[Pars]

Supposedly the packaged bridges have diodes that are matched. I doubt that they are matched that closely, however. I would probably use some 11DQ10 or 31DQ10 Schottkys (reduced switching noise). Or get some UF400x diodes (but the Schottkys are better IHMO).

 

[DolbyR]

Well, more questions

I was just making some research about making the OPAs to sound better and I was advised to add some bypassing caps. From + and - pins of the opamps to ground rail and one more from the + to the - pins. I'd like some feedback on this, should I get a significant improvement with this? As far as Tangents article says, the best would be some ceramic caps at around 1uF?

 

[balou]

Well, if you want fast/bipolar/otherwise cranky opamps in your amp, it may not even work without decoupling caps. You should go lower than 1uF - the main purpose of them is to filter out high frequency noise, high capacitance isn't the main purpose of them.

do you plan to use a real dual supply? Considering virtual ground circuits, majkel gave me some very good advice: you shouldn't bypass to GND there, because it's just a virtual ground, and you would unnecessarily pollute it with noise. Bypass from V- to V+ instead.

Bypass caps surely won't hurt in your circuit, and it's good engineering practice to add them. Some datasheets suggest that you use three bypass caps per power rail: 0.01, 0.1 and 1-10uF, for filtering out very high frequency noise, high frequency noise and to lower the power supply impedance respectively. But generally you should be fine by just using a 0.1uF from each power rail to ground (with a dual supply) or from rail to rail (virtual ground)

 

[DolbyR]

AFAIK this is a real dual supply http://www.raymondaudio.nl/projects/...7/psuschem.pdf. Correct me if I'm wrong

I'll be using OPA2134.

 

[balou]

Yes, it's a true dual supply. I'd suggest that you check out some alternatives to the OPA2134 - it got decent distortion specs, but it's soundstage is very limited. I would call it a solid general purpose opamp, but not really an audiophile component.

 

[fortney]

Note that on-line engineering sites recommend that the lead between the op amp V pins and the body of the capacitor be as short as you can make it if the bypass cap is to be effective.

F

 

[AudioCats]

So 2x 2134 sound better than 2x OPA551?

Just wondering why the 2134 is used, since even with the "op-amp buffer" the circuit has less output capability than the 551......

 

[balou]

yeah, the circuit isn't really high-end. the designer even confuses voltage swing with output current at the bottom of the page, and he says of himself that he's not really an audiophile. Looks like he built it mainly because his senns weren't getting enough voltage

 

[heatmizer]

Man that thing really looks like an a47. a47 used to be a popular amp
http://www.head-fi.org/forums/showthread.php?t=31941

 

[fortney]

Re original posting about current draw:

I prototyped a buffered amp from the data sheet of OPA 2227 using 2 of the above op amps and then substituted a 2132 for the buffer stage-which made the unit sound better-and my power supply indicated that both of these variations at idle drew about 30 ma @12 volts using the CMoy virtual ground supply and 1000uF electrolytics.

The buffered amp definitely presented more energy to the headphones (K81 DJ). I did not listen long, but could imagine listening would become fatiguing (for me.)

F

 

[DolbyR]

Well, I have it built now, but it keeps on blowing fuses.
The setup is as in the link before, i made the amp in veroboard but using the finnish guy's layout, the fuse is as in this drawing http://www.halmetaudio.cjb.net/projects/untitled.JPG

i'm wondering from where should i start searching the problem. I think the transformer is connected as it should.

 

[heatmizer]

Is that a drawing of the transformer?

 

[bearmann]

Greetings,
perhaps I'm wrong, but as far as I know not every type of transformer is usable for a dual supply, 'cause it needs two real separate secondary voltages.

Perhaps your fuse is too low? (you should find the needed fuse at the transformer or in the datasheet)

best regards,
bearmann

 

[heatmizer]

It's normal to make a dual supply with a center tapped transformer

 

[DolbyR]

yepp, thats from the datasheet of the transformer, it is with dual 12v secondaries so its for fual use. Apart from that, the datrasheet is not of much use though. I supposed 0.8A would be high enough, as the transformer is 2x 12v/0.25A, wouldn't that be something around 0.5A total current draw?

Here's the datasheet anyway, http://home.comet.bg/datasheets/kasc.../063930_00.pdf