Help intermittent crackling sound from act2 mk1 right side

[aleman]

Having late last year purchased a lp70s amplifier impressed with the sound.Well began thinking about another preampm ie a conrad johnson one always lusted after a ct5 but in the uk none to be found.What to do looking into the uk online second sites found an ac2 mki always liked the look of those after long conversation with seller purchased said item as he was only selling after acquiring an act mk2.
All was sweetnes and light combined with the lp70s some of the best sounds i have ever heard..However have now noticed after about 2 to 2.5 hours getting a loud crackling sound through the lp70s on the rightn side.
Having plenty of spare input output tube chnged tube re biased found the same problem .Changed amplifier for F1Jfirstwatt transcondutance clone amplifier built by myself thus known to have no problems in use with the act 2 mk1 same cracking on right side of amplifier after about two hours use.
Have ordered new valves for the act two from the tube dr outfit waiting for these to arrive .At the moment sovtec valves in place will replace with elctroharmonic equivilents.
Have replaced act 2 for now with my audio note kits line 2/phono tube preamp no problems with any of my amplifiers using lp70s as i type.
So any suggestions as to problem would be greatley appreciated also does anyone have the circuit diagram for the act 2 and which positions are for the left and right schannel valves .Regards Alrick

[AnotherJohnson]

If the ACT 2 is the culprit as shown by replacement, then the easiest hope is that it is a valve. Can you get the crackle to move to the other channel by moving the tubes from right channel to left? Be sure to shut off the unit and let caps discharge before removing/replacing tubes and restarting.

The 2 hour time lag is a puzzle. Usually that suggests something like a thermally sensitive crack somewhere.

See if you can get it to move by moving left channel tubes to right channel equivalent sockets. If you can, your new tube set is probably all you need. If the noise doesn’t follow the tubes, then you could look at the sockets on he bad side for burn marks or wallowed out pin sockets.

If you’ve designed and built amps, you are probably a better troubleshooter than most of us.

[admin]

Agree to look at the tubes first. I would also consider a cold solder joint as that could explain why after 2 hours the heat causes expansion.

[aleman]

Thanks for the reply helpful pointers tubes will arrive from the tube doctor tomorrow .Also dropped a line to cj via email just to find out about the update to series 2 no reply as of yet .Tried moving valves the problem persists Wil. have a look under the bonnet once new valves arrive.Regards Alrick

[aleman]

Read the replies again slowly i have built modifed ,amplifiers cd players dvd players cables speakers etc some from scratch others ikts thus whilst having a little knowledge over fifty years experience as a amateur iam not a designer i am sorry if anything i wrote gave this impression.
Regards Alrick

[AnotherJohnson]

You’re probably still ahead of most of us. No worries! I think you’ll get it sorted. Keep up the good work

[Big Dog RJ]

Ah! I certainly had that exact same damn issue with mine. However, that was just one of the issues, apart from a constant hiss on both channels, then this crackling noise after few hours of play, and the best of all, a sudden out of no where, paralysis on both channels, music stops, all the damn LEDs on the front display are on and it goes into mute mode, for no good reason.

At the time I mentioned this to CJ HQ, they advised to send the unit to them and they'll do a full assessment or I could purchase an ET5 instead. Uh, I don't think so... and I won't tolerate any quirkiness. So I got hold of my trusted tech, he opened it up and found a culprit. Or at least a probable culprit.

1. The main power lead was too long, hence it would interfere with a few other areas as the unit approached a certain temp range. So it was a thermal issue. So he shortened the power lead.
2. CJ sent him an extra copper plate for grounding, so this would sort out the sudden paralysis...
3. As for the annoying crackling noise, they advised to replace all four 6N30P's, so I did!

I couldn't figure out which channels those four tubes belonged to either, for crying out loud it was one of the most frustrating things to ascertain. Then my tech mentioned that with the ACT2 design, there's really no distinguished L & R channel, simply because those 6N30P's are wired in 8 parallel sections of input stage gain. Therefore, replacing just one or two tubes if crackling doesn't do didly squat! All four have to be replaced and all four must be perfectly matched! This is for that perfect or close gain matching aspect of this particular design.

That's it! After those three things / upgrades were done, the ACT2 worked well... until I sold it off. It did not give me peace of mind not knowing when it would have a hissy fit again, so I ordered the version 2 then looked out for a version 3 but since there weren't any, I then got hold of a CT5, modded it towards an ACT2 S3, the rest is history!

I must say, although those three things were attended to and the preamp worked ok for a while until I sold it, that annoying hiss never went away. The gain was just too high for a design that uses 8 parallel sections from a triode set of tubes for input gain. That gain is a single stage but it's quite complicated in terns of intricate wiring... takes a very very very steady hand to diagnose.

All the best! Cheers,
RJ

[aleman]

Just seen your reply plenty to go on snow has delayed my delivery of new elctro harmonix matched quad set of tubes hope to get monday and fit must start saving for a ct 5 as well.Regards Alrick

[aleman]

Tubes drlayed for three days now replaced bass suberb mid informative treble sweet and detailed.Used in conjunction with lp70s audio note kits 2.1 sinature dac and ls35a with falcon acoustics gold crossover and falcon reissue drivers Sound iss some of the best i have heard..Regards Alrick .Ps no further preamp issues playrd for quite some hours.

[aleman]

Tubes delayed for three days now replaced bass suberb mid informative treble sweet and detailed.Used in conjunction with lp70s audio note kits 2.1 signature dac and ls35a with falcon acoustics gold crossover and falcon reissue drivers Sound is some of the best i have heard..Regards Alrick .Ps no further preamp issues played for quite some hours.

[AnotherJohnson]

That’s great! Congratulations!

[Big Dog RJ]

That's always great news.

If after playing tunes for several hours and there were no problems with static or unwanted noise then just leave it!
There's no need to look for a CT5 or any other preamp. The ACT2 was one of CJ's finest and if everything is working perfectly without any quirks, it's SOTA!

Now just sit back and enjoy those fine tunes!
That deserves a mighty WOOF!
RJ