switchable output transformers on gssl

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regularjohn

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Jan 23, 2009
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I've been searching for about an hour now and I can't find anything on this.

I want to make the output transformers in my gssl switchable, so that I can switch back and forth between transformer and transformerless output.  I'm thinking a 4PDT switch coming off the gssl pcb might work, with the different output resistors on the switch leading to the respective outputs.

Basically what I'm concerned about is that with this configuration both output paths would remain connected to the same XLR jacks and it would be the output path of the pcb that would change (if that makes sense).  Is there going to be a impedance loading problem doing it this way?  Because if I was in transformerless mode, the secondary of the transformer would still be connected to the xlr, and vice versa.

What kind of switch or relay could I use that would switch both sides of the transformer connection if I can't do it as I described above?

Any advice on doing this mod?  

Thanks so much!
 
I suppose you could just get another switch with more decks to accomodate the extra actions necessary, or an additional deck for your switch, if its that "expandable" type, and use it to break those extra connections that you're concerned about. 
 
Yeah, I was kinda hoping to do it with a toggle and not a rotary though. 

Ideally I'd like to use relays, but I don't know much about setting up a relay circuit. 
Is it possible to simultaneously switch two 4PDT relays from one toggle switch?
 
regularjohn said:
Yeah, I was kinda hoping to do it with a toggle and not a rotary though. 

Ideally I'd like to use relays, but I don't know much about setting up a relay circuit. 
Is it possible to simultaneously switch two 4PDT relays from one toggle switch?
Yes, it is.
 
CJ said:
easy with a switch, just do it,

look at hp oscillator, they do it,

Thanks CJ.
So should I worry about having the "out" side of both output paths permanently connected to the XLR jack?  ...since I'd only be switching the front side of the output path.
 
If it's possible - wire it so that the XLR out is the center or common - that way the XLR could only be connected to one path or the other at a time.  The output paths in this case would only be permanently connected to the switch throws.

Depending on the grounding requirements you may be able to do it with a DPDT.
 
I'm not quite sure what you mean there.

If I go from the pcb to the pole of the switch, then one throw would go transformerless out, and the other throw would go transformer out.  But they still have to go out through the same XLR jack.  What I'm worried about is unwanted impedance loading while in transformerless output because the secondary of the output transformer would still be sitting there on the output.

Or should I put the pole of the switch on the XLR jack, and then have each throw connected to the pcb?  So that there would be two outputs coming right off the pcb.  Would there be any issues doing it this way?
 
Sorry about the confusion there - a DPDT would not work for keeping all connections separate. Dunno what I was thinking.

You do need a 4PDT wired as:  poles 1 & 2 = PCB out,  hot, cold
                                       
                                          poles 3 & 4 = XLR,  hot, cold

                                          throw 1 (PC poles) =  transformer pri(s)

                                          throw 2 (PC poles) =  no iron

                                          throw 1 (XLR poles)  =  transformer sec(s)

                                          throw 2 (XLR poles) =  no iron


This gives you two separate output paths and avoids the situation of a constant parallel path you were referring to.
 
I had a similar idea a while ago

check out this diagram (the transformer is wired incorrectly, but the signal flow is the same)

LL5402GSSLMOD.jpg
 
I had a similar idea a while ago

check out this diagram (the transformer is wired incorrectly, but the signal flow is the same)

LL5402GSSLMOD.jpg

Interesting mod ,
and for have the out from transformers as additional option without the ic out opamps section,
with a selection switch that allow to select between ic and transformer,
would many changes be required ?
thanks
 
..you can't run the output without the opamps, as the first is used for current-to-voltage conversion for the VCAs. The second opamp does not contribute much to any type of sonics.

Just change the four 100R*s to 22R, switch in and out the transformer. It's overkill to switch in and out the 100R resistors, the 22R do a fine job as is

/Jakob E.
 
Definitely a necro thread- but a year and a bit ago I did a custom GSSL build for a client that went from the 'Cavendish' DOA mod into two different transformers AND a THAT1646 line driver stage (so like, clean, API, UREI) and did it on a 4p3t rotary... Would have to look up my notes for the switching logic but it worked beautifully well and client uses it daily in a mastering context.
 
..you can't run the output without the opamps, as the first is used for current-to-voltage conversion for the VCAs. The second opamp does not contribute much to any type of sonics.

Just change the four 100R*s to 22R, switch in and out the transformer. It's overkill to switch in and out the 100R resistors, the 22R do a fine job as is

/Jakob E.
Hey Jakob,
thanks for the info,

just to avoid any misunderstood,

the 100R resistors to remove are those out of pcb,
as attached image,
correct ?
 

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    100r-out.png
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Definitely a necro thread- but a year and a bit ago I did a custom GSSL build for a client that went from the 'Cavendish' DOA mod into two different transformers AND a THAT1646 line driver stage (so like, clean, API, UREI) and did it on a 4p3t rotary... Would have to look up my notes for the switching logic but it worked beautifully well and client uses it daily in a mastering context.

Hey,
any info, scheme, about to share ?
thanks .
 
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