freestompboxes.org

Hi, I've got a lot of great info from this site so it's time I put something back...

I saw this thread and thought of my old Amdek CHK-100 Chorus. I built this kit in the early '80s (well... just wired it up really, the board was populated). It's still going strong, I've tried a lot of chorus pedals and this one can stand up against any of them.

Anyway, here are some pics for anyone who's interested:

So after a quick tracing (wo comp values) I can say, that the Amdek CHK-100 is basically a Boss CE-2 "upgraded" to "pseudo"-stereo....

The only "confusing" part is the MN3204, a 512-stage BBD.
in all Boss pedals there is useda 1024-stage BBD.

analogguru

AG, I am fairly sure i have the schematic for this one - give me some time and I will search my dusty filing cabinet and post it for you
bajaman

Just in case, here are the gutshots:

I've got the schematic in an original copy of E&MM which featured this pedal. I think I've got most of the copies of E&MM which featured the various Amdek pedals. The schematic in the article is tiny, only about 3"x4" - really hard to make it out. It's basically a CE-2, but apparently it sounds way better. Maybe because of the use of a mn3204, instead of the mn3207. Here's a photo of the schematic, I can scan it if anyone's interested, but it's not going to get much better:

frequencycentral wrote:I've got the schematic in an original copy of E&MM which featured this pedal. I think I've got most of the copies of E&MM which featured the various Amdek pedals. The schematic in the article is tiny, only about 3"x4" - really hard to make it out. It's basically a CE-2, but apparently it sounds way better. Maybe because of the use of a mn3204, instead of the mn3207. Here's a photo of the schematic, I can scan it if anyone's interested, but it's not going to get much better:

Yes please. Scan the schematic! I've got two of these in a box of broken junk, and if they can sound good, then it's worth mending them!

mictester wrote: Yes please. Scan the schematic! I've got two of these in a box of broken junk, and if they can sound good, then it's worth mending them!

Considering your wealtht of design experience, even in the range of Class D amplification for a renown manufacturer of audio equipment, as well as your chocolate flavour personal chorus, this basic application of BBD technology should be a piece of cake without a schem.

smellin a bllshitter here?

Dirk_Hendrik wrote:

mictester wrote: Yes please. Scan the schematic! I've got two of these in a box of broken junk, and if they can sound good, then it's worth mending them!

Considering your wealth of design experience, even in the range of Class D amplification for a renown manufacturer of audio equipment, as well as your chocolate flavour personal chorus, this basic application of BBD technology should be a piece of cake without a schem.

smellin a bllshitter here?

No need to get unpleasant, Dirk-head. I'm just interested in the filtering pre-and post the delay line.

I'm playing with a couple of MN3207s at the moment, with differing delays, modulated differently in an effort to improve the basic Chorus idea. I'm having a hell of a time getting rid of clock and aliasing artifacts - and it's NOT a layout issue or a miscalculation of the filter values. I remember that these things sounded pretty good, and was wondering if it was going be worth spending some time mending them, or if I should just recover the ICs and throw the boards away.

C.

mictester wrote:

Dirk_Hendrik wrote:

mictester wrote: Yes please. Scan the schematic! I've got two of these in a box of broken junk, and if they can sound good, then it's worth mending them!

I'm just interested in the filtering pre-and post the delay line.

C.

The filter values on the boards I've got give a turnover point quite a bit higher than is normal with a 3007-based chorus, and these boards have 3007s and 3101s in them, so they're a bit different to the ones scanned above. I've got one of them working (it had a couple of cracked PCB tracks). It's pretty good, and with the replacement of one resistor in the summing circuit to improve the depth, I've got pretty sweet chorus. It's a bit noisy, but no more than you'd expect for this technology. The clock frequency is also a bit higher than usual, so obviously the manufacturer had calculated that they could get away with a shortened delay, improved "wet" frequency response, and thereby get more top end out of the thing whilst still getting a reasonable chorus sound.

I've just got the PCBs (no cases connectors or anything else). I even had to find a battery connector!. I'm wondering if it's worth putting these in boxes and ebaying them as "vintage chorus pedals" with a starting price of $200....

A nice article with scans and schematic of the Amdek CHK-100 chorus can be found here:
https://www.muzines.co.uk/articles/amde ... s-kit/4433