258r V3.0 with vintage resistors in waveshaper, expo FM

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Peake
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258r V3.0 with vintage resistors in waveshaper, expo FM

Post by Peake » Fri Mar 20, 2020 12:50 pm

258r V3.0 with vintage resistors in waveshaper, expo FM
DSC01232.JPG
I'll add more photos when I'm able.

It's easy to add a switch between the standard linear FM and the exponential FM found in earlier versions of the 258.

-Clip the center pin of the FM Amount pots but leave enough to solder to.
-The pot's center pin should be wired to the center pin of an SPDT switch. Clip the switch pins fairly short but enough to solder to.
-The pot center pin PCB solder pad is the linear FM input. One side the switch is wired to this solder pad.
-The other side of the SPDT is wired to the negative input of a 1uF tantalum capacitor; the positive lead to a 33K resistor.
-That resistor is wired to one or the other side of a nearby CV Amount inverting pot, on an outside leg.
-The switch can mount in a hole you have to drill in the front panel on the left between the standoff and plastic-shaft pot. Horizontal placement.

SPDT : 108-2MS1T1B1M2QE-EVX (cut the pins down a bit but of course leave enough to solder to)

I have photos of some of the above but have to retrieve them in a few days.

Carbon film and carbon composition resistors in the waveshaping section.

Some transistor pairs should be matched.

Refers to this schematic: http://www.fluxmonkey.com/historicBuchl ... _1_200.jpg

Roman BOM: Schemo name:

R43 = R65 680r
IC1 = IC5 section 1 pin 1 to R65
R36 = R63 15K
R40 = R62 3K3 to ground
TR4 = R61, 20K Sine trimmer
R39 = R60 to ground 6K8

Q12 = Q10, Idss selected 2N4339

R35 = R59, 6K8
R29 = R33 6K8 to ground
R28 = R32 33K to -15V
R23 = R33 10K to FET
R8 = R36 3K3


Q1 = Q9?

Q9 = Q6, triangle source?
R45 = R55 330K tri shaper
R41 = R54 330K tri shaper
R38, R47 = 680r sine shaper
Q13 = Q11 2N4341
R49 = R53 680r?
R42 = R58 470r
R51 = R44 820K
IC4 = IC1 section 3
R37 = R34 150K saw
R46 = R41 68K
R52 = R42 10K to ground

R30 = R35 15K
R42 = R58, 470r
R49 = 680r film

Square shaper
Q6 might be Q8; base goes to 2.49K to ground, to 15K 1% to -15V
Q5 is Q7

Q5/6 = Q7/Q8 MATCH

Q7/Q8 = Q2/Q3 MUST MATCH



Q23 = Q10, Idss selected 2N4339
R103, R106 = R54, R55 330K sine shaper
R100, R108 = R56, R57 680r sine shaper
R108 to ground with D4
R100 to
R104 = R58 2K2 square
R102 = R62 3K3 to ground
TR12 = R45 1M waveshape trimmer
Q24 = Q11 2N4341
R109 = R53 680r
IC5 = IC 5 section 4
R98 = R63 15K
R015 = R65 680r
R97 = R59, 6K8 to sine shaper
R101 = R60 to ground, 6K8
IC4 = IC5 section 3
R107 = R41 68K
R110 = R42, 10K to ground
R99 = R40 330K square
R93 = R39 15K 1%
R104 = R58 2K2 carbon

Q16/Q17 = Q6/Q7? Matched

Q14 = Q9
R70 = R36 3K3 to +V
R90 = R32 33K to -V
R92 = R35, 15K
R85 = R31 10K to FET
R111 = R43 square, 680K – 1M

Square shaper
Q16 = Q7
Q17 = Q8. Base to 2.49K to ground and 6.81K. Emitter to 15K 1% and emitter of Q16.
Q16/Q17 MUST MATCH


Q18 = Q2 Collector connects to collector of left side of 2N3802
Q19 = Q3 Emitter connects to emitter of Q18. Collector connects to right side of 2N3802.
Q18 = Q2 collector connects to timing cap, base connects to 4.99K, 33K
Q19 = Q3 base connects to 15K and 68K, emitter connects to Q18 emitter

Q18/Q19 MUST MATCH

Q12/Q23 = Idss selected 2N4339, Gate is the third/right pin.

Q13/Q24 =2N4341, Gate is third/right pin.




R26 and R88 = R16 33K, the linear FM signal path.

Linear FM: Signal in to top of pot, wiper/center of pot to – lead of 15uF to 33K to destination.

Exponential FM: Signal in to – side of 1uF tantalum capacitor to 33K resistor to wiper/center of FM amount pot; top of pot to destination.


Seems to work fine thus far without grounding the unused paths so a simple SPDT can be used and thus be able to be mounted at the word “FM” if desired, or up next to the left-most banana jack in the grid.

Cut FM Amount pot’s center pin leaving enough to solder onto.
That is the out to the center leg of the SPDT.
One side of the SPDT goes to the solder pad for the center leg of the FM Amount pot (Linear path).
The other side of the SPDT goes to the – in of a 1uF cap to a 33K resistor (shrink wrap it all) and out to the upper leg of the left CV amount pot.

SPDT : 108-2MS1T1B1M2QE-EVX (cut the pins down a bit but of course leave enough to solder to)
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This is not the place I'd imagined it to be.

jimfowler
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Re: 258r V3.0 with vintage resistors in waveshaper, expo FM

Post by jimfowler » Fri Mar 20, 2020 5:37 pm

Mike -

I’d love to compare results - both visible (scope) and audible. On my 258C builds I use all original spec’d trannies and am really happy with the results.

- Jim

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Peake
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Re: 258r V3.0 with vintage resistors in waveshaper, expo FM

Post by Peake » Fri Mar 20, 2020 7:43 pm

It was a build for a customer, already shipped. The waveforms looked as expected on the oscilloscope!
This is not the place I'd imagined it to be.

tardishead
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Re: 258r V3.0 with vintage resistors in waveshaper, expo FM

Post by tardishead » Tue Mar 24, 2020 5:20 am

Peake wrote:
Fri Mar 20, 2020 7:43 pm
It was a build for a customer, already shipped. The waveforms looked as expected on the oscilloscope!
Are you selling these PCBs ?
If not where are they from?

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Peake
I'm in ur DIY. Filling cases with Buchla
Posts: 6530
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Re: 258r V3.0 with vintage resistors in waveshaper, expo FM

Post by Peake » Tue Mar 24, 2020 1:23 pm

This is not the place I'd imagined it to be.

tardishead
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Re: 258r V3.0 with vintage resistors in waveshaper, expo FM

Post by tardishead » Wed Mar 25, 2020 2:30 am

wow thats about the most expensive DIY I've ever seen!

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search64
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Re: 258r V3.0 with vintage resistors in waveshaper, expo FM

Post by search64 » Wed Mar 25, 2020 2:36 am

tardishead wrote:
Wed Mar 25, 2020 2:30 am
wow thats about the most expensive DIY I've ever seen!
Courtesy of Roman F.

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