For each 4 IRFP240s I have heatsinks rated at .31C/W (convection) and will experiment with forcing air through a duct formed by the finned surface of the plates. From what I've read, it is not uncommon for moderate forced air to increase aluminum heatsink efficiency three fold. So perhaps as little as .1 C/W. Seem reasonable?
You'd think they would offer a circuit diagram on their website! I don't want any caps nor inductors. ...looks like nasty wirewound resistors in the photo of the old model... dunno if they are in the signal path...
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Speaker protection
I have managed to convert PCB for 2-channel protection as on My F5
It worked fine a couple of times while I was doing rely silly things
NTE7100 or similar (there are 2 or 3 versions al the same different manufacturer)
Values for dc detect are as in data sheet 56 K for resistors
Ac loss detect power down when mains is off I have taken 24 V ac from pin of bridge rectifier.
Work out your own values of C3 and R5 for power up delay.(mine set at 10 seconds)
I am not using the Ac overload protection
The relays are Amplimo speaker protection relay (special contacts for this use) gogle it
The third relay is for aux and leds.
I am using a transistor (overkill) but chip can sink 300 mA
C1 0.47U is for automatic reset pin above for dill switch to over ride this.
If needed I can send gerbers or DXF.
Hope it helps
http://www.diyaudio.com/forums/swap-meet/182480-holco-mfr-15ppm-2w-sale.html
I have managed to convert PCB for 2-channel protection as on My F5
It worked fine a couple of times while I was doing rely silly things
NTE7100 or similar (there are 2 or 3 versions al the same different manufacturer)
Values for dc detect are as in data sheet 56 K for resistors
Ac loss detect power down when mains is off I have taken 24 V ac from pin of bridge rectifier.
Work out your own values of C3 and R5 for power up delay.(mine set at 10 seconds)
I am not using the Ac overload protection
The relays are Amplimo speaker protection relay (special contacts for this use) gogle it
The third relay is for aux and leds.
I am using a transistor (overkill) but chip can sink 300 mA
C1 0.47U is for automatic reset pin above for dill switch to over ride this.
If needed I can send gerbers or DXF.
Hope it helps
http://www.diyaudio.com/forums/swap-meet/182480-holco-mfr-15ppm-2w-sale.html
Nope.
Resulting thermal resistance number of a blown heatsink depends on the air flow and ; heatsink type, fan, synergy between the two.
A factor three reduction generally requires a substantial air speed, something in the order of >16ft/s.
Which is too high/noisy for audio purposes, a reduction of the natural convection number by half is more realistic for moderate air speed numbers.
The obtainable air speed at the max permittable sound pressure level primarily depends on the noise figure of the fan and heatsink height, there's a couple of tweaks to lower the dB number of the combo a bit.
(most exotic fan with the highest air flow number per dB of noise is one with the blade tips pointing inwards, but out of reach for the average DIYer)
Thanks everyone so far for helping me in my search for 2sj109bl. They are expensive as I learned and prices seem to have doubled last couple of month.
However some weeks a go I managed to get one single piece of 2sj109bl from the inventory of a very long existing local electronics parts store that went broke (for just 5 euro's).
So now here's my question: I need one for left channel and one for right channel.
S0 I ques for this mathing won't be nescesarry? Altough if I buy one additional 2sj109bl the production dates between the one already in my possesion and the new one could differ many years? Would it be likely for this to cause problems, imbalances or whatssoever ?
Could anyone please advise?
Thanks in advance
However some weeks a go I managed to get one single piece of 2sj109bl from the inventory of a very long existing local electronics parts store that went broke (for just 5 euro's).
So now here's my question: I need one for left channel and one for right channel.
S0 I ques for this mathing won't be nescesarry? Altough if I buy one additional 2sj109bl the production dates between the one already in my possesion and the new one could differ many years? Would it be likely for this to cause problems, imbalances or whatssoever ?
Could anyone please advise?
Thanks in advance
Channel to channel matching is not necessary but the Idss of both should be over 8ma or you may need to do a little tweaking of resistor values in the front end. Probably not a problem though.
Matched pairs of 2SJ74 are much easier to find. That's what generally is used instead of the 109s.
Best, Bill
Matched pairs of 2SJ74 are much easier to find. That's what generally is used instead of the 109s.
Best, Bill
For each 4 IRFP240s I have heatsinks rated at .31C/W (convection) and will experiment with forcing air through a duct formed by the finned surface of the plates. From what I've read, it is not uncommon for moderate forced air to increase aluminum heatsink efficiency three fold. So perhaps as little as .1 C/W. Seem reasonable?
