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 Forum index » DIY Hardware and Software » Lunettas - circuits inspired by Stanley Lunetta
Volume Buffer
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synthesist



Joined: Feb 17, 2011
Posts: 79
Location: austria
Audio files: 2

PostPosted: Tue Feb 22, 2011 6:44 am    Post subject: Volume Buffer
Subject description: my op amp is way too loud
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Hey there!!

I've been watching this forum for a few weeks now and I really like it a lot.
I am glad that there is actually a real forum for cmos synths.

So, I've build a few modules and they all hang on a single 6 volt supply.
Some VCOs, LFOs, 4-Step Sequencer, a WSG- Filter, Atari Punk Console and a Cacophonator.

The main- problem is that the sound output of the cacophonator (Art Harrisson design) is very low. Also the output of the WSG- Filter. You can almost not hear it.
I made an op- amp circuit to raise the volume to line level using the LM 386. Of course it is way too loud now. The LM 386 I guess is made to drive speakers only.

Of course I can use some resistors to lower the volume now, but isn't this a waste of power? (Sorry but indeed I have no idea of electronics.)
And does it matter if I put the resistor after the amplifier or before the signal gets into the amplifier, to save some power?
Or does someone have a better idea how to buffer the volume to line level?

This is the shema of the amp

circuit:http://www.hobbielektronika.hu/forum/files/30/30b186a707557adee3a4c5300efdc80c.gif


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egasimus



Joined: Feb 11, 2011
Posts: 113
Location: Bulgaria

PostPosted: Wed Feb 23, 2011 11:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

You put the resistor in the feedback loop of the opamp (between the output and the inverting (-) input). There's probably a resistor already there, so increase its value. For starters, try putting a resistor of twice the value there.

Also check out those two links:
http://en.wikipedia.org/wiki/Voltage_divider
http://en.wikipedia.org/wiki/Operational_amplifier_applications (see Inverting amplifier)
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richardc64



Joined: Jun 01, 2006
Posts: 679
Location: NYC
Audio files: 26

PostPosted: Thu Feb 24, 2011 12:24 am    Post subject: Re: Volume Buffer
Subject description: my op amp is way too loud
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synthesist wrote:
Hey there!!


I made an op- amp circuit to raise the volume to line level using the LM 386. Of course it is way too loud now. The LM 386 I guess is made to drive speakers only.

Of course I can use some resistors to lower the volume now, but isn't this a waste of power? (Sorry but indeed I have no idea of electronics.)
And does it matter if I put the resistor after the amplifier or before the signal gets into the amplifier, to save some power?


You're on the right track. Decreasing the signal level going in won't waste power: it will reduce the '386 power consumption.

Internally, the '386 input has a 50k resistor to ground. A resistor in series with the input will form a voltage divider with that, reducing the input level: 47k or 51k will cut it roughly in half. Increase or decrease as needed.

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