Not yet: this is the very first power up.
I might try first some old fashioned uPC1237 boards I developed a while back.
Thanks, I just followed the instructions! X's pictures helped a lot.
I am planning a downsized 20W/8ohm near field version in a 3U 300mm chassis that can be used during hot summers as well. I think I can put my hands on 2x15V 500VA toroid somewhere. It will be followed by a 'full bridge rectifier' and some beefy electrolytics: a very minimalist PSU...
It’s a poor man’s soft start to limit in rush current into the trafo. It’s 8ohms cold and 0.5ohms hot. Takes a few seconds to heat up - they run at like 125C so be careful. CL-60 is often used by Pass PSU designs. I use 8D-20 because they are cheaper and seem to work well for what it is.
This kind of soft start only works once unless allowed to cool down. So quick on off won’t work anymore.
We are working on an active soft start using SSR with several power resistors in series. After a few seconds, the SSR shorts out the resistors so you don’t run hot and lose some voltage drop.
Congratulations Jacques! Nice build - and glad that it works! No adjustments Class A is the way to go isn’t it?
Thanks X!
I was wondering is separate snubber boards are available (without the main PCB) ? I might want to swap IRFPs outputs for FQAs.
xrk971, have you considering using PulseEater resistors instead of power resistor for the soft start circuit?
https://www.mouser.com/datasheet/2/303/res_a-1228682.pdf
They are intended for inrush current limiting and give a joules rating which needs to be followed, not the wattage rating for continuous operation.
https://www.mouser.com/datasheet/2/303/res_a-1228682.pdf
They are intended for inrush current limiting and give a joules rating which needs to be followed, not the wattage rating for continuous operation.
Soft start, maybe Aleksandar's hard...
PCB for Soft Start (inrush current limiter) for toroidal transformers | ATL Audio Ltd.
PCB for Soft Start (inrush current limiter) for toroidal transformers | ATL Audio Ltd.
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I say enjoy mono - it has much to commend it - you can spend twice as much on the parts 🙂
Please look at links in Post 1 of the SLB thread.
The SLB (Smooth Like Butter) Active Rect/CRC/Cap Mx Class A Power Supply GB
That is a bit of a chase. I think what X has in mind is post #306 here:
https://www.diyaudio.com/forums/gro...-mx-class-power-supply-gb-31.html#post5812929
However, the Mouser project total X quoted two posts down is different from the current Mouser total, so check carefully. Likely due to price creep, but who knows.
Hugh/X,
This amp's closed loop gain is 28.5dB. Is there any possibility of lower overall (closed loop) gain, such as 20-22dB without changing damping factor/output impedance, overall THD or THD spectra dramatically?
Gain structure in the system overall (with regards to dac, amp, speakers, room, listening position, etc...) is important to optimize, hence my question.
Thanks,
Anand.
This amp's closed loop gain is 28.5dB. Is there any possibility of lower overall (closed loop) gain, such as 20-22dB without changing damping factor/output impedance, overall THD or THD spectra dramatically?
Gain structure in the system overall (with regards to dac, amp, speakers, room, listening position, etc...) is important to optimize, hence my question.
Thanks,
Anand.
Hi Poseidon,
You can change the feedback shunt resistor value (make it bigger) to decrease gain. This will not affect the level of feedback that imparts the amp with its characteristic sound qualities. Make R124 1.7k and this will give you 23dB. Make it 2k and you get 21.6dB. Is that close enough? Use carbon film resistors if you can and measure them and match them by hand to get the same gain on bith channels as carbon film tends to come only as good as 5%. But the SQ is better than metal thin film. In a pinch, good metal thin films like CMF55's work fine. There is a miild difference in H2/H3 distribution with MTF vs CF.
I think we had a similar question on the regular Alpha 20 amp and Danny did a good study on that amp.
You can change the feedback shunt resistor value (make it bigger) to decrease gain. This will not affect the level of feedback that imparts the amp with its characteristic sound qualities. Make R124 1.7k and this will give you 23dB. Make it 2k and you get 21.6dB. Is that close enough? Use carbon film resistors if you can and measure them and match them by hand to get the same gain on bith channels as carbon film tends to come only as good as 5%. But the SQ is better than metal thin film. In a pinch, good metal thin films like CMF55's work fine. There is a miild difference in H2/H3 distribution with MTF vs CF.
I think we had a similar question on the regular Alpha 20 amp and Danny did a good study on that amp.
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Thanks!
For 20dB then, R124 can be 2.4K or 2.5K ohms, and R126 is 22k ohms.
Lots of options as you have shown in your post.
Best,
Anand.
For 20dB then, R124 can be 2.4K or 2.5K ohms, and R126 is 22k ohms.
Lots of options as you have shown in your post.
Best,
Anand.
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