[joneeboi]

Here is the situation:

I normally run my PIMETA on a single NiMH 9V which outputs 7.2V. I tried tomb's trickle charger with a 19V supply, but when I plugged in my headphones (Zune buds for testing) I get a loud pop when they plug in and then when I listen there is no bass. When I switch to my KSC75s, there is again no bass to be found. Thinking it was only a problem with the wall plug, I returned to my normal setup of the 9V. Trying to up the ante to dual 9V, I once again found the same thin and non-existent bass.

Any ideas what is going wrong? I have in the board an OPA2132PA, AD823AN, 3 BUF634s, 4 Panasonic FM 220uF rated at 25V, 0.1uF generic box caps at C4, and Alps RK09. What other part values are relevant here? Does this mean I have to implement the PPA bass boost?

 

[tomb]

Quote:

Originally Posted by joneeboi /img/forum/go_quote.gif Here is the situation: I normally run my PIMETA on a single NiMH 9V which outputs 7.2V. I tried tomb's trickle charger with a 19V supply, but when I plugged in my headphones (Zune buds for testing) I get a loud pop when they plug in and then when I listen there is no bass. When I switch to my KSC75s, there is again no bass to be found. Thinking it was only a problem with the wall plug, I returned to my normal setup of the 9V. Trying to up the ante to dual 9V, I once again found the same thin and non-existent bass. Any ideas what is going wrong? I have in the board an OPA2132PA, AD823AN, 3 BUF634s, 4 Panasonic FM 220uF rated at 25V, 0.1uF generic box caps at C4, and Alps RK09. What other part values are relevant here? Does this mean I have to implement the PPA bass boost?

As I was reminded only recently, check to make sure your output jack is isolated from the case/board ground. If not, it will short your ground opamp or drive it into oscillation - resulting in a lack of bass.

That's assuming you've checked the obvious things about having jacks/pot wired incorrectly. That can cause offset and a lack of bass, too.

Start measuring your output channels referenced to the output ground, while you're troubleshooting this. If you've got offset, at least you won't be exposing your headphones to that potentially damaging pop in the meantime.

 

[mminutel]

Is the amp oscillating or getting hot? Check the voltages at all of the chips and make sure they are the correct values. Make sure you have no solder bridges and make sure nothing is grounded that isn't supposed to be.

 

[joneeboi]

I checked the output wires and I'm getting 1.5V for both channels relative the ground channel. It's in a plastic case, the Serpac H-65, so I don't think I need isolation.

While I'm checking the pins for my opamps, do I just measure V- and V+ or are there other things I need to check?

Also, which pictures would help?

edit: That 1.5V is OG - OL and OG - OR

 

[MisterX]

Measure the offset of all three channels relative to in ground.
Measure V- and V+ relative to in ground as well.
I would also suggest that you measure the current draw.

 

[joneeboi]

Here are my readings with the red coloured lead to IG and the black traveling to the various hotspots and nothing plugged in:

A) IG - OG yields 1.98V
B) IG - OL yields 0.002V
C) IG - OR yields 0.000V
D) IG - V+ yields -3.76V
E) IG - V- yields 3.76V

Now with the Zune buds in and both the pot from my laptop out and the RK09 at full blast:

A) IG - OG yields 1.033V and dropping
B) IG - OL yields 0.005V
C) IG - OR yields 0.003V
D) IG - V+ yields -3.63V and slowly approaching 0V
E) IG - V- yields 3.63V and slowly approaching 0V

I tried measuring DCA but for some reason I got 0.000mA and 7.62V. I disconnected one lead of the battery and used the MM in series with the board but I still didn't get any current.

 

[threepointone]

so OL-OG/OR-OG = ~1-2V? you've got a prettyy big DC offset problem. unplug those 'phones now! don't plug headphones in an amp if the DC offset between OL-OG and OR-OG is more than maybe 50mV or so.

 

[MisterX]

Quote:

A) IG - OG yields 1.98V

This is a clear indication of a problem but your test methodology is flawed when the inputs are not terminated and as such your readings are also suspect.
Either way it looks like you have a problem with your ground channel.
(master of the obvious here)

Quote:

Now with the Zune buds in and both the pot from my laptop out and the RK09 at full blast:

With music playing or not?

Quote:

D) IG - V+ yields -3.63V and slowly approaching 0V E) IG - V- yields 3.63V and slowly approaching 0V

It is also a good idea to test with a new battery or some other type of known good power source (it appears your battery is dead or very close to it)

Quote:

I disconnected one lead of the battery and used the MM in series with the board but I still didn't get any current.

