[ChrioN]

I've built a Grado RA-1 amp, with the help of the schematic here: http://www.geocities.com/rubin_jpk/r...RADO_schem.gif

The problem is, as stated in the title, distortion. Atleast when I plug in a JRC4556 in the ic-socket. When I swap to the OPA2134, everything sounds very nice and clean. The distortion from the JRC-chip isn't mindbending, but its defenently there, you can hear it easely. I've tried several JRC4556-chips, and the result is the same. The original RA-1 uses JRC4556 chips too, so whats the problem? Is there many kinds of 4556-chips?

Mine says:

4556AD
JRC
9127H

I've tried 3 different gains: 5 and 7.5 and 14. Same result. Distortion. Any ideas?

 

[ChrioN]

I've noticed one thing. When I check the voltage between pin 4 and 8, when the amp is up and running, I only get 2.7 volt. And thats with one 9 volt battery. Is that right?

 

[dip16amp]

Two 9 volt batteries are required and there should be 18 volts between pins 4 and 8.

 

[ChrioN]

Did that too, the voltage didn't go up. The batteries are pretty new. Hmm...

Batt1: 7.93v
Batt2: 7.57v

A wierd thing was that, one second after I unplugged the batteries and measured them, they were down to 5 volts or so, but climbing. Like a reversed capacitor. Are they "bad"?

 

[ChrioN]

I changed battery and now it sounds very good. Wierd. But the opamp gets hot as heck! You get burned if you touch it. Should it be like that? Even the battery gets very hot.

 

[dip16amp]

No, it should not get hot. One battery provides positive voltage to the chip and the other battery provides negative voltage. Ground is connected between the batteries. Connecting only one battery should not be done. Try measuring the voltage between pins 4 and 8 with the chip removed. It should equal the sum of both batteries.

 

[jcx]

check dc offset, 100K source/feedback resistance seems a little large to me for an old bipolar input amp, also the feedback is scaled to have the same impedance which is good for reducing offset but since the value is so high you may have problems with high frequency oscilation too

what does your high frequency layout look like, good bypassing at the op amp pins?

for a bipolar input op amp I would start by dividing all resistors by 10x, and a few pF across the feedback resistor may be needed too - possibly a small cap across the feedback R would stop a high frequency oscillation even with the high value resistors

 

[ChrioN]

Then the chip isnt attached the voltage is the sum of the 2 batteries. When I connect the chip, 1.2 volts or so between the pins :/ The chip didn't get burning hot when I didn't connect any music to it either, which must mean something. What I don't know though.

 

[dip16amp]

Something is loading it down. Check that the resistors are in K ohms and that there are no short circuits.