Integration dim LEDs on c2s boards?

[jciii]

Just installed the integration kit this afternoon - great instructions and everything went smoothly. The first board was fine - voltages all looked within spec. When I started doing the voltage checks after installing the 2 c4s boards, I noticed that the LEDs are quite dim compared to the LEDs on the shunt regulator board - are all of the LED's supposed to glow with approximately the same intensity or do the LEDs on the c2s boards glow dimmer?

The voltages at terminals 2, 18, 26, and 31 are close to 65v, bit not quite there - the lowest was 63.9. I'm going to look for loose solder connections on Monday evening, but answers to these questions first would be helpful.

Thanks!

Joe

 

[Paul Birkeland]

More current is run through the LED's on the center shunt regulator board, so those LED's will indeed grow more brightly. 

-PB

 

[jciii]

Thanks for the info - my next question is how much more brightly? I had to turn off the lights to see that the LEDs on the c2s boards were lit at all.

I hooked the pre back up to my system and I have less apparent volume than I did before the mod and the mids seem to be very subdued and really lacking. Will re-check all of my work Monday evening, solder joints, etc; but given those symptoms, any nuggets of wisdom?

 

[Paul Birkeland]

I don't see anything in your voltages that would indicate a problem.  Slightly lower than 65V would actually indicate a stronger than normal tube.

On the MJE350's and MJE5731A transistors, the center leg is tied to the heatsink, so they aren't all that easy to solder.

Funky solder joints can indeed trash the sound, and you should notice the extra gain quite easily after installing the integration. 

 

[jciii]

Just resoldered all of the joints for the transistors. They all definitely have good connections with the circuit trace. I didn't have time to do a voltage check, but hooked it back into the system and spun up Cake's Fashion Nugget - Frank Sinatra was the first track I played the other night putting the preamp back into service. I know this album very well. Before I modified the preamp, the trumpet was forward when it came in, now it is very subdued. The vocals also appear to be much softer than previously. The bass is a notable exception - it appears that the bass has gone up in volume. On this particular record, I have to turn the volume up to 55 - 60% to achieve the same volume I used to get at 50%... It seems the mids and highs have decreased in gain, while the lows have increased in gain.

Tomorrow evening, or perhaps tonight as time allows, I'll recheck all of the voltages. I also rechecked all of the diode and led directions, and they are all in the right way round. I'm scratching my head...

 

[Paul Joppa]

The change in frequency response suggest that there might have been a bad connection in the RIAA equalization circuit. It is possible that you had more apparent gain due to that, which was fixed in the re-soldering.

The RIAA attenuated the mids and treble (relative to the bass), so if that part was not working the mid/treble would be a lot louder but the bass would be relatively weak.

Might be worth checking that area very closely.