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Old 1st March 2011, 10:03 PM   #3621
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Hi bernhard,

Quote:
A much better and well proofed solution is angel dust scattered all over the pcb.
The graphite compound may have RF absorbing properties, some RF absorbing foams are based on carbon:

Graphite - Wikipedia, the free encyclopedia

RF and Microwave Absorber - Ferrite Tiles and Foam Absorber
RF Absorbing Material
RF Microwave Absorbers| ETS-Lindgren

Above materials are described as microwave absorbers. Modern wireless communication devices use and generate frequencies in the microwave spectrum.

Altmann already indicates that the graphite compound is intended to attenuate higher harmonics.


Here is an example of a practical application of such RF absorbing foam in a masterclock:

NewClassD Neutron Star
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Old 1st March 2011, 10:51 PM   #3622
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Hi Sandor,

Quote:
Hello John,
how does your circlotron amp perform with loads as low as 2 ohms?
The measured output impedance of my Circlotron monoblocks equals approx. 0.4 Ohms and I run them with 8 Ohm load.

When using 2 Ohm loads, efficiency will drop. Speaker interlinks and connections could also become more problematic (increased voltage drop caused by increased currents).

The circlotrons remain fully stable, even when output is short-circuit or the speakers are connected / disconnected during operation.

One could experiment with different power MOSFETs in the output stage in order to lower output impedance if required.
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Old 2nd March 2011, 07:13 AM   #3623
WT is offline WT
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Hello ecdesigns,

You Circlotron amp looks very interesting and full of knowledge. I would like to build them to use on my speakers and would like to ask some question.

How to connect to input on your Circlotron amp circuit? Cap input on both input and ground? Or just cap input.

2sj79 is also hard to find. Is there an alternative part?

On your "hybridge smoothing cap", seem like you use small parallel cap instead of one big cap. Is there a guide on how to choose and combine cap? For example, if I want to use 22,000uF cap, how to choose small combine caps? (4,700UF + 3,300uF + 2,200uF + 2200uF )x2 ?

Thanks for sharing your knowledge.
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Old 2nd March 2011, 10:53 AM   #3624
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Hi John,

I sent you PM re. the MK6 DAC. have you seen the message.

Brad
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Old 3rd March 2011, 10:18 AM   #3625
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Hi WT,

Quote:
How to connect to input on your Circlotron amp circuit? Cap input on both input and ground? Or just cap input.
I can only advice not to use any coupling caps, anywhere in the signal path. Even the very best distort, add coloration and reduce resolution and speed. This sound coloration can produce an "impressive" or warm sound with lots of "air", but the sound won't be transparent as it is simply distorted by adding harmonics that weren't present in the original recording. The use of coupling caps also increases the risk of improving the sound of specific recording and degrading sound of others.

With a highly transparent (DC-coupled) set, all recordings sound at their very best and there is no preference for any type of music.

The Circlotron power amp is fully DC-coupled, so no coupling caps needed, provided input signal has low DC offset (few millivolts DC or less).

The schematic shows a single-ended input version.

It is possible to connect both P-MOSFET gates to GND using 100K resistor and use balanced interface. In this case the symmetry circuit consisting of R20 (12K) and C26 (4u7) can be removed as both P-MOSFETs now operate in grounded-source mode and thus have equal gain.

Quote:
2sj79 is also hard to find. Is there an alternative part?
Other pats can be used, preferably lateral MOSFETs with high enough gain. Popular JFETs (2SJ109 / 2SJ74) sound grainy with less far less resolution by comparison. I suspect this has something to do with thermal memory effects.

Depending on MOSFET specs (gate threshold voltage) value of some parts like R15 may need to be changed. Remember that the differential input stage bias current (DC voltage drop across R18 and R19) directly affects Circlotron output stage bias current. In practice you either end up with too high bias current or no bias current at all. Also very important, both P-MOSFETS and both N-power MOSFETs need to be matched pairs.

