[Sennator]

Hi group,
many DACs (like CS4398, AKM, Sony..) have balanced voltage output. To check how much music really comes out there I connected my balanced HD650 DIRECTLY to the DAC for a moment: guess what...? No noise or any digital artefacts - music almost at full listening level with some SACDs

. Of course sound lacks power and punch. But anyway, the question came up to me - how much amplification is really needed? How easy can "fully balanced" be?
-NO I/V converter needed for DACs with voltage output.
-NO OP needed to make the signal unbalanced
-Built in output stages in CD- or SACD-players could be bypassed.
-4 identical mono amps with two stages for each "leg" and a volume control - that's all?

Now I am looking for an easy discrete Solid State circuit. Any ideas?

Cheers,
sennator

 

[nikongod]

szeekers mosfet

a balanced variant of the "sol" amp.

 

[dsavitsk]

Try variation 1 here

http://headwize.com/ubb/showpage.php?fnum=3&tid=7032

You can leave out the transformer and the 12K resistor if your source is balanced.

 

[Sennator]

Thank you alot for this advice! It's even easier than I expected. Great! Using Mosfets was my intention, too. So, "matching Mosfets" will be a new aspect of the hobby...

DC-offset will be an issue since the DAC has 20mV in the CD mode. Zero in SACD mode.

The implementation of volume control is a big help. Finding a Pot with 4 identical channels is almost impossible.

I will check Variation 1 with cheap components and then report!

Regards,
sennator

 

[dsavitsk]

Keep in mind that this is as yet untested. i have the parts to put one together, but have not gotten to it yet.

As for offset, as there is no amplification, the offset will not increase. Moreover, if you attenuate the signal, it will be attenuated as well. You might get some noise on the pot, so cap coupling might not be the worst idea.

 

[BrianDonegan]

If you can access it, you can also use the digital volume inside you DAC (if present)

 

[amb]

Quote:

Originally Posted by dsavitsk /img/forum/go_quote.gif Try variation 1 here http://headwize.com/ubb/showpage.php?fnum=3&tid=7032 You can leave out the transformer and the 12K resistor if your source is balanced.

As PRR noted in the headwize thread, there is a problem with that circuit because the MOSFETs have no proper bias. You need more than just the audio signal itself to bias them...

 

[dsavitsk]

Ah, right, I see what you are saying. Should be sufficient to just connect the bottom of the source resistors to a negative supply?

 

[Sennator]

I built a "balanced Szekeres" following dsavitsk's corrected "Variation 1" yesterday. Yes, the bottom of the source resistors have to be connected to the negative rail. Actually it is a clone of rjm's "Szekeres VE" without the virtual ground-channel and fed with inverted/non-inverted signal instead of L+/R+. I took two IRF510 (available at local dealer).

Good news: It works in the balanced mode

- no noise, hum, anomalies etc. Sound is also very good - though I can't make a final review right now because only the left channel is ready and the right one was driven with my old amp. And best of all: the volume control as suggested in "Variation 1" works aswell. To discuss further details, i suggest to to switch to the headwize thread:

http://headwize.com/ubb/showpage.php?fnum=3&tid=7032

sennator