View Full Version : adding a pluse transformer to the digital input

2007-08-13, 03:20
looking at a lot of high end kit the digital interface often has a pulse transformer...more modest kit does not..

So I've built a small male female rca adapter that carries the pulse transformer. The effect of placing this in the digital output, for me, is cleaner sound. That not all but the effects are hard to describe but in my opinion worth the 10 to build the unit.

you need a long barreled rca plug ...the type that the barrel locks onto the ground collar of the socket. A bulkhead mount socket the type that has a thread. Discard the barrel of the rca plug and the earth tab and nut from the socket. Solder a wire from each of the plugs center pin and the sockets center pin. Then solder a wire from the ground of the socket ..this can be tricky. Then another wire from the ground of the rca plug. Thread the socket into the cable end of the plug and insulate the socket from the body of the rca plug. I use tape or heat shrink whatevers to hand. The 1:1 pulse transformers I use have four pins and an orientation blob. Orientate so that the signal from the center pins enter from the same side and the grounds connect on the other. Making certain that you have the input side separate from the output side . Tidy up the wires and manover the cube of the transformer to the flat side of the rca plug body ...cover in 25mm dia heatshrink ..but keep the ends clear.

fit the plug into the dac end and the digital ic into the socket ....

hopefully it will work as well for you as it does for me.

2007-08-13, 13:05
If you go through the trouble of adding a transformer, then change the connection to a balanced one at the same time.

2007-08-13, 23:54
yes ....you could

but I didn't want to mess with my expensive dac!

2007-08-14, 01:06
Hi Zanash,

What transformer did you use?

There was a thread started by GaryB which talked about putting one inside the SB3 and removing a couple of inductors.


He reported an improvement overall. At the time he thought his analogue mods (by-pass caps etc) sounded better, but I'm sure i've read since he now prefers the modded digital into I think a CityPulse DAC.

Like the idea of being able to try it without opening the SB3. I have analogue mods (from GaryB thread) but am thinking about getting an external DAC so may give this a go.

2007-08-14, 04:57
Thats a very good question ....

I got mine from RSWWW.com ...the 1:1 ecapsulated version oep 1200 rings a bell .

2007-08-15, 02:50
the 1:1 ecapsulated version oep 1200 rings a bell .

That isn't a pulse transformer but a telephone line transformer. Bandwidth to about 4000Hz.

I used a MCL T1-1T from Mini-Circuits.

2007-08-16, 23:51
you right its not the one I used either ....but remember you dealing with a digital signal not an analouge one sop the importance is not freq ...the aim is to get a a clean waveform

2007-08-17, 10:26
but remember you dealing with a digital signal not an analouge one sop the importance is not freq ...the aim is to get a a clean waveform

Wrong. Any electrical signal is an analog signal when it is travelling through a conductor (in fact it is an electromagnetic wave). It isn't a 1 or a 0 it is a continously changing voltage in time. The act of deciding if what it digitally represents is done at the receiver.

You will never get a clean waveform if your transformer doesn't pass a good portion of the bandwidth of your signal.

2007-08-20, 21:22
The Newava S22083 is good for galvanic isolation of SPDIF signals between DAC and transport. My ezdac utilizes this transformer.

2007-08-20, 23:44
I agree ....

but for the purposes of this discussion the signal must be considered to be digital.

the pulse transformer will remove enough hash to allow the reciever chip to have an easier time decoding the digital [square wave] signal.

The test is easy just hook it up to an osciloscope and view the results.

2007-08-22, 11:34
Every good DAC I have had there is a pulse or interface transformer after the digital connector (SPDIF or BNC). I also installed the SC947-02 in the SB3 (Tx) and my SB3 sounds much much better than a stock and other digital modded SB3 (basically they swapped a better quality caps and bypassed some input regulated circuit.

2007-08-22, 14:55
How much are they?
The SC947-02 that is.

2007-08-22, 23:08
none are cheap ....the oep4 I use was about 6 ....

2007-08-23, 12:15
How much are they?
The SC947-02 that is.

Where are you located?
Outside USA it costs $16.00 with lead free (the only choice you can get)
In CONUS it costs $10.00 non-lead free. You can purchase it at www.scientificonversion.com or www.mauimods.com

I also suggest you should get a Newava S22083 1:1 pulse transformer. It sounds more musical and smooth details in my system (I just modified it to my SB2) if you prefer this kind of sound.

2008-01-23, 18:16
I just finished remodified my SB2 with Newava S22083 1:1 pulse transformer by connection serially 300R to 0.2mF to pin3 of primary site and 120R across pin1 and pin2 on the secondary site. Pin2 and pin4 to ground. Pin1 to center pin of RCA or BNC connector. Pin3-->0.2mF-->300R-->C1(found parallel to the chip).

The sound is astonishing, very neutral (I coould not hear any analytical mixing sound), smooth mid and high, tighter and deep bass. Here is a link to AC forum: