[JamesL]

Quote:

Originally Posted by tangent /img/forum/go_quote.gif I'd test the opamps in another known-working circuit. Maybe build my op-amp tester. That will only tell you if the chips are still plausibly op-amps; valuable, but it doesn't rule out all forms of damage.

sweet deal. I wonder if I can scrap pieces from the old board for your little circuit.

For r1-r4, do the absolute values matter much, as opposed to the relative values?
(eg. can I use 4.32k & 3.32k at r1/r2 for a x0.56 divider, and do a similar thing at r3/r4 long as it provides appropriate gain.. or is that stupid)

 

[tangent]

I cover all that in the docs.

 

[Spacehead]

I have DC offset on my source. I need to add input capacitors. I have two 2.2 uF Wimas. Any suggestions where to put them?

I have not yet received 2N5088 and 2N5087. I wonder how long Futurlec shipments take to arrive here.
I have been thinking if I absolutely cannot wait to start building, how bad it would be to use BC337 and BC327 or 2SC1815 and 2SA1015 (except japanese transistor won't fit at all?)

 

[tangent]

Quote:

Originally Posted by Spacehead /img/forum/go_quote.gif Any suggestions where to put them?

See the PIMETA v2 schematic. Essentially, the cap and R1 go in series using the existing two R1 pads on the PPA.

Quote:

how bad it would be to use BC337 and BC327

Probably not a big difference. I don't know that it's been tried, though.

 

[Spacehead]

I have now matched pretty closely most of the transistors.
2N5486 by 1 mA from 12 to -15 mA
J310 40 mA , 25 mA , 30 mA
2N5087 of 5 hFe
2N5088 of 5 hFe
output transistor don't need matching and I cannot do that because I have only 6
still need to check BF246
I have all the resistors, there is some carbon resistors, most of them are metal. I have socket strips , sockets, most of the misc parts,
polyester capacitors and Panasonic FM and FC for power supply

I have OPA1611 op amps too, I wonder If Should balance the inputs right away so that I could use all op amps.

What I am missing is A PROPER SOLDERING STATION!

I ordered a very cheap electronically power controlled soldering station, VTSS4 and some solder wick.
I bought a 2 euro soldering iron and tried to do some proper joints with that:

I think I am ready to start soldering the resistors tomorrow, it should be easy if my head is clear.

I will use strips on gain resistors, input resistor (1M), gain to ground resistor maybe, so I can balance the input bias currents.
This is pretty easy to comprehend, but many many things must be taken care of for successful build.

 

[Spacehead]

Quote:

Originally Posted by tangent /img/forum/go_quote.gif See the PIMETA v2 schematic. Essentially, the cap and R1 go in series using the existing two R1 pads on the PPA.

there is only R1 L , G , R
on my PPA v.2.0E version

I can of course solder the cap into input rca jacks. I'll start now adding socket strips.
Are the + and - inputs now balanced? 1M down and 470K + 1K + 10K on input -

 

[FallenAngel]

Quote:

Originally Posted by Spacehead /img/forum/go_quote.gif there is only R1 L , G , R on my PPA v.2.0E version I can of course solder the cap into input rca jacks. I'll start now adding socket strips. Are the + and - inputs now balanced? 1M down and 470K + 1K + 10K on input -

You shouldn't need to solder the caps on the RCAs. If they are small, you can make them "stand", have R1L/R1R "stand" as well and solder them together at the top. This way you can actually use considerably smaller caps.

With an R2 of 470K (should be approximately 10x higher than POT and I'm assuming you're using a 50K pot), you can use a 0.1uF capacitor.

There are no balanced inputs on the PPAv2 overall, though opamps have both + and - inputs. This does not change.

 

[Spacehead]

Quote:

Originally Posted by FallenAngel /img/forum/go_quote.gif You shouldn't need to solder the caps on the RCAs. If they are small, you can make them "stand", have R1L/R1R "stand" as well and solder them together at the top. This way you can actually use considerably smaller caps. With an R2 of 470K (should be approximately 10x higher than POT and I'm assuming you're using a 50K pot), you can use a 0.1uF capacitor. There are no balanced inputs on the PPAv2 overall, though opamps have both + and - inputs. This does not change.

I maybe understand what you mean.

And about + - inputs, I have read the article about Working with cranky op amps and section Balancing the Input Bias Currents
Working with Cranky Op-Amps

Both inputs should equal if I would like to use bipolar op amps like OPA1611 which is very good op amp. With 470K R2 I would need very large feedback loop resistors to make it "balanced" / equal.

How this would work on this multiloop setup? I am now building this amp and first I have been adding buffers resistors because they don't need tweaking, or could changing output resistors make a difference?

I noticed that if I solder a part down to the PCB, it will be very hard to desolder it. It sticks very hard to PCB.

PCB is GREAT quality! It is pleasure to handle it anyways!


Edit: I read the part selection guide:
"R1

The main purpose of R1 is to help balance the op-amp’s input impedances. You want it to be equal to R3 + R5.

R1 interacts with R2 to form a voltage divider. If R1 is much smaller than R2, this effect is negligible, which is the way you’ll almost certainly want it. I imagine someone might choose to configure this to divide the voltage down by a significant amount on purpose, but that’s not the intent of this layout.

Optional? Technically yes, you can jumper it, but you should put a resistor here."

So input impedances are balanced with default resistor values?

 

[FallenAngel]

Oh no, R2 is just a resistor to ground in case the pot tracking lifts, it's not a problem.

Overall, PPAv2 wasn't designed to work with bipolar opamps and I'm not sure if anybody has ever set it up to.

R1's value isn't really critical, but it's good to keep it = R3+R5. 1K-4K is what I see being quite common.

 

[Spacehead]

Do I need to jumper empty place near R1G Or does the ground channel op amp get its signal from TLEG?

 

[FallenAngel]

Do not jumper the empty position beside R1G, leave it empty.

 

[Spacehead]

I have added most of the resistors, click for larger pics




I use cheap soldering iron with power control pot

When testing this amplifier, I won't use volume pot, so my + and - op amp inputs are more closely equal, maybe OPA1611 will work, maybe not, but it doesn't matter, I have AD8597 x 2 , ADA4898-1 x 2 , ADA4627-1 x 2, OPA552 x 4 so I can get started.

I will add next buffer transistors

I match them in one channel at a time.

 

[Spacehead]

I added buffer small BJTs
Next JFETS

click for larger image




I will use 2N5486 15 mA for Q2 and 2N5486 12 mA for Q1

J310 30 mA Idss for Q4

Could I use higher Idss Q4 for higher bias point?

 

[Spacehead]

I didn't yet add Class A biasing parts as suggested.

I used 50 mA IDss J310 for Q4 , same pinout as PN4392

Q3 is rail isolation jfets, I used 2N5486 matched to 14 mA Idss

I bought 2SA1011/2SC2344 transistors 2.8€ per pair, very expensive

I installed them correctly, they are base collector emitter

Next I'll add buffer CCS trimmer and capacitors, then I can try the amplifier. Parts are closely matched, so it should sound pretty good. I will clean the flux before and check things with multimeter (feedback loop, voltages) visual inspection for solder bridges, I am pretty sure there ain't one because I always correct my mistakes right away.

Pics (click for larger image)

 

[Spacehead]

I am ready to fire up the PPA v2:

Click for larger images:








Voltages are right in every op amp

-11.9V

and 12V

referenced to input ground

I am going to put op amps in sockets after I have added input RCAs with input caps and output 6.3mm neutrik jack
I won't use volume pot yet, I have only cheap crap that would ruin the sound.