10kHz Square Wave
This is for the BB amp: here is a 17.5vpp 10kHz square wave into an 8ohm load. I am not sure if the rise time is limited by my cheap function generator or the amp. There is a tiny overshoot, with what looks like a ~1MHz ring that decays very quickly. I took it up to 40vpp and did not see anything worse. Shape stayed the same. Below 5vpp there is no overshoot.
This is for the BB amp: here is a 17.5vpp 10kHz square wave into an 8ohm load. I am not sure if the rise time is limited by my cheap function generator or the amp. There is a tiny overshoot, with what looks like a ~1MHz ring that decays very quickly. I took it up to 40vpp and did not see anything worse. Shape stayed the same. Below 5vpp there is no overshoot.
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X,
This is magnificent, I have really seen a better amp at 10k on square wave!
The resonance could be removed with a small 22pF from collector to emitter of the active CCS transistor, T5. It seems we are tilting at windmills, there really is no evident problem with this amplifier.
Cloosed,
TK39J60W5 is adequate but I would rather find one rated to 100-300V rather than something rated to 600V. This is much more voltage than you need.
HD
This is magnificent, I have really seen a better amp at 10k on square wave!
The resonance could be removed with a small 22pF from collector to emitter of the active CCS transistor, T5. It seems we are tilting at windmills, there really is no evident problem with this amplifier.
Cloosed,
TK39J60W5 is adequate but I would rather find one rated to 100-300V rather than something rated to 600V. This is much more voltage than you need.
HD
Hi Hugh,
For the 4R version is it not better to use the larger TO-264 or SOT-227 package ?
Grts,
Danny
For the 4R version is it not better to use the larger TO-264 or SOT-227 package ?
Grts,
Danny
Yes Danny, it is, but he seems not be able to buy the IXYS.
It is very difficult to recommend devices when people say they cannot buy one of the most important parameters, in this case a good thermal characteristic!
HD
It is very difficult to recommend devices when people say they cannot buy one of the most important parameters, in this case a good thermal characteristic!
HD
Problem is I could not find both n and p channel ixys, only n-channel is available (where i generally procure the parts)
Thx Hugh for clearing that out, I was confused.
Yes there are only N-channel T-264, SOT227 at in.rsdelivers.com.
There's also an Indian digikey and mouser with the larger T-264, SOT227 recommended N and P transistors.
Yes there are only N-channel T-264, SOT227 at in.rsdelivers.com.
There's also an Indian digikey and mouser with the larger T-264, SOT227 recommended N and P transistors.
Cloosed,
You must find a TO264, or TO247, or TO3P for the ALPHA. None of the smd SOTs are acceptable.
If you cannot buy them in India, try buy them from the US why I am forced to buy most of my parts from Australia. Many Indians have friends in the US who can buy for them and then bring them in their pocket as they fly home from time to time.
I become a little frustrated by all this stuff about inventory; it is difficult for EVERYONE, and requires a bit of effort to buy these parts. India is now opened to business, and you can generally buy from large corporations domiciled in Western countries but with branch offices in India. The market there is HUGE, growing middle class with lots of electronic machines in the country, so large corporations are all scrambling to get their branch offices working well...... these mosfets are used widely in smps, industrial controls, electric vehicles, forklifts, and much of medical equipment.
The first requirement is 264/247/3P, second is dissipation to 300W, third is 100-300V, fourth is current capacity to at least 40A, Gfs >25S and so on.
Good luck!
Hugh
You must find a TO264, or TO247, or TO3P for the ALPHA. None of the smd SOTs are acceptable.
If you cannot buy them in India, try buy them from the US why I am forced to buy most of my parts from Australia. Many Indians have friends in the US who can buy for them and then bring them in their pocket as they fly home from time to time.
I become a little frustrated by all this stuff about inventory; it is difficult for EVERYONE, and requires a bit of effort to buy these parts. India is now opened to business, and you can generally buy from large corporations domiciled in Western countries but with branch offices in India. The market there is HUGE, growing middle class with lots of electronic machines in the country, so large corporations are all scrambling to get their branch offices working well...... these mosfets are used widely in smps, industrial controls, electric vehicles, forklifts, and much of medical equipment.
The first requirement is 264/247/3P, second is dissipation to 300W, third is 100-300V, fourth is current capacity to at least 40A, Gfs >25S and so on.
Good luck!
Hugh
Thanks you so much for your explanation,
I will try to get them from Australia 😉, my cousin would be flying in the month of June or July (but the sad part is waiting, as am eagerly waiting to listen to the wonderful amp ).
