Sound Technology 1700B

No one else has answered so my best attempt is to make it yourself. Unless you need the best common mode noise rejection when twisted pair with an overall screen would be best.

I think that the input connections are just 4 mm terminal post sockets. Possibly the spacing is the 'standard 0.75 inch' so a 'BNC female to double stacking banana plugs adaptor' could be useful for testing single ended equipment. Common mode noise, apart from mains harmonics, is usually not a problem (grosss generalization).
 

Elvee

Member
2006-09-08 2:04 pm
If you use its balanced capabilities, you need indeed a shielded twisted pair.

If your sources are mainly unbalanced, you can use shielded or coax cable, and strap the (-) and ground posts.
That is the configuration I use myself in 99%+ of cases
 

Elvee

Member
2006-09-08 2:04 pm
I like it, but be sure to test it properly before you buy, because some of the parts do not age very well: the carb comp resistors, switch contacts, analogue optocouplers, potentiometers, etc.

Make it measure its own THD on the most sensitive scale: if there are such issues, they will generate extra noise, and the measurement floor will be too high
 
I have a 1700b also. When working, they are very nice instruments. The only complaint would be the size. They eat up a lot of work bench space. But the are capable instruments and seem to work well.
I like that the calibration procedure can be done without any expensive , rare equipment. It pretty much uses itself to calibrate itself. A good voltmeter, frequency counter and oscilloscope is all that is needed.
But if it isn't working, they are a bear to work on. Depending on which options it has, it can be difficult to get to the bottom side of the boards. The manual suggests for most repairs you cut the leads of the bad component on the top side and tack the new part to the remnants of the leads. For some parts that is not possible. Getting the boards out so you can work on them can be done, but it requires patience. Take careful notes and pictures, because none of the manuals I have found online show the board interconnects very well.
Check that the oscillator works in the low distortion setting. When you switch it to this position, it should turn off the LED and settle in. If if clicks back and forth from fast response to low distortion, then you have some work to do. Hopefully just an alignment, but the circuit uses a light dependant resistor that can fail. It is obsolete, so finding a new part that works may require some circuit modifications and re-tuning. There is info on the web on how to do it though.

Terry
 
A 1700B sold on eBay came with the following comment: Unfortunately, as far as I know,*the optos are no longer available. Fortunately, I have a second working unit, and*I was able to characterize the optos from that unit --two of the analyzer optos are installed in pin sockets, so they*are easy to remove. For replacement optos*I used the Silonex NSL-32SR3. These are readily available from Digikey. Two of the analyzer optos*act as switches, they are either totally on or totally off and therefore they are fairly easy to substitute, and the NSL-32SR3 works perfectly fine. The other two analyzer optos are critical and need to closely match*the original opto characteristics. For these I used two NSL-32SR3 optos with their LEDs wired in*parallel and used only one of the opto LDR outputs wired in series with a 120 ohm resistor. This combination very closely matches the original*optos taken from my other*working unit. The generator also required the NSL-32SR3 combination--refer to*photos.
 

1audio

Member
Paid Member
2004-03-24 5:16 am
SF Bay Area
I don't think that's necessary for the 1700. I believe there are direct crosses in the Silonex/whatever today. Digikey has them under Luna Special Purpose | Isolators | DigiKey Looking through the original Vactec specs : http://datasheet.octopart.com/VT935G-EG&G-datasheet-6396822.pdf my guess from several clues is the VTL5C9 which has the fastest response and the highest dynamic range and is the least stable. Off resistance is 50 Meg, on seems to be 100 Ohms I think the NSL32SR2 would be the best choice in their collection and available as 1 piece for $3.45 It should be lower distortion than the Vactec's were.

More info relevant to ST1700 stuff here: http://www.diyaudio.com/forums/equi...not-settling-distortion-mode.html#post2207208
 
I would like to share the results of my test for obtaining the resistive optocouplers' characteristics (output resistance of the photoconductive sell vs. the input LED current).
[IMGDEAD]http://onlyliveaudio.com/Images/Optocouplers - final.gif[/IMGDEAD]
The characteristics represented in the picture are averaged for at least 5-10 devices of each optocoupler type, these samples were kindly sent to me by their manufacturers (Silonex, Perkin Elmer, Tesla and others).
I also would be thankful if anybody could create the simulation models of these
optocouplers, based on adduced graphical data.
Some examples of using the the resistive optocouplers can be found on my site
Audio Test and Measurements in its instruments' section.
 

1audio

Member
Paid Member
2004-03-24 5:16 am
SF Bay Area
Great work. The other aspect that will affect the performance is the response time. Too fast and the amplitude of the oscillator or the nulling may oscillate. Too slow and the user may get frustrated.

The Luma (or whomever they are this month) are supposed to be lower distortion. That's also important. Have you been able to measure a difference? There are many variables to measuring an optocouplers distortion so its not easy to setup direct comparisons.
 