You'd think they would offer a circuit diagram on their website! I don't want any caps nor inductors. ...looks like nasty wirewound resistors in the photo of the old model... dunno if they are in the signal path...
The schematic is shown in the Velleman parts list on their website. The relay contacts are the only thing in the signal path, and there are 2 3K resistors feeding to the opamp input for the DC sensing. No problems.
haha yep, it may be a totally hairbrained idea with switching these currents live, i'll need to bypass it i guess too. although its unlikely that i would ever have a situation where i'm already playing music at high levels when its asked to engage, so really its just how fast it is disengaging in a fault condition.
with patrick's jfet heatsinks i would think that 2 x j74 is actually a better idea anyway, as toshiba duals do not specify a higher degree of matching than is possible with singles, so we are left with the advantages of being in the same package, offset by the singles being tied to a heatsink.
all the same i have j109bl in there to start
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Would the Conrad heatsink MF35-151.5 do for the X configuration of one channel?
Conrad Heatsinks - Products
Conrad Heatsinks - Products
Thanks for your thoughts. Well, I have never been afraid to 'experiment'!
The "proposed" heatsinks just today arrived in the mail. I'm guessing it should be adequate to almost halve their passive C/W figure (.3 C/W), simply based on the sizes of passive heatsinks I have seen in photos of beautiful cases that were successful. This is for an Aleph J, not a JX.
I *think* I can generate ~5 ft/sec of air movement over the 450 sq inches of surface for each channel, at a noise level that will be negligible. In any case, I was hoping to need less air velocity so the fan could run slower and quieter. The new fluid dynamic bearings in computer fans are quite an improvement in terms of noise. I don't mind if the amp runs hot, just so it is stable and I don't hear it over other background noise.
It will be a while before I'm ready to test, but I'm really looking forward to the project!
Cheers,
Frank
PCB design feedback
I would like feedback on my PCB design for an Aleph JX variant.
Some background information:
-- Peter
I would like feedback on my PCB design for an Aleph JX variant.
Some background information:
- The power supply rails are +22V and -22V respectively (determined by an old trafo I want to use for the project)
- The amplifier is biased to 2.5A per channel (to achieve 2x10W in 4 Ohm)
- The PCB tracks are 1.45mm. They should be able to handle 3.3A with a temperatur rise of 10C -- without accounting for any derating from nearby tracks and components
- I have tried to make the PCB design as symmetrical as possible for aesthetic reasons
- I have tried to reduce the length of the PCB tracks as much as possible
- The PCB is single-layer
- The board is 160x100mm
-- Peter
Attachments
I don't know if it's easy, or whether you have a different idea (a heatsink), but if you can face Q5 and Q7 toward each other, you could cable ties them together for better temperature matching.
I havent decided how to thermally coupling and heat sinking Q5/Q7. Ideally, I would like to get my hands on the dual TO92 heatsink (without having to buy 25 pcs). If I cannot manage that, I'll probably end up facing them toward eachother and clamping them to a piece of aluminium. In free air I believe they are rated at 180 C/W. At 10mA bias per JFET they should produce 170mW each, which is a 31C temperature rise (minimum). Thus, I would prefer a bit of heatsinking to reduce this.
Whatever I do it will require some minor modifications to the PCB layout.
Whatever I do it will require some minor modifications to the PCB layout.
Uh?
You run the tail current source at 0.7/1.1=6.4mA and that is shared between the two jfets. These little buggers run at far less than your figure.
170mW is anyway far above a reliable number, try to stick below 100mW for reliable long term use. You might want to think about a cascode, as it further cuts down power dissipation, Miller capacitance and improves noise.
Hannes
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My intention in the schematics was to make an adjustable current source in the range 16,5mA to 25mA (and to tune it around 20mA once I build it). This is how I came to those numbers: R23 is 1.1K. R25 and R26 are 500 Ohm each. Together they can be adjusted from 344 to 524 Ohm. I assume the voltage drop across the zener minus the drop of BC178 is 8,6V (should be close enough). That should allow me to adjust the current from 16,5mA (8,6/524) to 25mA (8,6/344).
I was thinking that it would be ok to run the JFets at 170mW each with some heat sinking, but I take your point and will reduce it further. I must admit that the 10mA bias (per JFET) was chosen somewhat arbitrarily.
I was thinking that it would be ok to run the JFets at 170mW each with some heat sinking, but I take your point and will reduce it further. I must admit that the 10mA bias (per JFET) was chosen somewhat arbitrarily.