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Old 18th June 2011, 07:14 PM   #81
Elvee is offline Elvee  Belgium
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I take two weeks off, so if you have questions about this topic, be patient.
Have fun!
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. .Circlophone your life !!!! . .
♫♪ My little cheap Circlophone© ♫♪
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Old 21st June 2011, 03:26 PM   #82
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Just need to aquire the 1.5nF and 27pF capacitors and I will be connecting power.

For the hell of it, I created a zip archive containing the final PCB gerbers, the builder's guide Elvee posted in text format, and the schematic:

http://dl.dropbox.com/u/5430178/circ...te%20Files.zip
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Old 30th June 2011, 02:11 PM   #83
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Elvee, I have one channel of the Circlophone up and running. Using a crappy test speaker so cannot comment on sound quality.


This is the setup:

http://dl.dropbox.com/u/5430178/proj...e/3TESTING.jpg

http://dl.dropbox.com/u/5430178/proj...e/4TESTING.jpg

I am using the MJW21196 as output transistors, and 2SB649 as drivers.

I have C11 (10nF) installed. I am using 270pF polystyrene as both C5 (input low pass) and C12 (the 180-820pF). For R8, R24, and R11 I am using 1.2R resistors for testing because I didn't have 1R. All other values are standard.

At first I had an electrolytic capacitor on the output to protect speaker in case of DC. After verifying offset stability I removed it. I also had 120R on the supply rails. After testing that it worked I removed those.

I had a scope (not the best -- a handheld digital DMM/Oscilloscope) on the output to check for oscillation. Before I connected power, I had extremely low level couple mV of 10-12MHz on the output, so when I did connect power and it was still this low level I am assuming this is just environmental noise. We have several LCD, Plasma televisions running at all times here where I am testing among other things.

For the supply I just rigged something up real quick. an 18-0-18 (DC) supply feeding only 2000uF of filtering going straight to the amp.

Playing music through it at low levels sounds good with the test speaker (beyond crappy). The heatsink, however, after a couple minutes to 10 minutes will get hot. I can hold my hand on it fine but it is uncomfortable. Not really painful, but not far from it.

I am wondering if this may be a problem. I think the heatsink is of decent size, as you can see in the picture. Could it be because I am using an incorrect suppy, or because I am using 1.2R instead of 1R for R8, 11, 24?

If so, then all else is fine, and we have a working channel.

Thanks.
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Old 30th June 2011, 04:35 PM   #84
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Quote:
Originally Posted by odysseybmx414 View Post
Elvee, I have one channel of the Circlophone up and running. Using a crappy test speaker so cannot comment on sound quality.


This is the setup:

http://dl.dropbox.com/u/5430178/proj...e/3TESTING.jpg

http://dl.dropbox.com/u/5430178/proj...e/4TESTING.jpg

I am using the MJW21196 as output transistors, and 2SB649 as drivers.

I have C11 (10nF) installed. I am using 270pF polystyrene as both C5 (input low pass) and C12 (the 180-820pF). For R8, R24, and R11 I am using 1.2R resistors for testing because I didn't have 1R. All other values are standard.

At first I had an electrolytic capacitor on the output to protect speaker in case of DC. After verifying offset stability I removed it. I also had 120R on the supply rails. After testing that it worked I removed those.

I had a scope (not the best -- a handheld digital DMM/Oscilloscope) on the output to check for oscillation. Before I connected power, I had extremely low level couple mV of 10-12MHz on the output, so when I did connect power and it was still this low level I am assuming this is just environmental noise. We have several LCD, Plasma televisions running at all times here where I am testing among other things.

For the supply I just rigged something up real quick. an 18-0-18 (DC) supply feeding only 2000uF of filtering going straight to the amp.

Playing music through it at low levels sounds good with the test speaker (beyond crappy). The heatsink, however, after a couple minutes to 10 minutes will get hot. I can hold my hand on it fine but it is uncomfortable. Not really painful, but not far from it.

I am wondering if this may be a problem. I think the heatsink is of decent size, as you can see in the picture. Could it be because I am using an incorrect suppy, or because I am using 1.2R instead of 1R for R8, 11, 24?

If so, then all else is fine, and we have a working channel.

Thanks.
Additional information: the positive rail has 2.42A of current flowing through it

But music plays fine. Even sounds okay.
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Old 30th June 2011, 05:12 PM   #85
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OOPS! Looks like I left R14 out completely. I'm guessing that doing so is not such a good idea... hah

Will report back.

OK. Installed R14 and now everything is good! ~140mA of draw on +V rail (18V). Sounds a hell of a lot better as well. Heatsink stays cool, time to let it run for an extended period.

Last edited by odysseybmx414; 30th June 2011 at 05:36 PM.
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Old 1st July 2011, 04:54 PM   #86
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Well, I've been playing it for a few hours continuous at low-ish levels at work, watching the scope on output looking for oscillation. Every now and then I see a waveform pop up, anywhere from 4-12MHz, about 20mVpp. It disappears after a few ms or so. Barely notice it pop up n leave. With amp switched off, and power drained from capacitors i.e. dead circuit, I still see that intermittent waveform. So, I conclude this is noise or coming from something else completely.

