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Old 28th July 2004, 09:24 AM   #1
AGGEMAM is offline AGGEMAM  Denmark
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Default Some question about the Zen V7-T

Excuse me if some of these question are so logical that I should be able to see the answers myself but I'm not an engineer of any sort rather a 'happy-go-lucky' loudspeaker DIY'er that has for a long time been interested in making a pair of SOZ's. The only thing that has really kept me from doing so was the staggering ineffeciency of the original design, luckily for me the lastest Zen versions (actually SOZ versions) has a much higher effeciency and are therefore of great interest to me but before I begin purchasing components in the dark I have some questions that I would like it if anyone could help me with.


The first series of questions is in regards to the inductance load.

1a. Do I have to make the coils from a scrapped transformer?

1b. Would some normal coils (aircore or ferrite core) do the same trick?

1c. If I have some double wound ringcore coils made would that be even better?

1d. Is there an optimum inductance value of these? (I assume as high as possible)

1e. Is there an optimum resistance value of these? (I assume as low as possible)

1f. How can I calculate a good compromise between resistance and inductance myself?

1g. I assume the coils work as a highpass filter, so how can I calculate the x-over frequency if I want to take advantage of that?


The second series of questions is about other aspects of the amplifier.

2a. I assume the input capacitor can be omitted safely but is that right?

2b. I also assume that it works like a highpass filter, so if leave them in how do I calculate the x-over frequency of that?

2c. And futhermore, is it possible to calculate the frequency where the input capacitor and the inductance load in combination would make a 2nd order highpass filter?

2d. Is there a way I can alter the bias circuit so that it allows for two different settings, one with the normal bias and one with a very low bias for putting the amplifier in standby mode?

2e. When the amplifier is finishedand adjusted, can I remove the pots and replace them with resistor of the value those read then?


I think that is all for now but I'm sure I will come up with some more eventually. I hope someone knows the answers to some or even all of these questions. It will be much appreciated, so thanks in advance.


Johnny
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Old 28th July 2004, 01:33 PM   #2
AGGEMAM is offline AGGEMAM  Denmark
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By cross-searching the board and reading _a_lot_ of responses I have found the answer to some of the questions myself. Those are:

1a. No. You can use any kind of coil you like

1b. Yes. But they would have to be _big_ for the aircore one at least, and the DC supression would lack if they aren't magnetically coupled.


And some partly answered:

1c. Yes. Probably the best solution when you comprimise cost with benefit. (Anyone up for a group order?)

2a. Yes. But only if I'm sure that the DC input is minimal.


Please correct me if I've gotten something wrong.
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Old 28th July 2004, 06:44 PM   #3
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I don't recommend omitting the input capacitors unless
you are prepared to bias the amplifier with DC from the
source.
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Old 28th July 2004, 07:00 PM   #4
AGGEMAM is offline AGGEMAM  Denmark
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And since I wouldn't have the faintest clue how to do that I think I'll leave them in plus if I calculate it right it might even improve the sound of the total system by filtering out low frequencies since the system is a Lowther single driver front and back horn loaded system.

But thank you for the help, Sensei.
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Old 28th July 2004, 08:18 PM   #5
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The point is that the Gates of the input devices must be biased
to a positive voltage for the amp to work, and this will occur
with the existing resistor networks if the inputs are capacitively
coupled.
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Old 28th July 2004, 08:31 PM   #6
AGGEMAM is offline AGGEMAM  Denmark
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And what does that mean in leyman's terms? I assume you mean the C1-C2, R1-R4, and P1-P2 circuit but how do I calculate it myself? And what happens if I just raise or lower the C1-C2 capacitors without changing anything else?


I'm sorry if this seems to be a waste of everyones time but I'd really like to learn the tools for calculating it myself. If anyone could tell me or alternately provide a link with useful information I would really be one happy camper.


Thanks in advance. And thank you, Mr. Nelson Pass for providing a simple, if not the simplest, educational tool in my learning process.
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Old 28th July 2004, 08:53 PM   #7
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You don't need to mess with the bias circuit. It's there to provide something on the order of +4V at the Gate (relative to the Source) of the MOSFET. This is like an alarm clock telling it to wake up and do some amplification.
As far as the input DC blocking cap goes, you can use any capacitance you like. Given that it's in series with the Gate, it functions as a high pass filter. If you want to raise the frequency where it becomes effective, the formula is:

F=1/(2*PI*R*C)

where:
F= the -3dB point of the filter frequency
R= the input resistance of the amp
C= the value of the cap (in Farads, so 1 uF would be 1E-6, for instance)

Feel free to set the frequency anywhere you want. It's not really very important to the overall functioning of the amplifier. It's just there to keep that DC bias voltage from rampaging upstream into the back end of your preamp.

Grey
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Old 28th July 2004, 09:32 PM   #8
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Ok. So with the current values the filtering frequency is roughly 3,4 Hz, right?

1/(2*pi*1,000*(47/1,000,000) (=) 3,4 Hz

So if I what to get as close as possible to the cut-off frequency of my horn which is 54 Hz, I would have to use a 3,3 uF capacitor?

1/(2*pi*1,000*(3.3/1,000,000) (=) 48,3 Hz

As I see it there are several advantages by this. Firstly I filter out unwanted frequencies, secondly it is a lot cheaper, and thirdly you can get much better quality capacitors at the smaller size as opposed to the larger ones.


Now I get that part. All I need now is to understand the inductance part.

What would happen if the I put a switch between the driver sources (Q1-Q2) and the bias drain (Q3) ? That would effectively shut down the amplifier with turning off the driver, or am I missing something here?
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Old 1st August 2004, 02:37 PM   #9
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Any help, please?
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