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Old 24th October 2008, 06:14 AM   #1921
Wasim is offline Wasim  Pakistan
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Hi all,

One thing I would like to ask. Can I use some other transistors who can replace ZTX550, ZTX450, K170,J74. they are not available here. One more thing I found IRFP250 and IRFP9240 can I use them or I must use IRFP240 with IRFP9240?

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Old 24th October 2008, 03:27 PM   #1922
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The bipolar devices are generic, so substitutions for them are not
a problem.

The JFET inputs should be as close to 2SK170, LSK170, 2SK370 and
2SJ74, 2SJ108 as possible. You might ask at the Solid State forum for
recommendations for replacements. Mostly you need the high
transconductance figure.

The IRF240 and IRF9240 will work, but the IR versions of the 9240
have the "P channel distortion" which has been discussed in this
forum and elsewhere, and so will not have as low a distortion figure.

The IRF250's and IRF9250'swill also work, but they have higher
capacitance, and might require some compensation, as well as
having the P channel distortion.

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Old 24th October 2008, 04:54 PM   #1923
vonfilm is offline vonfilm  United States
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This Ebay seller has 8.5" heat sinks in lengths up to 73.5"


What length would be good for each channel of the F5 to constitute a "really big" heat sink without any "stinkin calculations"?
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Old 24th October 2008, 05:23 PM   #1924
Tea-Bag is offline Tea-Bag  United States
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Originally posted by vonfilm
This Ebay seller has 8.5" heat sinks in lengths up to 73.5"


What length would be good for each channel of the F5 to constitute a "really big" heat sink without any "stinkin calculations"?

I find 18" is an great depth to get a good layout, then go a foot across.
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Old 24th October 2008, 07:24 PM   #1925
stein2 is offline stein2  Serbia
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It would be best to do a search on known heat sink profiles. I would prefer metric dimensions for making comparisons but from what I calculated, this one is somewhat smaller than my Fischer SK47 profile. Mine has 10mm thick body, 40mm full depth and I bought two pieces of 1 meter for having fun. With one meter sliced into four, the calculation added up 2x250mm height (length) for about 2x75Watts. As I'm about to use those for Aleph 5 which has about 150 Watts per channel, I'll have to go with 4 sections, that is, use up one whole meter block. With somewhat thinner and less like Fischer SK42 (not the one on ebay) with 100mm (roughly 4") height it's 1.0K/W and I would say roughly, 250mm (10") height would be just about enough. Per channel. The ones on ebay appear to be just between the two, so if you can afford to buy two 10" sections, that would allow the trannies to warm up most likely as much as they should, but not over that. Adding more to height would require a really tall box. In case you prefer without stinking calculations, then just measure how much height you need to nicely tuck in the filtering capacitore and buy four sections of that height. Take care not to go under that required 10" per channel. That's approximately if you don't want to calculate.
"Calculations? We don't need no stinkin calculations! We just make them really big!" - Papa
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Old 25th October 2008, 10:02 AM   #1926
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what's the maximum input in terms of voltage to the F5?
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Old 25th October 2008, 11:25 AM   #1927
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how about : (rail voltage minus ~4V) / gain.
It doesn't count how one deals with winning, but how to handle a loss (© DjT)
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Old 25th October 2008, 12:20 PM   #1928
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Hi owen,

When do you expect the boards for the F5 to be ready?

I'll be interested in a set. I live in Toronto as well.

Any suggestion for a local source for obtaining the heat sinks?

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Old 25th October 2008, 03:22 PM   #1929
opc is offline opc  Canada
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Hi Roumen,

The boards are here, I've built up and tested my set, and I only have two more single channels available to sell. All the other boards went pretty quickly. If there's enough interest I might have a proper run done which would further reduce the cost.

I'll set aside the last pair for you if you're interested. They're $15 each, and I have enough parts around here to put together a kit if you'd like.

Send me a PM and I'll email the PDF files and price list.

On that same note, I have attached a picture of my finished F5 (well almost finished, you know how it is)

I got the offset down to 0.01mV, rails are at 23.95 but they move around a little bit during the day depending on the wall voltage. Heatsinks are 51C directly behind the fet, and about 47C elsewhere with a 24C ambient. THD+N was 0.002 for the first channel, and 0.009 for the second, but it trimmed down to 0.003 with a lot of patience. All measured with an AP2 at 1 watt 1kHz and with a lab supply.

The AP wouldn't measure past 200kHz, but using a scope it looks flat out to about 600kHz, where it starts to drop off.

Now, I have two small issues that I'm a little curious about. The first is THD+N performance with the unregulated supply. When I substitute the lab supply with the unregulated one, the THD+N numbers jump up to 0.009 and 0.0101. The distortion vs. Freq also shows a bump at 60Hz and a notch at 120Hz, indicating that the added noise it definitely from 60Hz hum and the rectifiers.

Any suggestions on how to reduce this noise? All the above measurements were taken with the transformer well away from the chassis (not mounted in the middle like you see in the picture) so I don't think it's induced noise.

The second problem I was having was with square waves. I was looking at the square wave response at 200kHz, and I noticed that they didn't look that great (overshoot mostly). When I put the input up on the scope as well, I notice it was distorted too, and was overshooting in a similar manner to the output. I swapped the generator for a much better unit, and I got the exact same distortion on the input. When I disconnected the generator from the F5 the square wave went back to normal. This seemed to start happening at about 60kHz and got worse and worse the higher I went. If anyone knows what is causing this, please let me know.

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File Type: jpg finished amp small.jpg (98.9 KB, 2432 views)
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Old 25th October 2008, 03:39 PM   #1930
opc is offline opc  Canada
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I forgot to mention that I'm actually in Ottawa now (I just updated my profile). I went to school in Toronto but I neglected to change my location when I moved here 6 months ago.

As far as heatsinks go, I used to buy mine from R-theta who are located in Toronto. If you're gutsy you can also grab a flashlight and go dumpster diving there at night, but I suppose it would be more dignified to just go and ask them if they have some end cuts they would sell you for cheap. I bought mine cut and anodized, and they were a little expensive, but very nice heatsinks.

Also, check out Active Surplus on Queen street (with the giant gorilla) They often have some excellent amplifier parts in there (heatsinks, toroidal transformers, caps, etc...). Every time I go back to Toronto, I check that store out and stock up on goodies.

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