My focus is increasingly on the P101 bass amp at the moment. In fact I hope to complete the unit within a week or two (dependant on getting the metal panels).
Got one channel running now fully off of the proper supply (+/-42V). Other one just needs bolting to the heatsink hopefully, worked fine on test supply.
Can't really fault the sound with the test speaker, noticeably better than other amps I've used even with that quite basic speaker. Certainly should be successful as bass amplification, producing much more controlled bass than I've heard from the little speaker before; but then I knew it would be since I have one running my TL sub.
Heatsink is likely rather oversized for this power level but thats certainly no problem, the price break on over 5 was why I got all the same ones (0.4c/w), also gives similar aesthetics
A potential option for the tweeter amp is in fact to use another P101 amp but biased to give mabye 10W in class A. With my TO3 Profusion MOSFETs already in hand this is not too much of an expensive option, if slightly more difficult to build. I'd possibly need a bigger transformer as mine was bought for a DoZ and only has twin 12VAC; using more voltage gives the larger headroom even if it moves into class AB. Just an idea anyhow, don't think class A P101 has been greatly successful for many constructors? If anyone has a class A design for lateral MOSFET that would also be highly appreciated, I have 9 pairs of these things and it seems a shame not to use them
Dunno which is better between Symasym and SKA amp, but thanks for adding that in since it is another possible option for me. Far too powerful though I suppose a lower supply voltage is possible? At least the PCB is readily available if slightly pricey.
Got one channel running now fully off of the proper supply (+/-42V). Other one just needs bolting to the heatsink hopefully, worked fine on test supply.
Can't really fault the sound with the test speaker, noticeably better than other amps I've used even with that quite basic speaker. Certainly should be successful as bass amplification, producing much more controlled bass than I've heard from the little speaker before; but then I knew it would be since I have one running my TL sub.
Heatsink is likely rather oversized for this power level but thats certainly no problem, the price break on over 5 was why I got all the same ones (0.4c/w), also gives similar aesthetics
A potential option for the tweeter amp is in fact to use another P101 amp but biased to give mabye 10W in class A. With my TO3 Profusion MOSFETs already in hand this is not too much of an expensive option, if slightly more difficult to build. I'd possibly need a bigger transformer as mine was bought for a DoZ and only has twin 12VAC; using more voltage gives the larger headroom even if it moves into class AB. Just an idea anyhow, don't think class A P101 has been greatly successful for many constructors? If anyone has a class A design for lateral MOSFET that would also be highly appreciated, I have 9 pairs of these things and it seems a shame not to use them
Dunno which is better between Symasym and SKA amp, but thanks for adding that in since it is another possible option for me. Far too powerful though I suppose a lower supply voltage is possible? At least the PCB is readily available if slightly pricey.
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Thought I'd best post an update. The P101 amp is not completely completed , but in a working state.
It is running at +/-42V DC rails so should generate 80WPC. The transformer is 330VA. Filtering is 4x4700uF per rail. P33 project is used as speaker protection along with some relays rated at 30A 28VDC. Heatsinks are 0.4c/w per amp. Mains is switched remotely via the smaller relay on the mains inlet board (saves switching on the 3 eventual amps manually ).
Sorted out my panels with this rather useful company:
http://www.metalfast.co.uk/
Cut to size for me, and at a decent price. Material is 4mm 5083 aluminium. I've got panels for all the amps except the fronts. I figured 3 plain metal fronts could look a bit "military", so want to try wooden. Don't we all love chassis work
Sounds good so far, very dynamic and good tight bass. Abolutely silent too, even with ear pressed to speaker. Need to do some higher power tests, want to feel those heatsinks get warm . Could probably do with some cable ties before its finished.
