| Variac |
Yes it happened!!! I gave my friends who are in the electronics industry here in Silicon Valley a list of cool parts I expected them to get for me cheapo or free. This was precipitated by me seeing a business card from a friend with the Vishay logo!
Welll....... no luck for awhile, then I got some stuff - including these !!! YES !!a pair of Loveltech power jfets!!!
The DIY Audio equivalent of crack cocaine!
There is no way I can get more- I have already asked...
Even though I'm a mod, people that have gotten to know me online realize that I am a mod more because of my enthusism for cruelly mistreating misunderstood members than my technical chops.;)
So far I've made some speakers, some ambitious and some not, a few chip amps, and have been working on about the simplest amp in the universe- the Pass SOZ, for about 3 years now...Hey!, it requires a pretty sturdy setup for all those heatsinks!
1. So, I've got 2 of the these and it looks like I only need one per channel to get 15 watts?
2. Can I use one IRF P140 per channel as Q2?
3. Can I use an unregulated power supply with a pi filter putting out 50v to run it?
4. I'm planning to make the circuit on perf board, then attach it to a heatsink. Another idea is to have the power devices separate from the rest of the circuit by about 6".
Is this OK? Should the resistor r4 be kept close to Q2?
Helppp me!!! I'm sure I will make mistakes that will spare you from making the same! We can accumulate construction info here, and when your ship (full of jfets) comes in, you will be ready to go!
thanks,
Mark |
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| mpmarino |
| I think it's imperative that the first thing you do is send the jfets to me for testing. This, of course, so you know your devices are good. I'll simply reply by email to let you know if they work or not.:D |
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| Mark A. Gulbrandsen |
| quote: | | I think it's imperative that the first thing you do is send the jfets to me for testing. This, of course, so you know your devices are good. I'll simply reply by email to let you know if they work or not. |
Naw, We have much more comprehensive semiconductor testing facilities here in Utah.. cause of Hill AFB. I suggest you send them to me for a more comprehensive run down on them than the guy from Massachucets can give you... I am also closer to you so you'll know faster. I will also reply quickly by E-mail so you know exactly whats with them and where they've gone to(or into).....;)
Mark |
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| Variac |
All very generous offers-typical of the selfless spirit here on DIY Audio!
If they are bad it would be a problem, but I'm counting on you guys getting the order in soon so worst case I'm ready for their arrival. I promise to give you guys a report on how utterly fantastically GREAT they sound! :devilr:
Here's a blurry photo showing the devices to prove I'm not making this up.. They DO need to be clamped or something to attach them to a heatsink...
I am looking forward to answers to my questions- I have plenty more... |
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| jacco vermeulen |
| quote: | Originally posted by Variac
my enthusism for cruelly mistreating misunderstood members |
Speaking about swine throwing pearls. |
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| Variac |
Well, I DON"t think I mistreat people actually- Its just the ones taking the "long vacation" that seem to express this opinion ;)
Then again, my avatar seems to fit.
Here is an example of some heatsinks. I was planning to use one for each channel of the amp Nelson describes with one jfet and one mosfet. The power resisters will be lightbulbs so not on the heatsink.
Is that gonna be enough? |
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| Raoul |
| quote: | | Its just the ones taking the "long vacation" that seem to express this opinion |
What ever happened to Fred anyway? |
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| Variac |
I think he's on holiday...
__________
Gotta get the 50v power supply up and going.... |
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| Buhl |
Congrats on getting your hands on the holy crown jewels of DIY audio - I would love to offer you testing of your devices under extreme climate conditions here in the cold scandinavia, but sadly, I have no time due to my masters assignment, so you'll have to do with mark or mpmarinos offer ;-)
About the heatsink, I think you should consider cutting it in half - assuming the fins wil be vertical, thus giving you a sink that is twice your present hight - I write this, based on a suggestion I got when asking the same question as you, just for a A30 - to look at some graphs over heatsinks, that shows hight and cooling effect - about 15 centimeters the efficiency declines very, very rapidly. A heavy duty alu cabinet to mount the sinks on, will also help the amps contribution to the global warming.....
Or mabye a slow running fan, should your test run of the amp prove to hot ?
Cheers !
Buhl |
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| choky |
| quote: | Originally posted by Buhl
About the heatsink, I think you should consider cutting it in half - assuming the fins wil be vertical, thus giving you a sink that is twice your present hight - I write this, based on a suggestion I got when asking the same question as you, just for a A30 - to look at some graphs over heatsinks, that shows hight and cooling effect - about 15 centimeters the efficiency declines very, very rapidly. A heavy duty alu cabinet to mount the sinks on, will also help the amps contribution to the global warming.....