I will try to find the websites in Australia, if i couldn’t find them will seek your help 😉
Regards
Raj
We have an ease to get electronic components in North America but getting the chassis or heatsinks is much easier from Europe and Asia with huge import fees. Nothing is perfect!
Do
Do
Sometimes I can't figure out if the conversation in this thread is about the 20W or the BB amp. My understanding is that the 20W amp TO247 IRF devices in the schematic/BOM are sufficient for normal loads (but not optimal for 4ohm loads). Can I swap in the larger IXYS TO264 devices without making other changes to the standard 20W amp? This would be for "just because" and perhaps better heat dissipation/margin with the larger package - maybe later I'll have a 4 ohm load, but not at the moment.
BK
BK
BK,
Yes, you can put the big TO-264 IXYS devices on the 20W Alpha and it will work fine and leave you ability to run higher bias later. Not a bad idea actually to just make a 4R version from the get go.
Yes, you can put the big TO-264 IXYS devices on the 20W Alpha and it will work fine and leave you ability to run higher bias later. Not a bad idea actually to just make a 4R version from the get go.
Hi BK,
Yes, but use the schematic of the 4R version with following change:
- source resistor 0.33 instead of 0.27 for reduced bias.
- add also a snubber 220p+47r across the CCS transistor, this should also be in the 4R version (Thx X for testing this)
Don't use the schematic of the 8R when using the bigger Ixys transistors,
because you'll get higher distortion and the CCS will be out of balance with the output transistor.
This 8R Ixys schematic gives the same FFT as the normal 8R Irf version.
Here's the modified schematic.
Yes, but use the schematic of the 4R version with following change:
- source resistor 0.33 instead of 0.27 for reduced bias.
- add also a snubber 220p+47r across the CCS transistor, this should also be in the 4R version (Thx X for testing this)
Don't use the schematic of the 8R when using the bigger Ixys transistors,
because you'll get higher distortion and the CCS will be out of balance with the output transistor.
This 8R Ixys schematic gives the same FFT as the normal 8R Irf version.
Here's the modified schematic.
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Just for clarity: normal Alpha (Pmos hybrid) uses a 7.5A Pch Mosfet. Now when making a decent version that can also drive 8 ohm Kef speakers, Alpha4r, one needs a minimum 40A Pch Mosfet. For 6 ohm minimum load 7.5A is sufficient, why is at least 40A needed for Alpha4r, what is the formula for this ?
Irribeo,
Basically I select for thermal capacity and cost. If the 4R Alpha runs 2A quiescent, the dissipation on EACH device is 48W, the 8R version running around 36W. The BB running at 3A dissipates 108W in each device and this prompted me to specify 480W IXYS devices with 1KW devices even more suggested, but these are expensive.
I like to use devices with at least 280W dissipation rating on the Alpha 8R and 4R. These are FQA40N25 and FQA36P15 from Fairchild. They are economical and TO3P DEVICES and I can recommend them.
For the BB I specify a 480W devices minimum.
In early posts I have mentioned other parameters; Vds, Ciss, Id, gfs but any hexfet will work well within obvious limitations. There may be subtle differences in Sonics from diverse mosfets but I dare not go there..... generally I have always found the sound quality comes from the topology, the components (particularly the caps), and the operating points.
Hugh
Basically I select for thermal capacity and cost. If the 4R Alpha runs 2A quiescent, the dissipation on EACH device is 48W, the 8R version running around 36W. The BB running at 3A dissipates 108W in each device and this prompted me to specify 480W IXYS devices with 1KW devices even more suggested, but these are expensive.
I like to use devices with at least 280W dissipation rating on the Alpha 8R and 4R. These are FQA40N25 and FQA36P15 from Fairchild. They are economical and TO3P DEVICES and I can recommend them.
For the BB I specify a 480W devices minimum.
In early posts I have mentioned other parameters; Vds, Ciss, Id, gfs but any hexfet will work well within obvious limitations. There may be subtle differences in Sonics from diverse mosfets but I dare not go there..... generally I have always found the sound quality comes from the topology, the components (particularly the caps), and the operating points.
Hugh
It has been a slow go since I’ve had a successful working stereo ALPHA20 on the work bench. The enclosure has taken longer than expected but, I’m in the final stretch now. The rear panel needs to be completed and then wire it up!
Here are some progress pics:
Here are some progress pics:
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Very nice Vunce - has the feel of a tube amp chassis. It's almost a shame to cover the radiators with a wood tunnel shroud. If you left them exposed each with its own fan it would be more reminiscent of a tube amp with two transformers on top. But the wood tunnel is an original concept. Nice joinery! 