Boss HM-2 Heavy Metal LiteVerified

From the post

Quite a few people have asked for a layout for this over the last couple of years, and I was always put off because with 3 x ICs and at least 3 transistors (depending on which schematic I used for the layout) there was no way it was going to fit in a 1590B, and you know what I'm like, I have a pet hate about putting a pedal that you can have in a Boss-sized box into a 1590BB. I know some people don't mind, but I have a rack tray and space is at a premium so it does matter to me. I'd just prefer to use an original if my own version was going to be physically bigger.

Eventually Fredrik (Freppo) decided to do one himself, and he did and excellent job which you can find posted on the blog forum here, so I forgot about it for a few months. But I spend a lot of time just looking at schematics to see how the manufacturers do certain things, and I was looking at the HM2 scheme, and just thought how much smaller it would be without the gyrator tone stack that's used and so decided I was going to do my own version using an active Baxandall stack instead to see how compact it could become. This may not be capable of the "crushing lows" some people will want a HM2 for, but for others like me who just want a compact high gain distortion with a great tone control it could fit the bill perfectly. This is a graph showing the frequency response of the new tone stack and as you can see you can still get a nice boost in highs and lows,

but this was based on an opamp supplied with +/-15V and so a larger voltage swing than the 0 to 9V we usually have in our effects, and so in practise you won't get that sort of dB boost. It should however give you noticeably more of boost running the effect at 18V and so for anyone who wants a bit more meat out of the stack, I would suggest making sure appropriately rated caps are used and trying 18V.

This has been verified by a very nice man from Finland :o) and so is safe to build for those who fancy a Lite version of the HM2. As noted, this won't give you the exact response you can get from the original especially at 9V, and so if you're in a Swedish death metal band you may prefer Fredrik's layout, but it's still one of the highest gain stompboxes we have on here according to Miro and I think it has a very nice tone control in its own right, and so reckon it will be of interest to some.

If anyone wants to further experiment with the response of the tone control, or maybe to use it in another effect, check out this calculator: http://www.geocities.jp/dgb_studio/bax_calc_e.htm