section with half parametric mids is well designed and definitely the best part of this pedal. The schematic shows that the design is probably one of the biggest analog distortions around. Several gyrators in addition to several gain stages and fairly complex EQ. These are the things your Metal Zone is made of.


SIP opmaps on a crowded board with modern style techical looking traces. The board material makes me wonder if this unit is in fact older than i originally thought. When i hadn’t checked the serial number decoder to confirm…


Due to the price of used units this will probably never make it to DIY favourites. Maybe it is just a good thing. Too much of gain may not always be an advantage when the goal is to keep the sound reminding you of a guitar. Besides the EQ, the controls are Distortion and Level. Latter is good to have as this one can reach the unity level in early part of the sweep. For distortion control.. I have no clue why it is there. There’s basically 269 degrees of unusable area on the sweep.

To me it seems like this design has been sort of an competition. How much distortion and gain can you get out of 9V operated pedal without oscillation or massive noise content?

How does it sound?
As your standard ultra high-gain distortion with reasonably loud output should. This sound has been more or less the standard for ripping death metal since its inital release in 1992. EQ section adds a lot of usability, while the distortion control is completely useless. Or have you ever heard or seen someone to use MT-2 with minimal or even moderate distortion setting? I sure haven’t.

Boss SD-1 Super Overdrive

Wednesday, December 11th, 2013


What is it?
Boss SD-1 Super Overdrive. Made in taiwan, january 2010.

One of these boxes that i knew i had to have, no matter if i like or not. And the answer is not. Must be one of the most sold Roland Boss pedals ever. The design has been on the market since 1981. As the box has already reached 30 years of age without any changes to the design, it must be popular product. If it wasn’t, it wuold have been axed and/or replaced by some other design a long ago. Cool thing about the circuit is that it still looks and feels pretty much like the original japan made SD-1s, even though it’s taiwanese and nearly 30 years younger.


One of my friends has an early 80’s japanese version of the SD-1. According to him, the current production versions sound exactly the same, if not better. Haven’t had a pleasure of trying out really old unit myself. Value of those early 80s versions are through the roof. So i’m kinda hoping that 25000 of these units suddenly break up beyond repair and that 25 years passes very quickly. Maybe then my unit will have more value than twenty european dollars.

The board traces are the same as the photos of old units found on the web. Let’s then take a look at the schematic (from Doesn’t that look a bit similar to something we’ve seen before? With just a couple of component changes (a few values, a 1M pot for gain and asymmetric clipper diodes), and it surely does seem like something really familiar.


Funny. I thought it sounded and felt pretty familiar too. So in fact, it is a slightly modified Tubescreamer with added gain and asymmetric clipping. The pedal is so common that modding it is very popular. No one will ever cry after an original SD-1 because of the mods. One can simply use the mod sheets found on the internet that apply to TS-family.

With just couple of component swaps and one could easily mod this to TS808 specs. Sounds so bad as an idea, that i may have to aqcuire another cheap used unit and mod it to 808.

UPDATE. I did get another from around 2005 in a trade (thanks Kasperi!). And i did mod it to TS808. All it takes is removal of one cap, swapping the places of one resistor and a cap, swapping 25 components to different values (including two pots) and making a few slight modifications to the circuit board. In all, about 30 components need some attention. Doable, but it’ll take couple of hours to perform. I A/B’d the result with my TS9 (as i don’t have TS808, yet), and i really couldn’t tell which one of the pedals was on at a time. So yes. It can be done. Do i recommend it, or is it really worth the trouble? Can’t say for sure, but it feels pretty damn weird to have TS808 sound coming from SD-1 box. After trying the result out, i sanded the SD-1 text off from the label and used permanent marker to tag it as “SD-808”.

How does it sound?
Like a Tubescreamer with slightly more harmonics on the clipping due to asymmetrical clipping configuration. Oh. And lots more gain.  Does it sound better than TSs? No. But it doesn’t sound any worse either. Mid-humping overdrive that keeps slapping you on the top of your head. Doesn’t take good pickups well, jsut slaps you even harder. For P90s with  moderately low output, this shines. As do all the TSs. A classic, but not that great. I do get why some people do like this and keep using it. To me, it’s just another cheap TS alternative in yellow box. Swap the diodes for two silicon ones for symmetrical clipping and you’ll have something that’s close to a Tubescreamer. that’ll cost you a lot less than current reissue of TS9.

After the mods, it is a TS808. I think i want to keep them both.

Boss TR-2 Tremolo

Monday, September 9th, 2013


What is it?
Boss TR-2 Tremolo. Unknown manufacture date. No serial, as the label has vanished at some point alolng the way. This came to me in a trade as a defunct unit. Gladly, it was just polarity protection diode and one burned resistor. No visible damage to the board itself.

Of all the tremolos i’ve played, this one just seemed solid by construction and sound. Nothing special or anything that made me go wow. Just one of those tools that are good to have. TR-2 was first released to the public in 1997. The Pb-Free label on the board suggest that this is quite new unit, maybe around 2010-11.


As the photo above shows, all the opamps are SIP-chips. The LFO and gain recovery amps are M5218/NJM4558, while the modulation amplifier is M5207 VCA. The factory schematic (found on the internet) shows how the LFO is created – and how the modulation is applied to modulation amplifier. Neat and simple. Design is pretty straightforward and does not peak my interest more. Controls offer good range, while the wavefrom control is too subtle for my taste.


Traces on the back of the board show neat soldering, but dull design. Almost machine-like autorouted feeling to it.

Some people have reported that the output level of this design is lower than unity, aka volume drop. I would mostly blame that on human brain perception or psycho acoustics, but the issue can be dealt in other ways too.  As the modulation recovery amp is wired as standard inverting amplifier, there is one resistor responsibe for the output level. That resistor being R12, the feedback resitor of IC2A in the schematic. Original value is 22K, but you could swap it for 27K or try on different values to tweak the output to your taste. You could even replacce that resistor with 50K pot to get control over the output level. Other option to try is to snip the C4 – 100nF capacitor taming the oscillator output. One more option is to lower the value of input limiting resistor of the modulation amp. This being R9, the 10K resistor. 6.8K should offer unity or slight boost. One more mod would be to remove C7. This will omit the high frequency taming at the recovery amp and let more highs through.

One could of course play with all of the above to tune it just perfect to your ears.

How does it sound?
Decent. Not too special, but nothing’s amiss or wrong. Mass tremolo with no personal character to it. LFO wave control leaves me a bit puzzled. It could be a lot better or just a bit more drastic. Not a bad thing to have. Wouldn’t buy this as a new unit, but i’m glad i got.