CINEMAG 15B TRANSFORMERS balanced>unbalanced

[Hotze]

Dear all,

maybe one of you guys can help me with installing these trannies between a
balanced source and on OTL amplifier with SE (unbalanced inputs)
( the output impedance is only 50 Ohms and the voltage is 4.5V and giving me the gain I need for the OTL amplifier which has a low sensivity...)

I am aware there are already some old posts on diyaudio.

On Cinemag website they publish an adobe reader doc.: http://cinemag.biz/line_input/PDF/CMLI-15-15B.pdf

The thing is can I only add the + and the - connection to the primary side and
on the secondary only the + connector and ground and can I immy
connect the output to a 100 kOhm volume control without the use of the 15k
resistor which is normally used between the phase and ground on the unbalanced side?

Many thanks in advance.

Hotze
The Netherlands

 

[kevinkr]

How about a quick drawing of what you are trying to do?

 

[ruffrecords]

This transformer performs best with a secondary load of 15K. Using a higher value may result in resonant peaks.

Cheers

Ian

 

[Hotze]

Hello Ian,

Thanks for your help. I know by now how to connect these transformers.
Thing is that I so will have the volume control direct after the secondary side and I was being advised just try without the 15k load. I am yet busy on the installation of these transformers and see how this will affect the sound as by every volume change the load changes..... With regular transistor amplifiers the volume pot comes very rarely in the first stage of amplifier so using the 15k resistor will be ok but in most tube amplifiers the volume control comes in the first stage after the input connector...
Awaiting your comments,

Hotze

 

[ruffrecords]

Hello Ian,

Thanks for your help. I know by now how to connect these transformers.
Thing is that I so will have the volume control direct after the secondary side and I was being advised just try without the 15k load. I am yet busy on the installation of these transformers and see how this will affect the sound as by every volume change the load changes..... With regular transistor amplifiers the volume pot comes very rarely in the first stage of amplifier so using the 15k resistor will be ok but in most tube amplifiers the volume control comes in the first stage after the input connector...
Awaiting your comments,

Hotze

A lot depends on exactly what the volume control is connected to. If it is connected to the grid of a tube then the load it presents to the transformer will not change with the position of the pot. Just select the pot and the load resistor so their parallel resistance is close to 15K.

Cheers

Ian

 

[dirkwright]

In their "typical application" schematic in the data sheet, they show a 10k resistor across the secondary. I don't know if they considered the input impedance of the + input of the opamp, but it appears that it will work OK with a 10k pot if the wiper is directly connected to the grid of a vacuum tube.

 

[Hotze]

Thanks for your contributions, so far I am very happy with the results,
have installed the Cinemags and using the hot and cold connection from
the XLR output, (+ & -) without using the ground, and on the secondary
only the hot and ground direct to the 100k pot without (yet) the load resistor as I simply don't have it 🙁 at the moment, anyway now I have the gain I wanted
and my OTL project sounds better than ever and also the fact I am using the
balanced outputs of the HRT HD USB DAC now showing its best with a much
more balanced sound🙂
I am also yet working by the way on a Transformer Volume Control with super
transformers and giving me +9dB gain extra so let's see how that will work
out...
I will try the load resistor ( 10 or 15K) next week, see if that will affect the sound..

Hotze

 

[dirkwright]

Sowter makes a transformer volume control. I assume there are others out there.

 

[kevinkr]

Dave Slagle makes a nice auto-transformer based volume control as well: intact audio