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The Multi Amp aka Dynalo Mk2


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Correct. IIRC Kevin made the SMD-layout when On-semi announced that they were discontinuing the MPSW-devices and only keep the surface-mount PZTAs. As it's the same transistors I don't believe there are any difference in performance.

 

//UFN

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Here's an update on the mini. I've got the external regs running now.  This thing does throw off quite a bit of heat.  I've some sinks on the output transformers now, but I'd like to make them a

Almost there.  I've got one channel dialed in and working on the second.   

Well that was very quick shipping from FPE , Initially I was going for an all out black box, but FPE don’t do anodising after milling leaving the panels with silver edges, which got me thinking s

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I made a list on mouser.com for parts of the amp boards alone. I included both the 240 ohm and 255 ohm resistors but you could easily remove one. The only thing I don't have are the terminal blocks. Anyone know which blocks I should use?
kgssdynalobal9 - 2 channels

I noticed that most amps that are class A have a lot of heatsinks but this one doesn't seem to really need them. It is because the current is distributed among several transistors which spreads out the heat more efficiently without the need for heatsinking?

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Partly. From memory, the Dynalo runs app. 300mA at +/- 15-20V, i.e. an idle dissipation of around 10-12W per channel. This is not much by class A standards (a 20W/ch speaker amp like the Pass F5 or similar dissipates from 60W/channel and up).

Distributing the heat across many transistors means the Dynalo can use smaller output transistors - the MPSW/PZTA-ones are only rated for 1W dissipation each.

//UFN

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Here's an update on the mini.

I've got the external regs running now.  This thing does throw off quite a bit of heat.  I've some sinks on the output transformers now, but I'd like to make them a bit larger.  The regulators heatsinks are going to about 140 deg F at their peak and I'm ok with that.

I was testing at +/-14V before I put the heatsinks on.  The bump up to +/-20V seemed to smooth things out a bit on the top and bottom ends.  I'm very happy with this so far :D

 

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Just looking to get the bias back in line with original specs.  That plus the heatsinks I was testing should put us around 110 deg F on the output sinks.  The regulator sinks should also come down to 105 deg F.

Need some parts to test.

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What's the usual procedure for heatsinking smd devices? Sprinkling vias around or screwing on a small heatsink?

There are a few ways to do it. If you attach the heatsink to the transistor case, you pay a pretty large thermal penalty. I think the best way is a large land with an attached heatsink.

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How a about using the whole case as heatsink?

It's rather easy to calculate the distance between case and PCB. Customized aluminum block can do this job.

Or, hollow the case to expose the heat sink. My concern is if the whole PCB is cased and heat dissipation will be a problem after hours of running.

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