Or mabye a slow running fan, should your test run of the amp prove to hot ?
Cheers !
Buhl |
even better solution is to cut each of your Jfets in two (halfs,off course) and spread them on each end of heatsink;
in that case-results will be ,in worst case, same as you manage to send them to me for testing |
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| Andrew Eckhardt |
Mount a big power transistor over the second from right center hole in this picture:
http://www.diyaudio.com/forums/atta...tamp=1133239696
Rotate the sink 90 degrees clockwise from picture perspective and theta Z.
Drive the transistor at 52 watts and see if you like the temperatures you get after things level off. Given that aluminium has almost the specific heat of water, it will take a good half hour or so.
I think that you would like to give that whole thing to the IGFET and find something with about 4X the resistance to air just for the JFET, thermally isolated from IGFET sink, giving you the option to run lower case temperature for the JFET, which I would prefer.
If you're using the Pass circuit there's about 7 watts in the JFET and 45 in the IGFET. If you put it all on that sink you'll probably get about a 40C rise on that sink.
The fin pitch it's using would Really prefer a gentle breeze. If somebody were to produce some 10 CFM 120mm fans with totally noiseless commutators and precision bearings they could make a mint in the hi-fi audio market. |
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| Andrew Eckhardt |
I think that would be theta x but nevermind
just put the fins up and down and stuff, you know
and aluminum has 1/4 the specific heat of water :clown: |
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| Andrew Eckhardt |
..almost
and 2X the resistance to air, not four.
too bad I can't just edit my post, four ago, and just delete these silly notes.:smash: |
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| Variac |
Andrew- thanks for the advice. Especially about the watts needing to be dissipated for the 2 components. I am using the Pass circuit. I suspect he will update it at some point, but then I'll update my circuit!
I am glad you mentioned separate sinks for the JFETs . I was planning to do that but thought that maybe I was being too cautious.
I believe that you have a half hour to edit your messages. There is an "edit" button to the lower right of your post for this time. |
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| Andrew Eckhardt |
:) :(
If I would have realized my mistakes And known of the editing function soon enough I could have saved us all the irritation. Sometimes I start thinking real fast without actually thinking. Especially when yapping about something that used to be familiar but ain't really so much lately. |
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| Variac |
ok, here is one of the monoblock chassis-no electronics yet.
I got the bulbs at an electrical supply house as Nelson recommends.
I had to wait ''til a clerk could take me down to the deepest basement and look through boxes of old bulbs. 300 watt incandescent bulbs aren't really used much anymore, except halogen ones, and I wanted the "classic bulb look". Anyway, we found 4 good ones at $4 ea.
As with all DIY, it is all the additional parts that add up. The ceramic sockets were another $4 each. |
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| garbage |
| quote: | Originally posted by Variac
ok, here is one of the monoblock chassis-no electronics yet.
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it's a beauty! great work so far! |
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| Blues |
Hi Variac!
I've been looking for carburetor air intakes like the one you have (smokestack??). I'd like a couple for my HotRod Aleph :) Very nice chassis!! |
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| Variac |
Thanks guys,
The stainless box was sold as a spice rack. It hangs vertically on the wall and had all the holes to slide cylindrical spice jars into. I found it a a sidewalk sale and bought the pair for $3 with a future chassis in mind. I will cover the open holes with a piece of mesh below.
Blues, it is a velocity stack that I had two of sitting around for years. They are so pretty I wanted to save them for something special.
From a Weber or Dellorto carb. It fit perfectly in one of the holes in the chassis. It has no function and could be placed in any other hole!
Please help me think of a use! I guess a heat sink could be under it, but it extends into the box at least an inch so there isn't much room under it..... |
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| Mark A. Gulbrandsen |
Variac,
:wave2:
If you blow any 300 watters let me know. Some of the film transports in cinemas use them as ballast resistors for the motors. There is a lamp distributer here in SLC that normally stocks them.
Mark |
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| Variac |
They had 600 watters too I believe, which would have meant only one per channel. They had a mogul base (the big one) though, and I thought with only one per box, people would think I was trying to make a lamp!
My son already asked me if I had them on there just to look weird- what a letdown. I agree with Nelson- they look :cool:
Anyway, I suppose they might become rare, but at the output we are using them for, they shouldn't ever burn out, its physical damage to look out for.
