5 Watt Resistors on Aleph 4 and Holco Resistors - diyAudio
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Old 30th January 2002, 04:19 PM   #1
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Default 5 Watt Resistors on Aleph 4 and Holco Resistors

I can't find any reasonable quality 0.47 ohms resistors for Aleph 4. I was thinking of using those rectangular white color resistor, but my friend( electronic repair man) told me those resistors will measure about 0.22 ohm on a good digital meter even though it is written as 0.47 ohms. He asked me to find those round types, like those found in AR amp. He has some original AR 0.22 ohms resistors, but he is not selling it.

Kindly advice as I do not know what to do.
Should I use 0.22 ohms resistors?
Will it affect the bass of the amp?
Where can a find a better, more accurate 0.47 ohms resistors?
Last resort: Anyone has spare to sell?
Does any one has problems in this matter?

Is Holco resistors good alternative for Dale resistors?

Any help is deeply appreaciated.
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Old 30th January 2002, 05:06 PM   #2
tiroth is offline tiroth  United States
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Mouser has Vishay Wirewound
0.5R 1% 5W $1.24
0.5R 5% 5W $0.56

or Xicon 5% 0.47R 10W aluminum cased. (more expensive)

The cement (rectangular) wirewounds I have are 5%, so should be in the range 0.4465-0.4935. If you don't trust yours you might use the Xicon, or if the 0.5R is acceptable the Vishay 1% will provide better matching.
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Old 30th January 2002, 07:23 PM   #3
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Our experience with the Holcos was that they tended
to fail if operated near their power ratings. I suggest
not exceeding 1/2 the wattage rating of the Holco
resistor just to be safe.
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Old 30th January 2002, 07:56 PM   #4
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You might try the Panasonic 3W, 5% metal oxide resistors sold in the US by Digi-Key. The values start at .47 ohms, I believe.

Most DMMs I've seen don't have a good low-ohms scale. The ones that do should provide a function that lets you subtract the resistance of the test leads. These often come with other cool features that make them expensive. If you want to use a more common DMM to match the resistors, you could rig up a constant current source (say .1A), measure the voltage drop across the resistors at that current, and calculate the resistance that way.
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Old 30th January 2002, 08:36 PM   #5
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Default on second thought ...

Instead of a real constant current source, you could just use a reasonably stable DC voltage source (car or lantern battery, regulated power supply) and a power resistor about 100 times greater than the value you are matching (e.g. 50 ohms for .47 ohm). This will introduce a bit more absolute error into the measurement, but the relative error will be essentially zero, so you can still match parts very precisely.
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Old 30th January 2002, 11:04 PM   #6
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nicharis,

do you mean the white rectangular resistors often used in Japanese amplifiers?
They are MPC71 types, 5W, induction free.

You can get them in all sort of values from 0,1 to 1 Ohm with a 10% tolerance.

I´ve ordered them for the Aleph 5 I´m building.

The alternative is using metal oxide resistors of 1-2 watts and use a few in parallel. I did this with my current power amp (5x1Ohm) cause when I build it the resistors mentioned above were not available and the amp definitely did not like wirewound types (oscilation).

I don´t know where you live but the MPC71 are available in Germany for 0,60€ a piece.

william
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Old 31st January 2002, 07:10 AM   #7
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Yes,wuffwaff.
I saw it on Mark Finnes website, those white color rectangular thing that is giving me a headache.
I reside in Kota Kinabalu,Malaysian Sabah on North Borneo Island, famous for it's diving spots, turtle island, orang hutan sanctuary and mount Kinabalu, highest mountain(world heritage) in SE Asia. Her image is slightly tainted in recent years by Abu Sayabs in their kidnapping spree and 911 although it's generally safe here, no extremist activities here. Before I forget, my condolences to 911 victims of US and various nationalities. Majority of our tourists are Taiwanese and Europeans like to visit our natural spots. Hospitality is quite exceptable esp to foreigners. Should you ever visit this part of the world give me a call. You can get cheaper tour packages if you know your way around.

