EH Soul Preacher opinions (part-2)

[markm]

Heh. If I'd seen this a little sooner I could have read the numbers off the board before I sealed the envelope. I dropped it at the post office about two hours ago, so it will likely be a week or two before you can look at it. Hopefully the Christmas glut in the postal system and at the border won't be too bad.

That's quite alright, it's kinda like a "cliff-hanger" in the movies ya know 
I do have a "proto-type" layout I intend to test soon but, having the actual board to look at will certainly put some truth
to the mystery surrounding this circuit.
I guess I've persued this out of curiousity more than anything else.......Jeez I hope it's worth it! 

[markm]

I'm a bit suspicious of this resistor here.
I can't tell if it started life with a RED stripe on it or not but, it is missing a band PLUS it does not seem to match the other resistors in the circuit.
This could be the "elusive" resistor we have been talking about here Mark, changed later on as a Mod perhaps.....

[hank reynolds 3rd]

could be 100K,if thats a brown stripe at the very top,
I have some resistors that are missing a band ,usually means taking the final ,yellow band  (excluding the gold ones etc,as I think that denotes tolerance) down a 'step' :in this case to the orange '00's ' size...
could be wrong,but it kinda looks that way


ta

Sam

[markm]

My thoughts are that perhaps a 220K resided there originally and was replaced by a 200K missing a band at the top?
It does look to me like there was a band on that one at some point and something happened to it.....scraped maybe?

[hank reynolds 3rd]

Sounds right,if thats the only resistor missing (and if the repair was done on the fly,course a 200k will suffice ),I've had the paint flake off resistors a couple of times (down to pulling them off my aborted stuff when needs must !!)

[markm]

Sounds right,if thats the only resistor missing (and if the repair was done on the fly,course a 200k will suffice ),I've had the paint flake off resistors a couple of times (down to pulling them off my aborted stuff when needs must !!)

Same here....gotta break out the DMM then!

[markm]

Excuse the bump but, any comments?
Mark H. ??

[Mark Hammer]

Expecting rigid consistency across issues from that particular era is expecting a lot, and maybe too much.

As noted, the FET forms part of a virtual pot/attenuator, where the amount of attenuation is equal to the ratio of the FET's drain/source resistance, relative to the resistor+FET resistance.  If someone at E-H gets a great deal on a bunch of the same nominal FET from a different supplier, and the d-s specs are a little different, then the resistance forming the other leg of that virtual pot has to change in order to maintain the same attenuation response.  So, the pedal may not have been "modded" at all.  Rather, some component values may have been changed in order to maintain identical functioning in light of other changes elsewhere in the circuit.

Sometimes, the changes to a circuit in different issues is intended because people think it sounds better (as in the case of script vs block P90s, or changes in amount of resonance/emphasis in different issues of the MXR Envelope Filter), sometimes the changes may be in order to save current and/or extend battery life (e.g., changeover from MN3007 to MN3207 in many choruses), and sometimes the changes are adaptations to changing circumstances.  Before pedal-making became HUGE (and certainly before they had acquired enough corporate, sales and marketing data to have a sense of what sort of inventory they would need for the next 10 years), I gather many manufacturers would buy their components in modest quantities.  What they could score a great price on for a lot of 4000 might change between February and October of the same year, and circuits would be adjusted to compensate.

At least that's the sense I have of it.  There are some with a whole lot more corporate knowledge than I.  For instance, Stephen Giles probably has 20x more insight into the corporate workings of E-H during that period than any of us here ever will.

[markm]

The resistor I circled in the picture looks like the "mystery" resistor possibly.
Could be 100K or 200K I suppose.

[analogguru]

The circled resistor is the pulldown resistor after the input buffer and has a valu of 100k.

The resistor in question is on the right side of the green film cap and is hidden by this green cap on this photo.

As Mark Hammer stated, the cap and the resistor are in fact reversed in reality.

So a photo from an angle where the hidden resistor can be seen would be helpfull.

[Mark Hammer]

Many thanks for that information.  It would seem that in this instance, and by my count, the picture was only worth 928 words.

[markm]

The circled resistor is the pulldown resistor after the input buffer and has a valu of 100k.

The resistor in question is on the right side of the green film cap and is hidden by this green cap on this photo.

As Mark Hammer stated, the cap and the resistor are in fact reversed in reality.

So a photo from an angle where the hidden resistor can be seen would be helpfull.

I think I know the one you're referring to.
That DOES look like a 220K but as you mention perhaps needs to be reversed from what the schem shows.

[markm]

Here's the suspect right here;

[markm]

I have been assuming that the FET in this schem is a JFET such as the 2N5457 found in the Orange Squeezer.
Any one care to determine the orientation of this tranny.....I think the Source is going to 4.5 volts.
Any takers??

[Mark Hammer]

Yep.  All you need the FET to be is a variable resistance between the signal path and ground, or floating ground as the case may be.  So, source to ground, as described.

[R O Tiree]

Apologies for (a) dragging up a seriously old thread and/or (b) if this point has been raised before, but that power supply system in the schematic above intrigued me.

I saw another thread yesterday where someone observed that they were getting significantly below 9V into the circuit itself. Admittedly, I've only simulated it, so far, but the results are quite interesting, I think.

With just a battery connected, we get 8.29V at V+ and 3.86V at Vb.  So far, so good.

With just an external 9VDC source connected, we get 7.78V at V+ and 3.58V at Vb.  Not so good, really.

With both connected, we get 8.32V at V+ and 3.87V at Vb.  In addition, the battery is still providing just a little current.  Only about 40µA, to be sure, but still draining.  The external DC source has to be at least 9.6V to make sure that the battery is producing 0A.  Spookily, at that new voltage we get 8.34V at V+ and 3.88V at Vb, which is back up where we want it.

Two thoughts occur to me... Firstly, the DC adaptor that was sold for this pedal must have produced something like 10V, not the 9V that is the de facto industry standard these days.  Secondly, there is probably mileage to be had in simplifying or even removing that power supply circuitry altogether and replacing it with a simple voltage divider as "normal".  What it does do is to provide reverse-polarity protection for both the battery connections and the external power source, so that's a good thing.

Bottom line, if people try to power this using a "standard" 9V external DC supply, there's quite a big loss of supply voltage to the circuit.  I notice that Aron's layout omits the 220R and the separate external supply line through it to the collector of Q1 (on his layout... it's the top left transistor "on its back" in the schematic above).  Instead, he has routed both lines direct to the base of Q1.  That said, he's supplied 9V directly to other components, such as the opamp V+, for example...

Any thoughts?

[crane]

I was looking at this old thread as well since I'm trying to build this unit. Has anyone ever cloned it?
I'm trying to use layout from Aarons gallery which has the power part a little bid modified - so hard to answer your questions Mark, but voltages read about 8V and 4V when using 9V adapter. I'm having some problems though - it sounds very distorted and waveshape looks very weird (I will post an image tomorrow). That's why I'm interested if anyone ever built this...