Re-amp box

[nosamiam]

Hi folks!  I'm planning to build a re-amping device in the coming week or two and I have a couple of questions.  I'm planning on using this schematic:



Question:  What is that small square on the "hot" prong of the output jack? 

Question:  In order for the ground lift switch to work, wouldn't I have to use a plastic box or isolate both jacks, or at least the input jack?  If I want the ground to be "liftable" the ground can't be provided by the box, correct?  It has to be wired to the other two ground points with an SPST in between.  Am I on the right track?

Thanks a lot DIY'ers!

[spudulike]

Looks like J1 is an XLR ....

[nosamiam]

Looks like J1 is an XLR ....

I'm planning on using a 1/4" TRS jack so that I can use a regular sized hole.

[Peter Snowberg]

Question:  What is that small square on the "hot" prong of the output jack? 

That's just the schematic symbol of the jack. The wire connects at the square and to the right of that is the spring contact.

Question:  In order for the ground lift switch to work, wouldn't I have to use a plastic box or isolate both jacks, or at least the input jack?  If I want the ground to be "liftable" the ground can't be provided by the box, correct?  It has to be wired to the other two ground points with an SPST in between.  Am I on the right track?

Thanks a lot DIY'ers!

Correct.

If you want to use 1/4" jacks, run the signal positive (pin 2 on an XLR) to the tip, the signal return (pin 3) to the ring, and ground (pin 1) the sleeve as you normally would. Yes, you will need either a plastic box or to use insulating washers for your XLR substitute jack. The SPST goes between the ground tab on that jack and the rest of the circuit ground (which in this case is just two connections, but could also include the metal chassis if used). With such low impedance involved, stray hum will be less of a factor.

Since you're using TRS connections, I should also point out that you really need to use shielded twisted pair cable. If you don't, the advantages of balanced transmission are lost.

[Plectrum]

Isn't this basicaly a "backwards" DI box?

I've used a homemade Sowter transformer DI for this.

Grant

[Penguin]

question wouldnt' you want a higher imp coming out of the box if you are going to another amp.  i mean 150ohms is a little weak you would think you would want a much higher one.  or did i miss something.

[nosamiam]

question wouldnt' you want a higher imp coming out of the box if you are going to another amp.  i mean 150ohms is a little weak you would think you would want a much higher one.  or did i miss something.

Anyone?...

I hope not, because my tranny is already in the mail heading toward my house.  I don't really want to buy another one.

Now that I think about it (and if I understand correctly how the circuit works), isn't 150ohms really just the minimum impedance?  Or rather 150ohms, plus the 200ohm resistor?  Minimum 350ohms right there.  Plus the reistance available from the pots, right?

[markr04]

FWIW, I built this using a 10K-600 from Mouser. Works like a charm.