Tascam M-35 transformer replacement

[Deepdark]

Hi

Long story short, a friend of mine got some cards from a Tascam M-35 mixer. But, the guys who give them to him have taken out the input transformer from each cards. I did some research and found that the ratio is about 1:5. Probabl;y something like 150:4K or so, right? Or those mixer where 600ohm?? Anyway, since my friend have a restricted budget, And he already has to spent some $$ to make a decent power supply and some wood and other misc. to make a nice enclosure, he don't have a fortune to spent in transformer. I though about a CMMI-5C first, but budget don't allow such price for 8 cards. The only cheap option I think of is a Edcor but input Z is 600ohm, at 1:5 I'm about 15k at secondaries, probably not optmimal in term of noise performance. Other option, a opamp de-balancing circuit??

 

[PRR]

IIRC, 600:3K. (CMMI-3.5C 150-1.84K)

I don't see properly-shielded mic transformers on Edcor? Hum-catching is a much worse fault than a little hiss. Small studios can't just put AC gear far-away.  Anyway, UMM-4 wired 600:2.4K is probably a best-fit.

 

[Deepdark]

Thanks a bunch PRR. I think my friend will go with teh Cinemag CMMI-3.5C. I'm too much afraid of picking hum.  Next, I'll have to find a way to properly feed all the cards and groudn them all. I plan making an external psu, and probably use some screws terminals to feed all the board independently. I think daisy chaining is a big no-no, right?

 

[Deepdark]

Also, I guess this one would work, too: http://www.jensen-transformers.com/wp-content/uploads/2014/08/jt-11k8-apc.pdf

 

[Whoops]

if you are on a budget why not using OEP tranformers?

 

[Deepdark]

Hi. Finally, we went with jensen transformer jt-11k8. Now, the piwer supply. I found a nice board from silent art, negative, positive and fixed rail. Examing the board, we see we need +15 and -15v for the opamps and there is a +5v rail,which i didn't follow to trace where it goes yet. If i use a 15v dual secondary transformer to get my positive, negative and fix voltage, my guess is that i'll be ok since the +5v don't look to feed mush in the preamp card. Maybe PRR you know the use of that rail on the tascam? There is not much information on the manual. IIRC the enfire psu for the mixer required something like 80VA, but since i only have 8preamp cards to feed, no talkback or output cards, am i allright with 50 or 60VA? I don't know the total comsumption of the 5v rail, but maybe if i bolt the 7805 regulator on the case, it will be enought to dissipate the heat, in case the 5v rail would consume more thana few mA. You're thought?

 

[ln76d]

What's wrong with original power supply?
From what i remember it's very similar to M30 which i have.
Most of the preamp sound is tamura transformer.
Long time ago one of the members here had these transformers for sell.
But unfortunately i don't remember which...
I wanted to buy two trannies, but my priorities changed at the time and then i lost  all my correspondence.

 

[Deepdark]

My friend don't have the psu. In fact, he only have 8 preamp cards, and the previous owner removed the teansformers to sell them...

 

[ln76d]

Ahhh.. ok.

If you want Tamura trasnsformers you can write post on blackmarket, maybe this member will show up

 

[Deepdark]

one little clarification, there is a little typo latter on my post. The power requirement is not 80va, but 30W ac, so about 30VA for the entire mixer. So I just bought a 35VA toroidal and a Silent art's Positive-negative-fixed power supply and will manage the 5v within a 7805 regulator. Since the 5v requirement is only for the overload circuit, it's no big deal and not a big power eater.  ;D

 

[Deepdark]

quick one. I'm about to call everything to make a new power supply to feed 8 preamp board. Max power consumption is 30W ac. So i should be allright with a 30VA power transformer for the entire mixer. Since I only use the 8 preamp card, no master, no tape strip and no talkback, I guess I could be allright with a 25va power transformer, right? Other thing. I plan using a toroidal. There is no center tap, so I need to connect the secondary in serie and use this connection as my center tap. If I do this, I cut the maximum output current by half. 0.83A at 30VAC (but since I center taped the secondary, it's like 15-0-15, right?). I fear it's a little short. I don't have any schematics so I'm a little blind here.