The Multi Amp aka Dynalo Mk2

[spritzer]

The transformer will add noise.  Only way around that is to switch to an R-core and isolate it. Won't be perfect but it will help. 

Edited April 18, 2015 by spritzer

[sorenb]

Finished two sets of Dynalo this weekend and two sigma22 psu's.

 

The offset seems to drift a lot; without the servo's it's within a range of 40mV on all boards - fluktuate the full range within a couple of min or so.With the servo in place it's within a range of 0,5mV

Is that normal behavoir?

 

Using +/- 18V for rails I get approx 22-28mA through the output transistors across the four boards.

Would that be running those trans too hard? should I lower r38/39?

[kevin gilmore]

yep, wave a piece of paper over it, the thermals change and the offset drifts.

 

for 18v rails, that is a good current.

[sorenb]

Ok. I'll leave them as is, and give a listen to hear wheather the effort was worth it ( I guess it was ;-)

 

Many, many thanks Kevin for making and sharing your design. Also thanks to Spritzer, mypasswordis, GrindingThud, gepardcv, Pars, JimL, mwl168, and others sharing/contributing to the thread.

 

Pics, or i didn't happen:

[UFN]

Looks good! Still haven't actually powered mine up - must get round to that soon... 

 

 

//UFN

[Pars]

Finished two sets of Dynalo this weekend and two sigma22 psu's.

 

The offset seems to drift a lot; without the servo's it's within a range of 40mV on all boards - fluktuate the full range within a couple of min or so.With the servo in place it's within a range of 0,5mV

Is that normal behavoir?

 

Using +/- 18V for rails I get approx 22-28mA through the output transistors across the four boards.

Would that be running those trans too hard? should I lower r38/39?

Did you have the inputs grounded for this? Mine was < +/- 5mV, normally +/- 2mV without the servos in place.

[sorenb]

Did you have the inputs grounded for this? Mine was < +/- 5mV, normally +/- 2mV without the servos in place.

good one Pars )

No, did my measurement with open input  .... inputs grounded its within 4mV (+O - -O)

 

I haven't put the servos back in, but spend some time listning.

My Sennheiser HD800 have never sounded better )

 

Done my listning using my Tact Mill. mkIII, and the Dynalo is clearly better than hooking up the HD800 directly to the speaker terminals ....much better.

 

Thnx Kevin and Pars!

[kevin gilmore]

its definitely my favorite amp for hd800

 

not even close.

 

yep offset currents open input cause trouble.

[nopants]

For those using the haa15 supply, is it possible to remove the transformer+board from the metal on which it's mounted? I have a case but it's only 2in tall- the sheet lists the height as 2.1

[gepardcv]

The transformer is just held in place with four bolts, should be easy enough. The board might be trickier. The Mouser picture shows the bottom accurately, and I'm not sure how to remove and replace the two metal pieces on the bottom. Not sure what they are, actually.

[kevin gilmore]

the pass transistors go thru the bottom, so you would have to remount them on the new chassis

 

the transformer is 2.04 inches, so the 2.1 inches is right

Edited May 4, 2015 by kevin gilmore

[Pars]

Wasn't sure where to put this, so here seemed fine, though applicable to a bunch of amps here.

 

Balanced-SE input jack board with switch. I was playing around in Eagle (after having to manually wire one of these up).

 

 

 

This is set up to use either a 4PDT switch (for isolating all 4 signals) or a 2PDT if you only want to switch the - signals to ground for SE, but leave the + signals connected to the RCA jacks.

 

1. Pads are provided to connect RCAs.
2. I haven't verified the heights of the Neutrik NC3FAV jacks versus the switch height. My goal would be to have the board mounted to the faceplate via the Neutrik jacks only, with the switch sitting behind the faceplate and the toggle only extending through a slot. Might need a standoff or two as well.
3. Switches this is designed for are the NKK M2042 (633-M2042SS1G03) 4PDT or M2022 (633-M2022SS1G03) DPDT.
4. Board outputs are set up for either Molex 0.100 KK connectors, or you could use the pads as wirepads and solder the wiring in.

I know Birgir has a balanced input jack board, but his is for including a pass-through connection, and not for balanced and SE. Any comments welcome.

Edited May 5, 2015 by Pars

[Kerry]

Looks nice.

You might want to switch the output connectors to the back side of the board. If I understand it correctly, the inputs and switch face the back side of the amp and the outputs would face inside the amp.

Edited May 5, 2015 by Kerry

[Pars]

Kerry,

 

Thanks for the comments. Actually, the Neutrik XLRs and the switch are on the back side of the board. The Molex connectors are on the front. The switch is intended to protrude through the back panel (slot). As I mentioned, I haven't checked the mounted heights of the XLRs vs. the switch to see how that would work out. And for support, it might need a standoff or two on the back side.

 

EDIT: Actually you are right in that the XLRs were drawn from a front perspective. Corrected now (not in image above).

Edited May 6, 2015 by Pars

[sorenb]

Having read the SRX-revisited thread by JimL and the referenced articles by W.Jung I decided to replace the current sources in the one Dynalo I've built.

 

From the 1st article by Jung, it seems as if that the CCS design used in the Dynalo has indeed a very good performance. However as JimL has pointed out the cascoded CCSs seems to offer even better performance. Looking at the very simple LM334 with one resistor demonstrates 20db better rejection than the LED CCS although the performance rapidly degrades past 10kHz; the cascoded LM344/2N5486 however maintain the performance above 10kHz.

So, based on that I decided to try it out.

First I have implemented the non cascoded LM334.

At first hand it sounds like an improvement. However, not night and day difference; the sound is a bit more refined/detailed, and the soundstage as gained a bit more depth.

[kevin gilmore]

the current sources see the tails of the differential inputs.

So really its very close to a dc level that does not change

with input signal. maybe microvolts if that much, so the

current sources really have very little difference.

 

changing the current sources may change the current a bit

which changes the output stage current, so you may be

hearing that.

Edited May 7, 2015 by kevin gilmore

[sorenb]

Can't argue that, and you may be right, that it is rather the change in current than the CCS itself that I am hearing 

Though I did try to match the existing current as close as possible.

Anyway part of the fun doing DIY is also trying out stuff, and maybe realize that it didn't matter that much. For now  

 

In rgrds to the current in the output stage I haven't seen you recommend a sweetspot, other than commenting that one might 'get away' with 18mA ...is 18mA the sweet spot ?

[kevin gilmore]

for the surface mount version which can handle a bit more heat, 20ma per transistor

160ma on each rail per board

[nopants]

Is the SMD version in sync with the through hole version? I've been reading about regulators and this looks like a nice platform to conduct some tests with the power supply side of things

[kevin gilmore]

identical.  pzta56 silicon exactly the same as mpsw56

 

only difference is package and heatsinking the silicon to the tab

[nopants]

Sorry I was referring to the PCB not the part. I'm probably going to put in an order to Bay Area Circuits soon

[sorenb]

@nopants, can I ask to join your PCB buy for Dynalo SMD?

 

@Kevin: whats your opinion on adding a degenerated current-mirror to the input stage?

[nopants]

I found boards, and even if I was doing my own I would have only gotten 2 or 3 boards, literally

[kevin gilmore]

kgdynalobal7 is the all surface mount version.

no one that I know of has made this one yet, so maybe check for errors.

 

will look at the current mirror later, but the board would probably have to get bigger as its

stuffed.

[kevin gilmore]

finally updating my test equipment...

 

with a 30db attenuator and 50 ohm load...

 

http://gilmore.chem.northwestern.edu/ssdynalobalthd.jpg

 

surprisingly close to my 30+ year old antique