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Old 9th September 2006, 04:03 PM   #1
jblmar is offline jblmar  United States
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Default Sound Technology ST 1000A & 1701A

Hi all,
Just picked up an ST 1000A & 1701A. Anyone have suggestions regarding the best setup and practices to align an FM tuner as well as check amplifier distortion on these units?
I did find information on the web, but I'm starting with this equiptment and don't want to get into any bad habits.
Thanks for your input.

Ron
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Old 9th September 2006, 04:48 PM   #2
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Hi jblmar, I've got the same setup.

For amp power:
Set the Frequency (400Hz or 1kHz is common).
Set the ST1701's attenuator to -70 dB.
Connect your loads (4 ohm, 8 ohm) to speaker out (Amp DUT).
Connect the ST to speaker out (Amp DUT).
Turn on the Amp DUT
On the ST, set Function to Volts/Power
Set the input range to 100 or 1000 Watts.
Start reducing the attenuation from -70 dB to -60 dB, -50 dB etc while observing the waveform, ...looking for clipping.
.....There's an o'scope involved? right?
Reduce the ST osc level with the "Output Vernier" to just before clipping.
If you have connected to 8 ohm loads, you can read the power directly off of the Wattage scale. If you have other than 8 ohm, you'll have to get the voltage and calculate.
After you get Power (or Voltage), push "Set Level". Turn "Adj" until the meter is fully right at "set level".
Press "Distortion" and get your reading.

Have you aligned FM before? It's very easy to get "lost". It takes a lot of experience and talent to unwind a badly misaligned FM section.

As a general rule, I like to:
1. Peak the front-end (RF section, mono input)
2. Adjust discriminator (Center tune and min mono distortion)
3. Check IF (symmetrical de-detuning, etc, in mono)
4. Switch to Stereo modulation
5. Ajdust mixing transformer (Lo+RF) for minimum Stereo distortion.
6. In the dMPX, peak the modulated channel's output with the VCO control.
7. Adjust the 38kHz or "sep" control for best seperation.
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Old 9th September 2006, 06:06 PM   #3
jblmar is offline jblmar  United States
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Hi mrshow4u,
It is a nice set up. I do have an oscilloscope and no, I've never attempted an alignment. I need to do my homework before attempting it.
At the moment, I would like to check (check only my Marantz 2130 performance as per the service manual. That would be a good starting point.
I need to master alignment before turning things inside a tuner.
How do you find the results with yours?

Ron
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Old 9th September 2006, 06:43 PM   #4
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Yes the Sound Tech stuff is good. It's too bad they couldn't compete with Audio Precision. I get 0.002% THD+N with the 400Hz and 80kHz filters enabled. It seems there might be a small amout of hum. I left my input cables hooked up but pressed "Analyzer Select/Generator Output". Maybe it doesn't fully disconnect the input leads.

For the 1000A: I love that thing. Do you have the Sound Technology BALUN? I think it's called the T-100. Anyway, it changes the 50 ohm output on the 1000A into a 300 ohm output. If you have the BALUN, that's awesome because you can read the uV or dBf scale directly for sensitivity measurements. If you don't have the BALUN, you'll need to make a resistive matching network. ....and you will have to subtract 6dB from your 1000A RF Level reading.

Typical sensitivity measurements I get are anywhere from 3uV to 9uV.
Typical FM separation is 35 to 42 dB. Made way better ~50dB with bandpass filtering. That could be the limits of the 1000A.
Mono distortion anywhere from 0.2% to 1.5%
Stereo distortion 0.3% 2%

I think these are probably ballpark number for a properly aligned FM tuner. Best Tuner I ever aligned?? Hands down Tandberg 3001
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Old 9th September 2006, 09:52 PM   #5
jblmar is offline jblmar  United States
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Yes I have the BALUN.
Can't wait to see the performance of my Marantz 2130. Sounds great from day 1.
My oscilloscope has the back lighted feature for picture taking. When I get everything set and have a full understanding, I'll post pictures. Should have a digital camera by then.

Ron
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Old 1st March 2007, 02:41 PM   #6
jblmar is offline jblmar  United States
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HI MRSHOW4U,

What do you consider the best way to measure THD on the 1701A? The manual doesn't cover that area.
Thanks for your help.

Ron
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Old 1st March 2007, 06:36 PM   #7
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Hi JBLMAR,

Well, there's all kinds of way's to measure THD+N. The "+N" is important because you will be capturing Noise as well as the harmonics (THD). So, you can make a measurement referenced to 1 Watt output, or measure THD+N relative to full power output. ..this is for power amps, by the way. Since most power amps can put out one watt, you can make side by side measurements of different power amps putting out 1 watt.

