Effect Of Stacking Toroidal Transformers?

[Vikki]

I'm just building a couple of JLM 99 preamps and i've dropped on a 2u rack case ex equipment, the JLM boards look a wee bit lost in a case this size so i got to thinking... I could get 4 preamp boards at least in this case, i was going to build the first two pre's to jlm stock chips but if they work as well as many people describe it might be nice to add another 2 jlm pre's using a different brand of chip, transformer and voltage. I have room to stack two toroidal transformers directly on top of each other using one giant bolt, is this wise will the turns of one interact with the turns of the other and produce some funny effects?
Whats the advantage of using output transformers? Is it to give isolation, i think you can use them to step up step down the output or does it have a marked effect on the sound?
The saying around here seems to be the sound is in the iron! What frequency will an audio transformer pass will it not limit the frequency response of a pre?
So many questions from one who knows so little!
Vikki(uk) :grin:

 

[louder]

alo vikky
i stacked 2 p/t in my g9,and no problems.just keep them far as possible from the boards,and rotate them to the point you have the least noise.
as for o/t,i really can`t help.
best regards
pedro

 

[Lowfreq]

Hi Vicky

I'm in a simliar situation to you with building 4 JLM pre's into one box. I'm only using a 1u case though. I'm building an external box for my power supply (one of joes suggestions) as the transformer i had wouldn't fit in the case. I only have one pre at the moment, but the plan is to have 4.
2 as they come from joe, and 2 with different components.

Are you using any of the JLM power supplies? I'm using the AC/DC board. and i was thinking if i kept all 4 pre's the same voltage then i could avoid the whole two power supply thing, but then i guess i would be stuck to using the 99v op-amp, which is prob a very good thing, but limits the whole experimentation/leraning thing. Bare in mind that I still know nothing about this stuff yet :? so mmmmm.

But I'm also interested in knowing about the transformer out. I'm goin without at the moment, and according to joes site, the output becomes quasi balanced or something....................showing my ignorance here. :wink:

From my limtited understanding, the output transformer appears to be used to give us a balanced out? More of a question than an answer.......
But I have heard the "sound is in the iron" thing too. But I've only ever used cheap $300 pre's so I have no idea of what that sound is.

Well, I have probably only added more questions rather than give you any answers, but I'm very interested if someone has got the answers. :green:

Steve

 

[louder]

alo
my 99v has no o/t,it is damn quiet,sounds wonderfull,and needs a brother.
best regards
pedro

 

[JLM Audio]

The JLM99*MB has positions for a 78** & 79** regs on board which could be used to make 2 voltage rails of +/-12v to +/-24v to run another 2 pres at lower volts easily. Just remove the two wire straps and fit regs. You can get the + 78** rail at pin 8 of IC3 and the - 79** at pin 4 of IC3.

Just do NOT strap +OP to +S and and -OP to -S
Then wire the +28v to +34v to +S and -28v to -34v to -S
Wire pin 8 of IC3 to +OP and pin 4 to -OP
You now have the on board regulators running the opamps on that PCB

+S goes to the input of the 78**
-S goes to the input of the 79**