I hope you guys stay subscribed to this thread! I'll have questions soon! |
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| garbage |
| quote: | Originally posted by Variac
Please help me think of a use! I guess a heat sink could be under it, but it extends into the box at least an inch so there isn't much room under it..... |
not sure how much sense this would make, but you could consider using it to house the 10000uF output capacitor. |
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| Blues |
| Variac, without the other holes that would be a heatstack...drawing out heat from inside the chassis. With a slow moving fan under it your electronic components will live a good, long and easy life :cool: |
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| Variac |
I was planning originally to make a wood cube with the stack coming out the top. Maybe I'll still do that eventually. In the mean time I'll put the 10 watt resistor under the stack probably, Or the fan idea would be great if the heatsinks are too small.
While the cap would fit, I think I would rather use it for something to do with airflow.
I am planning on making rectangular wood caps for the sides... |
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| jacco vermeulen |
Piglet,
that is a smashing idea, think it would look great.
But only without the air horns from the double barrel 40DCNL Weber, it is essential that you leave these off and send them to me, Pronto !
Those bulbs look like Little Helper, you're Gyro Gearloose right ?
Can't be, you don't look like a chicken. |
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| Variac |
OK, then I have 3 people to send the JFETs to and two people that need the velocity stacks.
I guess I am rich in junk that only people as crazy as I are impressed by! :drool:
| quote: | | Little Helper, you're Gyro Gearloose right ? |
Need more input to understand.. |
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| jacco vermeulen |
| quote: | Originally posted by Variac
Need more input to understand.. |
1st clue : Donald Duck
Seems i've been kicked out the JFET deal by GreyLabs, make that 4 for the Lovoltech. |
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| Nelson Pass |
| quote: | Originally posted by Variac
I had to wait ''til a clerk could take me down to the deepest basement and look through boxes of old bulbs. 300 watt incandescent bulbs aren't really used much anymore, except halogen ones, and I wanted the "classic bulb look". |
Grainger carries them in stock. |
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| Blues |
| quote: | Originally posted by jacco vermeulen
Piglet,
But only without the air horns from the double barrel 40DCNL Weber, it is essential that you leave these off and send them to me, Pronto !
|
Wait a minute Hot Cat from Quesolandia!....Variac, sending the airhorns a few miles north of Frisco will be easier. |
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| Variac |
| quote: | | Grainger carries them in stock. |
But wots the sport in that?
Ok Ok, that's the first bit of information that would actually be useful to someone following in my footsteps... I DID claim that this thread would help those that follow...
Nelson, how DO you think the Jfets would respond if you heated a 1/8 inch plate of copper from the back with a torch until some solder placed on top melted, then slapped the jfet (brushed with flux) on top and let it cool to room temp? Would it be cooked? or do you think it would survive? |
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| Nelson Pass |
It appears that surface mount and its relatives were designed
for something like that, but I'm very hesitant to apply such
techniques.
I coat the surface with white goop and press it to an anodized
surface, trusting the anodizing to create an adequate insulated
layer. Then I solder the leads to the edge of a pc board whose
thickness is just about that of the offset of the leads from the
flat metal surface of the package (about .062 in).
It has worked without fail so far. |
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| GRollins |
The blowtorch idea sounds iffy to me. The amount of heat energy required to get that much copper up to 350-400 degrees or so isn't going to dissipate rapidly, so the device will be cooking for quite some time, comparatively speaking. Most temperature ratings for devices specify a time (e.g. 10 seconds) that you can raise the temperature to such-and-such. I think you'll exceed the time, if not the temperature.
So far, I'm still pleased with the basic clamp idea. Someone (grataku?) posted a diagram similar to what I'm doing in the JFET group buy thread. I just popped a couple of holes in the end of some junker heatsinks, tapped them for 6-32 screws, and strapped the little boogers down with a short piece of 1/8" aluminum. Grease, but no insulator. One device per heatsink. Insulate the heatsink electrically, rather than the device. Realistically, 5 to 10W isn't that intimidating to dissipate. It's a whole lot easier than getting rid of 30 to 50W like we do when we run up class A output devices.
If the 'GreyLabs' comment in an earlier post was directed at me, I haven't kicked anyone out of the JFET purchase. At the moment I'm waiting to hear back from Shawn Fogarty. Yes, it's frustrating to wait, but it's also frustrating to have everything going in twenty directions at once without a coherent game plan. Try to look at it from his point of view: Nelson publishes the Zen variant, without warning a hundred e-mails and phone calls come in, a few people willing to brave the initial buy-in emerge, then those fall silent, only to be replaced by others, who in turn are replaced by others...they poor guy has every reason not to take DIY folks seriously. From his point of view, he's had to work up quotes (even if he's just running a finger down a quantity/price chart) a couple of dozen times now and not made a single sale. How would you feel if you were in his shoes? A little frustrated, perhaps? As I said before...patience.
