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Old 5th September 2009, 10:16 PM   #11
Enzo is online now Enzo  United States
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I don;t think it is a secret. It is just not necessary information for service, so they don;t put it on the schematics.
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Old 6th September 2009, 03:45 AM   #12
labjr is offline labjr  United States
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Hard to say exactly what's causing the drift, but it seems like it's the crude oscillator circuit which is adjustable with a 100 ohm wire-wound pot. It just doesn't work well. It never did according to an old technician from Conn.

Changing the oscillator to a more stable one probably wouldn't be real difficult. It's doing it while retaining the adjustability without making major changes to the unit.

The motor in the ST-11 is a 24 V - 60 HZ - 1200 RPM synchronous motor. A while back I had measured some of the frequencies of the voltage applied to the motor while troubleshooting some of them, but I don't recall.

By the way Petersons virtual strobes are just that, virtual strobes. I have a Turbo-Tuner which is a real strobe. Great unit by the way. The best hand-held tuner I've ever used. Can't say enough about them.

Something about using an old Conn is cool though. Some professionals still use the ST-11.
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Old 8th September 2009, 04:45 AM   #13
Enzo is online now Enzo  United States
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The oscillator is the oscillator. The divider circuits don;t care what generated the signal. Changing the oscillator itself should have no effect on adjustability.

Put a freq meter on the old master oscillator and see what it does.

http://mmd.foxtail.com/Smythe/Conn_S...-11_Manual.pdf
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Old 8th September 2009, 12:56 PM   #14
labjr is offline labjr  United States
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Quote:
Originally Posted by Enzo View Post
The oscillator is the oscillator. The divider circuits don;t care what generated the signal. Changing the oscillator itself should have no effect on adjustability.

Put a freq meter on the old master oscillator and see what it does.

http://mmd.foxtail.com/Smythe/Conn_S...-11_Manual.pdf
The ST-11 is adjustable plus or minus 50 cents using the "cents" pot. If you want to retain the ability to to calibrate to non standard (440) tuning, the oscillator needs to be adjustable. This is the problem with just changing to a crystal oscillator.
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Old 9th September 2009, 12:06 AM   #15
Enzo is online now Enzo  United States
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SO how about a PLL instead of a crystal?
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Old 24th September 2012, 07:46 PM   #16
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Searching for ST-11 info got me here. The Conn users forum that was on the Peterson Electro-Musical Site is defunct.

I suppose by now the OP has built a stable master oscillator for his unit, I doubt if my information will help him, but maybe it will help someone else.

I looked at the ST-11 schematic and made a few measurements on the circuit. The Model ST-11 uses two 74121 dual one-shots to generate a 6.825usec clock pulse for a chain of six 7476 dual J-K flip flops which are configured as a 12-bit binary presettable ripple counter. When the most significant bit of the counter toggles, the counter is preset (reloaded) with a number, the value of this number is determined by the CAL switch, or if not in CAL then by the note selection switch. The twelfth (most significant) bit of the counter is always reloaded to 1, so only the lower 11 bits change according to switch position. The output of the counter at the MONITOR pin (pin 10 of the last 7476) is a square wave. The frequency of the square wave determines the motor speed.

In a positive-logic implementation, the amount of clock pulses needed to count from the preloaded count to the terminal count is the difference between those numbers. In this negative-logic implementation, the number of counts needed is the difference between the terminal count and the one's complement of the preloaded number. Simplified, this is the same as loading a number into the counter and then counting from that number down to zero. Ignoring the 12th bit, the numbers loaded into the counter are as follows:


Note Hz Count tw,msec Motor Hz Motor RPM
C 261.6 5D6 20.39 49.036 980.724
C# 277.2 582 19.25 51.957 1039.15
D 293.7 533 18.17 55.041 1100.83
D# 311.1 4E8 17.14 58.328 1166.56
E 329.6 4A2 16.19 61.771 1235.41
F 349.2 45F 15.27 65.469 1309.38
F# 370 420 14.41 69.375 1387.50
G 392 3E5 13.61 73.481 1469.61
G# 415.3 3AD 12.84 77.853 1557.07
A 440 378 12.12 82.500 1650.00
A# 466.2 346 11.44 87.423 1748.45
B 493.9 317 10.80 92.617 1852.34
CAL 120 32E 11.11 90.000 1800.00


The Hurst Model CA hysteresis synchronous motor used in this instrument has a standard speed rating of 1200 rpm for a 60Hz drive signal. The pattern wheel mounted to the shaft has two fundamental patterns per turn. For example, on the CAL setting 1800 rpm is 30rps, so the 2X fundamental pattern is occurring 60 patterns per second. The CAL light is pulsed 120 times per second, The ratio of CAL light pulses to fundamental pattern is 2:1. For tones, the ratio of note frequency to pattern frequency is 8:1.

