Bottlehead Forum
Bottlehead Kits => Legacy Kit Products => Foreplay III => Topic started by: audiblesoundwave on October 01, 2014, 07:25:19 PM
-
The crackle and static on my FPIII (non-extended version) left channel started a week ago. They can be heard from the listening position. The volume switch does not affect the crackle and static sound; however, they do get a bit louder sometime for a short burst.
I replaced a different set of the 12au7 tubes and swapped the position but no help!
I replaced the two 220 ohm 1/4w carbon composite resistors but no help!
I replaced the output capacitor but the outcome is the same which with the crackle and static on the left channel.
I also checked all voltage and resistance against the manual check list and the results are well within the reference results.
Any other pointers to resolve the crackle and static issues?
There are three more resistors (22.1k 3/4w and 470k 1/4w) and one LED. Should I go change those?
Is there anything else that I need to replace? Could the Goldpoint attenuator or the selector switch cause the crackle and static problem?
Thank you for your help!
Milton
-
Look for any parts that might be discolored from overheating. You might also want to reheat the solder joints on the left channel connections. Do you see the 0D3 flicker when you hear the crackle?
-
Thanks for the quick reply!
I replaced the 0D3 with another new one and the crackle and static are still there.
I will reheat the connections tomorrow and to see that would resolved the issues or not.
Thanks again,
Milton
-
If you dont see any flicker the crackle is likely to be coming from somewhere near the left channel 12AU7 socket. Since your voltages seem good it's likely to be an intermittent connection. A typical cause is connections on the socket getting loose or broken over time from tube rolling. Also if the left side output capacitor was ever accidentally nicked with a soldering iron and it penetrated through the outer jacket that could create a crackle.
-
It sounds like time for "the chopstick test." And since you are an "old timer" you don't need me to explain it.
I have seen a solder joint fall off after 6 years. I have seen non soldered joints work for 2 years. I expect there is a solder joint that just needs reheating.
-
Thank you!
I did the "chopstick test" last night but did not seem to locate anything. However, I will go try to reheat the joints tomorrow.
What is the chance that the 9-pin socket gone bad? I tried to "rocking" gently the 12au7 tube and there were loud static coming out to the left speaker from the left tube; however, the right side did not!
Thanks again,
Milton
-
Yes it sounds like you have found the issue. The socket is either has corrosion or the contacts are stretched from tube rolling. Take a very tiny screwdriver and gently work it between the ceramic and the metal contact in each hole to very slightly crimp the contact a little smaller to grab the pins better.
-
Thanks Doc!
I performed your suggestion on the socket hole contacts with the tiny screwdriver. It did seem to help a bit. The crackle and static seem to subside a bit more during idling, no music playing. However, the crackle and the static came back when music is going. I also did reheat all connections on the left channel.
Could it be the 470k ohm resistor? I am waiting a new one to come in a few days. I did take the resistor out for measurement and it seem to be ok with 469 ohm.
Thank you,
Milton
-
If it helped a little it's most likely that you found the problem area and it just needs a little more attention. If you have some contact cleaner try pulling the tube out, applying the cleaner to the tube pins and plugging and unplugging the tube a few times. That may remove that last bit of tarnish or dirt that is causing an intermittent connection.
-
Hello Milton,
Try the chopstick test on those 220 Ohm resistors.
Sometimes when I have to track something like this down, I will use a cheap headphone amp and garbage pair of heaphones on my head, with the volume turned down pretty low. Then, with the Foreplay driving the headphone amp, I can hear if my chopstick hits something funky (crackle crackle).
It might be that you have a 220 Ohm carbon comp that's given up. When I get a FP-III in for repair with crackles on one channel, I'll just yank those out and put carbon film resistors in instead.
-PB
-
Thanks Paul, Doc, and Grainger for all of the pointers.
After many days of chopstick testing, number of times of resistance and voltage readings, number of joints reheating, and resistors and capacitors swapping, I located the cause finally!
It turned out to be the 22.1k ohm metal film 3/4w resistor that was connected between pin 6 and pin 1 of the left channel. The resistor's external did not show any problem but it caused the crackling. May be internal issue.
Anyhow, the new resistors I purchased last week arrived today and I clipped the new one on. The crackling is no longer there. Back to pure music!
I decided I will replace all of the resistors (220 ohm, 22.1k ohm, and the 470k ohm) for both channels in the next couple of days.
Thanks again for the support and helps!
Have a wonderful week,
Milton
-
My advice is just leave the circuit as-is for a while now that you fixed the problem. That resistor failing is a pretty unusual occurence and changing all the rest out would, for me at least, be about a 50/50 proposition on whether there might just end up being a new sketchy solder joint somewhere in the rework. If it ain't broke don't fix it can be a worthwhile approach some times.
If on the other hand you see any resistors that looks obviously heat discolored they might be worth replacing.
-
Well Doc, I thought I had fixed the problem but the crackle and static are still there!
I did not hear the crackle and static when I was using two 10" clipper cable to clip the new resistor onto pin 6 and pin 1. However, the crackle and static are back after I solder the resistor in!
