[was ist los?]

All you have to do is follow the schematic in the PPA, add a .1uf cap and a 10k-100k ohm resistor in the feedback loop.

 

[iWeasel410]

In both danlaix's and tangent's schematic the opamp is represented by a triangle, how do I know what connects to what pin on the opamp? How do I interpret the triangle in the schematic? thanks (sorry for the n00bness)

 

[groggory]

Quote:

Originally posted by iWeasel410 In both danlaix's and tangent's schematic the opamp is represented by a triangle, how do I know what connects to what pin on the opamp? How do I interpret the triangle in the schematic? thanks (sorry for the n00bness)

Here's an example for one opamp

OPA2132 Product Info (easily found by a google search and the ever important tech sheet.

Most of the opamps we deal with around here have the same pinouts, but its always safer to check before you misdraw a PCB, or at the very least waste some solder, time, and breadboard.

If the "triangle" is unlabeled, it is generally safe to say that (referring to my diagram above) that:
pin1:inverting input ("-")
pin2:non-inverting input ("+")
pin3

ositive supply
pin4

utput
pin5:negative supply

Most schematics will give you at least a hint so you can figure out which is which, but if not it seems to me that the non-inverting pin is on top.

Hope that's helpful to you

 

[Porksoda]

k I have a question about designing amps in general, though I ask here because it applies to the schematic on the previous page.

Why does the amp have TWO feedback loops, one inside the follower and one outside? I am quite familiar with idealized op-amp circuits (digital and analog amps, filters, with no followers or biasing, etc) but I don't understand what the function of the two loops is.

Also, why do you need R7?

If someone could explain this in both technical and audio quality terms it would be greatly appreciated.

 

[danlaix]

All right guys. Got the problem fixed.
The bass boost is working now.
Now doing some fine tuning on the amp.
Thanks to all who helped.

Cheers!!

 

[guzzler]

Quote:

Originally posted by Porksoda Why does the amp have TWO feedback loops, one inside the follower and one outside? I am quite familiar with idealized op-amp circuits (digital and analog amps, filters, with no followers or biasing, etc) but I don't understand what the function of the two loops is. Also, why do you need R7?

all opamps on their datasheet have a graph usually labelled GBP (gain-bandwidth product), basically stating that as the gain increases, the bandwidth of the amp decreases. The AD8610 is a 16MHz piece, so if we only operated this at gain of 5, the bandwidth would be just over 3MHz. This is far more than needed for audio, and can lead to oscillation and instability due to RF interference. The inner loop has a very high gain, about 300 but doesn't greatly affect the overall gain of the amplifer which is set by the outer loop. Also, this topology (the Walt Jung Multiloop, do a search) helps to balance the input impedance to the opamp, although this is more of an issue with bi-polar input chips.

R7 prevents ringing, ie, when the opamp swings sharply, it can overshoot, then overcorrect until the output is right. This resistor reduces this

g

 

[iWeasel410]

What did you do? I'm thinking about adding switchable bass boost to my cmoy. Was it a resistor problem? Did you just use the resistors in your schematic?

one more question: is this the equivalent of just using a bass-boost equilizer on your portable device or is it better?

if I try to put bass boost on my cmoy with a 2132 opamp do I need to add 2 sets of R7/C7 (one for each channel)? Is it the lower value of R7 the higher value of bassboost?

thanks

 

[iWeasel410]

After looking at the schematic for the PPA bass boost and the cmoy layout, I'd be adding the R7/C7/Switch parallel layout between R4 and the jumper that goes down to the output right? thanks for the help!

 

[iWeasel410]

Does that sound about right? I think I may go and buy some 0.1uF caps and pimp my cmoy

 

[PeterR]

Yes, that's right. You might want to consider getting several different values for the cap and resistor to try out and tweak the boost to your liking...