someone upped this on "another" forum...worth a look!!!!!

[Keppy]

Can someone take a look at R65 (the big trimmer) for me? It's an unfamiliar shape to me, and I could only identify 2 solder points on the picture. That seems weird to me for a trimmer, but not unthinkable. Can anyone confirm whether I got that one right, or explain to me how I got it wrong?

There are some similar trimmers on the top board that appear to have up to six solder points, so I'm pretty sure I have no friggin' idea what those particular graphics are telling me. 

[thedefog]

Can someone take a look at R65 (the big trimmer) for me? It's an unfamiliar shape to me, and I could only identify 2 solder points on the picture. That seems weird to me for a trimmer, but not unthinkable. Can anyone confirm whether I got that one right, or explain to me how I got it wrong?

There are some similar trimmers on the top board that appear to have up to six solder points, so I'm pretty sure I have no friggin' idea what those particular graphics are telling me.  

Can't really tell from that top down picture, but it is probably just connected at the center and left/right lug and either NC or linked to the center on the opposite side. The trimmers with 6 legs are dual gang maybe? Never seen one, but who knows with this thing.

[pinkjimiphoton]

i've hit the hcfx forum and a few places putting out feelers for more info...wish me luck!!!!

"hi guys, long time...this is more for the old-timers here.
me and some other like-minded peeps on the diystompboxes forum are trying to ressurect and clone the mighty and venerable ludwig phase II guitar-synthesizer interface pedal.
big job...it's coming along.
but...

we need to know about the power supply. wiring harness info would be groovy too..

the billion dollar feckin' question...anyone HAVE one of these things? if so, anyone got the power supply layout/schematic?
pictures, scans, info in general. we've got the preliminary pcb boards being worked out, and have tracked down the actual schematics and a shit load of gut shots, but need some help...so if you're out there, or ya know someone who IS out there that can help, please either reply to this here thread, or send me a pm or something.

we wanna make this thing walk again so peeps can build their own...and that means you can, too.

thanks in advance.

peace
pink"

[Keppy]

I found a clearer scan of the top board layout/schem. Oddly, the pick of the fall plate board was one we already have.

[pinkjimiphoton]

that IS clearer. but it's the same one we already have...probably been compressed as a jpg a few less times, or cleared up with a photoshop style program.
i tried to do that with irfanview, reduced the color depth but the scan i was working on had too much degradation. nice find mate!! :thu:

[Keppy]

Q2 on the top board has 2 bases. Haven't seen that before. Who's gonna tell us noobs what that is?

[wavley]

Q2 on the top board has 2 bases. Haven't seen that before. Who's gonna tell us noobs what that is?

It's a Unijunction Transistor http://baec.tripod.com/DEC90/uni_tran.htm

I don't have much experience with them, but you see them sometimes in oscillator circuits.

[pinkjimiphoton]

http://baec.tripod.com/DEC90/uni_tran.htm


EDIT: thanks wavley!!





The basic structure of a unijunction transistor (UJT) is shown in Fig.1. It is essentially a bar of N type semiconductor material into which P type material has been diffused somewhere along its length. Contacts are then made to the device as shown; these are referred to as the emitter, base 1 and base 2 respectively. Fig.2 shows the schematic symbol used to denote a UJT in circuit diagrams. For ease of manufacture alternative methods of making contact with the bar have been developed, giving rise to the two types of structure - bar and cube - shown in Fig.3

P13_F123 P13_F4
The equivalent circuit shown in Fig.4 has been developed to explain how the device works, and it is necessary to define the terms used in this explanation.

RBB is known as the interbase resistance, and is the sum of RB1 and RB2:

RBB = RB1 + RB2 (1)

N.B. This is only true when the emitter is open circuit.

VRB1 is the voltage developed across RB1; this is given by the voltage divider rule:

         RB1
VRB1 =         (2)
      RB1 + RB2 

Since the denominator of equation 2 is equal to equation 1, the former can be rewritten as:

       RB1
VRB1 =    x VBB (3)
       RBB

The ratio RB1 / RBB is referred to as the intrinsic standoff ratio and is denoted by Eta (the Greek letter eta).

If an external voltage Ve is connected to the emitter, the equivalent circuit can be redrawn as shown in Fig.5.

If Ve is less than VRB1, the diode is reverse biased and the circuit behaves as though the emitter was open circuit. If however Ve is increased so that it exceeds VRB1 by at least 0.7V, the diode becomes forward biased and emitter current Ie flows into the base 1 region. Because of this, the value of RB1 decreases. It has been suggested that this is due to the presence of additional charge carriers (holes) in the bar. Further increase in Ve causes the emitter current to increase which in turn reduces RB1 and this causes a further increase in current. This runaway effect is termed regeneration. The value of emitter voltage at which this occurs is known as the peak voltage VP and is given by: VP = Eta AVVBB + VD (4)

The characteristics of the UJT are illustrated by the graph of emitter voltage against emitter current (Fig.6).