Incidentally--and again, this is assuming that the GreyLabs comment referred to me--have I ever billed myself as GreyLabs? I can't remember doing so, but then I get so absent-minded sometimes that I forget where I parked my car. Makes me wish I had one of those nifty little doo-dads like Batman has, where you push the button and the car comes to you.
Anyway, I am, as I always have been...Just Me.
Grey |
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| jacco vermeulen |
| quote: | Originally posted by Variac
slap the jfet |
a combination of glueing and clamping a JFET on a strip of copper with a spring looks like a safer way to me.
Having seen some of the modern applications in the car, aeroplane and yachting industry i'm very impressed by contemporary chemical bonding techniques.
Bonding, not bondage !
Mr Rolllins,
your A-X development is starting to have a life on its own, it seems.
As you are embarking to become a US Lovoltech distributor, you'd be a second customer of proportion next to NP.
In a stroke of vision, i saw Pass Labs and Grey Labs side by side on this forum, you should be familiar with having visions.
The thought struck me as amusing, pardon my awkward sense of humor.
I wanted the batmobile too, couldn't afford it.
Gotta run, there's a wave of molten queso reported heading for the coast line. |
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| Rodeodave |
| quote: | Originally posted by Variac
But wots the sport in that?
|
Well, down in Mexico they sell 'em almost everywhere. They even have bigger ones...
And I'll never forget the face the guy at the airport made when he realized that he's x-raying giant lightbulbs and that I'm going to take them (legally) on board... |
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| Variac |
Lots of good info coming out here.
My biggest concern about soldering the jfet was heat retention also but I didn't want to lead peoples responses.
If the plate is heated slowly until the solder just melts, I don't think there would be a problem with overheating, but I agree with Grey that it will take quite awhile for the copper to cool and in the interim the part might well cook. It is true that components are specced for a temp for a certain amount of time.. SO the idea of quickly cooling the copper comes to mind, but that might lead to warping which would require grinding the back of the plate.
The thought occured to me because the device looks like it was designed for surface mounting- but for our purposes there is probably no need. In the new state, when all citizens have access to JFETS, then I'll bet we see some experiments like this. Since I have just 2, no thanks!
Getting bulbs in Mexico- now that is sporting! and probably a lot of fun! |
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| Rick NL |
Variac,
I have done quite a lot of soldering to SMD and TO220 to copper bases for quite long times, much more than 10 sec's.
This was on switching fet's and charger pass fet's. Never ever had any trouble. Would not know if this also applies to a super JFET Amp. But I will certainly try it. I have some 15 x 3 mm copper bar and will mount them with two holes adjacent to the chip. I have the idea that a great heat capacity (mass) will be good to keep the chip temp constant.
All this when I can get hold of the parts!!
Rick |
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| Variac |
And here is a place that sells small squares of copper
http://www.enameling.com/page20.html#Squares
You have to make sure to get the flat, not domed ones. I guess we are off topic a bit, but I'd imagine that throwing the soldered copper plate/JFET on a wet towel would cool it pretty quick.
Advantages? Can use silpad or mica under the copper because the plate is big and will spread the heat. Can make higher output amp with a single device.
Anyway, we'll leave that for when we have lots to play with. |
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| MikeW |
| How many is Pass labs going to use in it's first Power JFET amp? 48? 64? :smash: |
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| jacco vermeulen |
| quote: | Originally posted by Variac
that might lead to warping
Getting bulbs in Mexico- now that is sporting! |
At those temperatures you expect warping ?
If you like sporting i recommend the PanAmerican.
Second suggestion: preferably not do this with a PuertoRican drunk who offers a cheap ride.
You've got a firearms permit, right? |
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| GRollins |
I considered soldering the devices to a larger piece of metal, but the thought of having to service such a thing was enough to give me nightmares. These days, people don't repair, they replace. A device that's been soldered down just goes in the trash can. I'm a little old-fashioned--not to mention hating to waste money--so I'd rather fix something if it's at all possible.
Grey |
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| gl |
I usually take this point of view too. In other words I'm painfully cheap and have tons of used parts in boxes and bags all over the place.
However, these parts are only 94 cents each. The copper plate Variac is talking about is probably more expensive.
I think that soldering the transistors to a copper plate is a good idea. Onlinemetals.com has lots of copper sheet stock.
