Reamp - Jensen Transformer Equivilant on Mouser

[facon]

I'm using this schematic to build a guitar reamp box: http://www.jensen-transformers.com/as/as092.pdf

The schematic calls for a Jensen JT-11P-1 transformer. Here is the datasheet: http://www.jensen-transformers.com/datashts/11p1.pdf

On Mouser I found a Hammond transformer that I think may work, but I'm not experienced enough with transformers to know for sure. Hammond 140UEX Datasheet: http://www.hammondmfg.com/pdf/140UEX.pdf

Can somebody tell me if this will work for my application? Or can you tell me what I should be looking for when trying to find the right transformer? Will the Hammond be close to the same quality as the Jensen? I'm stuck in a situation where I need a reamp, but also need to order from Mouser. Thanks ahead of time!

[PRR]

It will work very well.

At $87 it is the same price as the Jensen; I wonder if maybe it IS the Jensen relabeled or licensed.

[facon]

Great! Kind of a ridiculous price if it isn't close in quality. Seems to have the same casing.

[azrael]

Very cool, I've been looking at building a load box as well, but with a resistive load so that it stays constant. I've seen several line out circuits, including this transformer based one.
I was thinking about going with a resistive line out, like how Egnater does theirs.
Here's the schematic I was looking at, but I was only going to do one of the line outs, and use several resistors in parallel to improve head dissipation.
Any input on which is better, PRR?

[facon]

Well, the Jensen has black and white grounding wires. The Hammond does not. Only the four wires. So does this mean it can't be used?

[wavley]

I've had pretty good luck with Edcor transformers for these kinds of things, they're much cheaper than the Hammond or Jensen counterparts and a pleasure to deal with we had them reverse engineer some transformers to fake 3 phase power for cryogenic refrigerators at work and they were just wonderful to deal with, which only reinforced my opinion of them from ordering audio stuff.

Would I use them to make a Neve or API mic pre clone, maybe not, but for guitar related stuff they are wonderful.

[facon]

I've had pretty good luck with Edcor transformers for these kinds of things, they're much cheaper than the Hammond or Jensen counterparts and a pleasure to deal with we had them reverse engineer some transformers to fake 3 phase power for cryogenic refrigerators at work and they were just wonderful to deal with, which only reinforced my opinion of them from ordering audio stuff.

Would I use them to make a Neve or API mic pre clone, maybe not, but for guitar related stuff they are wonderful.

Thanks. I have these transformers sitting in front of me. So if I can get them to work, it would be convenient.

[facon]

Should I just bypass the white and black wires and connect the input ground and orange wire together on a transformer lug? Like the modification below?

Original:


Modified:

[PRR]

No. That defeats the point. You want NO conductivity from input to output. This breaks ground-loop.

Jensen's black lead is a frill. No healthy studio environment should need it.

Jensen's white is just the Case. Hammond's bracket is the same thing.

[facon]

No. That defeats the point. You want NO conductivity from input to output. This breaks ground-loop.

Jensen's black lead is a frill. No healthy studio environment should need it.

Jensen's white is just the Case. Hammond's bracket is the same thing.

You're awesome PRR. Thanks!

[facon]

Just wanted to update that I did use the Hammond transformers and they sound great. A lot better than my previous cheap reamp. However, it's clear enough now that I'm noticing flaws in my source

[facon]

Okay, now I'm noticing some bigger issues. I have the outputs isolated from the chassis, but whenever this box enters in the vicinity of some electrical source, it gets a buzzing sound. I'm wondering if I'm taking PRRs advice the wrong way. If I hold the box in one hand and touch a laptop or interface with the other, I get loud buzzing. When I plugged it into a small balanced line out interface, the problem seemed fine (just a bit of noise), but everything else I plug it into is really bad. When I'm near a laptop, hard drive or interface and I touch one of the switches, I'm getting buzzing.

Do I need to isolate everything from the chassis? Including pots and switches? I have the ground connected to one of the bolts that hold the transformer down. I'm not sure what else I'm supposed to be doing. A little embarrassed because it worked at first, so I brought it out and now I'm standing in a room full of disappointed band members.
"
Please keep in mind that vague explanations don't do me nearly as much good as actually saying "hey, you should do this". I really need some fool proof advice here.

[facon]

I should mention that I have two of these reamp circuits in one rack mount box.

Also, it seems to definitely be a grounding issue. It doesn't happen when I plug it into my laptop that is using the battery, but as soon as I plug in my laptop charger, it starts buzzing like crazy. And when I take an alligator clip and connect the transformer bolt to the sleeve of the output, some noise (not all) disappears.

I'm thinking "Hammond's bracket is the same thing" may have confused me? Or something. By bracket, do you mean the bracket that holds it to the chassis?

[facon]

*accidental double post

[ricothetroll]

Hi Facon,

I built the Jensen reamp circuit a few years ago, and it's working nicely ! I used the JT11P1.

Seems to me that your box isn't grounded correctly, that's why you have noise when you touch it and bad shielding. I always ground my stuff according to Rane Audio's recomandations :
http://rane.com/library.html#apm1_2 (see "wiring, interconnection and grounding").

What I would do for your case : what's called "GND" in Jensen's shematic must be tied to the ground of the device that feeds the reamp, via the shield of the XLR cable. This shield might be connected to the earth. Then the unbalanced output must be isolated from the enclosure to take profit of the galvanic isolation provided by the transformer, and to make sure there's no ground loop if both your source and your destination use the earth as a ground. Remember, the output is unbalanced so the shield of the unbalanced cable serves both for shielding and current return for the signal, and thus must be perfectly clean. Don't use a metal jack connector.