Did you blow the fuse in the DMM?
Err actually skip that one.
Does the amp power on when you have the dmm connected like that?


Quote:

unplug those 'phones now

I am not real sure but I think those might be disposable cans so.....

 

[joneeboi]

Quote:

Originally Posted by MisterX /img/forum/go_quote.gif With music playing or not?

Music is blasting a safe distance from my ears.





Quote:

Originally Posted by MisterX /img/forum/go_quote.gif It is also a good idea to test with a new battery or some other type of known good power source (it appears your battery is dead or very close to it)

I'm only using one battery here, so that would be the voltage split a la TLE2426. I'm thinking anyway.


Quote:

Originally Posted by MisterX /img/forum/go_quote.gif Did you blow the fuse in the DMM? Err actualy skip that one. Does the amp power on when you have the dmm connected like that?

No music comes out.

 

[achina]

Quote:

Originally Posted by joneeboi /img/forum/go_quote.gif I tried measuring DCA but for some reason I got 0.000mA and 7.62V. I disconnected one lead of the battery and used the MM in series with the board but I still didn't get any current.

Some meters have a different socket for measuring amps. Usually the red probe gets moved to another socket on the meter.

 

[mono]

Quote:

Originally Posted by joneeboi /img/forum/go_quote.gif Here is the situation: I normally run my PIMETA on a single NiMH 9V which outputs 7.2V. I tried tomb's trickle charger with a 19V supply, but when I plugged in my headphones (Zune buds for testing) I get a loud pop when they plug in and then when I listen there is no bass.

I hate to be picky but "no bass" isn't quite specific enough. If you had to randomly picky some value, what level of attenuation would you suggest at what frequency, I realize this is likely beyond perception or description but any further elaboration you have might help.

Are you using coupling caps between source and Pimeta? If so, was there DC offset from source? If not, short the coupling caps and see if bass improves. What value of caps were those (in other words. Pimeta specs 0.22uF but should we assume that and all resistor values are are spec'd unless stated othewise?).

Quote:

When I switch to my KSC75s, there is again no bass to be found. Thinking it was only a problem with the wall plug, I returned to my normal setup of the 9V. Trying to up the ante to dual 9V, I once again found the same thin and non-existent bass. Any ideas what is going wrong? I have in the board an OPA2132PA, AD823AN, 3 BUF634s, 4 Panasonic FM 220uF rated at 25V, 0.1uF generic box caps at C4, and Alps RK09. What other part values are relevant here? Does this mean I have to implement the PPA bass boost?

Are you sure these values are right? 4 x 220 uF is a bit low capacitance unless you had a very short path to low impedance PSU, generally most would consider at least 2 x 1000 or 4 x 470uF a minimum. Also, was it really 0.1uF (film?) box caps or was it 1uF or more? IIRC< Pimeta spec's at least 1uF or so up to 6.*uF box caps for decoupling. IF these two caps differences are as described, that could account for bass, particulary with higher impedance mult-cell battery. (Since a higher voltage battery, when small series cells, actually increases impedance).

There's also the other issue of whether your idea of enough bass is a flat response or a bass boost per se, but for the time being I ignore that.

 

[MisterX]

Quote:

Music is blasting a safe distance from my ears.

What exactly are you trying to measure with music playing?
The output voltage of the amplifier or the dc offset?
(you can't measure them both at the same time with the same meter)

Quote:

I'm only using one battery here

Yeah....your voltage measurements made that part pretty obvious.

The question is:
Why does the voltage drop from 3.63V to 0V?

Quote:

No music comes out.

If the amp does not power on you either have the meter connected wrong or it has a blown fuse.



Edit:
Quote:

have in the board an OPA2132PA, AD823AN

You do realize those are both dual channel op-amps right?

 

[tomb]

Quote:

Originally Posted by MisterX /img/forum/go_quote.gif ... snip ... Edit: Quote: have in the board an OPA2132PA, AD823AN You do realize those are both dual channel op-amps right?

That could explain a lot.

 

[joneeboi]

Quote:

Originally Posted by MisterX /img/forum/go_quote.gif You do realize those are both dual channel op-amps right?

u_u""

That's odd. I must have confused the AD843 and AD823 on Tangent's part list recommendations page. *sigh* And I was so excited to use it =T

You guys wouldn't happen to have any 843s lying around, would you? Or maybe a Brown-Dogged 8610. I just got in the market for either.

 

[FallenAngel]

For the OPA2132, I don't know if the AD843 is worthwhile, you can drop in an OPA132/OPA134/OPA227

Either case, drop me a PM with address and I'll send you a few opamps that you'll like in your Pimeta.