I'll try seaching MPC71 on the net to see if I can find any. I am told most parts here are of very low quality from Hong Kong, Taiwan or China.
Is it possible to check if the amp is oscillating or not with very very limited knowledge on electronics? Can I hear the oscillation on the speakers?
I've just received "Art of elecrtonics" and I am stuck in the formulas on capacitors and inductors in the first chapter and am depressed. I think maybe my dream of buildind a successful Alpeh 4 might vanished. I am worried.
Is there any website that anyone knows of that gives advice on basic electronics?

The DMM my friend use is fluke. I think he is the most extravagent repair man in town. He ask me to get a fluke because he says cheaper DMM from Japan cannot be trusted. I can't afford a fluke. I only want to built 1 amp and 1 preamp. I am think of getting a USD30 DMM once the parts arrived. Is it advisible to invest in a better DMM and around which price range?

Thank you Joe Berry for your tips. I will be building a 15v regulated power supply for mosfet match using LT1085CT and LT1033CT. I found the diagram on Sterephile website - Aunt Corey,s homemade Buffered Passive Preamp. I will be using this to test that troublesome 0.47 ohms resistors.

tiroth,
Do you mean that 0.5 ohm vishay is a good alternative?
I mean with reference to the sound. Should I just get the 0.47 xicon 10W to avoid any problem. Will it oscillate? Forgive me for asking such simple question as I am really stupid on electronics.

I actually wanted to built NP zen preamp. But it is not suitable for sensitive speakers according to NP in his article. I have my 2nd Proac response 2 speakers and it is very revealing( I think it is not amp friendly). I have tested the speakers on Holfi SE integreted amp and it sound very good. I think SE Aleph might be able to match this speaker. It's a risk I am taking. If only I can afford a commercial Passlab. I read X600 sound very good.

I have a 2nd handed meridian 506 cd player. I am thinking of building David Hurst preamp which I found on this forum to match with Aleph 4. Nelson commented it is a better zen preamp. Does anyone think it is quieter than zen? The other thing I am worry about zen is the variable in the circuit. I can't understand how to adjust it. I haven't order the volume pot from Michhael Percy yet for David Hurst preamp, except the transformer, same rating as Alpeh l preamp, only bigger ampere. What is your advice?


I will be glad if anyone can kindly point out resistors in Aleph 4 will have the risk of current operating near 0.5 watt power ratings.

Thank you.

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Old 31st January 2002, 02:28 PM   #8
tiroth is offline tiroth  United States
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Quote:
tiroth,
Do you mean that 0.5 ohm vishay is a good alternative?
I mean with reference to the sound. Should I just get the 0.47 xicon 10W to avoid any problem. Will it oscillate? Forgive me for asking such simple question as I am really stupid on electronics.
Please understand that I do not have any personal experience with the Aleph, so I am not aware if it has problems with WW output resistors. That being said, WW resistors are the norm. There are non-inductive types, but I do not have a source for any.

I did take a look at the Aleph schematic on the pass site (http://www.passdiy.com/gallery/aleph4-p1.htm) and it had no special comments about these resistors. So, I would say you are fine using the 0R5 Vishay, 5W. You could also use the standard 5W cement, which will provide better flame protection in the event of a complete failure, at the cost of poorer matching. (not critical anyway) I would prefer either to metal oxide. Please feel free to check this with someone more knowledgable about the Aleph 4.

As far as the multimeter, I would not buy a Fluke. While it would be nice to have one, it is not worth the expense for you. I bought both a decent DMM (US$70) and a 10MHz scope (US$60) for less than a fluke, so you can always scrounge a cheap scope later if you find you need one. (this is a much more informative setup)
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Old 31st January 2002, 02:40 PM   #9
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Tiroth,
Thank you for helping me out
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Old 31st January 2002, 02:57 PM   #10
tvi is offline tvi  Australia
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The MPC71 are made by Fukushima Futaba, if that is any help

<a href="http://www.koanet.co.jp/en/index.htm">KOA</a> make a similar resistor, except its nonmagnetic<a href="http://www.koanet.co.jp/custmr/pro-info/pdf/122-123-BPR.pdf"> BPR series</a>

Both are a metal plate resistors, and are used a lot in Computer PSUs.

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James
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