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 Forum index » DIY Hardware and Software
Stereo to Mono
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Cynosure
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PostPosted: Fri Jul 07, 2017 5:17 pm    Post subject: Stereo to Mono Reply with quote  Mark this post and the followings unread

1. When mixing a stereo signal into mono should the amplification be 0.5 since the two signals have the potential to be twice as loud once mixed?

2. What power supply voltages should I use for a line level signal? I am thinking of using a TL072.

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PostPosted: Fri Jul 07, 2017 5:46 pm    Post subject: Reply with quote  Mark this post and the followings unread

1 - yes and no and no .. to avoid clipping at all cost (for fully correlated signals - or split mono) use 0.5 ... however when the signals are uncorrelated (noise) you'd want to use 0.707 to keep the perceived volume level the same .. however when the signals are anti-correlated (like a left / right ping pong) you'd want 1 even. For music its somewhere in between usually ...

0.707 is the square root of 0.5 .. as to why .. it's all about throwing dice and counting .. erm statistics.

Ideally add a volume control Shocked

Ideally add a cross fader too Shocked

2 - a couple of volts of headroom, or maybe 3, should give decent performance .. as line levels are around a volt and a pibolar bower subbly is ideal .. +5 and -5V .. that would leave some headroom too.

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Cynosure
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PostPosted: Fri Jul 07, 2017 6:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks Jan! That should be easy to do. I will aim for 0.7 and use a trimpot to set it manually.
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PostPosted: Sat Jul 08, 2017 2:29 am    Post subject: Reply with quote  Mark this post and the followings unread

Blue Hell wrote:
.. a pibolar bower subbly ..

I've got to get me one of those! Shocked Laughing

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Blue Hell
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PostPosted: Sat Jul 08, 2017 3:54 am    Post subject: Reply with quote  Mark this post and the followings unread

Is easy to do PHOBos, just before order exchange p&b keys Laughing

what i forgot about the 5V ... that is a practical minimum of course .. the maximum is in the datasheet .. and then just pick what suits you.

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PostPosted: Sun Jul 09, 2017 3:32 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for the info. Is this suitable? Do I need to add small caps in the feedback of the opamps to filter out high frequency noise, or is that not required? If so, what would be a good value to use?


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PostPosted: Sun Jul 09, 2017 5:11 am    Post subject: Reply with quote  Mark this post and the followings unread

TL should be stable without the lil caps.

... But I would not do the volume control pot in the feedback ... at the very least connect the wiper to one of the sides .. as otherwise when the wiper has bad contact things will get LOUD.


... But also .. you will need wires from the opamp to the pot and you may introduce unwanted signals this way being picked up by the wires .. or introduce inductance when the wires are longish. Better to do do the 'traditional thing' .. with a pot after the first opamp .. when you do not want to allow the signal to go to zero add a resistor between the pot and the ground.

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PostPosted: Sun Jul 09, 2017 5:23 am    Post subject: Reply with quote  Mark this post and the followings unread

I'd leave the (trim)pot out altogether and just use a 33K resistor, that'll give you a gain of about 0.7.
Depending on what it is for you might be able to get away with a passive solution using just resistors.

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PostPosted: Wed Aug 16, 2017 10:02 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks Jan and Phobos for the help. I went with the fixed 33k. It works perfectly. It was for the TV input on this cabinet:

https://www.instagram.com/p/BX3KMSFFikd/

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PostPosted: Wed Aug 16, 2017 2:07 pm    Post subject: Reply with quote  Mark this post and the followings unread

good to hear it worked Smile

did you have to replace anything in the cabinet like capacitors, tubes, speakers, as it is rather old ?

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PostPosted: Wed Aug 16, 2017 9:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

Luckily, the radio/reveiver section worked fine.

I had to change some of the speakers. It has on old electrostatic tweeter that still works.

I had to do some work on the turntable, which was kind of a new and interesting project because it is all mechinal and I am used to electronics.

I also updated the ungrounded plug to a grounded version.


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New grounded plug.
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Stereo to mono
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RCA jack hang out the back - sloppy but simple.
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