One idea would be to hack saw two cuts about .5" deep about .5" apart on one edge of the plate and solder the transistor to the resulting tab. It would make the soldering easier but probably not affect the cooling properties of the plate at the lower operating temperature.
Regards,
Graeme |
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| woody |
| How is Firstwatt mounting this jfet? |
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| Variac |
3/4"x3/4 or 1"x1" are 40 cents each and require no cutting, BUT they are 18ga which isn't too thick, but copper is so heat conductive even that thickness is prob OK. Also thin helps quick cooling. after solder..
Nelson says there is no problem with clamping them on a heatsink, so this is kind of a non-issue,
BUT some people prefer having only one output device rather than many in parallel, so this is a way to get more power out of one device. |
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| choky |
| quote: | Originally posted by woody
How is Firstwatt mounting this jfet? |
I bet -in some non-complicated engineer way
:clown:
simple clamp with screw and sort of rest? |
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| gl |
Hi Variac,
If you are using 1" x 1" copper plates then your heat dissipation capability will be very limited.
My understanding is that you are intending to build the JFET Zen in the PassDIY article (more or lass) which means that the JFET is dissipating about 7 watts of heat. This is small compared to some of the other Zen amp applications but it is still a serious amount of heat.
I have used aluminum plates for heat sinks for several projects in the past. I have never used copper. If I was going to try and get rid of 7 watts of heat using an aluminum plate I would start experimenting with one 6" x 6" and .1" to .125" thick based on past experience. It needs to be mounted vertically and the transistor should be mounted in from the edge as much as practically possible.
Alternatively you could use one of the bigger Aavid TO-220 standalone sinks and using the mounting hole for a spring clip. You'll still have a tough time keeping the temp rise under 30C above ambient.
You may end up just going back to mounting all the power transistors (somehow) on a common large sink.
Hope this helps.
Graeme |
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| Variac |
gl
The idea was to spread the heat with the copper plate so that the copper plate can then can be attached to the aluminum heatsink. My thought was that Nelson recommends not using an insulating layer such as mica or ceramic or silicone sheet, but just attaching the device directly to the heatsink using the anodized layer of the heat sink as electrical iinsulation. Grey points out a similar approach, but use a separate heatsink for each device, and electrically isolate the entire heatsink.
My question was whether one could mount the Jfet directly to the small copper plate with solder (excellent heat transfer) then, since the plate would have about 6 times the area of the jfet, mount the plate to the heatsink with an insulating layer, which should work fine since it has a lot more area to transfer the heat through the insulator to the heatsink.
Anyway, it was just a question. I am probably just going to mount the Jfet directly to a small separarate heatsink, electrically isolated from the chassis. This seems the safest for the moment, and should get rid of the heat fine.
Thanks for the concern,
Variac |
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| gl |
Hi Variac,
I guess I had missed the point that you were using the copper plate as a heat spreader. Sounds good. My major point was to say out that 7W was a non-trivial amount of heat to get rid of.
Regards,
Graeme |
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| flg |
I don't want to be off thread... I want to make one!!! Let me plant a seed... I once worked with a product testing application where we had to use a Bismouth solder (might check my spelling there) on all the associated test hardware... I beleive this requirement (customer based) was to protect the integrity of the very high $$$ boards we were soldering. Bismouth is a lower temp solder. This product was also some of the highest speed ECL logic available. Very sensitive to further "processing" by over temp conditions... Just a thought that may solve that time/temp delema...
FYI we here in the USA have to hunt fowl with non Lead shot in our shotguns (HazMat). We either use steel or Bismouth shot...
So Grey, guess you did'nt like the Grey Labs thing??? Sounded good to me. You should be honored to be there next to XXXXLabs... I did not really like the flg thing when it started but I got used to it ( Found in Lee's Garage)...:D :D :D |
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| GRollins |
Didn't like? No, it just confused me. Setting aside all the usual confusions and demands on my time, there have been a lot of things going on at work and the Lovoltech buy and the author thing and Christmas and so forth.
Interestingly enough, I have four rooms in my basement. The one where I do electronics I call the Lab, with tongue firmly in cheek.
I make no claims to being in Nelson's league. He does this stuff all day, every day. I just play at it.
Grey |
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| Variac |
I'm going on a 2 week vacation, so you guys keep the discussion going... I'll be back!:zombie:
Maybe nelson will have a new version by then! (keep the bulbs as an option-please!!) |
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| jacco vermeulen |
Have a nice holiday, Mark.
