Cinemag Trafo Repurp

[sr1200]

I recently put together another Royer Tube Mod from an MXL 2001.  Ordered the Jensen db/e trafo, then heard nothing back from them for a matter of weeks.  In the interim, i found something close (the  CM-9766 from cinemag).  The Jensen actually wound up showing up at my door about 2 days before the cinemag.  Since my other Mod mic had the jensen, i decided to make a pair of the same instead of going w/ different parts.

I hate returning stuff, since im a packrat and usually find a re-purpose for things. But Im at a loss for this one.  Can anyone think of a project I could use this for?

I have a C-12 kit on order with Chunger, but ordered the AMI transformer with the kit (probably more suited anyway). 

If anyone saw my embarassment with the Rode NTK, would be kinda cool to make a circuit with a trafo to replace those guts...

If anyone has been looking to buy one of these, let me know before you get one from CM, I dont mind taking a bit of a hit on it.
specs - CM-9766 - 21.6K:150 (12:1) +28dBu Condenser mic output transformer for moderately high plate resistance tube circuits.  Faraday shielding.  CM-9766.pdf

 

[mabell313]

I always though that a 12:1 ratio was a little high for the Royer mod. With that said, you could use it for a passive DI or a reamp box. I just built a passive DI/reamp box out of an old Shure transformer which is 12:1. It sounds pretty damn good too. It is very clean and crisp. It reveals detail of the instrument(bass) like no other PASSIVE DI I have ever used. I would just keep the transformer but, I am a bit of a parts horder too. ;D

 

[sr1200]

Oh if you only knew.... I inherited about 20,000 parts and components (and some hardware) from one of Harmons old technicians.  After they laid everyone off, he had to move out of state and didn't want to bring any of that stuff with him (giant bit bins, 40+ drawers in each)  But that doesnt sound like a half bad idea.  Do you happen to have a schematic for that DI/RA box?

 

[mabell313]

No schematic needed! It is just the Shure transformer connected to the jacks. Very simple indeed. The Hi-Z side(1/4") has the hot connected to the + on the primary side. The - on the primary is connected to ground as is the 1/4" jack's ground(sleeve in the tip-ring-sleeve way of saying). The secondary(Low-Z) has the +(inverting) side connected to pin 2 of the XLR and the -(non-inverting) connected to pin 3 of the XLR. Pin 1 is connected to ground but a ground lift switch could be used. The Hi-Z 1/4" input also has a 1/4" thru jack. I hope this helps!

 

[sr1200]

Thanks! 
I did some googling around and came up with this:
http://www.muzique.com/lab/patent1.htm
which is the jensen re-amp circuit.

Yours sounds a bit easier; though a different purpose.

 

[mabell313]

That is exactly what I was after, easy. It can be connected in either direction, DI or re amp. I plan on making a dedicated reamp box with some of the features of the Jensen.

 

[HellfireStudios]

This probably isn't the place to talk about reamp boxes, but I just ordered a couple of DIY reamp PCB/transformer bundles from DIY Recording Equipment. Are the Jensen features (impedance and level mainly) applicable to my transformer selection, or do the values of any parts need to change? If so, what parts/values? Thanks.

Speaking of transformer re-purposing, I used the stock Alctron tube mic transformer in a box with jacks similar to yours, but mine is used to boost the volume on a telephone speaker-turned-mic and my transformerless SM-57. Kind of like a passive Cloudlifter. I wonder what it would do for my ribbon mics?

-James-

 

[mabell313]

This probably isn't the place to talk about reamp boxes, but I just ordered a couple of DIY reamp PCB/transformer bundles from DIY Recording Equipment. Are the Jensen features (impedance and level mainly) applicable to my transformer selection, or do the values of any parts need to change? If so, what parts/values? Thanks.

Speaking of transformer re-purposing, I used the stock Alctron tube mic transformer in a box with jacks similar to yours, but mine is used to boost the volume on a telephone speaker-turned-mic and my transformerless SM-57. Kind of like a passive Cloudlifter. I wonder what it would do for my ribbon mics?

-James-

Indeed, this is the wrong place to discuss reampers! The the question was about trans repurposing though and reamper/DI came up. Sorry if I pissed anyone off. Truely sorry, I am.

The values on the Jensen schematic should remain the same given a transformer with a similar(read:same!) ratio is used. Mine is 12:1 like the Jensen. I am using Shure transformers out of a Shure mixing board(I think!) and they work just the same as the Jensen. I love the idea of the outboard mic transformer for the SM57. I have a SM57 knock-off and was thinking of yanking the trans. Have you removed the resonator disc in front of the capsule? It is pretty easy and it does clean up some of the weird, harsh peakiness that it has(hey, it's a knock-off, what can I say!). I don't know if the results will be quite as drastic with the Shure but, it will change the sound for the better.

Speaking of transformer repurposing, I have used the Shure transformers I have in several projects. A passive DI/reamper, active DI(in the works actually), and in a MXL V67 to U87 mod. In the mic the 12:1 ratio was a little high. It killed too much volume for my liking. It didn't sound bad but, too quiet! I have a 10:1 Cinemag in there now and it sounds f%*#@^ great! I plan on making a dedicated reamper similar to the Jensen schematic out of one of the transformers.

