XFormer for DCX 2496 output ONLY

[WithTarragon]

I have been looking at the very long threads on mods for DCX 2496. There has been some very impressive work!

My interest is restricted to bypassing the op-amps & electrolytics at the output (after the DAC) only. Rather than upgrading the op-amps and using fancy caps, I am simply interested in using a transformer after the DAC.

In my case, each transformer should be in the $5-15 range (perhaps an edcor) and could be chosen to provide the the low pass filtering also (the anti-aliasing). I assume this could provide much of the benefit (I would be using a digital in & would not be using the unit's ADC).

Unless I am ignoring something, this could be an affordable alternative that others might like to try also.

Thanks in advance,
-Tom

 

[dublin78]

That is what these guys do I think.

http://www.audiosmile.co.uk/dcx2496.htm

 

[WithTarragon]

Thanks, I had a quick look.

I assume the resistor & capacitor was used to form the low pass (anti-alias filter). I have no idea about the specs on the transformer. This is the critical component to "get right" since these can be rather pricey and a cheap one can introduce all sorts of distortion.
-Tom

 

[DougL]

Here are some links I found to keep you Busy

http://www.audioasylum.com/forums/KandK/messages/6223.html

http://home.pacifier.com/~gpimm/behringer.htm
Talks about input and output transformers

http://www.dcx2496.fr/en/why.php

http://www.dcx2496.fr/en/tweakanalog8.php
Has header pin-outs of the analog section

http://beggingdogrecords.tripod.com/DAC.html
Look at the output transformer section of the schematic.

I think in one of the hobby mags there is an rs232 board documented. This is required if you wish to remove the input as well.

Doug

 

[WithTarragon]

Thanks for the links. Wow, transformers are expensive.

BTW, In my eventual configuration the analog output (DCX) will be going to a 4 channel volume control then to the amps.

The Z on the pot (conventionally wired) will be 12kOhm. If there is a transformer in the circuit, won't the output impedance of the source (DCX) change? I am trying to keep the input Z of the load (potentiometer) to be about 10x the output Z of the source (DCX).

Thanks ,
-Tom

 

[DougL]

transformers are expensive

The best ones are not inexpensive.

If there is a transformer in the circuit, won't the output impedance of the source (DCX) change?

If you use a 1:1 transformer, the output Z is unchanged.
I haven't looked up the data sheet for the DAC chip, but in one of the sites I read last night, they claimed the DAC had an output Z o5 50 ohms.
If you change the transformer to a 1:4 step-up, output Z would be 800 ohms. or 16 * 50

I was looking at these Edcor transformers:
Edcor PC 600 / 600
or Edcor TTPC103

If I do this, I will post the results.

Doug

 

[kepa1]

Hello there, guess what I bought 6 Edcor trannies for my DCX. Their products are inexpensive and have a good reputation so I thought I might give a try but I have been too lazy / afraid to do this mod so far...
You might have a look at this thread on the Edcor forum

 

[WithTarragon]

Thanks.
I had seen that thread, but I was confused on a couple of items.
1. Which transformer was the preferred one?
2. Does it fit in the DCX chassis?
3. What is the propsed wiring. For instance, is any reistor or cap going to be used?

Thanks and good luck on your project,
-Tom

 

[kepa1]

Well, I chose PC 600/600 for the mids and highs and PCW 600/600 for the lows, as they are supposed to go lower. The two models are small (the PCs, very small) and you'll have no problem putting them inside the DCX, provided you remove the stock output card. For the input I plan to follow the mod described here.

I'd say no caps or resistors are needed but someone might enlighten my basic knowledge. And if there is still DC at the transformers output, the input cap of my amps will kill it. This is easily measurable but distortion is another issue.

Good luck too!

 

[Michel_MRS]

So kepa1,

did you try the Edcor Xformers with the DCX?
I'm also interested in this solution.

Mic

 

[kepa1]

Well you know the story, little time and other things to do so the Xformers are collecting dust... but i should do it sometimes soon.