Edit: apparently this editor deleted all of the column-separating TABs in my data. Anybody know how to fix that?
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Last edited by scooperman; 24th September 2012 at 07:48 PM. Reason: Loss of formatting
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Old 24th September 2012, 08:33 PM   #17
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Quote:
Originally Posted by scooperman View Post
The Model ST-11 uses two 74121 dual one-shots to generate a 6.825usec clock pulse [146.520 KHz] for a chain of six 7476 dual J-K flip flops which are configured as a 12-bit binary presettable ripple counter. When the most significant bit of the counter toggles, the counter is preset (reloaded) with a number, the value of this number is determined by the CAL switch, or if not in CAL then by the note selection switch. The twelfth (most significant) bit of the counter is always reloaded to 1, so only the lower 11 bits change according to switch position. The output of the counter at the MONITOR pin (pin 10 of the last 7476) is a square wave. The frequency of the square wave determines the motor speed.

In a positive-logic implementation, the amount of clock pulses needed to count from the preloaded count to the terminal count is the difference between those numbers. In this negative-logic implementation, the number of counts needed is the difference between the terminal count and the one's complement of the preloaded number. Simplified, this is the same as loading a number into the counter and then counting from that number down to zero. Ignoring the 12th bit, the numbers loaded into the counter are as follows:


Note .... Hz ...... Count ..... tw (ms) ..... Motor Hz ....... Motor RPM
C ....... 261.6 ..... 5D6 ....... 20.39 ........ 49.036 .......... 980.724
C# ..... 277.2 ..... 582 ....... 19.25 ........ 51.957 ......... 1039.15
D ....... 293.7 ..... 533 ....... 18.17 ........ 55.041 ......... 1100.83
D# ..... 311.1 ..... 4E8 ....... 17.14 ........ 58.328 ......... 1166.56
E ....... 329.6 ..... 4A2 ....... 16.19 ........ 61.771 ......... 1235.41
F ....... 349.2 ..... 45F ....... 15.27 ........ 65.469 ......... 1309.38
F# ..... 370 ........ 420 ....... 14.41 ........ 69.375 ......... 1387.50
G ....... 392 ........ 3E5 ....... 13.61 ........ 73.481 ......... 1469.61
G# ..... 415.3 ..... 3AD ....... 12.84 ........ 77.853 ......... 1557.07
A ....... 440 ........ 378 ....... 12.12 ........ 82.500 ......... 1650.00
A# ..... 466.2 ..... 346 ....... 11.44 ........ 87.423 .......... 1748.45
B ....... 493.9 ..... 317 ....... 10.80 ........ 92.617 .......... 1852.34
CAL .... 120 ....... 32E ....... 11.11 ........ 90.000 .......... 1800.00


The Hurst Model CA hysteresis synchronous motor used in this instrument has a standard speed rating of 1200 rpm for a 60Hz drive signal. The pattern wheel mounted to the shaft has two fundamental patterns per turn. For example, on the CAL setting 1800 rpm is 30rps, so the 2X fundamental pattern is occurring 60 patterns per second. The CAL light is pulsed 120 times per second, The ratio of CAL light pulses to fundamental pattern is 2:1. For tones, the ratio of note frequency to pattern frequency is 8:1.
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Old 24th September 2012, 08:44 PM   #18
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hello Underhill, thank you. I have a text editor for programmable logic which has that kind of power, I could search out TABs and replace them with N periods, wish I did not have to do it though.
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Old 24th September 2012, 09:14 PM   #19
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Quote:
Originally Posted by labjr View Post
Hard to say exactly what's causing the drift, but it seems like it's the crude oscillator circuit which is adjustable with a 100 ohm wire-wound pot. It just doesn't work well. It never did according to an old technician from Conn.

Changing the oscillator to a more stable one probably wouldn't be real difficult. It's doing it while retaining the adjustability without making major changes to the unit.
So the Conn uses an RC clock made from 74LS121 mono stables ?
Isn't this text book of how not to build a Clock ?

The unit is about 40 years old.
Its pretty well vintage - so I would be concerned about modding it.

I remember one of my teachers, explaining how he made a thermally stable RC circuit
using an R and C that had complementary temperature co-efficients.
I'm wondering if this technique could be used with the Conn.


BTW: if you use a dynamics compressor with the Conn unit, it will make the tuning much easier.
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Old 24th September 2012, 09:30 PM   #20
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Scooperman,

Thanks for posting the technical info on the Conn ST-11.
Think I bought mine new circa 1979 ?

I guess they are not really collectable* - however, because of its vintage, I wouldn't want to mod the case.
Plus, from what you have described, the design is so archaic - I wouldn't try to mod the circuit.

If the RC clock uses a wire wound resistor - I'm wondering if it would be best to replace the clock's cap(s).


* I knew I should have bought a 1976 red wine Les Paul standard instead of the Conn Tuner.
There are a few decisions in my life I wish I could have back.
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