n72 no low frequencies

[theguitarman83]

Ok, so here Is something that has been killing me for a couple weeks. I finished my N72 about 2 months ago. But I am getting nothing in the lower hertz, any thing under about 400Hz Is silent. I ran a sine sweep from 20-20k and was getting nothing on the lower frequencies, and then is slowly started showing something around the 400k range, and then it slopped up from there, slowly. All my voltages are within range on my Q1 - Q6 transistors. My N72 is sitting in a one shot. I tried resoldering the transistors Q1-Q6, I checked and made sure I wired the transformer correctly. I removed all the extra one shot pad, do and other wires from the transformer cause those directions were a little tough to understand, but still not working. I am not a professional soldering technician, but I can hold my own, this isn't my first time. Any ideas on how to fix my N72 would be more than appreciated. Its driving me crazy!!! Please help!!! Thanks in advance.
Bob

[theguitarman83]

Ok, so Tim Ryans emailed me and said this.
"Lack of low end is usually a sign of transformer wiring problems. Make sure
all of the leads at T1 are correct and the jumpers at J5 and J6 are
installed properly. Make sure the output transformer phasing is correct.
You may also have the wrong value or bad solder joints at the tantalum
coupling capacitors."

I don't have an oscilloscope, but am looking for one to borrow from a friend. When I get it I can check the phasing of the output transformer, if I knew how. Anyone know how?
I rewired the input transformer, triple checked to make sure it was perfect, looks a lot better this time, but looks are deceiving cause I am still getting hardly anything from the low it. It slowly creeps up till about 2kHz, and then it id about even after that. I also checked the tantalums, reflowed them, values look good. Any other ideas????
Thansk

[theguitarman83]

Well... I guess I can just keep replying to myself. I returned my N72 with it's one shot and it arrived back with seventh circle audio on January 6th. After quite a bit of time... It showed up on my doorstep, on March 10th. Only to not work. So here is my email I sent back to seventhcircle.


Tim Ryan
I was more than excited when my N72 in its one shot showed up at my door today. You received it on January 6th, and I have been waiting quite a while for it to come back, so you can imagine how excited I was. But only to be totally disappointed when I plugged it in. It seems like I am still getting nothing on the low end frequencies.
I have tried multiple things:
I tried half a dozen different cables, but the sound didn't change. (I tried them on my other preamp and the cables worked fine.)
I tried a couple different outlets in my house... It was a long shot, but didn't help.
I ensured the 48v phantom switch worked, and I could here it change when it was engaged or not. Not engaged I got nothing from my condenser mic.
I tried a couple different mics, both condenser and dynamic. All of them sounded extremely thin. I tried them all on my other preamp, and they sounded fine.
I finally got tired of singing and plugged in my ipod through the instrument on the front, and tried from there. Still super thin.
But then, I tired the DI out, and it was crystal clear, no screeching upper end. But, with the DI out plugged in none of the controls on the front work....
So I am at a lose....
Please advise....
Bob

[Randyman...]

Just a shot in the dark (a "One Shot" in the dark ):

What is the N72 plugged into (A/D, Mixer, Compressor, etc), and exactly how is it wired?

The N72's output Pins 2+3 (transformer balanced output) must drive whatever input you have it connected to. If you are attempting to feed an unbalanced input and don't have it wired correctly you can experience issues (Pin 2 to Tip or "unbal +", Pin 3 to Sleeve or "unbal -"). (Edited a typo 03/13/14)

If Tim had it in his shop - I'd have to assume he had it working on the bench. Fingers crossed it is a connection issue!

[theguitarman83]

Thanks Randyman
The setup goes:
microphone connected to xlr cable,
xlr to input on back of the oneshot,
oneshot output connected with xlr male to 1/4" male (http://www.musiciansfriend.com/accessor ... s-m--xlr-f)
then the 1/4" male is connected to the the Line Input on my Line6 UX2.
The line input is a line level input. I always use that for my other preamp (BLue Robbie) and had no issues.
The line 6 UX2 also has 2 mic inputs and 2 instrument cable inputs. Connecting it to the mic inputs would cause it to use it's builtin preamp, which is not what I want. But I tried both,and the sound was still thin, no bass.
I tried connecting it to the instrument inputs. Both sounded thin/no bass.

So, probably my XLR to 1/4" Stereo Jack is wired unbalance, and that could be the problem?
I guess I would have to open it up and see. I can't find anything online to tell me if it is or isn't.
Thanks again Randyman
Bob

[theguitarman83]

Ok, so here is the cable
http://www.zzounds.com/item--MONMSLCFX
It is balanced.
However, I am reading that my line inputes on my line 6 UX2 are not balanced.
I am not sure why this woud cause the sound to be thin... but I am no expert. Thanks

[Randyman...]

It sounds like the cable is the issue. If driving an unbalanced input, you'll need an XLR cable that connects XLR Pin 2 to "Tip", and XLR Pin 3 to "Sleeve" to complete the N72's transformer balanced output circuit.

Your current cable is connecting XLR Pin 2 to Tip, but then connects XLR Pin 3 to Ring, and your interface doesn't connect the Ring - so the N72 is only connected by 1 wire and can't make a complete circuit.

Your other preamp does not have transformer balanced outputs, and is why it works with your current cable.

You can easily mod your existing cable: Chop-off one of the 1/4" TRS connectors and re-solder a 1/4" TS jack (wired accordingly). I don't believe "off the shelf" XLR-to-1/4" cables would come wired correctly for this scenario anyways (would likely connect XLR Pin 1 to Sleeve)...

Best luck!

[theguitarman83]

Thanks Randyman
I will tear appart some cables after work. Just to make sure I don't mess it up. It looks like I should be wiring like example 3b on this link
http://www.rane.com/note110.html

Bob

[Randyman...]

Diagram #5 is what you want, but don't tie Pin 1 to Pin 3 (an option listed on that Rane PDF).

XLR pin 2 connects to 1/4" Tip
XLR Pin 3 connects to 1/4" Sleeve
XLR pin 1 is generally left unconnected if using unbalanced cable (and NOT jumped to Pin 3!)

If your cable is balanced (2 inner conductors and a shield), you can use the 2 inner conductors for Pin 2/3 to the 1/4" TS, and connect the cable shield to XLR Pin 1 - but make sure to prevent the cable shield from contacting ANY portion of the 1/4" TS connector!

Rock and roll!
(edited 03/13/14)

[theguitarman83]

Thanks, but....it didn't work..... If I take my cable, and connect it to the DI output on the back of the one shot, before and after I rewired it, It worked. But when I hook it up to the output on the one shot it is very very thin and quite still. No matter what cable I use. Not so sure the cable is the issue.

[Randyman...]

Odd - I guess the module could still have an issue - but again the fact that Tim had it on the bench and shipped it back to you - it would seem to be something with how it is connected in your particular setup. I could not imagine Tim shipping your unit back without checking it first.

So on the modified cable, exactly how did you wire it?

[theguitarman83]

I moded it just like #5 on the link. I tried the original 1/4" TRS jack, and then tried with a 1/4" TS jack, same results. I will try to get a hold of a different interface from a friend and try the preamp on that. We will see what Tim says. I haven't heard back from him yet.

[Randyman...]

Bump for a curiosity update

[Randyman...]

Still curious for a status update...