[joneeboi]

What would be the bit opposite the BC337 and BC327? I'm guessing it's another BC337 and BC327, respectively, but I just want to make sure.

 

[Pars]

Yes, 337 on the top and 327 bottom.

 

[joneeboi]

Since I have some 2N5087 and 2N5088 lying around, I'm thinking of building of with those instead of the BC327 and BC337. Anything I should know before I fry my dad's PIMETA?

 

[Pars]

check the pinout...

 

[joneeboi]

I just built it with the 2N5087 and 2N5088. I didn't have exact resistors though, but I think they were close; 6.5R and 3.32K. The first one I made didn't drop in, so I built a second to make sure. The layout is the same, with compensation for the reverse pinout of the 2N5087 relative the BC327 and the 2N5088 the BC337. It's not playing anything, so maybe you guys can help me out a bit. Is there some kind of balancing act I need to perform with the hfe to get things to work?

edit: If it helps, checking the offset on the discrete buffered channel shows that the DC level grows in magnitude, where the output is negative relative the input ground.

 

[heatmizer]

Pictures please. Where is it plugged into the socket?

 

[Pars]

Do you have V+ and V- on the right pins (7 and 4 in the socket)? Does it measure OK?

 

[joneeboi]

Quote:

Originally Posted by heatmizer /img/forum/go_quote.gif Pictures please. Where is it plugged into the socket?

Yes, I plugged them into the wrong socket positions. Always check the datasheet. u_u Oh well, now I'm enjoying the PIMETA without making a $30 order to Digikey that wouldn't happen because of the stock issue. Huzzah!

 

[FallenAngel]

Hey guys,

I'm building one of these buffers with a 2N5486 + 1K Trimpot CCS and was wandering how do I set the current flow through the CCS? I want 3mA through it. What voltage through the resistor am I looking for for it to be so?

 

[TzeYang]

you cant calculate it this way.

Think of the idss spread like the hfe spread in bipolar transistors. They vary alot. So the thing is to measure the current flow and tune it with the trimpot. Normally it's very hard to do so, which is why we alternatively, tune the bias using the trimpots of each half of the circuit respectively. (you must get equal bias for each of the output transistors).

 

[Spacehead]

Quote:

Originally Posted by FallenAngel /img/forum/go_quote.gif Hey guys, I'm thinking of building another Pimeta with some discrete buffers and wanted to double check the schematics and layouts by you guys. I don't have an input resistor like heatmizer showed at the beginning, I can probably add one if it's necessary so the opamp doesn't drive the buffer directly. Class-A This Class-A buffer would run 22mA of current as per the formula. Output current = CCS * (Input resistors / Output resistors).

Your Class-A buffer seems to be working. I used 1K constant current resistors, or even smaller, I should check it out and do another. I only have one yet. I used 2SK117 JFETs so I had to improvise a little. Thanks!!

 

[FallenAngel]

Nice, glad you got it working. I never managed to complete this one unfortunately.

 

[Spacehead]

Quote:

Originally Posted by FallenAngel /img/forum/go_quote.gif Nice, glad you got it working. I never managed to complete this one unfortunately.

I used 300 ohm resistors instead of 1K trimpot, 75 ohm resistors input, 2SK117, and 2.8 ohm emitter resistors on BD139 and BD140.

But now I hear distortions, like it would be running out of current. Class AB Buffer works flawlessly in the same spot. I buffer left and right channels on a cmoy core.

What resistor value would you suggest changing? I could try if I need 200 ohm resistor in between buffer and op amp. Now I have only bare wire. Buffers are not warm so I guess they are not oscillating, though distortion means there is a problem.

protoboard fun

 

[Spacehead]

I tried 620 ohm resistors instead of 1K trimpot which I don't have, then I tried 200 ohm,

then instead of 75 ohm I tried 29 ohm, I also tried 2.9 ohm emitter resistors

But NO GO! I just cannot get that distortion free.

I have 2SK117 JFET which is rated for 6 mA IDSS , that should be enough for biasing...

I don't understand how I could make that circuit working like it should. Now it gives bad distortions into bass.

I got mad to that and abandonded it, I put single ended BJT BD139 instead with 82 ohm emitter resistor (91 mA bias). Now I have bass but somehow boring sound and too easy.

 

[hiker101]

That buffer is meant to be wrapped in a global feedback loop- that's why it's suggested as an option for the PiMeta. It's not clear how your circuit is set up in that regard.

It's also not clear what you're doing about the ground, maybe that's the part of the circuit that's current starved. You said you had another class AB buffer working in the same circuit- was it a discrete buffer, or something else?