As the emitter voltage is increased, the current is very small - just a few microamps. When the peak point is reached, the current rises rapidly, until at the valley point the device runs into saturation. At this point RB1 is at its lowest value, which is known as the saturation resistance.

The simplest application of a UJT is as a relaxation oscillator, which is defined as one in which a capacitor is charged gradually and then discharged rapidly. The basic circuit is shown in Fig.7; in the practical circuit of Fig.8 R3 limits the emitter current and provides a voltage pulse, while R2 provides a measure of temperature compensation. Fig. 9 shows the waveforms occurring at the emitter and base 1; the first is an approximation to a sawtooth and the second is a pulse of short duration.



The operation of the circuit is as follows: C1 charges through R1 until the voltage across it reaches the peak point. The emitter current then rises rapidly, discharging C1 through the base 1 region and R3. The sudden rise of current through R3 produces the voltage pulse. When the current falls to IV the UJT switches off and the cycle is repeated.

It can be shown that the time t between successive pulses is given by:

           VBB - VV
t + R1C ln         secs (5) N.B. R measured in Megaohms. C in µF.
           VBB - VP

Design for a lKHz relaxation oscillator

The oscillator uses a 2N2646 UJT, which is the most readily available device, and is to operate from a 10V D.C. power supply.

From the relevant data sheet the specifications for the 2N2646 are:

VEB2O IE(peak) PTOT(max) IP(max) IV(max)      Eta      Case style TO18
30V  2A       300mw     5µA    4ma    0.56 - 0.75

It is important that the value of R1 is small enough to allow the emitter current to reach IP when the capacitor voltage reaches VP and large enough so that the emitter current is less than IV when the capacitor discharges to VV. The limiting values for R1 are given by:

          VBB - VP               VBB - VV
R1(max) =         and R2(min) =         
             IP                    IV

From the specifications for the 2N2646 the average value of Eta is 0.56 + 0.75/2 = 0.655. Substituting this value in equation (4) and assuming VD = 0/7V: VP = 0.655 x 10 + 0.7 = 7.25V.

So R1(max) = 10 - 7.25/5µA = 550K, and if VV = approx VBB/10,
   R1(min) = 10 - 1/4mA = 2.25K.

If we choose a value for R1 somewhere between these limits, e.g. lOK, the value of C can be calculated from equation (5)

If f = 1MHz, t = 1/f = 1msec. VBB - VP = 10 - 7.25 = 2.75 and VBB - VV = 10 - 1 = 9

                                                          t
                                                               
Rearranging equation(5) to make C the subject: C =        VBB - VV
                                                   R1 ln         
                                                          VBB - VP

            0.001
so C =                = approx 84nF.
       104 ln (9/2.75)

Because of component and UJT tolerances it is sufficient in most circumstances to use an approximate formula: f = 1/CR, which assumes that Eta is 0.63 - well within 5% of the average value for the 2N2646. In practice one would use a variable resistance (or a variable resistance in series with a fixed resistance) for R1 so that the frequency of oscillation could be adjusted to give the required value.

R2 is not essential; if it is included, a value of 470 ohms is appropriate for the 2N2646. The value of R3 should be small in comparison with RBB, with which it is in series, so as to prevent it from affecting the value of the peak voltage. A value of 47 ohms or thereabouts is satisfactory.

Editor's notes: The above design points are illustrated in the circuit of the enlarger timer which was described earlier this year in the April Newsletter. In that circuit the UJT provides clock pulses at 20Hz. R1 is a combination of a 47K variable and a 150K fixed resistance; R2 is omitted and R3 is 33 ohms. The timing capacitor has a value of 220nF. In addition to the 2N2646, the component list for this timer also includes the TIS43 and the 2N4891. Most suppliers list only the 2N2646, but Maplin also include the TIS43. This device was used with a transistor constant current generator as the sawtooth oscillator in the timebase of the "Student's Oscilloscope" published in "Practical Wireless" in August 1973.

In his book "110 Semiconductor Projects for the Home Constructor" (2nd edition 1978), R.M.Marston gives twenty circuits for UJT projects using the 2N2646. These include pulse and sawtooth generators, analogue/digital converters, relay time delay circuits and frequency dividers. If any member would like to experiment with UJTs there is a good number of 2N2646 and TIS43 in Cyril's stock, and Ray Marston's book can be borrowed from me for 38p postage.

There is also a device called a programmable UJT - the BRY39 is an example so called because its parameters can be set by external components. It is a PNPN device, similar in some ways to a thyristor, and can be used in applications similar to those for the UJT. Perhaps we could have an article about this in a future Newsletter.

[R.G.]

Anyone notice yet that it wants +35V?

[wavley]

No prob Jimi.  I don't have a lot of time for board tracing, but I would really like to assist this project in any way that I can.

Whelp boys, looks like we got us here one of dem fancy pants big city relaxation oscillators.

[wavley]

Anyone notice yet that it wants +35V?

