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Old 25th July 2001, 05:02 PM   #11
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Location: Lund, Sweden
Default Uhmmm

Obviously missintrepreted what GRollins said, and now that ive been looking around a bit i actually found the IRFP140 but still cant find any IRFP 9240, what should i look for in a substitute for it?`

Thanks
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Old 26th July 2001, 04:29 AM   #12
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Fyhr,
As far as supply problems in Sweden, I'm not sure where to direct you; Petter is using IRF parts (I think) in his X-amp experiments. Being closer to your part of the world, he may be able to direct you to sources for IRF parts in northern Europe. At least as far as North America is concerned (as of ten minutes ago...) Digikey was showing stock for the IRFP140, IRFP9140, and IRFP9240, depending on which version of the Zen you want to build. Other suppliers, such as Newark, also stock IRF parts. For what it's worth, I've found Newark a bit of a nuisance to deal with, so don't take that as a recommendation.
If you want to substitute parts, go to the IRF website: http://www.irf.com and look up the specs on the parts you want to replace, then look for another part with a different case, but the same specs. There's plenty of lattitude in Nelson's design, so don't be afraid to substitute parts if you want--just make sure to keep heat dissipation and voltage & current ratings in mind.

Grey
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Old 26th July 2001, 07:55 AM   #13
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WRT MOSFETs for a ZEN amplifier, Nelson Pass did some tests will similar MOSFETs (IRF040, 140 and 240), and found that the lower voltage version (040) created lower distortion (see http://www.passlabs.com/projects/znret_4.htm). I'm not sure what reason he gave (if he did), but I think the reason is lower input capacitance.

Also, I can't remember who did the testing, but I seem to recall someone finding that MOSFETs with higher transconductance (sometimes called Forward Transfer Admittance on the spec. sheets) will lower distortion in a ZEN.

Finally, the IRF9140 is the current source. It has little effect on the sound. You should be able to substitute almost any high-power P-Channel MOSFET. Watch the pinout.

You might want to keep this information in mind when you select your MOSFETs. With all the new MOSFETs out there, you might be able to find some that are even better that the IRF040.

According to what I've seen, the ZEN is probably a good amplifier for your first Class-A. By all reports (I've never built one), the amp sounds good (necessary for a first project). Overall, it's fairly simple to construct, with fairly few components. This amp doesn't deal with lethal voltages, and the currents aren't too bad, for a Class-A. The latest version (ZEN Revisited) has a PCB layout (someone might even sell the PCB; I've never checked). Getting good heatsinks, and a heavy enough transformer might be a little expensive, but it's still not too bad.

The one item it's missing (along with >90% of DIY schematics) is safety features (Overcurrent Protection, DC Output Protection, Temperature Sensor and Speaker Turn-on Delay).

Overcurrent protection could be as simple as a fuse in the power rail (actually, that's the only place I see to put it). All of the rest can operate by opening a relay in the speaker line. This is a minimal invasion of the circuit path (assuming you pick a good relay), considering what it may save.
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Old 26th July 2001, 08:20 AM   #14
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Default Aah yes..

Well now boys n grrls Thanks alot for all the help, I've found both the IRFP140 and IRFP9140 (assuming that it will work just as good as the 9240) so i think im ready to order all the parts, obviously i won't have to worry about shipping since the parts are sold just 20km from my home!
So thanks again for all the help.

Pontus
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Old 27th July 2001, 09:53 AM   #15
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Pontus,

Watch out for the difference in the Power Dissipation of the device you finally choose to use. Pd rating should not be exceeded. Being your first project, get some local help in thermal management and have on hand fairly low value but high wattage resistors to slowly discharge the huge capacitor bank. Inexperience in these areas could be highly dangerous.

Although this might be too late a post, a medium power class A/B amplifier might be a good choice for a first-timer.

Anyhow, all the best.
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Old 3rd August 2001, 12:24 AM   #16
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Default agree with Paulb on powersupply $$

Pontus,

I can confirm PaulB's and Samuel's remark about the power-supply.
I've kept a log of money spent and give a breakdown:

for one channel:
amp components + heatsink: 35 EUR
I got a chance to select matched pairs from a tray in a shop myself.
heatsinking once-off price: I got out the last 4 from the shop, next one will cost me around 40 EUR.

ps components+ hs: 140 EUR
transformer and capacitors are 50% of that money.

I've had my pcb's made by a factory: 40 EUR for 1 amp+ 1 ps board..

Gold-plated terminals, case, wiring, nuts&bots, mains plug etc :
around 100 EUR.

AND around 10 EUR in 'replacement' stuff, I smoked some transistors/voltage regulators in the process.

So, yep the ps is expensive.

Succes
Jos

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Old 3rd August 2001, 02:04 PM   #17
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Default Money issue is solved..

Since i got my dad to sponsor my project, money is no longer an issue. Having found the components I need but not yet placed an order things are starting to look pretty good, still heatsinking is a problem. I don't know much about it, but im sure ill figure it out sooner or later.

Thanks alot for all your help.
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Old 3rd August 2001, 05:16 PM   #18
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An other complication is to convince the electronic sales man to sale you the part (very disapointing, I agree)

He don't believe that a little amp of 30 W (the Aleph3 but he does'nt know it) need so many caps. He simply refuse to sale the caps filtor, it's the reverse world. And in my region (Rouen, France) it's hard to find surplus parts.

I stay in expectative...
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