OK, I just measured both of my amps. The first one measures L=-1,5mVDC R=-1,2mVDC with nothing plugged into the input. It changes to L=-12.4mVDC, R=-30.1mVDC with the input shorted and L=-9.5mVDC, R=-12,0mVDC with the Preamp plugged in.
The second one measures L=0,5mVDC R=0,2mVDC with nothing plugged into the input. It changes to L=154,0mVDC, R=102,1mVDC with the input shorted and L=81,2mVDC, R=27,0mVDC with the Preamp plugged in.
Looks like I should pop the hood on the Pinkmouse amp and make some adjustments. Maybe both of them. It's been a long time since I've been in there. I listen to thefirst one the most because it has a quieter fan. I think I'll add some resistors to the fans in the Pinkmouse amp while I'm uin there and see if I can quiet those fans a bit more.
Hope these measurements help.
Blessings, Terry
The second one measures L=0,5mVDC R=0,2mVDC with nothing plugged into the input. It changes to L=154,0mVDC, R=102,1mVDC with the input shorted and L=81,2mVDC, R=27,0mVDC with the Preamp plugged in.
Looks like I should pop the hood on the Pinkmouse amp and make some adjustments. Maybe both of them. It's been a long time since I've been in there. I listen to thefirst one the most because it has a quieter fan. I think I'll add some resistors to the fans in the Pinkmouse amp while I'm uin there and see if I can quiet those fans a bit more.
Hope these measurements help.
Blessings, Terry
lgreen said:
Hi John,
I've been trying to follow your progress on the A-X. I didn't know you had finished it. I'd love to hear you opinions in comparison to the KSA 50. I know you did a lot more to your A-X than I did but I would still like to know how you think it compares.
Blessings, Terry
still4given said:
Hi Terry, thank you for giving me the opportunity to go off topic!!!!!
The A-X is not done, only 1 channel is tested and now is upright. You see my usual birds nest of wires running everywhere... I wanted to leave enough slack to test it flat and that is what I did but they did not like being moved when it was time to put them standing up. Its DIY you can do what you want!! I worked all last night and all day today on this, had a lot of bias and DC offset issues that caused me much grief. This is using a massive passive cooling case and is like a toaster oven-- HOT!!! 60 or 63 in the center between the MOSFETs (after 45 min) and hot to touch after only 5 minutes; Only 0.55VDC across the (3x) 0.6 ohm (x4) source resistors.
Have not hooked it up to an actual speaker but I am working all day tomorrow to get channel #2 on-line. This thing is touchy- after I turned it off and then on when it was hot the absolute DC went way down but relative went way up. Crazy. I even broke down and bought a variac to bring this up to line voltage slowly so as not to blow up the matched MOSFETs, and luckily no magic smoke as they say has been released yet.
Anyway, even though I am working off-line with a really smart person (pestering him constantly with emails) I miss the guidance that Stewart, Jacco (did I say Jacco? yeah ok I admit it) and ya'all gave me on this thread with the Krell. Then again, I don't feel as embarrased as my bad questions (and in-progress pics) which are mostly off line (unlike when you all made fun of my Krell ventilation holes) go unnoticed (oh and you were probably right about those).
If I can get this done next week stay tuned for a comparison.
Will this 120VAC primary w/2 31VAC sec. @ 500VA works
All,
Will a transformer 500VA, 120VAC primary w/2 31VAC sec. Works with Pinkmourse PCB and BOM? Is $45+ship reasonable price?
I got a set of PingMouse PCB and looking for suggestion on Transformer and Heatsink. I would appreciate any comment on this.
All,
Will a transformer 500VA, 120VAC primary w/2 31VAC sec. Works with Pinkmourse PCB and BOM? Is $45+ship reasonable price?
I got a set of PingMouse PCB and looking for suggestion on Transformer and Heatsink. I would appreciate any comment on this.
The original had two 400VA trannies.
A single 500 would work but would not have the headroom of a larger transformer. I wouldn't expect it to do the full 50 WPC Class A and if it did, I certainly wouldn't expect it to be under-rated as the original having the ablity to edge closer to 60 ish...
A single 500 would work but would not have the headroom of a larger transformer. I wouldn't expect it to do the full 50 WPC Class A and if it did, I certainly wouldn't expect it to be under-rated as the original having the ablity to edge closer to 60 ish...
Re: Will this 120VAC primary w/2 31VAC sec. @ 500VA works
I experienced much the same thing. My A-X was all over the place on voltages. Especially the absolute offset. Makes those grounding resistors run pretty hot at times. Mine really cooks too. I have have large heatsinks as well and it still is almost painful after a while of running. Looking forward to your assesment.
I bet that is the Antek Inc tranny.
This is only 1V higher than the one I used in my first KSA50. It is working just fine.