Yeah, I see that 36V zener in there.

Looks like (if I'm not mistaken) all we're missing from the power supply is a center tapped transformer.

[Keppy]

Anyone notice yet that it wants +35V?

Noticed both the voltage and your periodic hints to check it out

[Keppy]

R.G., would your charge pump scheme work to power this? Your site shows how to get +33v from a +9v supply with a MAX1044. If we used an LT1054, which is a drop-in replacement and can accept up to +15v supply, could we power it with 12v and get something in the right range, or high enough to regulate down to +35v?

[wavley]

R.G., would your charge pump scheme work to power this? Your site shows how to get +33v from a +9v supply with a MAX1044. If we used an LT1054, which is a drop-in replacement and can accept up to +15v supply, could we power it with 12v and get something in the right range, or high enough to regulate down to +35v?

Personally I would rather see this pedal AC powered.  +12v isn't something readily available on most of our pedal boards so it means yet another wall wart, the thing is already going to be a massive effect, there's no getting around that.  I'm thinking more like the old Morley PFL http://www.effectsdatabase.com/model/morley/telray/pfl

What I would do, not that anybody else's way is wrong by any means because maybe a charge pump is a great idea and I'm just not seeing it right, is ditch the center tapped full wave rectifier for a bridge rectifier package with a small transformer.

Just my opinion, don't want to step on any toes.

[Keppy]

Personally I would rather see this pedal AC powered.  +12v isn't something readily available on most of our pedal boards so it means yet another wall wart, the thing is already going to be a massive effect, there's no getting around that.  I'm thinking more like the old Morley PFL http://www.effectsdatabase.com/model/morley/telray/pfl

What I would do, not that anybody else's way is wrong by any means because maybe a charge pump is a great idea and I'm just not seeing it right, is ditch the center tapped full wave rectifier for a bridge rectifier package with a small transformer.

Just my opinion, don't want to step on any toes.

My toes will be fine. I'm asking more as a matter of curiosity. I've used charge pumps a few times now, with more projects planned that will require them, and I want to know their capabilities. I haven't dealt too much with AC conversion yet. The CX-3 Leslie I'm working on uses it, but I was having trouble locating the large capacitor required and figured it would just be easier to supply it with the 12v DC it's gonna end up with anyway. Regardless, I'm interested in any and all convenient ways of doing this.

[rousejeremy]

I think it was about $1000 at Pauls Boutique in Toronto.

[R.G.]

Yeah, I see that 36V zener in there.
Looks like (if I'm not mistaken) all we're missing from the power supply is a center tapped transformer.

Anyone notice yet that it wants +35V?

Noticed both the voltage and your periodic hints to check it out

Just checking guys. Trying to prod it in the right direction.   

R.G., would your charge pump scheme work to power this? Your site shows how to get +33v from a +9v supply with a MAX1044. If we used an LT1054, which is a drop-in replacement and can accept up to +15v supply, could we power it with 12v and get something in the right range, or high enough to regulate down to +35v?

It would somewhere between maybe and probably work. A lot depends on how much current the thing draws. They only use 100uF for the first filter cap, so it can't be all that much. And they have 100 ohms in series in front of the regulator transistor. If it were me, I'd use a charge pump running from 9V to get 40+V and then regulate, probably with the circuit that's already on the board. 9V is a lot more common.

Or, I might just use a 12V or 24Vac wall wart and use a multiplier on it to get more than 40Vdc. The multiplier could all be in the rectifier/filter for an AC output wart.

Mouser has 48V wall warts, and possibly 36V, for about $15 each. Goodwill stores sometimes have 24Vac wall warts for $1 - $2.

Personally I would rather see this pedal AC powered.  +12v isn't something readily available on most of our pedal boards so it means yet another wall wart, the thing is already going to be a massive effect, there's no getting around that.  I'm thinking more like the old Morley PFL http://www.effectsdatabase.com/model/morley/telray/pfl

What I would do, not that anybody else's way is wrong by any means because maybe a charge pump is a great idea and I'm just not seeing it right, is ditch the center tapped full wave rectifier for a bridge rectifier package with a small transformer.

Probably the best thing to do is to come up with a variety of power schemes. Volts is volts. The electrons don't know where they came from.

[Keppy]

If it were me, I'd use a charge pump running from 9V to get 40+V and then regulate, probably with the circuit that's already on the board. 9V is a lot more common.

Thanks! Good to know the multiplication can be taken that far.

[Keppy]

New layouts. I realized it doesn't matter that the trimpots look weird because the ones we get will be different anyway. I reworked the layout to include and additional solder pad for R65 and to include the mounting holes. I also added the top board. Both are laid out for .3" resistor lead spacing, so increase by 33% if you want .4" spacing.




The parts for my other projects arrive tomorrow, so it's someone else's turn for now unless I need to correct my files.

[MoltenVoltage]

I don't know how exact the trimpots need to be, but I'd recommend multi-turn cermet trimpots so you can really get it dialed in.