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Old 13th November 2010, 07:59 AM   #3511
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Hello John

I have done an error in my simulation, the 5 volt dc are inverted.

I will redo the simulation.

Thank

Bye

Gaetan
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Old 13th November 2010, 08:42 AM   #3512
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Hello John

I've redone my simulation, and will trying few thing I've get -100 db thd with that sim, maby it will not be as good in real life but in simulation it's very good.

Thank

Bye

Gaetan
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Old 13th November 2010, 02:14 PM   #3513
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John,
I am interested by your Circlotron deign. I though, I have read that you biased this amplifier in class A operation. Somewhere you said 55W output.
Here are my questions.
Examining the power supply section in your post 3467, I presume the 25va transformers are for a lower output amplifier?
The class A operation interest me, so dissipating 100W of heat with 2 devices will make the temperature rise to unsafe limits. Would it be possible to parralell a few 2SKs without reducing the performance of this amplifier?
What would be a maximum of devices before degrading the preformance?
Of course it will require sufficient heatsinking and adequate supply, but do you have any suggestions, or changes for such a project?
Thank you for sharing your experience with us.
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Old 13th November 2010, 05:08 PM   #3514
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Jean-Charles- back in post #3467 John mentions running 150mA through the outputs.

I'm also intrigued by this Circlotron (and EUVL's), and watching closely. I would like to try a circuit like this with some SemiSouth R100's in class A ("Sic Circlotron"?), driving the top of a bi-amped setup, ~300 hz on up. The wirewound pot is interesting also, comments of others? inductance too high.. rolls of treble... but their example is always a 100k pot.... 10k or 20k may be just fine? what about a 3 turn vs. 5 turn vs. 10, does it make any difference?

Seems like a balanced source is really what you would want driving a circuit like this. And class A operation. But, what do I know. I really need to get off my duff and build something, and snap out of the analysis paralysis.
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Old 14th November 2010, 09:34 AM   #3515
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Hi Jean Charles,

Quote:
I am interested by your Circlotron deign. I though, I have read that you biased this amplifier in class A operation. Somewhere you said 55W output.
Circlotrons can work in both class A or AB. I run it in class AB (200mA bias).

Output stage runs on 2 separate 25V / 25VA power supplies, this consumes 10 watts during idling (5 watts for each FET). This way I get around 25 watts rms in 8 Ohms. Differential input / driver stage runs on 18mA bias (class A) and offers 15x gain. The Circlotron bridge output stage doubles it to 30x.

Max output power with 0.7V rms from the TDA1541A-MK4 module equals 0.7 * 30 = 21V rms. This results in max. 55 watts in 8 Ohms with given 15x input / driver stage gain.

Quote:
Examining the power supply section in your post 3467, I presume the 25va transformers are for a lower output amplifier?
Yes, approx. 25 watts in 8 Ohms.

Quote:
The class A operation interest me, so dissipating 100W of heat with 2 devices will make the temperature rise to unsafe limits.
You could try MOSFETs similar to these:

STMICROELECTRONICS|STE53NC50|MOSFET, N, SOT-227B | Farnell Nederland

Temperature compensation would also be required.

Quote:
What would be a maximum of devices before degrading the preformance?
One MOSFET for each bridge half. I tested multiple matched MOSFETs in parallel, but this resulted in degrading (loss of resolution and transparency). Note that this design has only 4 power MOSFETs in total and has no global feedback to cover-up flaws.

Quote:
Of course it will require sufficient heatsinking and adequate supply, but do you have any suggestions, or changes for such a project?
Higher power consumption will also significantly increase power supply noise (transformer EM fields and rectifier switching noise). Stepped rectifiers would be a must, and the transformers need to be placed further apart to avoid coupling between the EM fields of both transformers powering the Circlotron output. In order to minimize magnetic coupling it would be best to use toroidal transformers that offer low external magnetic field.

Note that with a circlotron power amp the speaker (output) sits between both power supplies. Any (capacitive) coupling between both power supplies would then occur in parallel with the speaker / output.
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Old 14th November 2010, 09:47 AM   #3516
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Hi William2001,

Quote:
The wirewound pot is interesting also, comments of others? inductance too high.. rolls of treble... but their example is always a 100k pot.... 10k or 20k may be just fine? what about a 3 turn vs. 5 turn vs. 10, does it make any difference?
The inductance is rather small (uH range), too small to cause trebles roll-off. Both inductances are placed in series (input-wiper, wiper-GND) so impedance increase should have little effect too.

Only problem is that they are linear. With a 1 turn pot it's difficult to set lowest volume. Multi turn pots offer better control at lowest volume settings. Inductance of multiturn versions is comparable with single turn versions.

Quote:
I'm also intrigued by this Circlotron (and EUVL's), and watching closely. I would like to try a circuit like this with some SemiSouth R100's in class A ("Sic Circlotron"?), driving the top of a bi-amped setup, ~300 hz on up.
No problem, you might need to change value of R3 (250 Ohms) in the latest schematic to achieve correct bias setting range. Temperature compensation (bias current) would also be required to prevent thermal runaway.
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Old 14th November 2010, 03:20 PM   #3517
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Default Discrete mini regulators

I attached some pictures of the completed discrete regulators that I plan to use in both, TDA1541A-MK4 and Circlotron.

I made a positive (78XX) and negative (79XX) version. The PCB measures approx. 11 x 28mm. Voltage is indicated by a color on top of the PCB.

Both voltage and max. output current (short circuit protection) are set by resistors. There are 2 sets of pads for voltage setting resistors for more accurate voltage trimming.

The regulators are pin-compatible with 78XX and 79XX regulators and can be mounted on a heatsink for higher output currents.

Low noise references (zener / LED) are used for CCS and error amp. These produce around 500nV noise, much lower compared to bandgap or XFET references.

Capacitors could be left out (low noise references and low impedance voltage divider) for achieving lowest possible sound coloration.


I also placed an extra filter between -15V rail and 150K bias resistors in the TDA1541A-MK4 module for better performance. The filter consists of 22K resistor in series with 10mH choke and a 470uF cap.
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Old 14th November 2010, 05:56 PM   #3518
Ryssen is offline Ryssen  Sweden
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You made the pcbs to?
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Old 15th November 2010, 12:41 AM   #3519
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Quote:
Originally Posted by william2001 View Post
Jean-Charles- back in post #3467 John mentions running 150mA through the outputs.
s.
Thank you William, I overlooked this information.
150ma is not much and represents around 350mw class A power.
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Old 16th November 2010, 10:00 AM   #3520
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Default TDA1541 in Simultaneous mode

Hello to everyone..

I'm writing here because it seems the guru's place about the TDA1541..!!

I would like to run it in Simultaneous mode in a Philips 304..

Is it possible to use the DEM from ECDesign for this configuration..?

ECDesign...do you hava any comment or suggestion for me?

Thanks to everyone will helo me...and regards from Italy..

Maurizio.
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