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Old 30th May 2013, 06:29 PM   #1
00940 is offline 00940  Belgium
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Question Simple analog vu-meter driver ?

Wrapping up some projects...

I cased an headphones amplifier into an old tape recorder and it has a pair of nice analog VU-meters (Kyoritsu KM-86) on the frontplate. I'd like to use the meters to roughly monitor the output level into sennheiser HD650 (300 ohms). I don't need perfect ballistics. Cheap and easy to breadboard are more important factors here.

Would the following circuit do it ? (it's mostly a simplification of http://www.jlmaudio.com/AT51%20DIY%20VU.pdf ).

Click the image to open in full size.

R7-R8 are trimmers to adjust the vu-meter (I'm aiming to set the 0VU at a max "reasonable" level for long term listening). The headphones amplifier I'm using won't clip before +/-13V (peak) into 300r, so I need the to pad the signal going into the tl072. 10k in // with a 300r load is ok.

Thanks
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Old 30th May 2013, 08:03 PM   #2
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Here are some integrated VU-meter drivers K 157 DA 1 ( = 2 Kanal Ansteuer - IC fŁr VU - Meter ) | eBay
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Old 30th May 2013, 09:39 PM   #3
00940 is offline 00940  Belgium
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Thanks, those look like interesting parts but I've got all the parts on hand for the schematic above with the tl072. I'd rather avoid collecting even more parts ;-)
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Old 31st May 2013, 09:12 PM   #4
gpapag is offline gpapag  Greece
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Ben
I think you will be OK with you circuit.
If you donít care about ballistics you can go with something really simple, like the attached, one transistor circuit..

for a better circuit (VU-PPM), you can have a look here
VU And PPM Audio Metering

George
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Old 31st May 2013, 11:19 PM   #5
00940 is offline 00940  Belgium
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Thanks George. I'll save this schematic, very simple indeed :-)

I put the first one together this evening. It works quite ok. 100uf is too much in // with the meters I have, it makes it too slow. I'll try 10uf later on.

Btw, I enjoyed some fireworks in the process. Soldered the PS backwards and fed a poor tl072 -20Vdc. It didn't explode but started fuming and slowly split in two right in the middle. Oh happy times.
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Old 1st June 2013, 07:37 AM   #6
gpapag is offline gpapag  Greece
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Yes. 1uF to 10uF.

When I test new circuits or repair old ones, I wear safety glasses.

George
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Old 28th June 2013, 03:19 PM   #7
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Quote:
Originally Posted by 00940 View Post
Thanks George. I'll save this schematic, very simple indeed :-)

I put the first one together this evening. It works quite ok. 100uf is too much in // with the meters I have, it makes it too slow. I'll try 10uf later on.
Sorry could I ask if you're referring to the one-transistor circuit, I've planned to try that out too. Did it originally have a 100uF cap., it's not in the circuit?
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Old 28th June 2013, 04:25 PM   #8
00940 is offline 00940  Belgium
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I was referring to the one in the original post (with the tl072). I finally didn't try for myself the one suggested by gpapag.
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Old 28th June 2013, 04:30 PM   #9
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Thank you
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Old 2nd July 2013, 08:24 PM   #10
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Quote:
Originally Posted by gpapag View Post
Ben
If you donít care about ballistics you can go with something really simple, like the attached, one transistor circuit..
George
Hi ...quick question...is C31 Electrolytic?
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