Letting this channel run and listening to some select songs, I can say it sounds very good. I hooked up a better test speaker as well. Very musical, and the highs are crisp and liquid. Crystal clear.

Time to get the rest of my work done so I can get the other pcb done and listen in stereo.

Also, I am still using the small test supply with crappy filtering and bypassing. So, I expect another improvement in sound once I get a proper supply connected.

One more thing to add: The amp is absolutely dead as a rock silent with no signal. Ear crammed up to tweeter or woofer and I can perceive nothing.
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Old 4th July 2011, 09:30 AM   #87
Elvee is offline Elvee  Belgium
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I'm back

Your amp looks OK.
140mA of Iq is marginally low, compared to my own prototypes and the expected spread of 150 to 250mA, but it still sufficient, nothing to worry about.

I recommend you make a squarewave test, this will immediately highlight any stability issue and will let you know wether the compensation caps are adequate or not.
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Old 11th July 2011, 09:11 AM   #88
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by Elvee View Post
Here is the confirmation of what I said earlier, and also of the versatility of the Circlophone's topology:
I simply dropped two NMOS in place of the darlingtons, in the Ndarlington version, and it worked exactly as expected.

The only things that required adaptation are the G-S resistors that have been increased to 390ohm.

Also, the lower clipping value predicted on the positive side is observed: the clipping occurs ~5V below the positive rail.

If the input voltage is reduced to just under the clipping, the behavior becomes almost identical to that of the BJT version: the THD is a bit higher, probably because of the lower transconductance of the MOS compared to the bipolars.

The bias servo too works in an identical manner.

A reminder:
all this is simulation, and nothing has been built yet.

But I will come up with a version using the same trick as the CircloMOS, build it, and launch a dedicated thread when it's mature and working well enough.
Here is this idea in sim.

The threshold of the MOSfets is cancelled by a memory capacitor, just as in the CircloMOS.
For simulation purposes, the capacitors have been replaced by voltage sources, V4 and V5, to avoid initial conditions issues.

The circuit does work, and the output clipping is now symetrical, but the linearity is disappointing: there is a ten-fold increase in the THD compared to other versions.

For this reason, I will not go further into this direction and I won't build a physical prototype.
Attached Images
File Type: gif CircloPhMOS.GIF (61.1 KB, 920 views)
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Old 12th July 2011, 03:03 PM   #89
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Quote:
Originally Posted by Elvee View Post
I'm back

Your amp looks OK.
140mA of Iq is marginally low, compared to my own prototypes and the expected spread of 150 to 250mA, but it still sufficient, nothing to worry about.

I recommend you make a squarewave test, this will immediately highlight any stability issue and will let you know wether the compensation caps are adequate or not.
You think it is just because of lower testing supply voltages? Also to note I used BC556/546 all in "C" suffix. Input pair is matched.

Unfortunately, Elvee, I do not know how I can do a squarewave test. I do not have a function generator. I have an oscilloscope though. Is there anything you would like me to do with that?

I have almost finished the second channel PCB. Soon I will be listening in stereo to give it a much better evaluation. So far, though, I am thoroughly enjoying it! It makes mainstream music enjoyable! Quite musical, and I find my self catching and understanding perfectly words in a song that I could not understand before. The midrange and high end is spectacular, yet I cannot comment on the bass (I am still using test speakers).
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Old 13th July 2011, 07:39 AM   #90
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by odysseybmx414 View Post
You think it is just because of lower testing supply voltages? Also to note I used BC556/546 all in "C" suffix. Input pair is matched.
Could be the C suffix, I mainly used unsorted ones, without suffix.

Anyway, 140mA is large enough for the circuit to operate properly, nothing to worry about.


Quote:
Unfortunately, Elvee, I do not know how I can do a squarewave test. I do not have a function generator. I have an oscilloscope though. Is there anything you would like me to do with that?
If you're happy with the sonics, and the amplifier looks well behaved, that's sufficient.

But more generally, squarewaves are a useful tool to quickly uncover hidden issues, like marginal stability, insufficient internal bias currents, etc.
The squarewave behavior has little relation with the sonic performances, but it highlights any weakness in the design, like poor decoupling or compensation, inadequate wiring, unsuitable Zobel, etc.

You don't need a full feature function generator: for a buck or two, you can improvise an excellent generator on a scrap of veroboard, with a CMOS oscillator, see an example below
Quote:
I have almost finished the second channel PCB. Soon I will be listening in stereo to give it a much better evaluation. So far, though, I am thoroughly enjoying it! It makes mainstream music enjoyable! Quite musical, and I find my self catching and understanding perfectly words in a song that I could not understand before. The midrange and high end is spectacular, yet I cannot comment on the bass (I am still using test speakers).
Looks promising.
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File Type: gif MinSqWaGen.GIF (9.8 KB, 751 views)
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