[izquierdaste]

Hello,

I switched the opamp in my TEC (Beresford) TC-7510 from a JRC4558 to a LM4562. It sounds much better except that I now hear distortion during loud sections of songs. (It sounds great otherwise). The TC-7510 runs at 12vdc. I checked with the manufacturer and the opamps also see 12v (or +/-6v). The lm4562 is supposed is well within +- 2.5 to +-17, so I think that should be fine. So I was wondering if the issue stems from the circuit being designed for the jrc4558. THe pinouts are the same, but the lm4562 has much more open loop gain 140db compared to 100db for the 4558. This difference in output is very evident as the dac output is now much louder than with the 4558.

Other info: the JRC4558 was surface mount, so I installed a brown dog dip to soic adapter with a socket to roll opamps. I am not great at SMD soldering so I could have a bad connection or bridged two pins, but it looked clean to me. I also swapped a number of the caps, but I did this before I swapped the opamps and did not notice a problem. The bass is very strong and not rolled off, so I think the caps are installed ok?

Anyways, does anyone know why the opamp change could sound much better, but then cause distortion during loud sections. Does the increased output that require a change in resistance? If anyone knows of a good source for info for opamp circuit design, that might help me out.

Thanks for looking.

 

[Godfather007]

Hi mate, any comments/reviews on the beresford TC-7510 MKIII?

 

[izquierdaste]

I don't have the beresford tc-7510 mkiii. I have the standard TEC version tc-7510 that should be the same as the tc-7510 mkii. However, I changed a number of caps and the dac opamp so my dac is likely substantially different than either the old or new mkiii versions. I'll post more on the sound in the source component section after I sort this out.

I am starting to think maybe there is a burn-in effect because the distortion seems to be going away.

 

[Pars]

Quote:

Originally Posted by izquierdaste /img/forum/go_quote.gif Hello, I switched the opamp in my TEC (Beresford) TC-7510 from a JRC4558 to a LM4562. It sounds much better except that I now hear distortion during loud sections of songs. (It sounds great otherwise). The TC-7510 runs at 12vdc. I checked with the manufacturer and the opamps also see 12v (or +/-6v). The lm4562 is supposed is well within +- 2.5 to +-17, so I think that should be fine. So I was wondering if the issue stems from the circuit being designed for the jrc4558. THe pinouts are the same, but the lm4562 has much more open loop gain 140db compared to 100db for the 4558. This difference in output is very evident as the dac output is now much louder than with the 4558. Other info: the JRC4558 was surface mount, so I installed a brown dog dip to soic adapter with a socket to roll opamps. I am not great at SMD soldering so I could have a bad connection or bridged two pins, but it looked clean to me. I also swapped a number of the caps, but I did this before I swapped the opamps and did not notice a problem. The bass is very strong and not rolled off, so I think the caps are installed ok? Anyways, does anyone know why the opamp change could sound much better, but then cause distortion during loud sections. Does the increased output that require a change in resistance? If anyone knows of a good source for info for opamp circuit design, that might help me out. Thanks for looking.

You are still running with the stock feedback values from the JRC (which control the gain), so I wouldn't think the output should be louder than before. I would check the opamp connections carefully (use magnification). Clean the board area for flux as well (rubbing alcohol, flux cleaner, etc.). You might want to ohm out the opamp socket (w/o the opamp in it) pins to ground to see if you see differences between R/L channels and also ohm it out pin to pin looking for shorts.

 

[izquierdaste]

Thanks for the advice. I will try to redo the SMD soldering.