 

[WithTarragon]

So kepa1,

did you try the Edcor Xformers with the DCX?
I'm also interested in this solution.

Mic

Well, Michael I can't change the physics of time, but I am also interested in your progress on this.
Please let us know the specifics of the wiring (are going into a unbalanced output, and are you using a capacitor etc)?
Good luck with the project,
-Tom

 

[Michel_MRS]

I plan to put the Xformers in a separate box:
- inside the DCX, just bypass the active output, linking directly from the output of the dacs to the XLR plugs (some wires have to be cut).
- inside the Xformer box: XLR in, 6 Xformers, XLR and RCA out. (At this time I will use asym outputs, but balanced may be useful for future use).

I found some interesting informations on: http://www.dcx2496.fr/en/index_en.php

I have little electronics knowledge, my understanding is that:
- coupling cap is not needed, as it is used to cancel dc, and this is done by xformers.
- LP filter, as described in the link above, is 6db with 48kHz or 72kHz fc. so depending on the frequency response of the Xformer, this filter may be omited or not. (Perhaps with a high quality Lundahl, this filter has to be added)

EDCOR models seem to be interesting, but it's difficult to figure which model to choose from their website, and also frequency response curve is needed.

Other option is to use a TVC (Xformer Volume control) as preamp, in this case it would replace my Xformer box, and one could plug dcx-> TVC -> Power amps. This particular TVC has to be 6 ways and balanced input, but should not be difficult to diy.

M.

 

[WithTarragon]

M, I am interested in how this works out.

The Edcor's are certainly affordable, but I am also confused about which exact model and whether filtering will be required. In my case, the output will ultimately be an unbalanced connection into a passive pre-amp (10Kohm pot).

Good luck with your project.
-Tom

 

[saucybmw540i]

Status report !!! ???

I was totally pumped to find this thread. $8/transformer is doable for this diyer.

 

[Michel_MRS]

Acording to AKM specs, dac impedance should be 600R per phase so Xformer should be 1200R balanced (ie 1200 with ct).
http://www.diyaudio.com/forums/showthread/t-15943-p-6.html

So my understanding is that no standard Edcor fits (they are 600R with ct). And a lot of posts may be eroneous refering to 600R ct instead of 600+600 or 1200R ct
Am I right ?

Mic

 

[DougL]

So my understanding is that no standard Edcor fits (they are 600R with ct). And a lot of posts may be erroneous referring to 600R ct instead of 600+600 or 1200R ct

Transformers have a ratio. 1:1 or 1:2, etc. They are designed to be driven by a minimum impedance, IE 10K or 600R.

A 600R:600R CT Edcor would be appropriate for this application.
For that Matter, the 10K:10K would work for our application.

Doug

 

[saucybmw540i]

Nice.

Does Edcor not post frequency response specs for their products?

 

[Michel_MRS]

Here are the frequency response I got from Edcor for PC600/600 and for WSM10K/10K.

They said that they don't have it for the WSM600/600 but it would be the same drawing than the WSM10k/10k.

I still don't understand why in 1:1 we should use 600ct/600 instead of 1200ct/1200 with these akm dacs.
Is 600ct/600 the optimal value ?
Or is 1200ct/1200 optimal but 600ct/600 also fits with no audible difference?

Mic

 

[DougL]

I still don't understand why in 1:1 we should use 600ct/600 instead of 1200ct/1200 with these akm dacs.

Someone can probably explain it better, but a "600R:600R" transformer is more of a marketing name than a specification.
My take on it is that the transformer was designed to be driven by source Z less than 600R, and designed to "drive" loads of 600R or higher. The AKM DAC has a 50R output Z, and most of our amps are 10K or higher. So a 600R:600R meets our requirements, and a 1200R:1200R design would be indistinguishable for our purposes.
The reason that the 600R transformers are so common is that professional equipment uses them for long runs to minimize noise pickup in long runs. Again, my take on the DCX2496 output stage with the op-amp board was an inexpensive substitute for a 600R:600R transformer.

Hope this helps,

Doug