Replacing resistors for higher output?

I was wondering if it would be possible to replace the resistors in and just outside the feedback loop portion of the output stage with different ones to increase the gain and thus output voltage of the analog output stage through the rear RCA jacks. I don't care what anybody says, the voltage from the jacks is just too low. If these particular resistors could be pointed out, it would be really helpful.

I wouldn't benefit much from it, because I only use digital outs to my much louder DAC, but maybe others would.

Stu

I would imagine that increasing the gain of the output stage would cause the outputs to clip earlier.

I'm sure the current values were chosen to prevent clipping at 0dB.

Rod.

Considering that the car outputs are 4 volts, I don't think so. Opamps are more than capable of handling increased gain and outputting voltage far beyond 4 volts. The 1 volt levels there now are pathetic. My other home gear reaches around 4 volts as measured by my multimeter. Obviously without knowing the actual circuit used, I can't be sure, but clipping is not likely an issue.

The DSP outputs .72 volts. Assuming the .72 and 1 volt values are P-P, the present gain in the circuit would be ~ 1.39. Which is almost unity gain. A more reasonable gain would be 5.56, yielding 4 volts through the RCA jacks. In fact, some opamps are not stable until reaching gains of 5 or more (ex. OPA637).

Stu

The opamps are 6dB gain fixed (see Burr Brown's datasheet on the INA2137) but you can tweak this yourself; really, the use of this opamp is a hang-over from the Mk1's diff board which cleaned up the audio outputs. Note that a meter may well be showing you the RMS value, the full swing is almost 4v on a scope with a 0dB 1kHz sine ISTR.

They're fed from a 10v rail, so there is room to get the swing up but ISTR it won't just be a component change, it'll be a lifting pins job. We have plenty of spare INA2137's if you make a mistake, though

Hugo

Thanks Hugo. Anyone interested in such a mod to their player?

Stu

Hmm, I might be. Not quite sure what good it will do me. I mean, my amp. already does a good job. What can I expect to get, better sound/noise ratio???

TommyE

For me I just found it irritating to have to raise the volume at home whenever switching to the Empeg from a louder source such as my CD player. I guess you would technically get better S/N ratio as you would be applying less gain from your amp or preamp. However, the Empeg's signal is so quiet (free of noise) I'm not sure you'd notice. I guess it would be more for convenience.

I'll have to pour over the opamp doc and see how to go about raising volume to 4 volts.

Stu

Note that a meter may well be showing you the RMS value, the full swing is almost 4v on a scope with a 0dB 1kHz sine ISTR.

The manual says 1 volt out and doesn't elaborate. I've actually never measured the outputs on the Empeg, just the other equipment. I will have to drag out the oscilloscope and compare the outputs of my various equipment to the RCAs on the Empeg.

Stu

Thats the home output. The car outputs are 4V, and some people choose to use these at home as well. It would be a slight hack but you could easily break out the 4V outputs to the rear panel RCA's.

Rob