Volume control Circuit

Ray Thomas · Post by **Ray Thomas** » 22 Sep 2015 6:34 pm

Can anyone suggest a simple circuit to adjust the volume on a signal going from a cassette player to computer. The computer has a mike input only and the cassette player signal drives it wild, Any help or suggestions appreciated, my email rthomas17@nc.rr.com

Jerry Roller · Post by **Jerry Roller** » 22 Sep 2015 9:31 pm

Peavey speaker direct box?

Scott Duckworth · Post by **Scott Duckworth** » 23 Sep 2015 3:08 am

This is a setup we use in ham radio to go from a speaker out on a receiver to a computer in...

The parts "may" be available at Radio Shack...

Tim Russell · Post by **Tim Russell** » 23 Sep 2015 3:12 am

Radioshack used to (& still might have it in stock) an attenuator box that will do this - for short money.

I can't remember, I think it may have been less than $10-$15.

Georg Sørtun · Post by **Georg Sørtun** » 23 Sep 2015 4:00 am

As long as there's common ground, the following simple, and cheap, attenuator circuit will work just fine...

Line output can be stereo or mono, while the switch may be needed for combining stereo lines to a mono mic input.

Craig Baker · Post by **Craig Baker** » 23 Sep 2015 4:10 am

Georg, Scott,
May I suggest, while either circuit will work, if you're coming out of a speaker jack, you should replace the speaker with the proper load across the output.(8 ohms?)

In order to avoid high frequency loss, the volume control components should all be located as close to the computer as possible. As in the world of pedal steel guitars, the longer cable run should be at low impedance in order to avoid the dreaded T S S. (Tone Suck Syndrome)

Scott,
Why don't you feed both channels (mono) of your sound card?

Best regards,
Craig Baker 706-485-8792

cmbakerelectronics@gmail.com

C.M. Baker Electronics
P.O. Box 3965
Eatonton, GA 31024

Georg Sørtun · Post by **Georg Sørtun** » 23 Sep 2015 4:25 am

Craig, you're right of course - put such a circuit as close to the mic-input as possible. But, with most line-outs in the <500ohm>5Kohm range (not 600ohm or anything), coax cables have to be above 10 feet in length to get an appreciable loss of highs in the audio - <20KHz - range.

Craig Baker · Post by **Craig Baker** » 23 Sep 2015 4:31 am

George,
True, but don't forget you're going through a 47K resistor and another 47k pot. (By the way, where did you find a 47K pot? Your line impedance could be anywhere between 47K and 94K ohms.

Best regards,
Craig Baker 706-485-8792

cmbakerelectronics@gmail.com

C.M. Baker Electronics
P.O. Box 3965
Eatonton, GA 31024

Georg Sørtun · Post by **Georg Sørtun** » 23 Sep 2015 5:01 am

Craig

1: standard pot-values - lin and log - are 10K, 22K, 47K, 100K etc ... have loads of them in my workshop, and I just picked a value in the usable range for such a simple circuit.

2: line-load can vary that much in my circuit - depends on the mic-input load actually, which for the typical unbalanced line-out of a cassette player is quite OK. Any load that is at least 10 times higher in resistive value than an output's impedance, will work.

If I knew exactly what line-output and mic-input I had to deal with here, those resistor and pot values would have been "tuned optimally" for those - most likely much smaller resistive values. Instead I chose values based on "educated guesses" for what will work reasonably well no matter what, and components with the values shown should be available everywhere.

Just keep such a "medium impedance" circuit well away from sources of electrical noise - or screen it well, and it should "just work".

Craig Baker · Post by **Craig Baker** » 23 Sep 2015 5:32 am

Georg,
No doubt we are on the same page, and the circuit will perform perfectly well in the "real world".

My suppliers show those as standard resistor values, but not for pots. Here's a screenshot:

That's why I raised the question regarding the 47K pots. Maybe they think it's too much trouble to stock all values.

Best regards,
Craig Baker 706-485-8792

cmbakerelectronics@gmail.com

C.M. Baker Electronics
P.O. Box 3965
Eatonton, GA 31024

Georg Sørtun · Post by **Georg Sørtun** » 23 Sep 2015 5:41 am

Craig Baker wrote: Maybe they think it's too much trouble to stock all values.

...or maybe my lists, and actual components, are a bit old. I haven't stocked up on passive components for about a decade or so, and expect to have enough to last me for life now that I only play with private projects

Stephen Cowell · Post by **Stephen Cowell** » 23 Sep 2015 7:01 am

http://www.bhphotovideo.com/c/product/8 ... uator.html

Craig Baker · Post by **Craig Baker** » 23 Sep 2015 7:27 am

Stephen,
Interesting find, but the attenuation isn't great enough, and for a cord that isn't long enough, the price isn't low enough.

Best regards,
Craig Baker 706-485-8792

cmbakerelectronics@gmail.com

C.M. Baker Electronics
P.O. Box 3965
Eatonton, GA 31024

Olli Haavisto · Post by **Olli Haavisto** » 23 Sep 2015 7:46 am

I would get a cheap USB souncard with line inputs.