[Nerull]

I'm currently building a DAC, and need a nice I/V converter and differential to single output. The sequence is this *of my DAC*:
CS8416 -> PCM1794 -> ???? (I/V converter) -> differential to single outputs *or visa versa*

I thought about op-amps, but saw this:
K&K Audio
Which is too expensive for me right now, so I'm looking for a nice supplement to it.
So basically what I'm looking for is a transformer that'll cover the differential to single outputs and possibly the I/V conversion *right now, I'm thinking a nice resistor for the I/V conversion right after the transformer*.
Like here:
Passive Output Transformer
So I need the transformer to fit that criteria *if I wasn't specific enough.*

PS: I'm also looking for a good clock so any input on that would also be appreciated!

Thanks,
~Tom

 

[rickcr42]

When talking about line level audio transformers cheap and good really don't belong in the same sentence and this is one time you really do get what you pay for.
options ?

Lundahl,Sowter,S&B,Jensen,Cinemag,Paeng,and if there is one contender for "inexpensive" it would be Edcor U.S.A.

The links section has the web addresses to the above companies.

A good "free" clock would be the Kwak Klock : search here :

http://www.diyaudio.com/forums/)

and for a kit type the Tent Clock :

http://www.diyhifisupply.com/diyhs_Tentlabs.htm

 

[Nerull]

So is it worth it to spend that much money on the line audio transformer over using an opamp *or CFB amp*? Just curious, you know, because if it's a significant improvement, I'll be willing to fork out the money.

 

[rickcr42]

I personally always use a transformer at some point after the DAc chip but this can be at several locations :

1-in combination with a resistor as the IV stage.all gain is by this combination so you need to scope the IV resistor voltage output for best response then use a transformer to make up the rest of the gain (usually 20:1)

2-the above resistor IV with a gain stage following for the rest of the gain then on to a 1:1 transormer for coupling to the next stage

3-acive IV,active gain,1:1 transformer coupling

The common here is the transformer which i personally find to be an essential part of digital audio and that means ALL digital audio.DAC,Computer,CDP,DVD,everything !
the reason is the digital ground noise that can and does leak through from the digital grounds and into the analog grounds.The fact that it is there barely noticed but once gone there is no doubt it was there but not identified for what it is.

Aa couple of examples are the one you referenced above,this one from K &K Audio (U.S. Lundahl dealer) which uses passive IV to active buffering for a low impedance to the final gain transformer stage :

http://www.kandkaudio.com/images/idacoutputstage.pdf

and for a triode version this :

http://www.wavelengthaudio.com/Cosine-det.html

To not use the trafos is usually due to cost in a commercial product.Not always but a good amouint of the time and that simply because unless you charge a LOT it is hard to make up the added product cost.With two seemingly identical (in specs) DACs side by side under consideration for purchase most go with the cheaper even though the more expensive one having a coupling transformer will usually be a better all around design,just not on paper.This added cost is no small thing when the "raw" transformewrs alone cost close to or more than $100 for a stereo pair.that is not installing them plus the additonal hardware but just the transformer in the box as sent to the end user (manufacturer).You can see how this cost must be passed on to the customer.


Of course,this is just personal opinion though the few who i managed to weasle into going the transformer route ended up liking the end results far more than they originally thought possible.For example :

http://www6.head-fi.org/forums/showthread.php?t=134816

good luck man whatever path you take

Rick

 

[rickcr42]

http://www.royaldevice.com/autocostruzione.htm

 

[Dougigs]

I agree very much with Rick that a transformer output is a very good way to go for I/V conversion.

The approach I use is to attach the output of my DAC chip (It's a PCM63) directly to a 1:20 transformer with nothing in between. The secondary of the transformer has a 50K resistor across it; this loads the transformer properly so that it produces a very strong audio-level voltage on the output.

I use the Lundahl LL1636 transformer, on the recommendation of Andrea Ciuffoli in Rome -- they are beautiful units, and cost about $50 each (i.e. cheaper than the tube output stage I'd previously used).

http://www.audiodesignguide.com/cdplayer/dac3.html

EDIT (after noticing you've already cited the Lundahl LL1674): 1) Jensen probably offers transformers with similar ratios at slightly lower cost... but you don't use a transformer output if you're

The resistor I/V approach is not *supposed* to work with the PCM1794, according to its datasheet. Yet there are plenty of designers who do this. BUT you're going to need a gain stage if you use this approach. If I were you, I'd stick wth a conventional op-amp output stage until you've got enough money to buy some transformers. Hell, you might decide you like the op amp approach and stick with it.

Aside from providing transparent I/V conversion, powerful drive and a great impedance match to just about anything, these transformers also are flat (+-1db) from 10Hz to 25kHz... *but* they roll off the really high frequencies -- therefore if you're using 8X oversampling, you don't need any kind of filter circuit; the transformer does the filtering for you (so you're not heating up your amp with RF signals).

 

[Garbz]

Hmmm a transformer on the output of my DAC. Now there's something that sounds good no pun intended. I didn't even think of that but my output transformers in my balanced line driver will become useless when my balanced dac is finished. I may just find another use for them