Hi all, just an opportunity to thank Mr Pass and all those that contribute to these forums. I've just finished my Pass ACA build. Two chassis with two ACA's in each and minidsp to make a full active setup for my LeCleach horns. Each chassis has two amps, one configured for hf and one for mid range. The output caps have been reduced and upgraded to good PP caps as the mid amp only has to have a response down to 350hz and the hf amp down to 5500hz so good caps are affordable. I also have a Berhringer DSP amp for the bass.
This setup sounds absolutely beautiful!
Thanks for sharing this design and knowledge.
Dave
This setup sounds absolutely beautiful!
Thanks for sharing this design and knowledge.
Dave
I may have spoken too soon..... one of the modules has developed a small hum, not really a hum but sort of like a high frequency clicking. Not mains hum as these are powered by SMPS's. The frequency isn't always constant, sometimes it slows down to nothing and goes away, then might just start again for no reason, doesn't change with input removed or connected. Also doesn't change with volume.
Not loud but just above the noise floor, my horns are around 118db so you hear everything!
Pretty confident that it's not a cold joint, also pressed all around the board to hear if anything changed but nothing. Comes and goes on its own.
Any ideas?
Not loud but just above the noise floor, my horns are around 118db so you hear everything!
Pretty confident that it's not a cold joint, also pressed all around the board to hear if anything changed but nothing. Comes and goes on its own.
Any ideas?
Good point, funny now that you mention it when you first turn them one the suspect one has a similar noise as the voltage builds then goes away after a few second's.
Just swapped them over and yea the issue appeared on the other pair! So it's power supply!
Many thanks once again.
The SMPS's are Lenovo 170w, one per pair of modules. These aren't cheap rubbish but maybe one has a fault. Maybe I should build a LPS?
The SMPS's are probably within specs for its purpose......but for a 118 dB speaker? ....you may even hear 100 uV of noise.....I have 94 dB speakers and 3 mV of hum at the output is very audible at the listening position. 1 mV I can only hear relative close to the speaker. So I go for 0.1 mV noise for my setup to have it 100% silent. Your output noise has to be many times lower....16 times lower noise or so.....than for my setup......depending on how far away from the speakers you listen. I have approx 3 m.....so relative close.
have u used linear power supply or SMPS, how did you filtered the power supply to 0.1mV noise?
I have not built the PSU for the ACA yet but the trafoes and chokes are in order (I have the capacitors....will be a LCLC filter). The goal is to have < 1 mV ripple (noise) on the PSU. For my 300B amp a RCLC filter is used and it has less than 1 mV ripple noise. This result in about 0.1 mV noise on the output. But in such an amp you also have the filament supply etc. My goal for the PSU is < 1 mV......think the simulation in PSU designer says 0.6 mV or so. 1 mV on the PSU should result in much much lower noise at the output on the amp. 10 mV ripple is probably also fine.......but when you do it as DIY it is fun to make it a bit "overkill". Should it be a commercial amp.....it would be expensive......
It will probably be a RLCLC filter.....the R to fine adjust the output voltage (it may also reduce the peak current out of the bridge). The chokes will be 2 x 250 mH each and configured like common mode chokes. Capacitors 4-pole. I have played and simulated a bit in PSU Designer II......
It worked very well for the tube amp.....so will try something similar......
The simulation file appended. I changed the .psu to .asc to have it accepted for upload. So has to be changed back for the PSU designer II.
There also has to be some bleeder resistors over the capacitors. Also to avoid a large voltage over the capacitors during break in......
It worked very well for the tube amp.....so will try something similar......
The simulation file appended. I changed the .psu to .asc to have it accepted for upload. So has to be changed back for the PSU designer II.
There also has to be some bleeder resistors over the capacitors. Also to avoid a large voltage over the capacitors during break in......
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