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The Multi Amp aka Dynalo Mk2


spritzer
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On 21 January 2016 at 11:38 AM, spritzer said:

The Susy needs max 10K so I had to use some of my TKD's. 

Hey Spritzer, just wondering, what do you mean by this? Is it a gain/stability issue to use a pot of say, 50K?

Reason I ask is I'm interested in understanding what effects volume pot resistances have on amps - some people say it makes a difference, others say doesn't matter. I've had to replace quite a few old amps that have had 20 K input pots with 50 K ones just because I couldn't source any of the original ones...

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For a completely different project I have a couple of Chinese ones, via eBay.  Two secondaries are rated at 17.5VA each - so 35VA total.

Looking at the product datasheet for Kitamura, the physical dimesions (including fixing hole spacing etc), the Chinese one correspinds to Kitamura's 25VA, so the 35VA chinese rating looks a bit hopeful.

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10 hours ago, Craig Sawyers said:

For a completely different project I have a couple of Chinese ones, via eBay.  Two secondaries are rated at 17.5VA each - so 35VA total.

Looking at the product datasheet for Kitamura, the physical dimesions (including fixing hole spacing etc), the Chinese one correspinds to Kitamura's 25VA, so the 35VA chinese rating looks a bit hopeful.

That is indeed the issue.  The core sizes for the R's are fixed but the Chinese manufacturers don't care too much about that. 

As for posting pics, that won't work as out of a batch of two, one transformer might be fine while the other one is garbage.  Some have been truly terrible with dangerous lead wires and truly terrifying build quality.  The bottom line is that I'm staying with toroids for now. 

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Ok. Total off-topic time.

So, zeroed the four-wire probes. They were 0.0012 ohms. Set to slow with 10 moving average samples. Using 100 range with a 100.000 .005% resistor. Last calibration 15 years (!)

Ok, spec after 1 year (max on datasheet) is 100+40, which is ppm reading plus range. So, I think this is 100*0.01%+100*0.004% or +/- 0.014 ohms.

So, my reading is 99.981.

So, in spec? Maybe?

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  • 2 weeks later...
4 hours ago, spritzer said:

Leave the - output floating and just use the +. 

 

3 hours ago, wink said:

Yep, and let all that balanced goodness go to waste.........  :o

 

14 minutes ago, kevin gilmore said:

SE to balanced is what you probably mean, and you can do that.

you can also do SE output, but then why?

 

Yes, i mean SE output. I will use both SE and Balanced output but SE is always more convenient because i have 5 headphones and recable all of them will cost quite a lot. 

I have another questions:

1. How do i wire the ground wire of SE output jack? to one board Gnd or to the Power supply GND?

2. I searched mouser for the Op27, there are 2 variant: Op27Gp (3.42$) and Op27Ep (6.61$), the different seem like only the operating temperature, so will the Gp work fine? I also have some spare opamps (opa1641 and opa551 which can run at +/-30V), can these work as servo opamp for the Susy Dynalo?

Thanks!

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I use TL-071 or TL-081 for singles (or 72s and 82s for duals). From testing opamps in a discrete I/V stage (0 feedback, so touchy), these seem to pull the offset in faster and lower than the OP27s I had do. Particularly the 08x. I believe Justin used to use these in the GS-1 and probably in the GSX as well.

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On 2016-01-21 at 1:38 AM, spritzer said:

As I've been promising to do for months I'm finally working on some dynamic amps.  Here is something new, a Susy Dynalo with switchers...  ;D 

uMgG9FNh.jpg

Running at +/-18V there. 

Are those switchers of the ready made or home made variety? Thinking about trying this, but not sure what requirements to set on switchers in this use (max ripple, for example)?

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mwl168 did a run of them awhile ago, probably the newer SMD version. The TO92 silicon is not available anymore; I was probably one of the last to build that version and got lucky on finding some. He will probably weigh in on whether he has any left or not. Otherwise, someplace like seeedstudio could run boards for you for pretty cheap. The later board runs seem to use heavier copper (2oz and sometimes 4oz), but I've never had any problems with 1oz copper boards even with some rework.

Kevin has the board files on his site. I see

  • dynalobal12
  • dynalobal13
  • dynalobal15
  • dynalobal17

Not sure what the differences are between them; would have to search the thread.

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