Important note: If the power amp's output is not common grounded, you must use the differential input of the 1701's input stage. Plus to Plus, Minus to Minus. ......without the chassis ground connected to Plus or Minus.

Connect a load resistor to the power amp output (4, 8, 16 ohm, whatever)
Connect the power amp output to the Sound Tech's Analyzer Input ...Red, or Plus to ST + (unless you have a Carver amp) and power amp Minus to Sound Tech -.

Turn the Sound Tech's Generator low (Full CCW) and the output attenuator full-CCW. Connect generator output to power amp in, tape in, tuner in, whatever. Turn on power ap (or receiver). Set volume on product half way, or so.

In the case of a receiver, you'll want the ST generator at full output (Full CW), then use the volume control on the product to scale the output. In the case of a power amp with no input level setting controls, you'll use the Sound Tech's output level control to scale the output.

You select "input" pushbutton. increase the output of the device using the volume control or the generator output level control. You increase the level until the voltmeter reads 2.828 Vrms sqrt(PxR). Note: the Sound Tech has a Watt scale that is accurate when 8 ohms is the load. Press set level and adjust the Set level control full-CCW, then adjust the "dB/dist" control fully clockwise. Push the "set level" button and turn the set level knob until the meter reads "-0 dB", or full right without pegging.
Now push the "dB" pushbutton and read your THD+N. I usually engage the 80kHz filter to prevent ultrasonic noise from impacting the measurement.

Typical operating level measurements are:
1 Watt for power amps
200mV for consumer line level gear.

The Sound Tech's voltmeter reads the level.
The Set Level knob set the reference level from which the THD+N measurement is made relative to.
The "dB" meter sets the senstivity of the THD+N measurement. The "dB" reading is the output of the notch filter that is locked to the generators output.

Let me know if you want more clarifications. Happy Measuring.
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Old 2nd March 2007, 05:29 PM   #8
jblmar is offline jblmar  United States
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Hi mrshow4u,
Thanks for the quick response.
What I don't understand is the following. In the Owners Manual, it states the following example of how to measure THD.

"For example: If meter reading is .67, and RATIO switch is at .1%, distortion is .067%."

My question is how do you read .67? Is it the result of the Distortion Meter's range from 0 to 3 and the pointer settling on '2' in this example? (2/3 of full scale?)
That's where I'm stuck. I'm familar with the WPC at 8 ohms scale and have no problem measuring WPC.
I do have option 003 (Set Level) and I set the Ratio level when the Over & Under LEDs went out. I'm not sure what I'm reading on the distortion scale.

TIA

Ron
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Old 2nd March 2007, 09:34 PM   #9
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Hi jblmar,

Hmmmmmm, the meter is scaled from 0 to 3?? Only??? I have a 1701A and it's meter has a 0 to 3, a 0 to 1 calibration, as well as a dB scale. Is it possible that the manual you have is not for your version of the instrument? Yeah, I think ST's example of "0.67" is supposed to be used with the 0 to 1 scale.

Does the Ratio knob's legend show Percent and dB?

I ask because that's what made readings really convenient. For after pressing set level and adjusting for Full meter deflection, then pressing distortion and adjusting the Ratio knob, I get some meter reading mid-scale. If the ratio knob is at "0.01" Percent, the "0.01" Percent value is at full needle deflection. Since my reading is mid-scale, it is below 0.01% THD+N. My reading is something like 0.005% THD+N.

If the meter is scaled from 0 to 3, you could use the same method, except the full scale readings would be: 3%, 0.3%, 0.03% etc

Does that make any sense? You should be able to measure THD+N @1kHz of the 1701's generator, somewhere about -95 dBr/ 0.002%

Good Luck,

Jon
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Old 3rd March 2007, 05:41 PM   #10
jblmar is offline jblmar  United States
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Hi Jon,
Thanks for the info. I see where I made my mistake. I was using the 0 to 3 scale, the scale above the dB markings or third from the top.

I have the following scales;

WATTS: 0.5 to 1.0

VOLTS RMS: 0 to 1.0 (This is the scale I believe I should use for THD).

No mention of what the next scale is for, but I would think it's for the 'extended voltage' rating.

dB: The dB scale.

I believe that the VOLTS RMS scale (0 to 1.0) scale should be used for the THD measurements. 0.67 now makes sense.
I used the unmarked scale (0 to 3), but here I had to do some calculations. This will work, but it's the long way.

Do I make sense to you?

I do have the % and dB markings on the Ratio switch.

Thanks again for your help.

Ron
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