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The Multi Amp aka Dynalo Mk2


spritzer

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18 hours ago, Pars said:

As for an SE out, L+, R+ and gnd straight back to the power supply (not to the amp boards). Either use 2 conductors for the gnd, or a heavier wire (usually 24ga for signal, so maybe 20ga for the gnd).

I wouldn't use an epsilon 12 with this, as it won't properly handle balanced signals. I'd use one of Kevin's balanced protection boards instead.

400mA sounds about right (don't recall exact figures, but it's probably here in the thread somewhere).

Hmm yea, epsilon only switches half of the lines. In that case I'll probably just not use the epsilon lol but uh... it's claimed that it can handle balanced so i'll test it out 

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  • 1 month later...

I'm using 10K pot with JFETs (Linear Systems).

Batteries have noise as well, so if it were a GRLV, I'd be tempted to think it would be superior. Never tried it though. Can you fit the batteries in the case? And what would you do as far as the power switch goes?

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1 hour ago, Whitigir said:

Is anyone running mini Dynalo on battery supply ? Sony claims that battery supply is superior on their most expensive DMP-Z1.  So, I just wonder

See below.

 

On 8/30/2016 at 8:06 PM, JoaMat said:

I’ve had a great time the last couple of weeks building the mini Dynalo designed by Kerry.

Here is the Dynalo with a finished (almost) board. Side panels from Modushop, internal height 40 mm. Front and rear panel are copper clad boards milled myself and the top cover is  an aluminum net for better ventilation.

IMG_1502.JPG

Now, this amplifier turned to be a very nice one, so I started to modify it for my own personal preferences. I want a small portable amplifier to be used in my garden under a cheery tree - resulting in this.

_MG_1523.JPG

Switching power supplies, all connectors at the rear panel and some other stuff not needed removed to give room for Raspberry Pi 3 with a HiFiBerry DAC+ Pro on top. Changed front panel (easily done with a mill and copper clad board) and rear panel has two holes for connectors for the batteries and a wlan antenna.

Today I got a heat sink for the output transistors. Below is a picture showing them, they are just resting on some soft pad – have to figure out the best way to get them  fastened. I don’t think the sinks are needed but they are very much preferable.

_MG_1526.JPG

Many thanks to Kerry for an excellent work.

 

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My main concern with battery isn't so much noise but the varying voltage as power draws down. Usually this means some sort of power management circuit in between the batteries and the amp which can have their own noise. Also with a bipolar power supply there's an issue of one rail powering down before the other, leading to a large DC offset.

I'm sure Sony has a very competent implementation though.

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Found this in closet. I guess it’s some kind of charger I built a couple of years ago. Six Mean Wells and charger regulators and each cell has his own charger. Red light will probably turn green when fully charged. I don't remember but I will see in a couple of hours.

IMG_0224.thumb.JPG.03aeefd92a5e5c048f5a709f5a2d204a.JPG

 

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Yes to most of it. For the LED resistors, which set the bias, I used 422 402R with LTST-C170CKT Lite-On LEDs. This gave me the 14-15mA bias. Running 402 422R with these LEDs will give you 12-13mA.

You're going to try doing the onboard regs? Good luck, though the 2oz boards will make these easier than the 3oz were.

Edited by Pars
Fake news!
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So, a weird question.  But I have the onboard reg working just fine.  +20.11 and -20.03.  However, when I measure offset, each channel line is fluctuating from -3mV to +3mV, and the R- channel started out at -12mV then come down to +/-3mV.  I have not turned the trim pots or anything ? Should I be worried ? Or should I just throw in the 0 Ohms and see what coming out ?

I have no SE switch in place, I don’t think it should affect anything since I am not looking to use SE input atm.

Edited by Whitigir
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I wouldn't worry about that offset. I would adjust the trim pots a bit. The channel layout, looking at the top of the board from the front is:

L-    L+

R-    R+

The two pots by the LEDs will adjust the overall offset for its respective channel. The other 4 pots will adjust the channel it is nearest to. If you have two meters and can watch the + and - of each channel at the same time, that would be best, as the pots will have some effect on the opposite + or -. Don't go overboard in adjusting trying to 0 everything out. As the amp heats up, the channels will drift without the servos in place.

BTW, how did you do the onboard regs? Hot air station?

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12 minutes ago, Pars said:

I wouldn't worry about that offset. I would adjust the trim pots a bit. The channel layout, looking at the top of the board from the front is:

L-    L+

R-    R+

The two pots by the LEDs will adjust the overall offset for its respective channel. The other 4 pots will adjust the channel it is nearest to. If you have two meters and can watch the + and - of each channel at the same time, that would be best, as the pots will have some effect on the opposite + or -. Don't go overboard in adjusting trying to 0 everything out. As the amp heats up, the channels will drift without the servos in place.

BTW, how did you do the onboard regs? Hot air station?

I did the onboard reg by hot-air, and using chip-Quik paste.  It turned out pretty ok, and only the jumper legs were tricky as I had to sneak-in a piece of solid silver conductor as I think it would conduct better.  Needless to say, I was doing it and praying, and it turned out ok.  I spread the paste by the pointy tweezers as I don’t have any stencils

 

262D295F-A0E7-4F38-B174-927954F29F83.jpeg

Edited by Whitigir
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3 minutes ago, Whitigir said:

It turned out pretty sweet, and only the jumper legs were tricky as I had to sneak-in a piece of solid silver conductor as I think it would conduct better.  Needless to say, I was doing it and praying, and it turned out ok.

The jumpers don't transmit any significant current, they just are used to set the voltage. So silver solder is definitely overkill.

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Yep, when I tried the onboard regs, I had problems getting the jumpers to bridge properly as well. They do go to ground, and anything going to ground on the 3oz boards was a problem, particularly if you were trying to use a sane tip size for the application.

The tab on O23 looks a bit light on solder... looks like you used hot air and paste on most of the SMD?

Edited by Pars
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