[newtoamps]

I've just finished building my first amplifier (PIMETA). Unfortunatley, it doesn't work as it should. When the amp is turned on with no input signal, a lot of noise is heard in the left channel and a little noise in the right channel. Also the right channel buffer is heating up considerably when the amp is turned on with no input signal. The left channel buffer is OK (not hot at all). I replaced the right channel buffer only to find that the new one is still extremely hot to the touch when the amp is on with no input signal. When I plug in my cd player into the amp, all the above symptoms apply, amplified sound is coming from the right channel, and no sound is coming from the left channel (only noise is heard). Buffers were not stacked and there is no bias into class A.

Can anyone help me?

Note: My amp was never on for more than 40 sec. I was afraid something might go wrong with the overheating right buffer.

 

[tangent]

http://tangentsoft.net/audio/trouble.html

 

[newtoamps]

I tried all of that. I ohmed out the L and R outputs to IG and both were about 10K ohms. The current draw is 35mA. Is that good? bad? The DC offset is about 2.8-2.9 Volts for both channels. Is that good or bad?

 

[The Monkey]

Quote:

Originally Posted by newtoamps I tried all of that. I ohmed out the L and R outputs to IG and both were about 10K ohms. The current draw is 35mA. Is that good? bad? The DC offset is about 2.8-2.9 Volts for both channels. Is that good or bad?

If you can, post some pics and we can give you some better assistance.

 

[rsabo]

Quote:

Originally Posted by newtoamps The DC offset is about 2.8-2.9 Volts for both channels. Is that good or bad?

2.8 volts of DC offset? bad. very bad.

 

[Clutz]

Quote:

Originally Posted by newtoamps I tried all of that. I ohmed out the L and R outputs to IG and both were about 10K ohms. The current draw is 35mA. Is that good? bad? The DC offset is about 2.8-2.9 Volts for both channels. Is that good or bad?

Something is seriously wrong. Don't connect anything up to it that you value.

 

[The Monkey]

What's the power supply?

 

[MASantos]

What amps are you using? IF you are using the AD8610/8620, which adaptors are you using? I ask this because I soldered a AD8620 to a browndog adaptor I got from tangent, which was the wrong adaptor and this cause the amp to malfunction, giving me around 10 volts of dc ofset and sending my crappy test phones to headphones heaven. Some pictures of the board with several closeups may be helpful!

GOod luck!

Manuel

 

[newtoamps]

Quote:

Originally Posted by The Monkey What's the power supply?

The power supply is a 9 volt battery. A regular alkaline.normal renge.

How do you get the DC offset to be at

Here are some pic's of the amp. Note the right buffer. Note the replaced right buffer. Since I couldn't remove the adapter off the board, I ripped off the previous right buffer and creativley soldered the new right buffer as shown in the pictures.

Here's the link to the pictures of amp:

pimeta.blogspot.com

 

[n_maher]

I'm not going to sugar coat it, that's some of the weirdest stuff I've ever seen

. What the heck is going on with the right channel buffer? Did you check things like the power supply voltage at the opamps/buffers before turning it on the first time?

 

[Teerawit]

Quote:

Originally Posted by n_maher What the heck is going on with the right channel buffer?

I was wondering about that too....why not just solder it to the SOIC pads on the underside of the board?

 

[tangent]

Quote:

Originally Posted by newtoamps I ohmed out the L and R outputs to IG

In general, testing for ohms through paths that should be blocked by solid state components isn't very helpful.

Quote:

The current draw is 35mA. Is that good? bad?

You must not have read the entire troubleshooting guide. Down near the bottom, it tells you how to find out if it's good or bad. I don't have the information I need in order to answer this question, while you do.

Quote:

Here's the link to the pictures of amp:

Gee, you wonder why the right channel is acting up, with that lash-up?

The two posts above are right: solder those buffers to the SO-8 pads. They were placed there for a reason. Even if all your connections are correct, at minimum you've made the feedback loop and such longer with all those wires, allowing for more chance of oscillation and RF pickup.

 

[newtoamps]

Quote:

Originally Posted by Teerawit I was wondering about that too....why not just solder it to the SOIC pads on the underside of the board?

I don't know how to de-solder the buffer. The buffer that I soldered there before, I just ripped out with pliers. Then I just soldered the new buffer onto the old buffer's adapter (which I soldered last month onto it's adapter). I checked the connections on the buffer with an ohm meter. I'll try to de-solder the buffer, but I don't think I'll have any luck. I might just buy a de-soldering iron from radioshack and return it after I de-solder everything. Can I just connect the buffer like the left-channel buffer is? or would it be better if it's on the bottom of the board?

Quote:

Originally Posted by Tangent Gee, you wonder why the right channel is acting up, with that lash-up?

See the buffer that's on the adapter in the right challel? That is exactly like my left buffer was. Because it was overheating, I HAD TO REPLACE THE BUFFER WITHOUT DE-SOLDERING IT. The buffer that you see in the picture was the result.

Quote:

Originally Posted by n_maher Did you check things like the power supply voltage at the opamps/buffers before turning it on the first time?

No. I am completley new to this. I just followed Tangent's step-by-step guide and turned it on.

 

[The Monkey]

Quote:

Originally Posted by newtoamps I don't know how to de-solder the buffer. The buffer that I soldered there before, I just ripped out with pliers. Then I just soldered the new buffer onto the old buffer's adapter (which I soldered last month onto it's adapter). I checked the connections on the buffer with an ohm meter. I'll try to de-solder the buffer, but I don't think I'll have any luck. I might just buy a de-soldering iron from radioshack and return it after I de-solder everything. Can I just connect the buffer like the left-channel buffer is? or would it be better if it's on the bottom of the board?

I think you need to take a deep breath here. Maybe take the night off and tackle it tomorrow. First, for desoldering, you should get a desoldering pump and desoldering braid and plan to keep them. Over time, I think you'll find that desoldering braid is one of the most useful tools around. But, more importantly, take some time and print out Tangent's articles. I recommend printing out everything on his site (even from the other amps pages) and just reading them. And just let it soak in.

You're going to make this amp work, it's just going to take some time.

All that said, I think you should be able to set up the right before the same as the left, but someone else more knowledgeable than I should confirm.

 

[Teerawit]

Quote:

Originally Posted by newtoamps I don't know how to de-solder the buffer. The buffer that I soldered there before, I just ripped out with pliers.

You'd rather destroy a $6 buffer than buy $3 desoldering braid?

Quote:

I might just buy a de-soldering iron from radioshack and return it after I de-solder everything.

That's not very ethical. Besides, it would be very obvious that the desoldering iron was used.

Quote:

Can I just connect the buffer like the left-channel buffer is? or would it be better if it's on the bottom of the board?

It's fine the way it is, but it doesn't make much sense to me to install the SO-8 buffers on a Browndog and then solder that Browndog onto the Pimeta board, when you could have just soldered the SO-8 buffer onto the SO-8 pads in the first place....or at the very least you could have soldered DIP-8 sockets onto the Pimeta board so you could've rolled buffers.