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Old 12th January 2004, 03:46 PM   #1
Magura is offline Magura  Denmark
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Default Choke loads for SOZ

The initial question in the old thread was never really answered....it turned into source follower and the like, so id like to ask the initial question once again. Maybe the answer is obvious now after the development in the other thread....

It got as far as we agreed that 50mH chokes were a good idea for replacement of the bias resistors in the SOZ.
Now for the less talented electronic constructors there are a few questions that were left open.


Would it be clever to get as low resistance in the choke as possible? Or would it come to a limit where other factors make a difference?

I saw a question that were left un-answered on the old thread, if its possible to replace all the 8ohm resistors with chokes? (i guess id just lower the values for the other resistorsbut.....).

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Old 12th January 2004, 04:31 PM   #2
joensd is offline joensd  Germany
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Sorry to get offtopic again but its not possible to email you.
You were talking about doing some chokes yourself.
Do you have any offers already?
Might be interesting for others as well for a small group buy.
Please let me know if you do.

TIA
Cheers
Jens
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Old 12th January 2004, 04:50 PM   #3
Magura is offline Magura  Denmark
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Please try email again.

The email i use for the forum is :

travelling_mac@yahoo.com

It should work through the forum though.


Yes, it would be no problem to wind a few inductors for the members of the forum.


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Old 13th January 2004, 03:43 PM   #4
Magura is offline Magura  Denmark
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Havnt anyone got any actual experience with choke loads for SOZ at this point???

Sounds strange, since the choke load thread is fairly old.


Cheers

Magura
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Old 13th January 2004, 05:55 PM   #5
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When my Zen v.4 boards arrive from Pass DIY, I plan to listen to them "stock" for about a week. Since I have a regulated power supply, I will remove Z1-Z5 and R19 and ground C11.

Afterwards, I will replace Q2 with a choke and reduce the power supply voltage to 25V (to maintain 20V across Q1). I'm assuming that 4 volts will drop across Q5 and 1 volt will drop across the choke. R4 will adjusted to maintain 2A bias current. I need to study the circuit to be sure Q1's bias will function properly in this configuration, but I' also like to remove R0 and R1.

I will post my findings.

The choke will be a toroidal power choke rated at 3A static DC. I will order 10 of these at $50-$55 each. I will be interested in selling some of these.

As mentioned in the other thread, I will also be comparing the Zen v.4 with a source-follower amplifier:

Choke Loads for Zen/Aleph Amps
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Old 13th January 2004, 06:19 PM   #6
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Choke loads for SOZ are great. Use some value of resistor,
like 22 ohms (at the appropriate wattage) across the choke
to help keep it damped and stable.
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Old 13th January 2004, 06:21 PM   #7
Magura is offline Magura  Denmark
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ok, so choke loads it is. Wich resistors can be replaced with chokes? and can i just make the rest of the 8 ohms resistors the same value as the resistance of the chokes??

What about the 1 ohm resistor....it should not be changed, right??

Cheers.

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Old 13th January 2004, 07:44 PM   #8
eLarson is offline eLarson  United States
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I'm thinking you'll just want to replace the 8-ohm power resistors that serve as the drain loads.

eL
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Old 13th January 2004, 07:49 PM   #9
Magura is offline Magura  Denmark
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But dont i have to reduce the voltage as i reduce the resistance by replacing the resistors with chokes??

If so, wouldnt it be nessecery to reduce the values of the other resistors to maintain the same current?

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Old 14th January 2004, 12:01 AM   #10
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I'm not sure which 'old thread' you're talking about, but I don't think you'll like the results if you use inductors under the Sources of the MOSFETs in a SOZ.
Inductors as loads, on the other hand, will work just fine.
Inductors should have as low a DC resistance as possible. In the real world you won't get to 0, of course, but you should try. In a high current circuit such as the SOZ, the coils' DC resistance will make a difference in how cool the coils run. Use air core inductors. Ferrite or iron core inductors (regardless of construction) will tend to saturate since the DC current is already generating a large magnetic field. When the AC current--aka music--peaks, the long-suffering core will not be able to accept any more flux and the signal will be distorted. Tube folks deal with transformers because they have to, not because they want to. There's no reason, barring masochism, for solid state people to inflict such things upon themselves. Kinda makes you wonder about McIntosh and their autoformers, but that's another topic for another day.
No, you wouldn't replace all the resistors in the SOZ with inductors, just the load resistors (as eLarson notes)--the ones above the Drains of the MOSFETs.
(It seems that there's an echo effect around here. When a question comes up in one thread, you frequently see the same question in another thread. Almost exactly the same questions came up in the SOZ w/current source thread a week or two ago. For what it's worth, the answers haven't changed. Oh, well.)
The one ohm resistor stays.
The resistor values have no relation to the DC resistance of the inductors.
The 8 ohm resistors under the Sources of the MOSFETs determine the bias current. With the Gates at ground potential, the Sources will settle in at about -4 volts, plus or minus a bit. The Drains will then be connected to the inductors, which are connected to the positive rail. The larger the value of the inductor, the more output you'll get, and the more bass. A really big inductor will give you the same amount of bass that a resistor would, but with less heat for the same power output. How big an inductor? Infinite. Ugh. That gets difficult to deal with. Your fallback position is simply to buy or make the biggest inductor you can practically deal with and go from there.

Grey
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