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Old 15th May 2005, 08:21 AM   #11
oblong is offline oblong  Australia
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Quote:
Originally posted by mazeroth
The one used in the article is the 33-2050, while the one Radio Shack sells now is the 33-4050, and is $5 more than the one listed in the article. Can anyone confirm these are the same?
I just purchased a 33-4050 model (7 scale selector switch, Tandy catalog Q1461 here in Australia), and I have not seen any other models. I opened it up, and just from the description of the component values, I'd say it is different from the models described on Eric Wallin's site. The original values I see are:

C1, C2, C3: 1 uF
C4, C5, C14, C15: 100uF
C7, C12, C13, C16: 22uF
C17: 220uF

C6, 8, 9, 10, 11, 18, 19 are surface mounted tiny capacitors on the rear side of the board.

So it would be good to know if anyone has information on the calibration of this model. It does have a trim-pot called "cal" (VR1) for calibration, but no instructions other than to take it to an expert for that.

Bob Long
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Old 15th May 2005, 12:11 PM   #12
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Quote:
Originally posted by oblong
It does have a trim-pot called "cal" (VR1) for calibration, but no instructions other than to take it to an expert for that.
My Sonicshop SPLmeter arrived a few days ago (see previous posts of me in this thread), and it also has a calibration trimpot and the instruction to take it to an expert if nessesairly.

Since you mentioned the capacitors, I assume you want to calibrate it for maximally flat frequency response.
I believe the trimpot is for setting the gain factor(sensitivity) and not for the freq resp.

Maybe you know someone who has access to much better equipment and you can use that to create a correction curve?
I have a friend who still studies for civil engineer at university of Ghent, and he knows of a lab in his faculty that tests material with soundwaves. When I go to Ghent in a few days, I'll start harassing some assistents
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Old 15th May 2005, 12:58 PM   #13
Salas is offline Salas  Greece
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Default RadioShack RCA out cal. data

Here you are, this is the RCA out (C curve switch setting) calibration file for the stock RadioShack

"Radio Shack low cost condenser mic (Salas)"
"Hz" "Data"
20.0, 25
40.0, -2.5
50.0, -1.5
63.0, -1.5
80.0, -1.5
100.0, -2.0
110.0, -2.0
200.0, -1.5
1500.0, -1.5
1800.0, -1.0
2000.0, -1.0
2700.0, 3.5
2900.0, 3.5
3500.0, 4.0
4000.0, 3.5
5000.0, 3.5
6000.0, 3.5
7500.0, 1.8
8000.0, 1.3
9000.0, 0.5
10000.0, -0.3
11000.0, -1.5
12000.0, -2.5
13000.0, -4.0
14000.0, -6.5
15000.0, -7.5
17000.0, -5.5
19000.0 -8
20000.0 -12
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Old 16th May 2005, 03:03 AM   #14
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I just got myself an 33-4050 radio shack test meter to use with this test CD:
http://www.rivesaudio.com/software/TestCD.html
The CD has 3rd Octave test tones already calibrated for the Radio Shack meter. Pretty handy really.
Joe
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Old 16th May 2005, 06:48 AM   #15
Salas is offline Salas  Greece
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Default soft RTA

Using some RTA windows based application (even freeware), you can drive your computer soundcard input using the correction values I gave and have much more resolution and faster checks than using a cd and a paper chart. Mind, the values I give are only for RCA out and differ from the needle or digit readouts on the RS (analog or digital they are the same device). Each value you see in my data can be entered and counteracted by the mic calibration function of measuring software.
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Old 17th May 2005, 04:10 PM   #16
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Yeah the test Cd and some graph paper are a bit of a pain in the a**. But it is certainly the simplest to get started testing right away. I'm using a Mac so there is no freeware RTA measuring software that I'm aware of.
Joe
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