Help a newbie w/ a reamp box.

[jlarsen]

Hi,

I'm fairly new to electronics, but I can make cables and I've built a little headphone amp, so I think I've got the skills necissary, but not yet the knowledge to do what I want to do.

I'd like to build a reamp box, using the schematic http://www.jensen-transformers.com/as/as092.pdf and the Jensen transformer recommended in the diagram. The switch, wiring, and jacks are pretty straight foreward to me, but the variable resistors labeled "level" and "impedance", the resistor labeled "51" and the capacitor labeled 10n are confusing me.

I can't find any pots on Digi-Key that are audio taper but not IC's. I feel like I must be looking for the wrong thing. Can anyone here point me in the right direction? I'd be ready to order if only I knew which four parts I need.

Thanks in advance.

[RobPhill33]

Hey,

No one has helped you yet I see. Let me try. The 10n cap is 10 nanofarads (or 0.01 microfarads might make it easier) and is polarized in the schematic. I believe the resistor is a 51 ohm, but the value is probably not ultra critical (somewhere around fifty). The two pots are just regular non linear pots. I think the "Level" just means what it is used to control (the level or volume). Anyways, hoped some of that helped.

[leadbelly]

Originally posted by RobPhill33
is polarized in the schematic

I believe that's meant to be a non-polarized cap. I'm probably a bit older than you so I can remember when the rules were that that particular symbol (one straight, one curved) had to have a plus on it to mean polarized. In this application, it should be non-polarized.

[hankhank]

i am also in the process of building one of these......i am mounting it all in an aluminum hammond box......and am attempting to use a jensen JT-11P-1BN transformer.....the one that is in a metal can and mounts on an octal plug......on the schematic i downloaded from the jensen website, it looks as though there are six wiring points coming from the transformer, each color coded.....the transformer i have has no indication of color, just #'s for the pins......how do i translate the colors into pin #'s?.....also, what would be the ideal way to ground this project?......solder a grounding lug onto the aluminum chassis somewhere and run everything to that?....thanks and i apologize for my ignorance....this is my first attempt at building something like this......

[unclejed613]

you can pull pots from "parts beasts". the taper designation for audio taper is "B" and linear taper is "A". if you have a pot marked 104B, that is a 100k audio taper pot (or it might also be marked 100kB). in the first example, the first 2 digits are the number with the 3rd digit as a multiplier, so 472A would be a linear taper 4.7k and 105B would be a 1 meg audio taper.
HTH

[marthaman]

In the Jensen transformer diagram referenced in this thread, is there a recommendation for the type of connector labeled "J1 Line Input"? For example, should it be a shielded 1/4' phone jack with an incoming shielded 1/4" phone plug?

[leadbelly]

Originally posted by marthaman
In the Jensen transformer diagram referenced in this thread, is there a recommendation for the type of connector labeled "J1 Line Input"? For example, should it be a shielded 1/4' phone jack with an incoming shielded 1/4" phone plug?

In the diagram, J1 is an XLR connector, not 1/4" at all. Maybe you should give us an example of what you are trying to do?

[marthaman]

Thanks for the connector info.

The signal path is from mic to mixer to combo amp. The reamp is need to handle the line level output of the mixer so that the combo amp can handle the input without saturation/distortion.

The mixer output connector is normally 1/4", but I can switch to XLR.

[unclejed613]

sctually, it has become popular in music equipment to use a stereo 1/4" in place of an XLR, or side-by-side with one. since a standard single ended 1/4" would connect the (-) input to ground through the ground sleeve, this makes it a "universal" connector that will work with balanced or unbalanced inputs alike. this also makes for a less expensive cable for balanced inputs since stereo 1/4" phone plugs are about 1/10 the cost of XLR connectors.

[bnutz]

I'd like to try to build one of these myself, but it would be my first build (other than cables) and I'm virtually clueless. I'm hoping someone can help me with these (probably very simple) questions...

1. I'm having a hard time finding a 20k pot for the impedance adjustment. Will a 25k pot work instead?

2. I need a 10nf (.01mf, right?) cap. What material and voltage should I use? Small Bear sells these, will they work?

3. I need a 51 ohm resistor. What wattage and material do I need?

Thanks so much!
-b