To summarize :

- XLR pin1, enclosure (case), transformer bracket, white wire, 10n cap and switch are connected together.
- black wire, orange wire, bottom of 10kA pot and jack sleeve are connected together, with jack sleeve isolated from the enclosure.

Please correct me if I said something wrong !

Very cool, I've been looking at building a load box as well, but with a resistive load so that it stays constant. I've seen several line out circuits, including this transformer based one.
I was thinking about going with a resistive line out, like how Egnater does theirs.
Here's the schematic I was looking at, but I was only going to do one of the line outs, and use several resistors in parallel to improve head dissipation.
Any input on which is better, PRR?

I don't get the point of connecting both primary and secondary together at the bottom, you could enjoy the ground isolation of the transformer here !

I would put a buffer after the Egnater circuit, the output impedance is quite high for a line out. By the way, all 3 circuits have a quite high output impedance when the volume pot isn't maxed.

Best regards.

Eric

[PRR]

The laptop is apparently un-grounded. To reduce radio/TV hash, they put two capacitors across the power line. This puts the chassis at 60V _AC_. Anything audio connected to it buzzes. (There's also a weak electric shock.)

Ground the laptop to the audio grounds. This may be difficult. The mike-jack sleeve is probably ground, but 1/8" plugs are dubious on the road. The headphone jack sleeve may *not* be ground, or worse: may-or-may-not be ground depending what its tiny brain thinks is plugged in. The USB shell is pretty sure to be ground and reliable, but I don't recall if standard USB cables have the 5th wire.

[facon]

There are two ways that I've used it so far. One is on a laptop that is grounded with a three prong power adapter and I used an Audio 2 DJ interface which has balanced 1/4 inch outputs (USB powered). Connected like normal I get a ton of crazy noise. If I unplug the power adapter, it gets a little better. If I take an alligator clip and attach it from the output sleeve to the transformer chassis, the noise dies down quite a bit, but is t perfect.

I noticed something very strange with this setup. When connected with the alligator clip, the volume control on the Audio 2 DJ went up until around half way, then it started going down. It's never done this on anything else I've connected to.

I've used it on another rig with a laptop that was not connected and an M-Box Pro that had a power adapter that was not grounded. When I plugged straight from the interface to my amp (line level), there was a ton of noise. So I'm assuming the noise is simply from the ungrounded interface. When I plugged it into the reamp, the noise was still there. When I took an alligator clip and plugged it from the sleeve output to the transformer chassis, the noise went away and it sounded good.

I'm not connecting to any headphone jacks.

Eventually, I'm going to be running a stand alone digital recorder (Roland VSR-880). So I'm hoping these issues are laptop related and the interface works better. Worst case scenario, I know that connecting the output sleeve to the chassis is wrong and defeats the purpose, but it actually helped in this situation.. And doing this, I could tell a difference when using the ground lift when the ground lift didn't do a thing before.

One last thing that I think may be messing with this, I wired a polarity switch in between the last pot and the output jack. I didn't isolated it from the chassis, but I'm also not using the second reamp yet.

Thanks for all the time you've spent in responding to this. I really appreciate it!!!

[facon]

Here are some things that may help. This is a comparison between the two transformers:



And this is exactly how I wired it:



Just in case, here are a couple pics of the wiring:




EDIT: Isolated the phase switch from the chassis. Didn't really notice too much of a difference. I'm noticing that there is no volume difference from when I plug directly into the interface and when I go through the reamp. The noise goes away when plugging directly into the interface.

[facon]

Hi Facon,

I built the Jensen reamp circuit a few years ago, and it's working nicely ! I used the JT11P1.

Seems to me that your box isn't grounded correctly, that's why you have noise when you touch it and bad shielding. I always ground my stuff according to Rane Audio's recomandations :
http://rane.com/library.html#apm1_2 (see "wiring, interconnection and grounding").

What I would do for your case : what's called "GND" in Jensen's shematic must be tied to the ground of the device that feeds the reamp, via the shield of the XLR cable. This shield might be connected to the earth. Then the unbalanced output must be isolated from the enclosure to take profit of the galvanic isolation provided by the transformer, and to make sure there's no ground loop if both your source and your destination use the earth as a ground. Remember, the output is unbalanced so the shield of the unbalanced cable serves both for shielding and current return for the signal, and thus must be perfectly clean. Don't use a metal jack connector.

To summarize :

- XLR pin1, enclosure (case), transformer bracket, white wire, 10n cap and switch are connected together.
- black wire, orange wire, bottom of 10kA pot and jack sleeve are connected together, with jack sleeve isolated from the enclosure.

Please correct me if I said something wrong !

Best regards.

Eric

Thanks for that link! I'll spend some time going over everything on that site so I don't end up continuing to come back here with these basic questions

[ricothetroll]

Hi,
IMHO your wiring is correct ! If the noise continues then I would actually suspect the laptop ground, as PRR said. Maybe you could try to put an alligator clip between your case and the mains earth, see if there's any improvement. Then you can install a 3 prong mains socket with only the earth connectedf to the chassis, phase and neutral unused. And then if you'rez using the reamp with an earthed ground source, use the ground lift switch or, better, disconnect the mains connector.
Best regards.
Eric