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Author Topic: Sunn Dymos  (Read 852 times)

gbono

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Sunn Dymos
« on: June 06, 2020, 07:02:30 PM »
I have a Sunn Dymos with all the output/driver/reverb transistors removed. Looking at the schematic, it looks like these transistor's collectors (they are all TO-3 2N3055) should be isolated from the chassis - is that correct? Point A and B on the schematic would be grounded without isolation but i don't have any mounting hardware with this chassis to verify how the collectors should be connected.

The jpeg is off the net for reference only.
« Last Edit: June 06, 2020, 07:06:07 PM by gbono »

Enzo

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Re: Sunn Dymos
« Reply #1 on: June 06, 2020, 07:07:34 PM »
They appear to be mounted in your photo.

gbono

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Re: Sunn Dymos
« Reply #2 on: June 07, 2020, 04:22:22 PM »
Yes the image shows the hardware mounted but that's not what I have on the bench it's an image off the web. What happens if points A and B are connected to chassis ground -i.e.  the collectors are not isolated?
« Last Edit: June 07, 2020, 04:23:49 PM by gbono »

duckduckgoose

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Re: Sunn Dymos
« Reply #3 on: June 07, 2020, 04:25:10 PM »
all of those old sunn's look awesome  :dbtu:

g1

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Re: Sunn Dymos
« Reply #4 on: June 07, 2020, 05:33:31 PM »
You need mica spacers (& thermal paste) for the TO-3 transistors, and insulating bushings for their mounting screws.

phatt

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Re: Sunn Dymos
« Reply #5 on: June 07, 2020, 08:24:22 PM »
Yes the image shows the hardware mounted but that's not what I have on the bench it's an image off the web. What happens if points A and B are connected to chassis ground -i.e.  the collectors are not isolated?

I think you are missing something about how the circuit works and is confusing your question.

Point A is the supply for the collector (NOT GROUND)

Look at the bottom of Schem and find the rectifier D101
You will See that point A is the Positive supply for the collector (pointA)

The *Emitter* of the lower transistor is Point B
That is the Negative supply shown at bottom of D101.
Those 2 points DO NOT connect to ground.

To add even more confusion
This is an odd circuit and someone here with better understanding may know more.
note the speaker neg returns to neg voltage rail????
So it makes no sense to me.  :loco xP

hope it helps, Phil.


Enzo

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Re: Sunn Dymos
« Reply #6 on: June 07, 2020, 09:22:54 PM »
Points A and B are power supplies.  If you do not insulate the transistors from the grounded heat sink, it will short out the power supply, and blow fuses the instant you turn it on.


Think of this as a single supply, like a bunch of old Acoustics.  The output would sit half way up the power supply with a big cap to block DC.  On this they didn't reference the speaker to ground because the "ground" is now V-.  But same deal.  Just cannot allow speaker jacks or cables to touch ground.

g1

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Re: Sunn Dymos
« Reply #7 on: June 08, 2020, 01:37:40 PM »
  The output would sit half way up the power supply with a big cap to block DC.  On this they didn't reference the speaker to ground because the "ground" is now V-. 
This is truly bizarre as shown if correct.  The output of the bridge rectifier is +35/-15 ?  So the power amp output sits at +10V ?

Enzo

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Re: Sunn Dymos
« Reply #8 on: June 08, 2020, 11:51:14 PM »
Looks that way to me.  I hadn't paid that close attention.  The -16v rail comes right off the bridge, while the +16 comes through dropping resistors.

SO just like the one supply Acoustics, this thing is powered between A and B, and it really doesn't matter at all where on the spectrum that sits.  If we call A to B the supply voltage, the speaker will be drawing from 1/2 of that and B.

Kinda clever really, they have a 50v supply, split offcenter.  And only one of the low voltage rails needs dropping resistors.

gbono

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Re: Sunn Dymos
« Reply #9 on: June 09, 2020, 02:45:57 AM »
So if I should see +15V across C105 and -15V across C104? Supply voltages not referenced to chassis ground.

Enzo

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Re: Sunn Dymos
« Reply #10 on: June 09, 2020, 10:46:28 AM »
Main rails not referenced to ground, but 15v rails are.

g1

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Re: Sunn Dymos
« Reply #11 on: June 09, 2020, 03:14:20 PM »
Still a little surprised at this one, but I thought B+ will read +34V with respect to chassis ground.
What else can it be referenced too?

Enzo

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Re: Sunn Dymos
« Reply #12 on: June 10, 2020, 02:48:46 AM »
Probably will.   Whole 50v supply referenced to ground through the -16v supply. 

gbono

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Re: Sunn Dymos
« Reply #13 on: June 10, 2020, 06:28:27 PM »
I'm having a problem with the supply voltages. If I measure across the bridge (A-B) I get +2VDC. How do I verify supply voltages?

Okay just saw your post - still only get 2VDC from B to chassis ground. 40VRMS into bridge. Bad bridge?
« Last Edit: June 10, 2020, 06:36:35 PM by gbono »

Enzo

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Re: Sunn Dymos
« Reply #14 on: June 10, 2020, 08:41:30 PM »
40v AC?  Turn the thing off, and measure resistance of that 40v winding - just to be sure.  An open winding can still induce voltage into your meter.

Bad bridge?  A bridge is nothing more than four diodes in a single package, get out your meter and test it.