(envoy me your adress and leave the key under the door mat) |
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| Nelson Pass |
| quote: | Originally posted by Variac
(keep the bulbs as an option-please!!) |
Sorry, the bulbs are the first thing to go. I do have a nice
Zalman "mushroom" heat sink that fits where the bulbs went.
:cool: |
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| BDP |
Anyone who has Zen Ver 4 boards can easily configure the boards for the Pass JFET amp with a few cut traces and jumpers. You would get a regulated supply and constant current source.
:xmasman: |
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| Variac |
I'm back, and I plan to keep the bulbs.
I have to agree, it shouldn't be any surprise that the first improvement is a CCS. However I will console myself that Nelson seems to still like his enlightened Zen and some really like the SOZ so I'm sure it will sound great! Just will use a bit of power. |
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| GRollins |
(...and look nifty in the bargain...)
Grey |
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| stefanobilliani |
| quote: | Originally posted by Variac
I'm back, and I plan to keep the bulbs.
I have to agree, it shouldn't be any surprise that the first improvement is a CCS. However I will console myself that Nelson seems to still like his enlightened Zen and some really like the SOZ so I'm sure it will sound great! Just will use a bit of power. |
While waiting for the JFets... I found nice halogen sticks for the amp .
They are 1500W 230Volt , 2Amps @ 26 volts , 13 ohm .
The stick-holders are pratical to use and easy to mount parts .
Good Year to all. |
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| Variac |
Stefano,
I'm sure people would love to see photos of the halogen sticks and holders. I have generally cleaned up the complications of returning from vacation and hope to quickly finish the amp.
Mark |
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| GRollins |
Given that the resistance of the filament in a light bulb will increase along with the temperature, it occured to me that you're introducing a distortion mechanism by having an inconstant load.
Grey |
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| flg |
Some Years ago, after reading the Zenlite paper, I tested some bulbs myself. N.P. did not clearly state any particular conditions, but he said he tested many bulbs also. All my tests showed a variable R vs. V or I in the expected range of use. I was only doing static testing(turning knobs with my hand). I eventually assumed that the temperature lag was entering into the results. I never actually tryed an AC modulated around 2A or anything. It is very possible that N.P., in all his wisdom, just left that part for us to figure out.
For instance, I hate monitors or lights that dont go any faster than 60hz unless there persistance is long enough that I dont see the blinking. Regular incondecent bulbs rarely blink to my perception although, they obviously have a large signal 60hz on them:D :D :D |
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| Nelson Pass |
Obviously filaments have some flaws, different than other biasing
options, but I haven't found them to be objectionable. A big
power resistor is more pure, but isn't as fun to look at. |
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| Variac |
Someone:
Can the caps all be electrolytic? ie polar?
I guess the little plus sign means YES!
Can C1 be more that 10k ?
How about 30k?
What does this change?
|
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| GRollins |
Fella, if you would kindly tell me where I could find film caps of that size, I'd be grateful. Translate that as, yes, electrolytics are the order of the day. (Of course, you could always bypass them with film caps.)
Yes, C1 can be more than 10,000uF. It will lower the low frequency cutoff point. More bass won't really hurt your feelings, will it?
Loser?
Nope.
What have you lost?
Nothing.
You're about to gain a nice amp...and there's nothing wrong with that. Look at it this way--I've got two ideas on the front burners and a half-dozen in reserve in case one or both bomb out, but I'm not able to listen to them yet. You'll be listening to music through these JFETs before I do.
Grey |
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| Variac |
Thanks Grey. Actually I fooled myself! Boy, I guess this was too simple.
On my list of caps was C1A which DOESN"T EXIST! I now realize it was a 10 mfd bypass cap that I invented and added to the purchase list. I was then apalled that the local electronics emporium didn't stock any poly caps in that value. Of course you are right, a 10,000MFD poly would probably be the size of a garbage can in a decent voltage! It was the 10 MFD (not on schematic ) that I was hoping to get in a poly.
The store was NOT R. Shack, but a moldy old storefront that should have been a treasure trove of reasonably priced goodies. They only stocked ONE brand of metal film resistors (Xicom of course) All the stock was old and the leads were corroded-BUT, instead of paying surplus prices they wanted top dollar. When they wanted $29.95 for a 10,000 MFD no name 60v electrolytic I politely paid for my resistors and walked out, figuring that the 30,000mfd 63 v. caps I have at home (that I paid $6 for online) might do the job!
So, I guess I did the right thing- thanks for the help.
