Amp Camp Amp - ACA

The trick is to use a high quality name brand 19v SMPS brick from HP/Dell/Etc. then use a DC to DC step up converter. Now you can dial in any voltage to 35 or 45 in some models. Mains hum will be non existent and use a CRCRC to filter out any residual hash.

This is quite intriguing to me. Would you care to specify the DC-to-DC converter that you used in this application? I have couple of amps nearing completion, and the power supply options are many, given what I have on hand.
 
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This is quite intriguing to me. Would you care to specify the DC-to-DC converter that you used in this application? I have couple of amps nearing completion, and the power supply options are many, given what I have on hand.

These work well. But they must have a cap Mx after them and before the CRCRC filter , otherwise the large C in the filter appears as a short and the unit auto shuts down and turns back on and repeats. With a cap Mx, it is a graceful turn on over 5sec ramp up. Prevents speaker pop too. These are available from eBay as well as Aliexpress for less.

Amazon.com: DROK 150W DC Boost Converter Power Module Voltage Regulator Board 10-32V/8-16V to 8-46V 12/24V Step-up Volt Inverter Controller Stabilizer for Car Automotive Vehicle Motor Generator: Industrial & Scientific

I am using it for powering two channels of SE Class A at up to 1.5amps and 32v, going into 2 cap Mxs for isolation so amps are like true mono blocks despite common 19v SMPS and common DC step up.

Here is a photo of the Silicon Harmony amp that I took to the HeadFi organized SchiitStorm meet in Gaithersburg MD. It uses the above DC step up followed by two Juma Easy Peasy cap Mx's (IRFP240 with 470uF and 4700uF Pan FC output cap). This feeds a CRCRC (22mF & 0.47R), then that goes to the amp. Measurements show stereo separation as limited by measurement DAC (-88dB). They act like true monoblocks for all intents and purposes as the Cap Mx is like a one way valve.

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Cheap 24V switching supplies arrived.
Not really happy with the noise at 50kHz.
I have some Roland Keyboard supplies to test tomorrow. If they are no better I'll build my own regulated supply.

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This is a very strange picture. It looks as if the supply switches at 1kHz - which almost certainly is not the case. How did you get this, what did you probe?
The interesting stuff is upwards from 50kHz and that is not shown (assuming it switches at > 50kHz which is almost certainly the case).

Jan
 
No that is a 1kHz distortion plot. 1W into 8 Ohms.

The peak out at 40kHz to 50kHz is purely due to the switch mode power supply. The noise floor of the amp between 20Hz to 20kHz is below -100dB (it's around -105dB), it's just the switching noise around 50kHz that is annoying the few neurons I have left.

Maybe I should put all the results into a word document. Sorry for not explaining each post properly.

If you look at post 3376 and 3377 the distortion results are performed with a linear regulated supply. The switching noise is now gone.

I spoke to the manufacture about adding an LC filter to get rid of the 50kHz switching noise, but I have a few other ideas that should completely remove it.
 
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I run a pair of ACA's, with the 2k2 mod and stock switchers, in a biamp speaker setup driving compression drivers. Totally happy with the sound quality.

There is some noise if close to the CD's, as these are not padded down, but have a protection cap in circuit. I noticed 2 picoDumbs got a much lower noise result using the ASUS switcher than the stock supplies. Go ASUS? Alternates?

Thanks!
 
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I think the results vary wildly for SMPS - you just have to listen or measure it. Now with REW or RMAA, it's so easy - no reason why anyone couldn't do it. With speakers you need a mic, here, all you need is a dummy resistor.

I had great luck with a nice OEM HP 19v smps brick. A cheap $24 24v 5A SMPS worked great, but terrible noise with cheap $7 SMPS brick from Amazon. But a nice Fujitsu OEM SMPS was noisy! Just can't tell.
 
Thanks 2 picoDumbs, xrk971 and Bare.

Re: results vary wildly for SMPS... Yes, I have had that experience as well. It seems 2 picoDumbs Asus power supply measures 20 dB less noise than the stock switchers, which is a significant improvement. But finding the exact model online has not been easy and it is questionable as to the part to part consistency...

In Canada it is bit harder as the supply of switchers seems to be in the US, but with currency exchange/customs/shipping, they all end up being a pricy exercise in measuring and potentially not coming across anything quieter...

Any manufacturers of "low noise" SMPS folks can recommend? Or another approach that has some guarantee of low noise PS?

Cheers!
 
I've been working on a second pair of ACA boards on a big heatsink over the last couple of weeks. The first heatsink/board pair has served well in my main system for four months now. One channel on the newer assembly has not biased up, staying at near zero VDC Q1 drain to ground. Since it didn't vary with changes on P1, I replaced the original pot (as specified in the parts list) with another 5K pot, but this one is a multi-turn vertical pot. I measured it before installation and it checked out fine. When I powered up, it controlled the Q1 D to ground voltage but ran out of travel at 7.65 VDC, when the target is 11.2 VDC. Would a 10k pot work here or is another issue needing to be addressed?

thanks,

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