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Hifisonix kx-Amplifier
Hifisonix kx-Amplifier
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Old Yesterday, 08:08 AM   #651
polsol is offline polsol  South Africa
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Join Date: Aug 2004
Location: Cape Town
Still putting the final touches to the xK amplifier. The amps themselves have been mounted on the heatsinks on both sides of the chassis. Have had to find some bits of hardware for completion which has held it back somewhat.

The configuration thus far is:
1) Rear input switch with integrated fuse and RFI circuitry.
2) Power to DIYAudio soft start circuit and then to a 25-0-25V 500 VA transformer.
3) Transformer to dual fuse block (white)
4) Fuses to a pair of 40A bridge rectifiers and from their to 2 banks of 3 by 4,700 uF Caps per channel. Centre 'bus bar' is a virtual earth which will be connected to earth by one of the ripple eaters 'ground lift' circuits (I assume connecting both REs to earth would result in a 'ground loop' (?)
5) Inputs are the red and green wires (dual core screened) earthed to the chassis by 2.5N Polystyrene caps

2 ripple eaters are mounted on the front panel (10mm Aluminium).

My original thoughts were to use the cap banks to feed the ripple eaters and from the REs to the amps themselves via the REs bridge diodes.

The alternative would be to connect the fuses to the REs bridges (bypassing the chassis 35A ones) and from there to the cap banks and then to the xK amplifies.

Question arises as to:
1) Which would be the best topology from an electrical point of view.
2) Would the RE be able to handle the switch on current requirements in its output stage with an additional 14,100 uF across the output of each channel in addition to the xK Amp current on 'switch on'? (The input bridge rectifiers on the REs are 25A)

Additionally, the internal chassis plate is attached to the chassis frame by 12 mm plastic spacers (I think they are polyprop) except for the rear right one which is an 8 mm metal spacer with a 3mm S/S nut and lock washer which 'earths' the internal chassis base to the frame in that corner. Have not been able to source 12mm metal spacers and 10 mm is too small (internal thread length with available bolts - smallest countersunk I have is 8mm [Modushop chassis requires C/S head] and a 15 mm spacer makes the internal chassis base too high).
If I was to earth each corner of the internal base plate (using earth wires or obtaining 12mm metal spacers) would that also possibly cause earth loops?
Comments please?

Some pics attached.
Attached Images
File Type: jpg _DSC1561.jpg (1,002.0 KB, 73 views)
File Type: jpg _DSC1563.jpg (1.04 MB, 76 views)
File Type: jpg _DSC1557.jpg (648.3 KB, 72 views)
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Old Yesterday, 05:04 PM   #652
Rallyfinnen is offline Rallyfinnen  Sweden
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Join Date: Jan 2017
Quote:
Originally Posted by Bonsai View Post
Rallyfinnen,

The output Zout of the kx-Amp is low. The action of the feedback is to lower the open loop Zout by the loop gain. On a sim at 20 kHz, the output Z is around 80 milli Ohms peak after the output coil. Your speaker cabling and internal speaker wires will probably be higher.

By all means use larger PSU caps since they will reduce the ripple at the expense of higher charging currents so watch out with your layout and keep wiring loop areas small as possible by twisting etc.

The same feedback action also applies to the PSU, which we state as Power Supply Rejection Ratio'. If the PSU impedance is say 100 milli Oms and you are drawing 1.2 Amp from it, that gives a ripple (over and above the smoothing cap ripple) of 120 milli volts. But the amplifier PSRR at 50 Hz is 55 dB to this gets reduced by about 400x referred to the input. For frequencies above 1kHz, the kx-Amp PSRR is >90 dB. A ripple eater improves this by at least 40 dB.

Yes, caps are actually larger per channel too, since I have one for each channel. But my point was that I want to try to skip the ripple eater for the outputs to keep the supply impedance low, and have a separate rectifier and simple ripple eater for the front end, which does seem to help the PSRR significantly in sim. It also isolates the front end from whatever other stuff the outputs might cause on the rails, which also makes me sleep better at night

As mentioned before, I was a bit unsure of the behavior at startup/shutdown with supply voltage delayed for the front end, but as I understood it, you think it should be ok.
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Old Yesterday, 05:09 PM   #653
Rallyfinnen is offline Rallyfinnen  Sweden
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Join Date: Jan 2017
Quote:
Originally Posted by polsol View Post
Question arises as to:
1) Which would be the best topology from an electrical point of view.
2) Would the RE be able to handle the switch on current requirements in its output stage with an additional 14,100 uF across the output of each channel in addition to the xK Amp current on 'switch on'? (The input bridge rectifiers on the REs are 25A)
1. Because of my beliefs as mentioned above(low supply impedance), I would prefer the cap bank after the ripple eater.

2. I think the ripple eater should be fine like that, because it ramps up the voltage slowly, so the current 'should' not be a problem.
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Old Yesterday, 10:30 PM   #654
Bonsai is offline Bonsai  Europe
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Location: Europe
Hifisonix kx-Amplifier
Tony, can you make a quick sketch?
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Old Today, 07:37 AM   #655
polsol is offline polsol  South Africa
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Join Date: Aug 2004
Location: Cape Town
Quote:
Originally Posted by Rallyfinnen View Post
1. Because of my beliefs as mentioned above(low supply impedance), I would prefer the cap bank after the ripple eater.

2. I think the ripple eater should be fine like that, because it ramps up the voltage slowly, so the current 'should' not be a problem.
Thanks Rally,

Your previous comments are the ones that got me thinking of my PSU configuration.
BTW, I had 12 by 4,700 uF cap cans lying around which is why I put them in (A bit of 'bling' as well with the copper busbars for fun). Plus I could only get 10,000 uF Caps at 50 V (because of the 35V DC transformer voltage out), with the required 35 mm size, giving a total of 24,100 uF per dual power rail.

The 4K7 resistors across each cap bank in the photo are temporary to discharge the caps with the power off. Had some nasty surprises when the mains power was off but the caps still charged, even quite a few minutes later, when there was no power draw
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Old Today, 07:50 AM   #656
polsol is offline polsol  South Africa
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Join Date: Aug 2004
Location: Cape Town
Quote:
Originally Posted by Bonsai View Post
Tony, can you make a quick sketch?
Hi Bonsai,

Knocked together a quick PSU flow diagram (attached) (I still draw stick people ...)
Hope this is sufficient.

Note that the 'Cap banks' are composed of 12 by 50V, 4,700uF caps I had lying around. 2 banks of 6 caps, 3 caps per rail. Common '0V' rail as per previous picture.
I used them because I couldn't get anything over 10,000 uf > 35V with the 35mm cap size on the RE boards, and the supply voltages are 35V, so I opted for 50V, 10,000 uF (35mm) caps. I have since found 22,000 uF/50V with a 35 mm diameter but anything of higher capacitance at 50V or higher are generally 40 mm or larger diameter.

Anyway, would appreciate your comments on the attached options.
Thanks
Attached Files
File Type: pdf kX Amp PSU Topology.pdf (144.6 KB, 9 views)
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Old Today, 08:14 AM   #657
potepuh is offline potepuh  Slovenia
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Join Date: Feb 2004
Location: Slovenia
Quote:
Originally Posted by vargasmongo3435 View Post
hi Bonsai I was able to fix the ugly jumper solution and now is better
Is possible to get the gerbers? I would like to build one.
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