The Multi Amp aka Dynalo Mk2

[mwl168]

My build drives my LCD2 (50 ohm impedance) as well as I have heard them. I configured mine to run on lower voltage rails (16V ) so I can raise the output current.

Don't have other ortho cans so cannot comment on how it may work on vintage orthos.

[nopants]

I'm expecting good results with the k401...

 

but I realized the last amplifier I used with the k[4,5]0[0,1] was a little dot mk2 almost 10 years ago, damn

[Luke]

Can someone explain to me if a SuSy feedback arrangement work with a single ended input? For example I want to run this amp as a HP amp and preamp that accepts single ended and balanced inputs. If I use it for single ended then there is no feedback loop coming from the other half. 

KG, if you are listening, thanks for your design, Dynalo is my favourite to date, I've built a few now and I really like this amp. Which of your designs is your favourite amp for non ES cans?

[kevin gilmore]

yep fully differential input.  balanced or unbalanced.

 

for unbalanced in, you tie the - input to ground.

[nopants]

usps fucked up delivery of my psu, but I also need to downgrade to 25v silmics to get everything to fit properly in this case.

was also thinking of using the 5/-+12 supplies to make a version with a relay attenuator

[sorenb]

@nopants: I see that you have left the 'open architecture' of the Megatron :-D ....looks promising though!

[nopants]

that is getting the treatment too, just waiting on some filament transformers

[Pars]

You really should use better sockets for the opamps and I presume the THAT340 that one you have there (those are junk).

 

Mill-Max or equivalent machine pin sockets

575-193308 for the 8 pin

575-193314 for the 14 pin

 

are good ones.

Edited May 16, 2015 by Pars

[sorenb]

Wouw ... emerging from steel, glass and rocks ...very nice. Con grats :-D

 

@Pars: DIPs rated at 1000V and 3A ....

Edited May 16, 2015 by sorenb

[nopants]

You really should use better sockets for the opamps and I presume the THAT340 that one you have there (those are junk).

 

Mill-Max or equivalent machine pin sockets

575-193308 for the 8 pin

575-193314 for the 14 pin

 

are good ones.

 

Thanks for the heads up, I was trying to recycle some leftover parts since the boards were on the cheap and the case is free. What makes these sockets better than the standard fare?

[Pars]

Machine pin sockets like Mill-Max, Augat, etc. hold the IC pins much more securely than the type you are using. When I was a tech back in the '80s I spent a lot of time reseating chips in the kind of sockets you are using; once reseated, equipment back in business (for another day or so). Sockets are so cheap you might as well use good ones. Kevin commented on this in post 95, parts list using 571-1825093-3.

 

  vs.

[nopants]

Thanks for the heads up. I just used the last of my sockets so I'll buy a few during the next mouser order. I'm not sure it's worth reworking the board for the servos. The input bipolar socket looks like it has the round receptacles you're picturing

[kevin gilmore]

major error in the surface mount version of this board, fixed I think, someone please check

 

http://gilmore.chem.northwestern.edu/boards/kgdynalobal7.zip

Edited May 17, 2015 by kevin gilmore

[gepardcv]

Was the error that some of the SMT parts were backwards in the pre 2015-05-17 version?

[kevin gilmore]

yep, how I did that I do not know.

 

it was still possible to build that board, you had to bend the pins and

solder all the parts that were not the output devices standing up

and backwards.

 

a lot of clean up and various traces on both sides the same exact

length just for extra fun. and some ground plane on the bottom.

 

new version

http://gilmore.chem.northwestern.edu/kgdynalobal7.jpg

Edited May 18, 2015 by kevin gilmore

[nopants]

I tried to disassemble the sola/powerone/etc. power supply, it's pretty hard. The screws they use for the transformer are super soft- I destroyed the head after one slip of the screwdriver

[sorenb]

@nopants: sounds like its easier to drill those out?

[Pars]

Listened to my multiamp a bit yesterday and this morning. I seem to have a slight channel imbalance, using SE inputs with the L/R- inputs tied to ground. Swapping the input and output cabling around, it seems to be the pot that is causing the problem. The R channel is slightly louder than the left. Measuring the pot, this is what I get at the approximate rotation I was using for listening:

	L+	L-	R+	R-
pot				
total	9.884	9.707	9.721	9.811
3/4 rot	5.714	5.768	5.643	5.776
%	57.81%	59.42%	58.05%	58.87%

This doesn't seem off that much (57.81% vs. 58.05%). All figures in K ohms. Output taken to ground. Any thoughts? It seems worse at lower volumes and gets a bit better at higher volumes, though going much beyond 3/4 rotation gets louder than I care to listen to.

 

I've checked resistances some on the cabling from input through the pot, and I didn't find any bad solder joints or anything yet.

 

Any thoughts?

Edited May 19, 2015 by Pars

[GrindingThud]

Use a battery and DC as input, it's a DC amp. Measure the output voltage with a meter....you'll see whatever imbalance you have, including effects of the pot.

[kevin gilmore]

it is a dc amp, however the servo's will cause issues measuring dc.

of the 5 pots i bought for this, i was only able to use 2 of them the

others had problems either at low volumes and high volumes

[Pars]

Thanks GT and Kevin. I could always pull the opamps for what GT is saying. I could also just measure it on RMAA (I think my Audiophile 24/96 will do balanced?).

 

Not only for L/R channel balance, but what effect do pot imbalances have regarding +/- channels? I would certainly think some as well, but not sure how that manifests itself.

 

I wonder if Birgir has any of the 4CP-601 TKD pots he'd be willing to part with?

 

Also, I recall the thing you can do to a 2 channel pot to use it for 4-channel, but it seems that only typically works on certain types of inputs?

 

EDIT: No on my m-audio box doing balanced

Edited May 19, 2015 by Pars

[gepardcv]

What volume pot are you using now?

[Pars]

Alps RK27 10K motorized

[kevin gilmore]

if that is one of the 2 sections in one section things, those are awful.

[UFN]

The RK27 is the standard Alps "Blue". The "double-decker" ones are called RK168

 

 

//UFN