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Spec-1 ACV-314 pot lessons learned

Do you have a stable, 150 mV, 1khz sine wave signal source?
also a decent AC (milli) voltmeter ?

You could pipe in the 1 khz, read the ac volts at it's output and record the volts at each switch position.
The rest is calculation, which can be done anywhere & anytime if the data is posted in the thread.
 
markthefixer said:
Do you have a stable, 150 mV, 1khz sine wave signal source?
also a decent AC (milli) voltmeter ?

You could pipe in the 1 khz, read the ac volts at it's output and record the volts at each switch position.
The rest is calculation, which can be done anywhere & anytime if the data is posted in the thread.
Click to expand...
Well, I have used a laptop for the 1khz tone and I guess I could put it thru another preamp to adjust the output to 150mv then put that into the Spec1? Is that right?
Or maybe I can adjust the laptop output to 150mv....
 
The 150 mV is a maximum voltage for the Spec-1 aux and tuner inputs. They both have an input impedance of 100 kilo ohms.

I thought the greater obstacle would be something that measured 0 to 990 millivolts at 1,000 Hz AC

When I did this with mine I believe I sent in 100 millivolts and the output voltage was about ~ 950 millivolts. Nothing is in concrete, nor does it need to be.
Just an accurate reading at the output, somewhere around 1 volt at the 0 db position.
then accurate readings at the -2 db, -4db and so on positions.

No need for a second preamp, the unused Spec-1 ACV-314 will do quite nicely....

Quite frankly, use the "a" wafer of the disconnected Spec-1 ACV-314 to control the computer's output level :
connect the computer's sinewave output to the A wafer's input. (orange)
connect the A wafer's slider output to the Spec-1 aux input. (green)
And of course, the computer, ACV-314 and Spec-1 grounds (black)


upload_2021-5-26_14-57-7.png


Start at the ACV-314's infinity position, and adjust the ACV-314's output upwards (feeding more and more volume)
until the Spec-1's output ( which should initially be set at the 0 db position ) gets about 1 volt on your AC voltmeter.

Doing it UPWARDS compensates for any input impedance effects caused by the input impedance of the Spec-1 preamp aux or tuner input.

Once you have about a volt AC reading on the meter monitoring the Spec-1's output AT the Spec-1's 0 db position, stop.

This is now the 0 db reading. record it. It is the "reference level".
turn the Spec-1 PREAMP to the -2db position, record it's new lower reading.
turn the Spec-1 PREAMP to the -4db position, record it's new lower reading.
"rinse and repeat" until you reach the infinity position (right after -60 db), \
after which the readings are posted.

You could fool with this online calculator: http://www.sengpielaudio.com/calculator-amplification.htm
 
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markthefixer said:
The 150 mV is a maximum voltage for the Spec-1 aux and tuner inputs. They both have an input impedance of 100 kilo ohms.

I thought the greater obstacle would be something that measured 0 to 990 millivolts at 1,000 Hz AC

When I did this with mine I believe I sent in 100 millivolts and the output voltage was about ~ 950 millivolts. Nothing is in concrete, nor does it need to be.
Just an accurate reading at the output, somewhere around 1 volt at the 0 db position.
then accurate readings at the -2 db, -4db and so on positions.

Quite frankly, use the "a" wafer of the disconnected Spec-1 volume control to control the computer's output level :
run the computer output to the pot's input.
take the wafer's slider output and send it to the Spec-1 aux input.

Start at the volume control's ZERO output, and adjust the volume control's output upwards (feeding more and more volume)
until the Spec-'s output ( which is set at the 0 db position ) gets about 1 volt on your AC voltmeter.

Doing it UPWARDS compensates for any input impedance effects caused by the Spec-1 preamp aux or tuner inputs.

View attachment 2238523
Click to expand...

So...once I get that set, I can record the voltage of each step of the homemade switch back down to infinity?
 
let me get my post FINISHED!!!!


here is a theoretical table of calculated readings, using the sengpielaudio (dot) com calculator:

0 0.990
-2 0.786
-4 0.624
-6 0.496
-8 0.394
-10 0.313
-12 0.248
-14 0.197
-16 0.156
-18 0.124
-20 0.099
-22 0.078638
-24 0.0624
-26 0.0496
-28 0.0394
-30 0.03130
-33 0.02216
-37 0.013983
-42 0.00786
-50 0.003130
-60 0.00099
inf 0.00000
 
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I think I am done with that post. And I believe that your question is answered, BTW I didn't see your question during the time I was editing in the post.

My process is to do it, reread the post playing the other guy and finding where misunderstandings, assumptions and gaps exist, and fixing it. Sometimes I post it unfinished in defense of loss of the whole (darn) thing - which has happened to me in the past.
 
markthefixer said:
I think I am done with that post. And I believe that your question is answered, BTW I didn't see your question during the time I was editing in the post.

My process is to do it, reread the post playing the other guy and finding where misunderstandings, assumptions and gaps exist, and fixing it. Sometimes I post it unfinished in defense of loss of the whole (darn) thing - which has happened to me in the past.
Click to expand...
Thank you for all your help. I believe one of the fastest ways to become less stupid is not be afraid to ask stupid questions. So I do it often...
 
Has anyone built a replacement pot for the spec 1 yet? If so I need to figure out a way to get a replacement for a spare spec 1.
 
I have the parts for one, two or up to five controls,
but have not yet been able to take the time
to build one and actually TEST it with accurate instruments
to see how closely they mimic the originals.

Something always pops up with a higher "fix" priority....

Between crapped out computers and clapped out chairs, the end is fading out of sight in the distance.
 
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