OPTO's

I have made several test systems for testing and matching OPTO's for compressors, expanders and limiters in audio products for several clients.
I used a Audio Precision System One, Two & Cascade and a DCX-127 and custom interfaces to match for several modes. I sorted the opto into bins of 100. I had spent MANY HOURS developing testing times, currents pulsing, delays, dark resistances, voltages across the cells needed to match them. One thing that helped was that the clients had selected what opto they wanted. It was a great learning process.
Duke:)
 
Of course, the optocoupler response time is a hindering factor when optimizing the settling process in oscillators and automatic tuning systems.
The only its positive effect is additional filtering of the signal coming, say, from the oscillator's amplitude control and being still slightly AC modulated. This is beneficial for reducing the oscillator distortion.
As for the optocoupler own distortion, it can be made sufficiently low, if the voltage across its photocell is kept below 100mV and its resistance doesn't exceed 1-2kohm.
The optocoupler linearity also has the tendency to be better for the devices which require higher LED currents to reach the same output resistance. My experiments show that Tesla 3WK163-43 optocouplers exhibit slightly lower distortion in the equal working conditions.
 

1audio

Member
Paid Member
2004-03-24 5:16 am
SF Bay Area
The first generation of optocouplers used incandescent lamps with the photocells. Those worked very well for filtering out ripple in the drive signal etc. But incandescent lamps have issues with life and heat so they were obsoleted long ago. However they may be well suited to AGC type applications.

The Tesla optocouplers are interesting and unknown in the US. Optoelectronic elements - photoconductive cells, optocouplers with photoresistor .
 
The output characteristic of the optocoupler with miniature incandescent lamp isn't so good reproducible as in its LED counterpart. It's enough to shake the device and the value of its output resistance may be changed due to the filament's flexible suspension, the lamp being simultaneously a source of light and heat.
This drawback is particularly annoying in the dual optocouplers where the close matching of both resistive outputs is very important.
But these so-called obsolete optocouplers have an excellent ability to convert the RMS value of input AC current to the output resistance and then to a DC current.
In comparison with traditional thermo-couples these devices have smaller thermal inertia, higher output signal level and wider dynamic range of input AC voltage.
In my VK-8 RMS converter the optocoupler's lamp is alternately supplied with the AC and DC currents being correspondingly proportional to the unknown AC voltage and a regulated DC voltage. The lamp heating produces light which acts upon a photoresistor, the converter's automatic system maintaining its resistance always the same.
Therefore, the produced DC voltage can serve an exact (0,3%) RMS equivalent of the input AC voltage lying within 0,1-1V and having frequency range of 10Hz-1MHz.
Vladimir.
 

Elvee

Member
2006-09-08 2:04 pm
The output characteristic of the optocoupler with miniature incandescent lamp isn't so good reproducible as in its LED counterpart. It's enough to shake the device and the value of its output resistance may be changed due to the filament's flexible suspension, the lamp being simultaneously a source of light and heat.
This drawback is particularly annoying in the dual optocouplers where the close matching of both resistive outputs is very important.
But these so-called obsolete optocouplers have an excellent ability to convert the RMS value of input AC current to the output resistance and then to a DC current.
In comparison with traditional thermo-couples these devices have smaller thermal inertia, higher output signal level and wider dynamic range of input AC voltage.
In my VK-8 RMS converter the optocoupler's lamp is alternately supplied with the AC and DC currents being correspondingly proportional to the unknown AC voltage and a regulated DC voltage. The lamp heating produces light which acts upon a photoresistor, the converter's automatic system maintaining its resistance always the same.
Therefore, the produced DC voltage can serve an exact (0,3%) RMS equivalent of the input AC voltage lying within 0,1-1V and having frequency range of 10Hz-1MHz.
Vladimir.
In fact, with a bit of ingenuity, the lamp itself can serve as sensor: no need to use a photoresistor:
http://www.diyaudio.com/forums/equi...escent-light-bulbs-into-rms-dc-converter.html
 

1audio

Member
Paid Member
2004-03-24 5:16 am
SF Bay Area
As for the optocoupler own distortion, it can be made sufficiently low, if the voltage across its photocell is kept below 100mV and its resistance doesn't exceed 1-2kohm.
The optocoupler linearity also has the tendency to be better for the devices which require higher LED currents to reach the same output resistance. My experiments show that Tesla 3WK163-43 optocouplers exhibit slightly lower distortion in the equal working conditions.

I just want to confirm-
for a given level (100 mV) lower resistance on the opto has lower distortion and the cells that need more light will have lower distortion under those conditions.

My understanding also is that the distortion decreases rapidly with level. This suggests using the couplers at low levels and low resistances will get the best results.
 
To reduce distortion contributed by the optocouplers and JFETs, the regulated element of automatic control or tuning systems should contain these inherently non-linear devices in series and parallel connection with ordinary metal-film resistors.
This reduces the control's effectiveness, but the art here is to maintain this control at a sufficient level by using such methods as narrowing its dynamic range, making it two-channel (fast and precision) and others.
A single 2N4391 JFET with its 100-150ohm on-resistance and the series resistor of several kohms can perform tight amplitude control of the oscillator and ensure its distortion below -140dB even at high (16kHz) audio frequencies.
 
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1audio

Member
Paid Member
2004-03-24 5:16 am
SF Bay Area
Thanks for the details. What you describe is essentially what Sound Technology did in the 1700. I found a reference on the schematics to a Clairex CM6000 as the optocoupler. And the datasheet for that says on resistance 500 Ohms at 20 mA, off 500 Kohm, rise time (on) 3.5 mS fall (off) 500 mS. This should make finding a match pretty straightforward. It looks like they used the same for all locations but did an internal sort. This is similar to old HP practice (where they came from) but a bit of a pain to reconstruct.