, but in a working state. It is running at +/-42V DC rails so should generate 80WPC. The transformer is 330VA. Filtering is 4x4700uF per rail. P33 project is used as speaker protection along with some relays rated at 30A 28VDC. Heatsinks are 0.4c/w per amp. Mains is switched remotely via the smaller relay on the mains inlet board (saves switching on the 3 eventual amps manually
).Sorted out my panels with this rather useful company:
http://www.metalfast.co.uk/
Cut to size for me, and at a decent price. Material is 4mm 5083 aluminium. I've got panels for all the amps except the fronts. I figured 3 plain metal fronts could look a bit "military", so want to try wooden. Don't we all love chassis work
Sounds good so far, very dynamic and good tight bass. Abolutely silent too, even with ear pressed to speaker. Need to do some higher power tests, want to feel those heatsinks get warm
. Could probably do with some cable ties before its finished.Attachments
Ok, that amplifier has been running most days since I posted that pic and seems to be good. Did power tests and it had no problem at all, heatsinks literally just got warm.
I have this time been working away on a Symasym for the mids. Its now just about complete (needs mains input relay switching is all). It sounds good and is generally very satisfying, a very detailed amp this!
One slight problem though, my transformer is humming. Now its the same make as the one in my P101 amp and is actually smaller (250VA), the 330VA in the P101 is silent. The only difference I can see is that the P101 has an NTC in the live to reduce inrush, but apparently it shouldn't even be there with class AB amps so I planned to perhaps remove it. What can be done to cure a buzzing transformer like this? It can be heard over very quiet passages (note I haven't fitted the top panel yet). The speaker output is very quiet just like the P101, tiny amount of hiss is all.
I made this as per MikeB's 5.3 board. Power supply is 250VA with 14,100uF per rail. ESP P33 speaker protector is fitted, 16A relays used this time (smaller than the P101 ones but this is lower supply voltage and may be used at 16ohms anyway). Interestingly this is using the 2SC5200 and 2SA1943 from that same batch and seems to be working fine, they can't have been fakes afterall!
Anyway, heres some pics!
I have this time been working away on a Symasym for the mids. Its now just about complete (needs mains input relay switching is all). It sounds good and is generally very satisfying, a very detailed amp this!
One slight problem though, my transformer is humming. Now its the same make as the one in my P101 amp and is actually smaller (250VA), the 330VA in the P101 is silent. The only difference I can see is that the P101 has an NTC in the live to reduce inrush, but apparently it shouldn't even be there with class AB amps so I planned to perhaps remove it. What can be done to cure a buzzing transformer like this? It can be heard over very quiet passages (note I haven't fitted the top panel yet). The speaker output is very quiet just like the P101, tiny amount of hiss is all.
I made this as per MikeB's 5.3 board. Power supply is 250VA with 14,100uF per rail. ESP P33 speaker protector is fitted, 16A relays used this time (smaller than the P101 ones but this is lower supply voltage and may be used at 16ohms anyway). Interestingly this is using the 2SC5200 and 2SA1943 from that same batch and seems to be working fine, they can't have been fakes afterall!
Anyway, heres some pics!
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Been running power tests into 8ohm resistive dummy load, 56W RMS. Both channels work pretty much flawlessly. There is a (hopefully) minor issue though with some possible oscillation. I attach the waveforms, left is zoomed in on the bad part and right is overall how it appears. 500Hz sinewave is the source. It varies, this is at worst, it can be virtually invisable (took me some time to notice it). Otherwise, the heatsinks just get warm and the transistor packages are quite warm (can keep finger on them indefinately), so no worries there.
Transformer buzzing is the bigger issue I think, it is very annoying. It also varies from a tolerable hum to a much more aggresive sounding buzz, with more low frequency. Touching it the vibration can just about be felt but isn't large. Is this a DC issue? How come my other amp doesn't have this problem, does the NTC make any difference?
Transformer buzzing is the bigger issue I think, it is very annoying. It also varies from a tolerable hum to a much more aggresive sounding buzz, with more low frequency. Touching it the vibration can just about be felt but isn't large. Is this a DC issue? How come my other amp doesn't have this problem, does the NTC make any difference?
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I seriously doubt it would, but could a mains filter like pictured help with this problem? I think it is more for getting rid of high frequency noise but could the twin capacitors to earth help "balance" the feed? Looking at it it says 0.5A rating too, and I could be taking 1A so perhaps it can't be used anyway, though I'm not sure how something like that has a current rating.
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