Question About Organ Service Manual Test Procedure

Mike Rivers wrote:
===============
>
> I think you're over-thinking this. Measurements with your meter will get
> you well into the ballpark. At that point, take on the job of "organ
> technician" and use your ears. If some notes stick out, adjust those so
> they blend in with the rest of the instrument.

** Absolutely.

This Q has been thoroughly over answered.

The OP is being too pedantic for words.

> In the Amphenol VTVM era, we didn't use dBu or dBV, and 0 "dB"
> represented the voltage required to pump 1 milliwatt into a 600 ohm
> load, which is the reference voltage for dBu.
>
> [(0.775 V)^2 / 600 Ω = .001 mW]

** Errr - might be .001 Watts ?


...... Phil

On 1/24/2021 6:00 PM, wrote:
>> [(0.775 V)^2 / 600 Ω = .001 mW]
> ** Errr - might be .001 Watts ?

Yup. I had milliwatts on the brain.

--
For a good time, call http://mikeriversaudio.wordpress.com

On 25/01/2021 3:04 am, Mike Rivers wrote:
> On 1/24/2021 6:03 AM, Paul Dorman wrote:
>
>> Â*Â*Â*Â* I have a standard Digital multimeter.Â* The test notes go up to
>> A#4, which is 466 Hz, which might be pushing the frequency response of
>> the meter.
>
>> Â*Â*Â*Â* The organ stop tabs used are Diapason 8' and Tibia 8'.Â* I am not
>> sure about the Fourier Transform of these waveforms, but hopefully they
>> are close enough to an ideal sinewave, that the measured RMS value
>> will be close enough.
>>
>> Â*Â*Â*Â* But the harmonics of a 466 Hz fundamental, can be far beyond
>> 500 Hz, and hence out of the meter's range.
>
> >Â*Â*Â*Â*Â*Â* This test procedure appears to be a simple level-
> > setting adjustment for volume, for the different groups > of stop
> tabs in the organ.Â* Some measurements are at > the voice coil of the 12"
> speaker, and some are
> > measured at a crossover network.
>
> I think you're over-thinking this. Measurements with your meter will get
> you well into the ballpark. At that point, take on the job of "organ
> technician" and use your ears. If some notes stick out, adjust those so
> they blend in with the rest of the instrument. Not all organs are voiced
> perfectly, so get it close with your meter and then touch it up as needed.
>
>> Â*Â*Â*Â*Â* I just noticed that the service manual mentions that a model
>> 870 Amphenol is an excellent choice for "measuring audio signals
>> as low as -50dB".
>
> That's the kind of multimeter that was the standard bench instrument on
> a radio/tv repair shop. Because measurements often must be made at the
> grid of a tube, the megohms-input impedance of the VTVM, because of the
> tube at the front end, wouldn't load down the signal that's there.
>
> The input impedance of a modern DMM is pretty high, so you shouldn't
> have any problem making measurements either at the speaker terminals or
> the input of the crossover network, even if it's a tube amplifier.
>
> In the Amphenol VTVM era, we didn't use dBu or dBV, and 0 "dB"
> represented the voltage required to pump 1 milliwatt into a 600 ohm
> load, which is the reference voltage for dBu.
>
> [(0.775 V)^2 / 600 Ω = .001 mW]
>
> -50 dBu is about 2.5 mV. If this is a tone wheel organ, you'd find
> voltages in that range coming right off the pickups (I think - I don't
> know for sure), so unless the adjustment procedure involves mechanical
> adjustment of the pickups to adjust the level going into the amplifier
> section, you'll be fine with the sensitivity range of your meter.
>
> Happy tweaking, Mr. Organ Technician.
>
>
>

Here are some organ technicians. Or specialists at least , though mostly
Hammond-centric.

Have got useful info and replacement parts off them in the past for my
C3 and L122 ....

http://www.tonewheelgeneral.com/

geoff

And for those suspicious of the link:
view-source:http://www.tonewheelgeneral.com/

On 1/24/2021 7:04 AM, Mike Rivers wrote:
> On 1/24/2021 6:03 AM, Paul Dorman wrote:
>
>> Â*Â*Â*Â* I have a standard Digital multimeter.Â* The test notes go up to
>> A#4, which is 466 Hz, which might be pushing the frequency response of
>> the meter.
>
>> Â*Â*Â*Â* The organ stop tabs used are Diapason 8' and Tibia 8'.Â* I am not
>> sure about the Fourier Transform of these waveforms, but hopefully they
>> are close enough to an ideal sinewave, that the measured RMS value
>> will be close enough.
>>
>> Â*Â*Â*Â* But the harmonics of a 466 Hz fundamental, can be far beyond
>> 500 Hz, and hence out of the meter's range.
>
> >Â*Â*Â*Â*Â*Â* This test procedure appears to be a simple level-
> > setting adjustment for volume, for the different groups > of stop
> tabs in the organ.Â* Some measurements are at > the voice coil of the 12"
> speaker, and some are
> > measured at a crossover network.
>
> I think you're over-thinking this. Measurements with your meter will get
> you well into the ballpark. At that point, take on the job of "organ
> technician" and use your ears. If some notes stick out, adjust those so
> they blend in with the rest of the instrument. Not all organs are voiced
> perfectly, so get it close with your meter and then touch it up as needed.
>
>> Â*Â*Â*Â*Â* I just noticed that the service manual mentions that a model
>> 870 Amphenol is an excellent choice for "measuring audio signals
>> as low as -50dB".
>
> That's the kind of multimeter that was the standard bench instrument on
> a radio/tv repair shop. Because measurements often must be made at the
> grid of a tube, the megohms-input impedance of the VTVM, because of the
> tube at the front end, wouldn't load down the signal that's there.
>
> The input impedance of a modern DMM is pretty high, so you shouldn't
> have any problem making measurements either at the speaker terminals or
> the input of the crossover network, even if it's a tube amplifier.
>
> In the Amphenol VTVM era, we didn't use dBu or dBV, and 0 "dB"
> represented the voltage required to pump 1 milliwatt into a 600 ohm
> load, which is the reference voltage for dBu.
>
> [(0.775 V)^2 / 600 Ω = .001 mW]
>

If we calculate 1 milliWatt into a speaker 8 Ohm load, it will be:

(0.089 Vrms)^2 / 8 Ohms = .001 Watt

And 5dB above that would be .00316 Watts = (0.159 Vrms)^2 / 8 Ohms.

So it's obviously impedance dependent.


> -50 dBu is about 2.5 mV. If this is a tone wheel organ, you'd find
> voltages in that range coming right off the pickups (I think - I don't
> know for sure), so unless the adjustment procedure involves mechanical
> adjustment of the pickups to adjust the level going into the amplifier
> section, you'll be fine with the sensitivity range of your meter.
>
> Happy tweaking, Mr. Organ Technician.
>
>
>