The Multi Amp aka Dynalo Mk2

[gepardcv]

Finally getting around to building a Mini Dynalo, and ordering parts. What fuse(s) should I order?

[JoaMat]

On 3/2/2019 at 9:50 AM, mdr30 said:

Wow, I like that Scanivox box – beautiful.

[joehpj]

Time for some old fashioned design. You can't go wrong with through hole. 

[Kerry]

Nicely done!

Where'd you get the case?

[samsie]

And how do you do the printing?

 

Sam

[joehpj]

It was a small batch made customized. The factory did everything for me.  

ps. I have some spare.

Edited April 18, 2019 by joehpj

[gepardcv]

On the mini Dynalo, I never understood the pieces labeled "AOT". They're marked optional in the BOM, and no one seems to have soldered them. What do they do in the circuit? From the photos posted, most people populated the 10k resistors next to AOT. They aren't in the Mouser shopping list, but are they needed? I plan to use the on-board regulator (soldered with paste and hot air) if that makes a difference.

[Pars]

AOT is "Adjust On Test" and is meant to tweak the negative rail output to match the positive.

 

[gepardcv]

Is the AOT resistor supposed to form a voltage divider with the 10k it's next to? Trying to figure out reasonable values for that resistor to order.

[Pars]

I think it is in parallel. IIRC 1.43M was a value that was suggested...

Edited May 7, 2019 by Pars

[purk]

On 4/7/2019 at 11:49 AM, Pars said:

I could consider it. I don't have any cases, so would have to have one made. If you wanted the TKD version, I would have to get a board and the TKD pot as well. As well as all of the other parts (not a problem), so not cheap.

What if you don't like it?

He/She will love it Chris.    Hard to beat the Mini Dynalo.  I have the GSX Mini on loan from Justin and I'm splitting hair to hear difference.  Thank you so much for making one for me.  

[Pars]

Thanks Purk... I appreciate it!


Sent from my iPhone using Tapatalk

[Pars]

Re: Mini Dynalo

I thought I had posted this here, but apparently I didn't (had some PMs going at the time).

When I was getting ready to ship the last mini out that I built, I noticed an odd problem in that occasionally DC offset on the SE would jump to ~500mV at startup. To make a long story short, I determined via scope that the Meanwell bricks don't always start up at the same time. When the + comes up first, the servo opamps freak out briefly, causing the offset. Without the 0R jumpers in you'll never see this. And it only affects SE output; the balanced output offset is always fine.

A month or so ago, while perusing diyaudio, I ran across a comparator circuit used for power management in, of all things, the O2 amp. This circuit, placed before or after the regs, with proper parts selection for voltages, would cure this "problem". I realize virtually no one would build one of these for SE output use, but one thing to be aware of. If you are using SE phones with these, wait about 30 secs. before plugging them in.

I did PM this info, and this circuit to Kerry, but he has a lot of fires burning and redoing the mini probably isn't even on his radar

[sbelyo]

On 4/7/2019 at 11:49 AM, Pars said:

I could consider it. I don't have any cases, so would have to have one made. If you wanted the TKD version, I would have to get a board and the TKD pot as well. As well as all of the other parts (not a problem), so not cheap.

What if you don't like it?

I have an Alpha board, pot and case that I will not use if you need it

[mdr30]

On 4/18/2019 at 12:18 AM, JoaMat said:

Wow, I like that Scanivox box – beautiful.

Thanks. Of course a small homage to the Swedish radio manufacturer 'voice of Scandinavia' (1940s). The vintage knob has the patented double dot feature which guarantees perfect channel balance. On-off switch is a spiffy little Russian thing with nice M1,6 threads. Bought a pair from Bulgaria delivered in oiled paper. Strange thing: manufacturer has the same name as me.

 

[bluebyte60]

Anyone has extra sets of pcb boards to spare? I kind of want to get rid of my b22 and build a dynalo for hd800.  

[Pars]

Thinking about doing something possibly daft, and just wanted to float it out there.

I am going to build myself a mini, and since I have plenty of MPSW06/56, was thinking about using these instead of the PZTAs for the outputs, mainly to look at the thermal characteristics compared to the hot running PZTAs. I know the pin-out is different, but I did a feasibility check with one with a touch of teflon tubing and found it is quite doable. Pain in the ass, but doable.

Head-case? Anti-Head-case? So daft you don't know what to say?

[gepardcv]

Don't know about Mini compatibility (I'm still working on mine), but I built two full-size Dynalos with MPSW parts (I have a small stockpile). They run entirely cool as far as I can tell. I never checked with a thermometer, but there's no sensation of ambient heat if I hold my hand near the boards. Honestly seems like a good idea to use the cooler parts if you can get away with it, though it seems to me like it'll be a tight fit to stuff all those TO92 packages in such a small space.

[Pars]

Agreed on the heat (full size vs. mini). I really don't view the MPSWs as being a problem though. Rough install... if I do this, I will attempt to get everything aligned all nice and purdy...

I don't know for sure, but in my current estimation, the minis I've built sound better than the full size

My full size is running at 17-18mA bias. Perhaps I've gone too far?

 

Edited June 7, 2019 by Pars

[Pars]

Another one lives... this one is sbeylos.

Haven't listened to it yet. I was doing current draw testing here. Without heatsinks: 275mA AC. With heatsinks: 249mA AC. Bias was around 15mA (~300mV across the 20R). Heatsinks should keep that in check.

Edited August 12, 2019 by Pars

[sbelyo]

F'n awesome !  Thanks Pars

Here's the parking spot

[G600]

Soldering in music... sounds like Head-Case panache!

[Pars]

Another mini, and hopefully the last that I build (#5), this time for me. I accordingly did some things a bit differently...

Headers and shunts instead of the 0R resistors...

And as earlier threatened:

MPSW thru-hole output transistors. A bit painful to do, but not so bad once I got going. Temps seem lower; 71°C is the highest I have measured so far. IIRC the PZTAs were often in the 80°C range. After casing it, etc. I'll report back. I have PZTAs so can go back to those if warranted.

 

Edited September 8, 2019 by Pars

[spritzer]

Interesting input fets.... 

[thuytn]

I'm working on a BOM for the Dynalo.  Most of the parts can be sourced locally but so far I couldn't find the 402R resistor. Would it be possible to replace them with 390R which is the closest value my local vendor carries?