Does this make any sense? I am back to step 1!
Milton
-
You may simply have needed to clean the tube sockets from the get go.
-PB
-
Thanks Paul.
I have used the DeoxIT to clean the socket a few time in the past week.
I have also performed Doc's suggestion that "Take a very tiny screwdriver and gently work it between the ceramic and the metal contact in each hole to very slightly crimp the contact a little smaller to grab the pins better".
I have already replaced the 220 ohm resistors and the 22.1k resistor connecting pin 6 and pin 1.
The only one resistor left is the 22.1k ohm connecting pin 8 and terminal 39. Can it be the LED gone bad?
Thanks again for help,
Milton
-
The only one resistor left is the 22.1k ohm connecting pin 8 and terminal 39. Can it be the LED gone bad?
I'd be doing my best to measure voltages while the noises are happening, to see if any are jumping around.
The LED is likely OK. If you poke the LED and the preamp makes a ton of noise, it could be damaged.
-PB
-
Thanks Paul. I chopstick testing the remaining resistor and the led and they seem to be ok as you have suspected!
I am going to try and to catch the "crackle and static" moment for the measurement.
Thanks again,
Milton
P.S. This is the most difficult one that I have encountered in the past 7/8 years with the Bottlehead gears I have.
-
Intermittent problems are maddening!
-
Is there a way to test out the socket to see it is still good or gone bad?
Thanks,
Milton
-
Do the chopstick test on the tube socket terminals themselves.
-
After a few more days of chopstick testing, I still could not locate any bad "things".
I ending up replaced the left channel socket and all of the resistors and the led. Very disappointed! The crackle and static are still there.
From the listening position, the crackle and static in much louder level come in a burst for few seconds and back to crackle, crackle in other time but much lower level. The attenuator has no impact on the level of the crackle and static.
I used Deoxit Cleaner on the 0D3 socket a couple times.
Any other ideas? I am pulling my hairs.
Could the 0D3 socket (if it is bad) cause this issue?
With my limited knowledge, I don't think the heater supply and B+ voltage would cause this problem in one channel! Both channels share the voltage. Would it?
Thank you so much for your helps and patience with me.
Milton
-
Yeah, your logic about the power supplies is 100% correct, and very useful in this situation.
What kind of level controls do you have on this FP-III? The old Sweetest Whispers switches are known to eventually go bad.
One thing you could do to test this would be to temporarily ground the output of the SW on the crackly side, then listen to see if the noise is still present.
Other than that, there may still be a funky connection on one of the terminal strips, or on the actual power supply wiring that feeds from the 0D3 to the offending side.
-PB
-
Thanks Paul.
I grounded the left channel that has the crackle and static and there is still crackle, static, and off cause no music. What does this mean?
I am using the Goldpoint stereo 10K attenuator and the selector.
I will continue to poke around 0D3 connections again to see any better luck.
Thanks again,
Milton
-
I may have missed it, but I don't see any test to confirm this is not downstream of the FP-III - output jacks, cables, power amp input jacks, power amp itself, speaker connections, speaker cable, or speakers.
-
Thanks Paul.
I isolated to the FPIII which is the one generating the crackle and static! I have switched and replaced the 12au7 tubes, 0d3, switched the interconnects between FPIII and power amp, switched the channel connection into my tube mono power amps, switched the source's channel connection into FPIII. The end result always is the FPIII's left channel has the crackle and static.
I have been trying to isolate the problem within the FPIII. I have replaced the left channel's socket and resistors. I have also pulled the 1K resistor bridged the two output RCA center pin. Up to this point, the crackle and static are still there. I am continuing on poking around as PB suggested the 0D3 connections which I have tried few time.
Anything else I should try, please let me know. I could have been chasing the wrong direction.
Thanks,
Milton
-
If it is only in one channel and it does not vary with volume you know that it is not the 0D3 or power supply, and not anything ahead of the volume pot. Does the output cap on that channel possibly have some damage? Do the LEDS flicker when the crackle happens?
-
Thanks Doc.
I have also replaced the output cap with new one! I had assumed the 0D3 and power supply were possibly not he cause last couple days but I am trying any suggestions to isolate the issue.
You just point out a new one that I have not tried which to see the LED (I also replaced with a new one) flicker or not when the crackle happens. Early on this thread that you suggested to see the 0D3 flicker or not when the crackle happens; so far I did not see 0D3 flicker when the crackle happened.
Anyhow, I will pay attention to the LED!
Thanks
Milton
-
When you grounded the signal from the Goldpoint, exactly what did you connect to ground? My thought would be to ground the actual grid of the tube on the noisy side. If that stops the noise it would tell you if there was a problem at the output of the pot, or maybe the 220 ohm grid stopper connected to pin 2. That connection would be pin 2 on either 12AU7 socket to the ground buss. If it doesn't stop the noise, then you may have to say "what's left to inspect?" and examine the things that you have not replaced. Another thought would be to wiggle the STP cable that goes from the output capacitor to the RCA output jacks to see if maybe a wire has broken inside the insulation.