Hahaha ... yes that's the one... since I got a nice pair of 1KW transformers, a bunch of electrolytic caps, KSA-50 MK II boards (same KSA-100B) .. it was an easy decision.. my KSA-50 project stalled by not having a cooling solution which I liked to use .. been looking for cooling tower for a while .. and now better with a pair .. I hope the original circuit boards can be refurbished.
What would regulated power supplies achieve on a Class A amp where the current is essentially constant?
Why would you want to insert active devices in series with the supply to the amp?
Surely the mono blocks just need a simple low impedance supply with nothing active to influence the performance?
When I read that a power amp has regulated supplies I think to myself that this is to save money. Reservoir caps are both costly and bulky so commercial amp manufacturers will save a significant sum by using a regulator, and of course these days, both amp and psu are switch mode to save even ore money.
Why would you want to insert active devices in series with the supply to the amp?
Surely the mono blocks just need a simple low impedance supply with nothing active to influence the performance?
When I read that a power amp has regulated supplies I think to myself that this is to save money. Reservoir caps are both costly and bulky so commercial amp manufacturers will save a significant sum by using a regulator, and of course these days, both amp and psu are switch mode to save even ore money.
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Basically an active regulated supply done right has advantages.., low noise equals more detail ...
Futher more they do work best with stady state loads (like with a Class A amp)
If you compare a KSA-100 to a KMA-100 the later is a lot more revealing (even the KMA-100 output stage is not feed from the regulated PSU)
In my circumstance it is an easy choice since I got a pair of regulated PSU boards with an Ampere rating suited to feed the entire amplifier .. so definitely worth a try
Since the 1970's several (not many) High End Class A amplifiers has used such an approach .. Mark Levinson ML-2 was and still is a magnificent amplifier
Futher more they do work best with stady state loads (like with a Class A amp)
If you compare a KSA-100 to a KMA-100 the later is a lot more revealing (even the KMA-100 output stage is not feed from the regulated PSU)
In my circumstance it is an easy choice since I got a pair of regulated PSU boards with an Ampere rating suited to feed the entire amplifier .. so definitely worth a try
Since the 1970's several (not many) High End Class A amplifiers has used such an approach .. Mark Levinson ML-2 was and still is a magnificent amplifier
I can see that there is an argument for supplying the input and driver stage from a regulated supply.
You said that the KMA100 is ' a lot more revealing and ....output stage is not fed from the regulated psu' which is what I would do.
I wonder if the simple zener regulated supply to many amp input stages might benefit from a very low noise alternative (LT3045 ?)
You said that the KMA100 is ' a lot more revealing and ....output stage is not fed from the regulated psu' which is what I would do.
I wonder if the simple zener regulated supply to many amp input stages might benefit from a very low noise alternative (LT3045 ?)
I think it would be an advantage ... in my project I will simply decouple the zeners .. been wondered why it was not done by Krell ..., but they have pretty much barely use any HF decoupling in their power supplies, only like a 10nF cap over each rail.., for decades more and more electrical noise has affecting our quest for our analog High Fidelity, decoupling do make a difference for the performance.
I got a pair of KMA-100 .. in them my refurbishment also included adding better HF rejection, the result was a quite noticeable improvement
I got a pair of KMA-100 .. in them my refurbishment also included adding better HF rejection, the result was a quite noticeable improvement
It's certainly true that there are many more sources of rf noise (wifi, bluetooth, phones etc) that can find a way into amps than was the case last century.
Many amps had an inductor in series with the output presumably to block rf picked up by the speaker cables but my Quad 306 and Linn LK100 don't but my KSA50 clone does.
Many amps had an inductor in series with the output presumably to block rf picked up by the speaker cables but my Quad 306 and Linn LK100 don't but my KSA50 clone does.
Snipped from tread "Function of output inductor"
The inductor is there primarily to isolate capacitance from the output and feedback loop, but it may stop some rf from getting back to the input stage of the amplifier …Jul 1, 2008
I dont like inductors i see them as a HF "antenna" ... futher more I do have Martin Logan ELS .. and never had any issues in choice of what amplifier which will cope the nastiness of there load
The inductor is there primarily to isolate capacitance from the output and feedback loop, but it may stop some rf from getting back to the input stage of the amplifier …Jul 1, 2008
I dont like inductors i see them as a HF "antenna" ... futher more I do have Martin Logan ELS .. and never had any issues in choice of what amplifier which will cope the nastiness of there load
Here is my KSA50 schematic with voltage references if anybody is using a similar voltage. I am getting right at 50 watts/RMS/8 ohm load.
My KSA50 amps use +/- 33.5VDC, so in order to keep the zener diode circuit from possibly falling out of regulation, I am using 910R instead of 1k5 for R1 & R38. This allows approximately 7mA to flow through the circuit (3mA for the LTP and 4mA for regulation).
I also replaced the emitter follower (emitter resistors) R5 & R42 3k3 with 1k2. This allows approximately 1.3mA instead of 425uA to flow through the emitter follower.
My KSA50 amps use +/- 33.5VDC, so in order to keep the zener diode circuit from possibly falling out of regulation, I am using 910R instead of 1k5 for R1 & R38. This allows approximately 7mA to flow through the circuit (3mA for the LTP and 4mA for regulation).
I also replaced the emitter follower (emitter resistors) R5 & R42 3k3 with 1k2. This allows approximately 1.3mA instead of 425uA to flow through the emitter follower.
Attachments
Been a long time since I've been on here. Was involved with this thread back in 2005 and did two large group buys of the PCB designed by Pinkmouse. Most of us back then also used six output devices per channel with an extra large power supply. My finished KSA-50 easily handles 2 ohm loads, and after all these years it still sounds magnificent. In case any one wonders, the open chassis prototype I built up in 2004 still exists and runs fine. A friend in central Illinois has it at the moment. I have lots of pictures from back then if anyone is interested, just let me know. Also, my amp was built in another manufacturers chassis as it had sufficient room for 12 O.P. devices, plus it already had forced air cooling.
Cheers,
Mark
Cheers,
Mark
A tip för ny fellow cloners who are looking for transformers.
The krell uses 2pcs of 2x27V transformers at 400VA each, if memory serves.
You can often find the the Logitech z-5500 speaker system for around $50.
That system includes the following:
1x transformer 2x26.4V and 1x14V at 330VA.
7x TDA7294 chips
2x heatsinks
5x Tangband W3-593SF 3" full range drivers (same as W3-871)
1x Tangband WT-644F 10" subwoofer.
That is what I call a good deal
I recently, since many years, went back to the DIYaudio hobby. I noticed this post about the Logitech and found myself 3x Z-5500 and 2x Z-2300 for 20 to 50 euro each.
I am going to keep one Z-5500 because I actually like the deep bass I am getting from it. The other two Z-5500 are ready for disassembling and feeding a KSA-50 lower power version clone. I already disassembled two Z-2300 and indeed they have a nice 21Vac toroid transformer (200VA?), 2x 10.000uF caps, large rectifier bridge and a nice large heatsink to which you can easily clamp any semiconductor formfactor. See attached test rig build Z-2300, feeding a LJM MX50SE stereo kit (which is great for the money and worked flawlessly on first power up). That 21Vac give me 27.8V unloaded, about 26.5 loaded and about 26.0V unppon clipping into 8R2.
Thanks for that Logitech parts tip
BTW
I have 6 pairs of pinkmouse KSA-50 PCBs available. Posting to The Nethlerlands only.
