Jensen JT-115K-E Mic input transformer

[mabell313]

I am looking for a 10:1 transformer for a MXL V67g U87 conversion. Right now I have a Shure 12:1 transformer in there now. Needless to say, the sound is not optimal. I came across the Jensen JT-1115K-E with its 1:10 ratio. Would this transformer be suitable wired backwards for a 10:1 ratio? Does anyone have experience with these transformers in this application?

 

[Blue Jinn]

No experience. I have not, but many have used the Cinemag 2480 transformers.  I have done this conversion to the MXL 2001 (removing the two transistors and increasing the ratio of the output transformer.) I am pretty sure it is the same circuit. I used a no name 11:1sh transformer I had on hand. 

I used (Marik's???) "U87 Front End Mod" as a guide.

 

[Govinda Doyle]

Hey there,
The jenson 115k is a great sounding mic input transformer suitable for a preamp not a mic, I don't know if you can reverse it for a mic but it's design purpose is on the front end of a preamp!
Hope this helps
G

 

[MatthisD]

No reason not to use it as 10:1, as long as 2.4K winding resistance is not a problem and wide frequency response is not a negative factor. I have a JT-DB-E which I have used as DI, mic output and currently as a mic input transformer.

 

[emrr]

I have used a Jensen mic input backwards as tube mic output. 

 

[mabell313]

Thank you for the replies. I noticed the 2.4k resistance right off the bat hence my question. I was a little apprehensive so, I went ahead and purchased a Cinemag CM-2480. It ended up being cheaper too! I have not recieved the trans let though. It should only be a few more days though. ;D  I also used the "U87 front end mod" as a guide along with various tidbits of knowledge from this and other forums. As of now, the V67 has only stock parts in it. Yes, the emitter follower circuit has been removed as well as said Shure transformer(12:1 ratio). Everything else is stock. I just ordered the parts today from Mouser to switch out the stock components. One question I do have is in regards to the HF attenuation circuit. I see 220p in the stock V67 circuit but, anything for 220p to 820p in various Neumann schematics. I am going to go with the 220p I think. What about the .01 cap in the V67? Neumann schematics once again have anything from .01 to .047! Is there any benefit to increasing the value of either of these caps?

I read somewhere to use the fat rubber bands from brocolli for body damping so, I tried it. I didn't notice much improvement but, there seems to be a little less ugliness and glare in the midrange. I could be hearing things though. More like wishful thinking! It seems every time you do a mod, it MUST sound better. The only problem is that is not always the case! I can hear money flushing down the toilet now.........

 

[bruce0]

I have used beyer 1:10 mic input transformers backwards in a royermod mic.  Works very well.

 

[mabell313]

I have used beyer 1:10 mic input transformers backwards in a royermod mic.  Works very well.

How does the Beyer trans sound? What about overload? I've been thinking of buying a 7:1 for an upcoming tube mic project and was wondering about the response.

 

[bruce0]

I think it sounds fine.

I had a 4:1 stepdown in there, and the mic was much too hot (and still sounded pretting good).

With the beyer, it is fine.

I do testing to look for what levels begin to distort (assuming saturation) and as a step up the levels are close to the 300 mv speced by Beyer for 30Hz (beyer has nice spec documenation including recommendations for zobel betworks which is nice.).

Running backwards and putting out "mic level" signals, it never gets near that level, so I think it is a good use of it, and it has screening CAN built in.  Mic is never going to put out anywhere near 300mv probably.  They are also small, and fit nicely into a mic, I have mounted them various ways.  In this posthttp://www.groupdiy.com/index.php?topic=43792.msg546670#msg546670 you can see one (but the trafo is an backwards altec mic trafo (1:4) later I replaced it with the Beyer 1:10 backwards.  But you can see where it fits.

I use them as mic input too, with pretty good results, though easier to overload.

I use them all over the place because I bought a bunch of RTS-1400 battery operated inline preamps for $10 each on ebay.  I pulled 16 of them apart, each one contained a 1:10 beyer (one had a JE-115!) and each also had a nice output transformer by Frost... a clone of the JT-123-SLPC.  I have used a bunch of those too.

 

[mabell313]

What really drew me towards the Beyer trans was the size. You can fit those things damn near anywhere! What my question should have been was how does the Beyer, which is a high quality trans, compare tonewise to other transformers i.e. Cinemag, Jensen, Sowter, Lundahl. Is it clear and hi fi? Warm and rich midrange? I am stoked to get a few of those transformers now! Lots of 7:1 and 10:1 Beyers floating around for cheap.

 

[bruce0]

What really drew me towards the Beyer trans was the size. You can fit those things damn near anywhere! What my question should have been was how does the Beyer, which is a high quality trans, compare tonewise to other transformers i.e. Cinemag, Jensen, Sowter, Lundahl. Is it clear and hi fi? Warm and rich midrange? I am stoked to get a few of those transformers now! Lots of 7:1 and 10:1 Beyers floating around for cheap.

Talking about sound is like singing about tax policy...(sorry it is early ... there is a better quote)...

I can tell you that I did several Royer mods, but two LDC Royer mod mics... one with the jensen direct box 12-1 step down (for get the number Jt-db-e or something) which is advised in the article...  and one with the beyer.

Everyone that uses the beyer one loves it (a good sax player, and a great double bass player have both said it gives them better sound than they have ever gotten before).

I think it has a texture somehow.... and even though both mic's use the same capsule and a similar circuit, I think that there are individual capsule to capsule differences that make for the difference.

(In the one folks like, I shortened the mic to tube lead by having them co-reside in the basket, so it glows....  maybe they are just woo'd by the sight of it!). 

In any case I can't tell you why but it is a beloved mic.  I have some AKG C414-TLII's and this Royer beyer mic has a much less pronounced top end (those mics push the "air" range pretty hard) and is very rich sounding.

I thought it was the capsule just happened to be a good one... or the fact that I cleaned out the head basket ... maybe it is the trafo...or all three.

I used a little 1:10 Beyer with 1 primary and one secondary and no center tap.  I have specs for it from the 1974 beyer list.  It is a 7 pin mount version of the trafo, and I have made an eagle part for it.  However in the mic I just carefully solder to the pins.

I have also used them for a Hi-Z input ( I protoboarded one of silent arts/classic API's Hi-Z modules with one as a step down, it works.).

Anyway if you want one, I have several left PM me and I will shift one.  I just bought a couple of similar beyers on ebay, so if you want I will shift you one or more of these at the same price. If you are interested, let me know I will send pictures, model numbers etc.  Each one also has a date stamp.

By the way the jensen direct box trafo is a very small trafo that fits well in those metal trafo cases MXL cases down near the XLR  (in the existing shield cans)...

I don't know about the U87 mod is that a tube mod?


b

 

[dmp]

I agree with Bruce0
I've used Beyer 10:1 peanut transformers in royer mod mics and the mics sound great.
Since I have  pair, I've been meaning to sub in a cm2480 to compare.

 

[mabell313]

Unfortunately, the U87 mod is not a tube mod. It converts a MXL V67g/2001 to a circuit that more closely resembles a Neumann U87 circuit. I would love to hear the difference between the Beyer and Cinemag transformers. I knew the Beyer trans high quality but, I had no idea what they sounded like. Sometimes "high quality" or "hi fi" parts can wind up sounding clinical in a musical format. BruceO, thank you for the offer! Once again I must say, this forum is great. The folks over here are much more reasonable than at other forums which I will not mention. Thank you guys! Much excellent information.