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Old 7th September 2012, 05:56 PM   #11
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by danielwritesbac View Post
Is MC7805, or maybe MC7806 okay to use?
Yes, with a good output bypass cap, like 1000µ. With a regulated supply, the NTC compensation would suffice.
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I forgot to ask about max operating voltage when driving 8 ohm speaker.
The same as for 4 ohm. This is a low voltage, low power amplifier and for higher voltages there are lots of (better) alternatives
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Is that amp an NTP input or a singleton input?
It doesn't apply, it is an inverting amplifier without a + input.
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And, would it be okay to bridge it or is the THD a bit too high for that?
It would be like turbo-charging your ride-on mower: makes little sense

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Other problem: It hangs up when it touches my face.
It is intended to be mainly used laid on a table. Only occasionally as a "phone", for low-level, hard to catch noises.
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Figured a name for it: Tracerphone!
Nice one
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Old 8th September 2012, 08:58 PM   #12
Elvee is offline Elvee  Belgium
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Two more pics of the thing in action. Note the "Universal Input Connector"
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File Type: jpg DSCF0007.JPG (330.5 KB, 174 views)
File Type: jpg DSCF0020.JPG (304.4 KB, 160 views)
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Old 8th September 2012, 09:44 PM   #13
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Quote:
Originally Posted by Elvee View Post
It would be like turbo-charging your ride-on mower: makes little sense
Totally makes sense--I live in the USA.
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Old 12th September 2012, 09:28 AM   #14
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Quote:
Originally Posted by Elvee View Post
Also note that the gain is very high, because of the intended application. More reasonable values would further decrease the THD, and increase the input impedance.
On the schematic in post 9, how to set the gain for a very weak MP3 player?
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Old 12th September 2012, 08:57 PM   #15
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Quote:
Originally Posted by danielwritesbac View Post
On the schematic in post 9, how to set the gain for a very weak MP3 player?
With the original values the gain will be huge, even for a very very weak MP3 player: it is around 40, meaning you will already clip at input voltages of ~25mV rms for a 3V supply.

For applications other than a signal tracer, the gain should be reduced by increasing R8: for a normal player, 33K or even more should be OK, you'll still have plenty of margin, and the distortion will be reduced by a 10x factor.

For a very weak signal source, you could try 10K: the full power will be attained for an input equivalent to 0.175mW on 32 ohm. I doubt even the weakest of players could play so low.
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Old 13th September 2012, 02:13 AM   #16
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Thank you!
Quote:
Originally Posted by Elvee View Post
For a very weak signal source, you could try 10K: the full power will be attained for an input equivalent to 0.175mW on 32 ohm. I doubt even the weakest of players could play so low.
Well, I wish to use a weak signal since the digiplayers will distort if set much more than ~70% (although it varies per player). These things all seem to have their sweet spots and most of the digital volume controls are pointless because of only one seemly setting. A rather high gain, or adjustable gain, amplifier seems to help a lot.

P.S.
Can this little amp drive my clipnipper if I use the 1.5v led's and trim a bit more carefully, or is the extraneous current consumption detrimental?
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Old 14th September 2012, 07:49 AM   #17
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Quote:
Originally Posted by danielwritesbac View Post
P.S.
Can this little amp drive my clipnipper if I use the 1.5v led's and trim a bit more carefully, or is the extraneous current consumption detrimental?
I doubt something good results, but you can always try it, that is the only way to know for sure
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Old 15th September 2012, 03:59 AM   #18
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Oh, idea.
If R8 is 22k and V+ is 5vdc. . . Then how much input voltage causes clipping?
Perhaps I could find a diode of a bit less than that voltage, put the diode series to a resistor and use it to engage a voltage divider at input?

I would choose to use a diode+resistor load for the upswing and a diode+resistor load for the downswing. The dual asymmetric soft clipper could be set to leave most symmetric signal unmodified but half-soft-clip asymmetric excursions.

If I had the ballpark figure for an input voltage that causes overload, I could then make R8 a trimmer to dial in the soft clipper.

Well, I don't know if this is a good idea. It may be nothing other than an extra complicated way to make a thump stopper (overload protector). But, there's only 2 diodes and 2 resistors to it (d+r for up and d+r for down). Possibly the soft clipper goes parallel to R6?

Edit:
The idea also seems a useful protection for a tracer, for cases where we didn't want to input huge signals.
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Last edited by danielwritesbac; 15th September 2012 at 04:05 AM.
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Old 15th September 2012, 02:54 PM   #19
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Quote:
Originally Posted by danielwritesbac View Post
Oh, idea.
If R8 is 22k and V+ is 5vdc. . . Then how much input voltage causes clipping?
Simple arithmetics: the gain becomes 120/22~=5.5, and since the clipping occurs practically at the rails, the input voltage is 5/5.5Vpp=0.91Vpp.
Translated in rms value, that is 0.91/2.828=320mVrms
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Perhaps I could find a diode of a bit less than that voltage, put the diode series to a resistor and use it to engage a voltage divider at input?

I would choose to use a diode+resistor load for the upswing and a diode+resistor load for the downswing. The dual asymmetric soft clipper could be set to leave most symmetric signal unmodified but half-soft-clip asymmetric excursions.

If I had the ballpark figure for an input voltage that causes overload, I could then make R8 a trimmer to dial in the soft clipper.

Well, I don't know if this is a good idea. It may be nothing other than an extra complicated way to make a thump stopper (overload protector). But, there's only 2 diodes and 2 resistors to it (d+r for up and d+r for down).
That's up to you....
Quote:
Possibly the soft clipper goes parallel to R6?
Certainly not R6: it is a virtual ground, with practically no voltage at all.
R7 could be a possibility, but you would need a blocking capacitor, since there also is a DC voltage

Quote:
Edit:
The idea also seems a useful protection for a tracer, for cases where we didn't want to input huge signals.
No, a tracer doesn't need that kind of subtlety: the protection is very rugged and consists of series resistor and clamping diodes to the supply rails.
For this type of instrument, a bullet-proof protection is essential.
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Old 15th September 2012, 10:49 PM   #20
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Originally Posted by Elvee View Post
Certainly not R6: it is a virtual ground, with practically no voltage at all. R7 could be a possibility, but you would need a blocking capacitor, since there also is a DC voltage.
Well, perhaps I didn't communicate right. So, here's the question as a photograph (attached). The diodes are silicon+1n5819=~0.9v, and then R8 dialed for adjust. Ac voltage to operate the diodes is provided by the source device at input. R8/R6 looks like input voltage divider and R6 looks like input load. But this is wrong (photo attached)?
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File Type: gif tracerphone.gif (8.3 KB, 105 views)
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