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The Multi Amp aka Dynalo Mk2


spritzer

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This one has been brewing for a while now but since I wanted to build a nice balanced amp it moved up in line.  :)  Basic setup is the same as the old Dynalo but now with Super Symmetry input, higher rail voltages and naturally a bit more power.  Input stage changed to THAT340 which is a quad bipolar transistor array with matched NPN and PNP pairs.  It is cheap and easy to source so no jfet drama.  The other transistors are new as well and the pinout is different to reflect that. 

 

Here is a look at the new PCB design which is pretty much ready:

 

Pg6Lp2lh.jpg

 

It is 138*86mm. 

 

Another thing from the same vein is a fully discrete unbalanced to balanced circuit that we have been working on so no DRV134 garbage.  I'll start with this one though and order some proto boards this week. 

Edited by spritzer
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Sorry about that, I had the thought of modifying the board so the same one could be setup for L+R instead of just balanced while writing the post.   :-[   Stock it can't be done but I'll see about changing it.  Might just change the board and offer a single ended one as well as I'm not really a fan of cryptic jumpers etc.  It should just have all the parts on the PCB, stuff it and it works. 

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Color me interested. I was actually pondering a balanced dynamic amp last weekend. But when are we going to see some supercharged, off-board heatsink version?

 

On a serious note, how critical is matching the transistors? And would an o22 be sufficient to power this?

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Looking good! I do like my Dynalo, but lately I've found it to be a tad rolled off at the extreme ends of the spectrum. At least compared to other amps I've listened to- Beta22 and simple hybrid amps. After I'm done with my speaker + amp project I might do another headamp. So far the Sjostrom QRV08 has been quite interesting to me.

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To be fair, the B22 is more than just a bit bright. 

 

Color me interested. I was actually pondering a balanced dynamic amp last weekend. But when are we going to see some supercharged, off-board heatsink version?

 

On a serious note, how critical is matching the transistors? And would an o22 be sufficient to power this?

 

There is already a supercharged offboard version... it's the Dynahi.  :D  We might do an on board version of that though given that the LSJ109 will finally be available soon. 

 

Matching isn't all that critical, the amp will function just fine without any matching and 1% resistors.  The servo should have no problem taking care of any extra offset. 

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To be fair, the B22 is more than just a bit bright. 

 

 

There is already a supercharged offboard version... it's the Dynahi.  :D  We might do an on board version of that though given that the LSJ109 will finally be available soon

 

Matching isn't all that critical, the amp will function just fine without any matching and 1% resistors.  The servo should have no problem taking care of any extra offset. 

Thanks for making me fall out of my chair... :laugh:

Edited by Pars
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Matching isn't all that critical, the amp will function just fine without any matching and 1% resistors.  The servo should have no problem taking care of any extra offset. 

When I built my dynalo, the transistor and diodes were too poorly matched for the servo to function. After swapping leds (and taking advices from Justin) it kicked in to reduce the offset to less than 1mV.

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I had matched input JFETs and LEDs on my Dynalo and it was possible to dial it in so it had about 1mV offset. The servo has saved my ass on one occasion tho- when my DAC output stage was misbiased and outputted 0.5V of DC.

 

In any case matching the LEDs is trivial. And in the case of Dynalo it was easy to get matched input devices as well.

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 Part Number Package 1-99 100-999 1000+
LSJ74A SOT-23 3L $6.93 $4.83 $4.59
LSJ74A TO-92 3L $6.63 $4.62 $4.38
LSJ74B SOT-23 3L $6.57 $4.14 $3.93
LSJ74B TO-92 3L $6.27 $4.02 $3.81
LSJ74C SOT-23 3L $6.21 $3.66 $3.48
LSJ74C TO-92 3L $5.91 $3.51 $3.33
LSJ74D SOT-23 3L $6.21 $3.66 $3.48
LSJ74D TO-92 3L $5.91 $3.51 $3.33
LSJ74E SOT-23 3L $6.21 $3.66 $3.48
LSJ74E TO-92 3L $5.91 $3.51 $3.33

 

The prices are way high, but at least they are available.

Edited by kevin gilmore
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