I’m still learning, so I’ve noticed that it seems to be agreed that using a screened cable or wires is the proper way to connect from the xlr to the transformers. I’m trying to build a redd clone like many others here. So the question is “can I use mic cable to do the connections?” Both to the transformers and from the transformer to the in and out of the amp. I’m using Sowter 9970 and 9980.
Input and output transformer wire type
- Thread starter BigPauly
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rock soderstrom
Tour de France
Yes, you can do that. The most important connection that should be shielded from my point of view is from the secondary of the IPT to the first tube, as this is the part with the highest impedance.
Shielding is also advantageous from the input of the preamp to the IPT. The signal is fed in via a XLR microphone cable, so it can't do any harm internally either, although thinner shielded cables are easier to lay.
I think shielding is not so necessary on the output side, as the signal here is already very strong. You can do it, but you don't have to.
Awesome, thanks for the reply! Screen /shield connected to pin 1 of the xlr to the ipt case? Connected on one end only?
rock soderstrom
Tour de France
I heard different opinions on this but I ground the incoming screen directly at the XLR input, the amp circuit also has its only contact to the housing here. This has the advantage that RF signals have a harder time getting into your case and no ground loops are created.
That depends on the situation. The rule here for me is that each point in the circuit must only have one path to the common ground point. This often means grounding the screen on one side only.
Altough I think I've read about instances where the added "parasitic" capacitance between conductor and shield can mess with the frequency response.
But that could also be because of wrong termination of the shield.
Optimum grounding depends on the type of transformer. Particularly if it has one or more internal shields.
Ideally, a transformer with two shields would have its first shield (the one closer to the primary) connecrted to chassis ground, and the second shield connected to the input stage ground.
When there's only one shield, it's debatable, and the best is to leave it as an option, to be connected to either ground, and eveluate the best choice.
If there is no shield wire, the case should be grounded, again with the option of either ground.