:D |
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| flg |
| Well, while looking over previously saved data to spark some ideas of what to do with my B20FU20 Full Ranges, I happened to run into my data from the bulb tests. I was wanting to throw out this idea before but was unsure of exactly what the data showed. I was suprised N.P. did not mention this. My data showed with higher current, a higher R and lower I less R. So, is this not a benificial form of non-linearity? Does this not flatten out the higher I more gain, lower I less gain, non-linearity of the gain transistor? At least to a small degree??? Along with looking cool of coarse... |
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| Nelson Pass |
| quote: | Originally posted by flg
Well, while looking over previously saved data to spark some ideas of what to do with my B20FU20 Full Ranges, I happened to run into my data from the bulb tests. I was wanting to throw out this idea before but was unsure of exactly what the data showed. I was suprised N.P. did not mention this. My data showed with higher current, a higher R and lower I less R. So, is this not a benificial form of non-linearity? Does this not flatten out the higher I more gain, lower I less gain, non-linearity of the gain transistor? At least to a small degree??? Along with looking cool of coarse... |
"to a small degree" describes it. The thermal energy in the bulb
is dramatically higher than that going to the speaker and the
time constant on it is subsonic. I can measure it, but it doesn't
bother me sonically. |
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| GRollins |
Shooting from the hip, I would think that "rough service" bulbs would be better in terms of maintaining a constant resistance. They have much heavier filaments than most other bulbs. That would, in turn, improve the thermal behavior. I have no idea what the resistance of the filament in a rough service bulb would be, but some series and/or parallel combination of them would probably come up to the required load.
Granted, they wouldn't look as cool.
On the other hand, they could handle physical abuse better. Those with children or pets might fare better with them. Also people who tend to move their amps about in the process of taking them to audiophile meetings and such.
Variac,
Digikey has a Panasonic film cap (polyester, I think, but it's better than nothing) 10uF 100V. I'm at work and so don't have the part number handy, but it shouldn't be too hard to find.
Grey |
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| Mark A. Gulbrandsen |
| quote: | | A big power resistor is more pure, but isn't as fun to look at. |
Yea, and the light will help to lead the way if the darn thing quits on ya.....;) .
Mark |
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| BDP |
| quote: | | Anyone who has Zen Ver 4 boards can easily configure the boards for the Pass JFET amp with a few cut traces and jumpers. You would get a regulated supply and constant current source. |
Thanks to Grey for the FET group buy I have one channel of a Zen "light" ver 8 with a regulated supply and single 300 watt light bulb biased for 1 amp burning in.
I had an old pro amp that has been waiting for such a project. The transformer is 325 VA and the heatsinks are only good for about 50 wattsper channel, hence the light bulbs.
The Zen ver 4 boards worked great, didn't even need to cut any traces, just some careful placement. In the future I can reuse them if I decide to add an Aleph CCS.
The source resistor on the FET is 1 ohm, 2 two ohm resistors in parallel. The 25K ohm pot. was adjusted for half the supply voltage at the output. The bias came out to .98 amps and 2 volts across drain to source of the fet.
I hope to listen to the one channel tonight after some brief tests.
BDP |
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| Variac |
| Then post some photos! I have had one channel wired on perf board for weeks but then needed to make a powersupply and..........nothing yet! |
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| BDP |
| Zen light ver 8 photo. The output pot. adjust was easy to set, so you don't have to worry about the amp drawing a bunch of current when you tweak the pot. I have a 40K ohm voltage divider with the 25K pot and its set 3/4 of the pots range. |
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| BDP |
Here is a picture of the finished Zen Ver 8. I did some measurements.
Frequency response was 80KHz with 600 ohm source.
10Khz square wave looked good with slight rounding of the edges.
My heatsinks could take a little more heat so I upped the regulated supply to 50 volts and adjusted for half the supply voltage at the output. The bias current ended up at 1.2 amps. Voltage across the FET was 2.7 volts.
I'm driving a mid tweeter in a Bi-amped pass Hi/Lo/ Moamps electronic crossover so I can't comment on the bass at this time. This amp is very smooth. Once you get to this level of equipment the difference in speakers becomes huge. The Audax PR170M0 mid becomes very detailed but never harsh. Listening to this amp will be fun.
In the back ground is my Aleph mono amp. |
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| Mark A. Gulbrandsen |
| Thats funny, I was just talking about making a BGW like chassis for my A-30! on this thread. |
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| Nelson Pass |
You can use it instead of the IRFP240's, I believe,
but of course it won't replace the JFET.
:cool: |
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| widowmaker |
offtopic:
Mr. Pass
A few months ago I wrote an email to You with attached schematic...
