Build Your Own Clone Message Board

Hi!

Newbie to this board but not a pedal building newbie making a first post here;-)
So, I’ve been enjoying building kits for a while and taking a break from having to source parts, etch PCB’s and so on. Most recent the BYOC Swede. I remember a guitarist at school having a HM-2 in 89 and I was just sooo jelaous. Also fitting that I am a genuine Swede too, living way up north in Sweden.

Here’s the thing though, doesn’t the 330 ohm resistor that is in series with the 9V input (R38 in 2018 rev. 1.1 schem) drop too much voltage at the current draw of the Swede? My build has a measured total current draw (including LED) of about 12 mA. This doesn’t seem out compared to stated HM-2 spec at 10mA draw.
And I get a measured voltage drop of 8.75V (battery in; one side of R38) - 5.15V (other side of R38 = V+) = 3.6V. 3.6V/330 ohm = 11 mA.
At a V+ of 5.15V it sounds really splatty. To me a classic misbiased sound, cool in a fuzzy way but not what I imagined for this pedal. When the battery was fresh, it did sound better but not like I remembered it. It can’t have gotten the full voltage even then, right?

I can’t really find anything wrong with the build. No signs of anything pulling a lot of current. No oscillating opamps or such either after a quick look on the scope. Been there before in another build and those op amps drew a lot. Luckily clearly visible on the scope, and felt as the op amp go a bit hot.

Please help. Am I thinking wrong here? Sometimes I get my Ohm’s law wrong, usually when tired and just want all my gear to work.
Do I have a fault somewhere or is this how it is? Reasonable current draw?

I see that the 330 ohm resistor R38 isn’t in the 2015 build instructions but is in the 2018 version. I’m thinking about jumpering it instead, as that’s what would be closest to to the original HM-2 fed by a battery.

Cheers!
Per

EDIT: Ok. Should have read the instructions better;-) Stated current draw in the 2018 instructions is 12.5 mA. Ok. I think my build basically is ok then. Will jumper R38 first and if I seem to need more power filtering, then I’ll put a lower than 330 ohm resistor instead of a jumper in there.

R38 is in the original HM-2. We left it out in Rev1.0. Actually, it was engaged with AC power, but not with battery. So we just left it out completely. We got a lot of complaints from people getting high pitch squealing when all the knobs were dimed. While we were never able to reproduce the squealing here in the shop, we had to assume that the reason was the slightly higher voltage creating just enough extra output to push it over the edge. So we added it to Rev1.1

So you can jumper it if you feel that it's the reason you aren't getting the sound you expect.

_________________
*patience is a virtue*

Please do not PM me. email is prefered. keith@buildyourownclone.com

Thanks for your reply!

Yes, I’ve already jumpered it. Much better to my tastes. It is a really cool pedal!
Haven’t noticed any ill effects yet.

The way I understand the reason for the 330 in the external powered line only of the original has to do with the Boss ACA adapter. The resistor is there and at that value exactly because Boss wanted/needed to drop quite a bit of voltage from the unregulated ACA. From 12V or more to something close to 9V as V+.
So to me the addition of R38@330 here is more like a reverse ACA mod but one that also effects battery operation

I haven’t tried it at 12V though but now there seems to be no need.

Will build a mighty mouse next! When Moodysounds get them back in stock.

Cheers!
Per