Quote:
On your "hybridge smoothing cap", seem like you use small parallel cap instead of one big cap. Is there a guide on how to choose and combine cap? For example, if I want to use 22,000uF cap, how to choose small combine caps? (4,700UF + 3,300uF + 2,200uF + 2200uF )x2 ?
Each capacitor has characteristic resonance spectrum. It is unlikely that resonance spectra of capacitors of different value or construction are exactly the same. By paralleling multiple "different" capacitors, resonance spectrum of one cap can be attenuated by another cap that's placed in parallel, and vice versa. The result is reduced resonance and reduced sound coloration as unwanted harmonics are being attenuated.

These resonances are audible when connecting a cap to a function generator and slowly sweep through the audio spectrum.

For 22,000uF cap you could approximate this value as closely as required using capacitors with different value (size) like 4700uF, 3300uF, 2200uF, 1000uF and so on.

With higher output power rating it is required to use suitable twisted pairs wire connection directly between smoothing cap bank and power MOSFET pins. This minimizes power interlink inductance and unwanted crosstalk.
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Old 4th March 2011, 04:02 AM   #3626
WT is offline WT
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Thanks for your reply. Highly appreciate that.

Just to make sure that I understand you correctly. For balance input circlotron, the schematic should look like this. Is it correct?
Attached Images
File Type: png Screen shot 2011-03-04 at 11.59.11 AM.png (57.1 KB, 1388 views)
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Old 4th March 2011, 09:22 AM   #3627
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Hi WT,

Quote:
Just to make sure that I understand you correctly. For balance input circlotron, the schematic should look like this. Is it correct?
This schematic is not fully correct, the 100K resistors should connect to +15V that serves as input signal reference, just like in the schematic I posted. This is required in order to maximize output signal amplitude of the combined differential input / driver stage.

In conventional designs the (differential) input stage is referenced to GND, but has limited output signal amplitude. The (differential) driver stage then amplifies this signal.

My first Circlotron prototype had a differential input stage that did have GND as reference, this input stage was connected to a driver stage that would provide required output signal amplitude to drive the power MOSFETs. Problem was increased distortion and loss of resolution caused by the two extra MOSFETs.

What I did was removing the differential input stage, and using the existing differential driver stage to serve as input stage as well. Since I needed full DC-coupling there was little other option than adding an extra +15V power supply for input / driver stage reference.

The Circlotron power amp is powered through a number of transformers, so the circuit basically "floats" as it isn't connected to any other circuits. Then one can use +15V as reference, provided one doesn't connect GND of the audio source with GND of Circlotron power amp. So the GND used in the Circlotron circuit is only used locally, and serves as reference for the power MOSFETs.
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Old 4th March 2011, 10:12 AM   #3628
WT is offline WT
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[QUOTE]This schematic is not fully correct, the 100K resistors should connect to +15V that serves as input signal reference, just like in the schematic I posted. This is required in order to maximize output signal amplitude of the combined differential input / driver stage./QUOTE]
Got this

One more question, Sorry if I ask too many questions. If I build the circlotron as stand alone amp, it will have 15 V at the input and ground input. What is your recommendation for connect it from pre-amp. Transformer coupling?
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Old 11th March 2011, 07:22 AM   #3629
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Hi WT,

Quote:
One more question, Sorry if I ask too many questions. If I build the circlotron as stand alone amp, it will have 15 V at the input and ground input. What is your recommendation for connect it from pre-amp. Transformer coupling?
There would be no ground input. Ground connections remain inside the monoblock housing. Signal reference and signal inputs will all be at same potential (+15V) with respect to the internal ground that is not present at any external terminal or metal housing. So one can simply imagine dealing with a plain differential input that can be connected like any other.

Pre-amps, (coupling) caps and (coupling) transformers in the signal path add clearly audible distortion / coloration and cause loss of resolution. So try not to use these in high performance audio equipment.
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Old 30th March 2011, 04:39 AM   #3630
tessier is offline tessier  Canada
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Hi

Does this TDA1541 reclock and dem clock circuit would work good ?

Any suggestions ?

I just found this circuit, there is almost everythings needed, all in one circuit.

Thanx

Paul
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File Type: gif tda1541a dac and reclock.gif (138.6 KB, 983 views)

Last edited by tessier; 30th March 2011 at 04:47 AM.
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