SOLVED Mesmerizer concern

mybud

mybud

Well-known member
Dear forum folks: Greetings from South Africa.

Just finished the Mesmerizer build. Strange symptoms as follow: The LED responds to changes in rate and depth, the volume pot also responds, signal is mildly amplified, but the only way to get the mesmerising aspect is by touching the board in the area of the 5457s. If I do this, it seems to function properly.

What's really strange is that the reading from the charge pump (positive side cap 19) is approximately 14V. I saw from an earlier post that this should be closer to 18V. I've tried three different charge pumps accordingly (TC1044SCPA and SEPA and LT 1054).

I wish I had socketed the transistors as I normally do, but I was itching to hear what this baby sounds like. You'll see that I replaced Q6 already (rather shoddily), thinking that it might be a dud 5457. No change in behaviour.

Any advice gratefully received and best wishes to all, Marc
 

Attachments

  • Mesmerizer bottom.jpg
    Mesmerizer bottom.jpg
    1.3 MB · Views: 21
  • Mesmerizer top.jpg
    Mesmerizer top.jpg
    1.2 MB · Views: 20
Sort by date Sort by votes
Voltages measured as best I can. Some of these seem to vary in accordance with the rate pot.

Vcc = 14.5 (D7 anode side)
Vdd = 7.6
Vref = 3.4-4.1

D (1) S (2) G(3)
Q1 9.3 1.79 0
Q2 14.5 9.3 0
Q3 9.3 2.16 0
Q4 14.5 9.3 6.9
Q5 0.1-1 1.27 -0.3-0.5
Q6 0.7-1.2 1.27 -0.1-0.1

1 2 3 4 5 6 7 8
IC1 (TL072) 3.5-3.8 3.4-4.1 3.4-4.1 0 2.9-4.6 2.9-4.6 2.9-4.6 7.56

IC3 (TC1044) 7.58 0 0 -2.43 -2.33 2.66 1.54 7.56

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
IC2 (XR2206) 0 3-4.5 0 7.56 3.3-4.4 3.3-4.4 2.9 3.7 1.60 2.9 0.251 0 1.5-2.1 1.5-2.1 0.98 0.98

As before, any advice gratefully received.
 
Upvote 0 Downvote
Do a search in the forums for Mesmerizer. I think there are some comments about the circuit being dependent on the characteristics of the transistors you use even if you are using the right parts.

Having said that, though, if it works when you are touching a part of the board try using something like a pencil to touch parts when you have a signal playing through it. If you can isolate a part that makes a difference try reflowing the solder on its connections to the board. That is better than trying to start by reflowing everything.
 
Upvote 0 Downvote
With all due apologies for reviving a dead thread (and this rather lengthy post), I wanted to close this one off and report a successful second attempt and my thanks to @zgrav for pointing me in the right direction.

For the first build (and one of my earliest PPCB attempts), I optimistically soldered the two 5457s in place. Given the wide variance in JFET characteristics, this was a mistake since the blighter didn't mesmerise (as above).

Next attempt with a fresh board, I socketed all the transistors and eventually replaced Q6 with a different 5457. What rapture when it did its nice throbbing thing (please refrain from any comments on the throbbery, colleagues) but in all seriousness, glad it's working.

When I'm feeling adventurous, I'll desolder the original 5457s from build 1 and replace them with sockets, since to all intents and purposes, it appears reparable. I have a spare 2206 from a previous Jameco function generator build, so with any luck, should be good to go and a stereo mesmerizer may loom in the near future.

I have noted, though, that Jameco no longer carry the 2206 as of recently, so this may be a moment to stock up if you can find legit ones in cyberspace somewhere.

What does it sound like? A bit like a phased tremolo, since there's a bit of filtering apparently going on. It comes into its own, though, in conjunction with a chorus and does a subtle but noticeable wobble.

I'm tempted to call it Hip Gnosis with a tip of the hat to Mesmer's original ideas on hypnosis, most of which turned out to be mistaken. Our more senior members may recall that Hipgnosis designed some 1970s psychedelic album covers, perhaps even some Floyd ones (Atom Heart Mother, if memory serves).

I remember being mildly amused by the powers that of the time be claiming that the name Hip Gnosis pointed to communism, satanism, and all sorts of nefarious activities designed to bring down the government. They then heavy-handedly parsed the phrase, so that lesser mortals might geddit and avoid such decadent, progressive, and no doubt subversive music.

MM_gutshot.jpg
MM_boxed.jpg
Perhaps someone could have explained that actually it was a pun on hypnosis, but that might have been a bridge too far for such a dour and humourless bunch to entertain.

<Plus ça change, plus c'est la même chose,> you might say. 'The more it changes, the more it stays the same.'

I'll mark this solved once I've figured out how to do so. Any pointers gratefully received.
 
Upvote 0 Downvote
You must log in or register to reply here.
Back
Top