For $11 more you can get this one. It is 800vA.
Blessings, Terry
lgreen said:
I experienced much the same thing. My A-X was all over the place on voltages. Especially the absolute offset. Makes those grounding resistors run pretty hot at times. Mine really cooks too. I have have large heatsinks as well and it still is almost painful after a while of running. Looking forward to your assesment.
Vuamp2 said:All,
Will a transformer 500VA, 120VAC primary w/2 31VAC sec. Works with Pinkmourse PCB and BOM? Is $45+ship reasonable price?
I got a set of PingMouse PCB and looking for suggestion on Transformer and Heatsink. I would appreciate any comment on this.
I bet that is the Antek Inc tranny.
This is only 1V higher than the one I used in my first KSA50. It is working just fine.
For $11 more you can get this one. It is 800vA.
Blessings, Terry
500 W tranny for 200 W consumption ? Why ? Or do you mean, that it will be two times better ? 
BTW, much more better should be to short all wires - it must be very stabil amp, that is not oscilating with these sparrow's nests..... 😉
BTW, much more better should be to short all wires - it must be very stabil amp, that is not oscilating with these sparrow's nests..... 😉
pinkmouse said:
Mine too. Someone along the way here said they heard a noticible difference by going to a 1KVA trans so I thought I would point out the large one. My second one used two 500vA transformers and I can't hear any difference.
Blessings, Terry
Upupa Epops said:500 W tranny for 200 W consumption ? Why ? Or do you mean, that it will be two times better ?
pinkmouse said:
still4given said:
Thanks Terry, Al and Upupa Epop, I will go with one 800VA transformer for two channels rather than two 400VA transformers just for wiring simplicity.
Hardest load with comfort
What is the lowest ohm load that a KSA50 can drive, without suffering reduced dynamics?
In particular, I’m thinking of the active midrange of the SL Phoenix, 100 –1500 Hz, (92 dB) and paralleled drivers having an effective load impedance of 3.5 ohms.
Or if rail voltages were dropped to comfortably allow 3.5 ohms to X volts, what would power drop to?
Thanks
What is the lowest ohm load that a KSA50 can drive, without suffering reduced dynamics?
In particular, I’m thinking of the active midrange of the SL Phoenix, 100 –1500 Hz, (92 dB) and paralleled drivers having an effective load impedance of 3.5 ohms.
Or if rail voltages were dropped to comfortably allow 3.5 ohms to X volts, what would power drop to?
Thanks
The KSA's were among the few amplifiers to be able to drive 2 ohms with ease. If you design yours to spec, 3.5 ohms should be no problem.
Rick,
i suppose you mean the Phoenix design by Siegfried Linkwitz(Audio Artistry) ?
(also assuming that's where you will be using the filter boards of Bob and Jens for)
Driving two 8" drivers in parallel on an active system will be a piece of cake for a KSA/KMA50.
i suppose you mean the Phoenix design by Siegfried Linkwitz(Audio Artistry) ?
(also assuming that's where you will be using the filter boards of Bob and Jens for)
Driving two 8" drivers in parallel on an active system will be a piece of cake for a KSA/KMA50.
However at 3.5 ohms you will not be getting all "pure" class-A output. With the stock Bias setting of approx: 1.76 amps (400mV across the 0.68 emitter resistors) you get 50 watts pure class-A at 8 ohms but only 22 watts at 3.5 ohms. This setting representing an idle bias of about 127 watts.
In order to get (if you care) 50 watts pure class-A into the 3.5 ohms (assuming nominal) impedance, you'd have to bias the little guy to about 606mV into 0.68 ohm or 2.67Amps. I am assuming 3 pairs of outputs.
However your idle dissipation would jump up to about 193 watts per channel. Your class-AB clipping headroom at 3.5 ohms would be about 165 watts or 73 watts into 8 ohms.
All these numbers would change if one variable changes, so they are approximates.
In order to get (if you care) 50 watts pure class-A into the 3.5 ohms (assuming nominal) impedance, you'd have to bias the little guy to about 606mV into 0.68 ohm or 2.67Amps. I am assuming 3 pairs of outputs.
However your idle dissipation would jump up to about 193 watts per channel. Your class-AB clipping headroom at 3.5 ohms would be about 165 watts or 73 watts into 8 ohms.
All these numbers would change if one variable changes, so they are approximates.
Hi,
but KSA50 will push just over 120W into 3r5.
The bias would need to be set to about 4A2 to maintain ClassA into a 3r5 load.
Quiescent dissipation would jump to 310W.
but KSA50 will push just over 120W into 3r5.
The bias would need to be set to about 4A2 to maintain ClassA into a 3r5 load.
Quiescent dissipation would jump to 310W.
Thanks Andrew, it would help if you laid out the assumptions under which the facts were stated. 😉