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The Multi Amp aka Dynalo Mk2


spritzer
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Yes, I had considered doing this (insert DMM in amps mode in place of fuse) in order to estimate bias (@15mA should be 4 * (4 * 15) or ~240mA + a bit for the other circuitry). I thought this way I might be able to estimate the bias with heatsinks attached. Sound reasonable?


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3 hours ago, rumina said:

my smd dynalo starts at 27 watt and gets stable at around 30 watt, near the max wattage of the two trafos. But its nice that the trafos are protected, i think bevor the amps overheats/runs away the trafos shut down at 115% (~35 watt). So no need for a thermal saftey switch i used in some pass amps i made.

 

Very interesting this "protection" system.

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Sounds ok, i use 20-30 % efficiency for class a amp after power supply. but that is a crude gess, good to take the magic appart from 20 watt class a amps with a mini powerbrick.

the two mean well irm-15-24 trafos have a build in protection for short, overload and over voltage http://www.meanwellusa.com/productPdf.aspx?i=681#1

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Ran a test after taking one amp back to its original config (402R, LTST-C170CKT and 255R bias resistors). I placed an ammeter in place of the fuse, and ran it for 30 minutes when it was no longer increasing. It showed a max of 245mA AC (is that RMS?). I checked the bias on this one and it was right around 15mA (300-315mV). I then installed the heatsinks and did the same test. Current draw had dropped to 235mA at a stable condition. So my theory: having the heatsinks on seems to reduce the transistor temperature a bit, resulting in lower current draw (a bit). For these two tests I was not able to have the top in place but did set it there as best I could.

Edited by Pars
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Thanks for the measurements - similar then mine ~26 watt with open lid, will rise a little with closed lid but i thinks thats should work fine as mine (i use the group buy case).

do you mean rms in terms of pmpo (or pure mystic power output ? )? then no - it's simply the overall power consumption of the amp.

rms would go something like= max watt out transformer - powerloss transformer (here 18%)  - powerloss regulator  (how efficiency are those regulators?) - powerloss transistors/cricuit design.

i don't like these rms values, take a big switched power supply, add some beefy mosfet and you get big fat rms values, sounds like shit and do to boooooommmmmm

 

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Yeah, just seems like the AC voltage measurements on the Fluke 89 at least are RMS. I used my bench HP 3269 or whatever it is for this though.
I was just trying to correlate the AC current draw with the DC biasing conditions but I can see that would get into a fairly complex calculation involving factors you mentioned and more probably.
Just knowing the current dropped with the heatsinks in place was enough confirmation. And 10mA AC is probably more significant that it seems.


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Something I noticed in the mini BOM was that the power switch listed (8161SH9AV2BE2) isn't rated for AC power duty. Instead, use either the "G" or "Q", which are both rated for 120/250VAC.

Use 8161SH9AV2GE2 or 8161SH9AV2QE2 instead. Mouser stocks the "Q".image.png.bcc7bf3263726ec99df4ece7832143c1.pngimage.png.c860df35c2d7f6c298bc5079b6f92fae.png

Edited by Pars
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Please help me with the TPS7A3301 modules, I could only find this

https://www.ebay.com/itm/TPS7A3301-Ultralow-noise-LDO-regulator-3V-18V-1V-step-1A-LM337-79x-replace/253593923500

It appears that it could only  provide -18v, not the -20.  Am I missing something?

After spending half a day staring at the pcb without any progress.  I gave up on soldering the chips to the board by myself.  :huh:

 

 

Edited by samsie
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^ search back in this thread for some suggestions. Should be easier with the 2oz copper boards than it was with the 3oz from the previous GB (who DID suggest going 3 oz... :indra: )? My personal suggestion would be stencil, solder paste and an oven.

On another subject:

One of the amp recipients that I did a build for has had some problems with his amp since it was delivered on Friday. Here is what he told me:

BAL source, SE headphones = slight hiss in left channel

BAL source, BAL headphones = no issues

SE source, SE headphones = large hiss in left channel

SE source, BAL headphones = no hiss in left channel, but turning the pot creates a lot of static

So far the suggestions I have made were

  1. swap the THAT chips (this is one who didn't opt for the FAR superior JFETs
  2. check the source in SE mode for DC offset, and
  3. try grounding the pot case.

When testing these, I did verify continuity on all of the case panels, at least on the first 2 I built. I never had to do anything as the screws seemed to make good contact. The eject tabs on all of the XLR connectors had continuity to ground as well.

Any thoughts? Thanks in advance!

 

Edited by Pars
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For me it doesn't look like IC (THAT) related issue. Does the hiss increase as he turns the volume up? If yes, then it's likely to be some grounding issue. Otherwise it may be oscillation (though I don't know if dynalo is prone to oscillation). Let him try to temporarily fasten hinged ferrite cores on either headphone cable or input cables or both and see if it makes difference.

Edited by Helium
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I’m not sure if it increases or not. Since everything in a Dynalo mini is integrated. I would think a grounding issue is unlikely unless maybe something to do with the house wiring. And these aren’t prone to oscillation from what I’ve seen. DynaFET is another story...


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Well it raises the input impedance for starters. I think Kevin told me you could go 10x on the gain resistor combo and use a 25k or 50k pot if you wanted to. I always left things stock on the ones I built so the users could go to BJT input if they wanted to.
I think the JFETs sound a bit better, but I could be delusional...


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You didn’t look hard enough :)
Looking at the amp from the front, the channel layout is
L- L+
R- R +

The two pots by the LEDs balance the +/- for that respective channel. The other 4 pots adjust the channel closest to it. There is some cross action with the other phase but not a lot. Normally you don’t need to do much with these. You can also get yourself in trouble with these if you go too far. If that happens, reset to midpoint (using a DMM on ohms) and start over.


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