I have an old Dukane transformer(the octal, plug-in type) that is 1:15. Any ideas with this one? It's a little high for a DI(original idea).

 

[HellfireStudios]

I have not messed with the resonator disc. I was able to tame the high-mid peak with an impedance matching resistor in the "Taming the Shure" article. I've got no complaints with its present configuration, but I may try that idea on some cheaper dynamics. Thanks.

-James-

 

[sr1200]

not at all  ;D ;D discuss! that's the spirit of this forum.  The jensen transformer for the reamp is NOT the same specs though (the DB-E is 12:1) the transformer used in the example i gave was
Model #JT-11P-1
Price $
Impedance Ratio 10k:10k
Turns Ratio 1:1.00
Max 20Hz Input +20dBu
THD 20Hz 0.025%
THD 1kHz <0.001%
20Hz/20kHz-0.04dB/-0.05dB
re:1kHz -3dB BW  100kHz

 

[sr1200]

the Cinemag i have is almost the same specs as the DB-E (what i meant to say)

 

[HellfireStudios]

I noticed last night that the Jensen was 1:1 and the Edcor is step-down not isolation (so not 1:1). I would love an Impedance control like the Jensen, but I'm not sure how to implement it within the Line2Amp kit. Any thoughts? Thanks.

-James-

 

[mabell313]

Let me check out the schematic for the line2amp and I will report back.

 

[mabell313]

The "level" control should go between 5 & 7 and the "impedance" control should connect to lug 2 of the "level" control. The values on the other hand will have to reflect the impedance(ratio) of the transformer. Looking at another Jensen schematic with the DB-E(12:1), I notice it uses the same values for the "value" and "impedance" pots.

 

[HellfireStudios]

Thanks.

That is weird. So Jensen just puts 20k ohms (max pot value) in series with the output with no variation of value dependent on transformer ratio? Like I said... weird. I've got a 25k ohm pot floating around here somewhere...

-James-

 

[sr1200]

Uses the same values in a bunch of places.  (pad, imp, level etc)  This is an interesting one huh?

 

[HellfireStudios]

Interesting... or lazy on Jensen's end. Does anyone who has built the Jensen re-ampers know if everything works as advertised or does it need tweaking? Thanks again.

-James-

 

[mabell313]

I found another schematic that is similar to the Jensen but, with different values for level and impedance. 1k and 50k respectively. It also has a different ratio transformer, 8:1. I hope this helps.

I have not messed with the resonator disc. I was able to tame the high-mid peak with an impedance matching resistor in the "Taming the Shure" article. I've got no complaints with its present configuration, but I may try that idea on some cheaper dynamics. Thanks.

-James-

I have read that article too and I am going to make several impedance "gizmos" out of barrel connectors. Did you use the 698 ohm resistor as suggested in the article?

 

[HellfireStudios]

I actually used the formula at the end of the article to obtain as an exact match as is possible for my gear (1.2k ohm mic pre input impedance). I, also, took a 6PDT rotary switch from Radio Shack to wire in multiple, selectable impedances sort of like the GT ViPRE (obviously this is put in an enclosure for shielding). Just don't switch impedances with phantom power from the mic pre turned on. A standalone 48volt phantom supply could be placed before the switch to as a workaround to this problem (luckily my Carvin CM-87S came with one).

I think you'l like the results, but remember it's more about voice coil damping, so the real benefit is to the mic's transient response moreso than its frequency response (although the nasty high-mid peak is attenuated).

-James-

 

[mabell313]

I actually used the formula at the end of the article to obtain as an exact match as is possible for my gear (1.2k ohm mic pre input impedance). I, also, took a 6PDT rotary switch from Radio Shack to wire in multiple, selectable impedances sort of like the GT ViPRE (obviously this is put in an enclosure for shielding). Just don't switch impedances with phantom power from the mic pre turned on. A standalone 48volt phantom supply could be placed before the switch to as a workaround to this problem (luckily my Carvin CM-87S came with one).

I think you'l like the results, but remember it's more about voice coil damping, so the real benefit is to the mic's transient response moreso than its frequency response (although the nasty high-mid peak is attenuated).

-James-

Sounds great! I was thinking of something along those lines namely a trimmer pot mounted inside the barrel jack. That would give some flexibility like your 6 pos. switch. Having it mounted in a separate box is a great idea. I may have to try that actually.

LIke I said before, I am dealing with a SM57 knock-off. Any help it can get would be great. It is not a Unidyne III. More like it's drunk hillbilly jailbird half-cousin! The attenuated high-mid peak sounds like it totally changed the character of the mic. That may make my mic actually useable. I shouldn't complain, sounds pretty good after removing the resonator disc. That too removes some of the high-mid peak. I generally use it on guitar cabs(read:farggin' loud!) and snare although I am starting to really like the e609. That thing sounds great on guitar cabs. It handles the volume like a champ. That is why I have been thinking about removing the transformer, to give it a little more dynamic range. It clips too fast on loud sources.  In the original article it had made mention of an output reduction.  Did you notice a large loss in volume level? Should I use the resistor with the transformerless mic? Sorry if I am rambling. It is most likely due to a massive hangover. Thank you for understanding. More like misunderstanding!