You didn't answer... |
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| Nelson Pass |
Not all emails are received, but all emails received get some
kind of response eventually. Some responses are bounced
back, address rejected. |
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| widowmaker |
offtopic:
To Nelson Pass:
Yes, of course, here, in bulgaria, we lift potatoes with dynamite and we've never heard about email :smash: :whazzat: :hot: :bigeyes: |
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| BillWW |
Looking at the data sheet, this device has at least double the input capacitance of an irfp240, so your highs will be more rolled, but better bass due to the higher transconductance.
It would be similar to the Aleph 3 that uses two irp240 in parallel.
It would probably still sound nice for using one amp for a full range driver. If biamping then you might want to consider a lower capacitance for midrange/tweeter.
Bill |
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| choky |
| quote: | Originally posted by widowmaker
Yes, of course, here, in bulgaria, we lift potatoes with dynamite and we've never heard about email :smash: :whazzat: :hot: :bigeyes: |
hehe
and,of course,here,in serbia,we don't even know what computer is..........
:clown:
so-in bulgaria is still better .......
don't be grumpy-NP answered to your post with no less than 3 rows of txt!
:devilr:
ps. just imagine number of emails to NP from this DIY bunch every day.................... |
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| widowmaker |
| quote: | Originally posted by choky
ps. just imagine number of emails to NP from this DIY bunch every day.................... |
My email was not sent from this DIY forum... |
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| choky |
| quote: | Originally posted by widowmaker
My email was not sent from this DIY forum... |
from personal experience,I know that NP don't make difference between mail addys,domains ,are you known on DIY or not.....
just a thought-he recently changed ISP,mebbe some sort of spam filter was in action (it happens all the time);
or-if you examine his post again (and that is often needed with NP :devilr: ) I have impression that his mail to you is maybe bounced...
dunno for sure..... |
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| Nelson Pass |
I don't currently employ a spam filter, each piece of mail is
actually glanced at, and since Network Solutions is now the
host, I don't expect future difficulties. |
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| choky |
| quote: | Originally posted by Nelson Pass
I don't currently employ a spam filter, each piece of mail is
actually glanced at, and since Network Solutions is now the
host, I don't expect future difficulties. |
woa! (blue car!) ;)
so-even I can send you personal e-mail ,with another one brilliant idea :devilr:
nah....
forum is good enough ;) |
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| widowmaker |
| quote: | Originally posted by Nelson Pass
I don't currently employ a spam filter, each piece of mail is
actually glanced at, and since Network Solutions is now the
host, I don't expect future difficulties. |
We talking about SE JFET amp -
I had (and still have) a few ideas (not only for jfet amp) ...
but...
It doesn't matter anymore... |
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| BDP |
After the Ver 8 Zen light, I started on a Ver 9 and before I could finish, the Firstwatt JFET F3 amp was released so i thought I would wait until Mr. Pass published the schematic. Here are some tips that might be useful to others building the F3. I used the Ver 9 PD boards for this project and modified them for the F3.
The JFETs were measured as per the Ver 9 article. The JFETS I used measured 1.02 volts across the 1 ohm source resistor. I adjusted P1 to get half the supply at the output and 2.5 volts Drain to Source on the JFET. Then I hooked up the distortion meter and adjusted the source resistor for the minimum distortion. The source resistor turned out to be about 1 ohm. When I tried to adjust for half the supply voltage at the output I couldn't get there. I was short a couple of volts. I changed R12, 10K to 15K and put in a 10K pot. at P1. Now I could make the adjustment.
After adjusments on P1 and the Aleph CCS P2, I measured .0126% at 1 watt @1KHz. I ended up with 1.5 VDS on the JFET. At .1 watt the distortion was .003% just what Mr. Pass had published.
Listening comes after I get the other board changed to the new values. Oh who am I kidding, I will have to listen to just one channel. I can't wait for the other channel!
Thanks Nelson for the great articles. With out them I would not have built so many amps.
First Pass DIY amp built in 1990.
BDP |
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| BDP |
I took a distortion measurement with a source resistor selected from the graph Mr Pass had for Vgs vs source resistance. The JFETS that measured 1.02 volts in the test setup would require a slightly less than 1.5 ohm source resistor for R5, (R3 for Ver 9). I used a 1.5 ohm. When the output voltage was adjusted for half the supply the VDS of the JFET was 2.46 volts and the 1 watt distortion measured .037%, not too bad.
Anyone else building the F3? Besides Mr Pass! |
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