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 Forum index » DIY Hardware and Software » Lunettas - circuits inspired by Stanley Lunetta
LunAmp
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elektrouwe



Joined: May 27, 2012
Posts: 129
Location: Germany

PostPosted: Thu Aug 28, 2014 5:51 am    Post subject: LunAmp
Subject description: a 2 chip Lunetta style stereo D-class amp
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yesterday I successfully breadboarded 1mono channel of a simple speaker/headphone stereo amp. It's made of a CD4069UB and a 74HC574, so it is true Lunetta style Smile I checked it with an 8 Ohm 130mm speaker and 30Ohm stereo headphones : sound quality is astonishing good for 2 digital chips . 2/6 4069 is used as preamp, 2/6 make a delta sigma ADC together with the 74HC574 (or '374) D-flip flops and the remaining 2 inverters make the clock generator. The circuit works nice with 3x1.5V AA cells, USB-5V or 6V lead battery.
There is some noise floor that is a bit annoying @ low volumes. So I would not recommend LunAmp as high end amp Wink, but for pure Lunetta synth boxes it should be good enough. Use short (<30cm), twisted speaker wires if you don't want to use it as 2MHz transmitter. For headphones use series resistors (~100R) or voltage dividers on the output to bring down noise and avoid bleeding ears Smile


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Last edited by elektrouwe on Thu Aug 28, 2014 9:33 am; edited 2 times in total
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PHOBoS



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PostPosted: Thu Aug 28, 2014 7:52 am    Post subject: Reply with quote  Mark this post and the followings unread

No idea how it works (guess I'll have to look up delta sigma ADC) but I think inputs D4+D5 should be connected to D6+D7 aswell, right ?
I don't have a 74HC574 but I might have something else to test with.

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elektrouwe



Joined: May 27, 2012
Posts: 129
Location: Germany

PostPosted: Thu Aug 28, 2014 9:43 am    Post subject: Reply with quote  Mark this post and the followings unread

PHOBoS wrote:
ADC) but I think inputs D4+D5 should be connected to ...
sorry, I had problems generating a correct picture. I updated the image now.
And yes, read about delta sigma ADC and look @ this, which shows the basic idea for this amp :
https://www.youtube.com/watch?v=DTCtx9eNHXE

you could use a 4013 instead of the 74HC574 and buffer each output with
with another 4069 (all inverters parallel). This will not be enough for 8Ohm speakers, but may be ok for headphones.
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PHOBoS



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PostPosted: Thu Aug 28, 2014 12:31 pm    Post subject: Reply with quote  Mark this post and the followings unread

thanks for the video link, Jeri made it perfectly clear Very Happy
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elektrouwe



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Posts: 129
Location: Germany

PostPosted: Sat Aug 30, 2014 12:09 am    Post subject: Reply with quote  Mark this post and the followings unread

update: my friend Chris, who did a lot of Schmitt-Trigger experiments in the last month sent me a link to his PWM-oscillator post:
http://hobby-roboter.de/forum/viewtopic.php?f=5&t=150
I suddenly realized that if I could rise clock frequeny to "infinite", that means
just using a buffer without any clock, the delta sigma amp smoothly transforms into a simple self clocking pulse width modulated oscillator !!!
I breadboarded it, and yes, it works like a charm : the "infinite" clock rate of a transparent latch 74HC573 avoids interference between sigma delta clock and time constant of the modulator. So less components & less noise now by just using a pure good old Schmitt-Trigger oscillator Smile


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