crate v33h channel switching pop noise

[ck54]

Hi,
This crate amp apparently has a channel switching design flaw which causes a popping noise when switching into the gain channel with both the footswitch and the button on the panel.
This is what the crate service centers told me and they were unable to fix it.
The switching components are on the right and the jack is on the left and it's running by a tube which is amplifying it. Does that make sense to anybody?
I f anyone has a solution please let me know and maybe Crate can authorize their Service center to fix it.
On the original amp I had the panel button worked with no noise but not th efootswitch.
On the replacement they sent, both the panel button and footswitch make a loud popping noise. They're probably going to give me a refund, but can it be fixed?

[Enzo]

It is quite common for many amps to pop at channel switching. Usually it is luck of the draw whether a particular amp does it more or less than another.

[ck54]

Is there any thing that can be done on the schematic?
The Crate service centers are very insistent that it's a design flaw.
Are they out to lunch?

[52 Bill]

Is there any thing that can be done on the schematic?
The Crate service centers are very insistent that it's a design flaw.
Are they out to lunch?

It looks like there is a design problem with the output of first stage going into the relay for the gain channel: The output coupling cap is left floating. Maybe if they add a high value resistor to ground to drain off any residual charge on the cap it might reduce the pop.

[JustRob]

2nd stage-C8 is also left floating, and relay-2C looks to be drawn wrong, wtf?
This is a more likely culprit, with higher DC potential. Nice work, Loud!

[The8]

It looks like there is a design problem with the output of first stage going into the relay for the gain channel: The output coupling cap is left floating. Maybe if they add a high value resistor to ground to drain off any residual charge on the cap it might reduce the pop.

Hello - this is my first post here, and there seem to be some very knowledgeable people on here, so I'm hoping someone might have some advice on this.

Does anyone know exactly how one would do what is written in the quote above? (which is the output coupling cap?) I have done some mods to my V33H, but my knowledge about amp circuits is limited. Most of what I did was done by simply following instructions posted by others on forums.

By the way, the amp popped even before the mods were done, so I don't think they are the cause here.

I have already tried removing C8 to see if that was the source of the popping when switching channels, but it did not help. Removal of C8 just seemed to make the amp a bit brighter.

Anyway, I realize this is an old thread, but would greatly appreciate any help at all!

[JustRob]

52 Bill is referring to C5 being left floating, you could try putting a bleeder resistor, maybe 4.7MΩ from pin 10 to 8 on relay 1C. I apparently meant C7 in my earlier post, you might also try putting a bleeder resistor, maybe 2.2MΩ from the junction of C7&R8 to ground. Anyone have a correction on relay 2C? As drawn, the output from V1-B would go to ground or nowhere, I don't think that's what they meant.

[The8]

Thanks a lot for the response. From reading other forums, many other people have this same amp (with the same mods that I did) and only a few have complained about popping, so it seems like there's more to it than just the circuit design.

My next attempt at fixing this will be to simply reflow the solder joints on the board - maybe there's a bad one that's causing issues, I dunno. I've looked them over and don't see anything obviously bad, but it's worth a shot.

[Enzo]

Don't use an internet sampling to decide if there are performance issues with amps. A lot of guys - myself included - wouldn't bother reporting pops in amp because they are so common.

Looking at the unterminated caps being switched by relays, I don't doubt the amp pops.

To terminate C5, 2.2meg or larger should be sufficient, tack the new resistor from the righthand end of R4 to ground. I pick R4 because it will be easier that C5 itself, and they are wired together. You could wire it to the telay, but I don;t find those as accessible, myself.


And do it again for C7. You don't really have to get between C7 and R8 unless it is convenient. A resistor to ground from either end of R8 will be OK.


Relay 2C? Look at the V50 to see how it should have been drawn.

R8 should have gone to pin 8 of the relay, not pin 10. Yes, connected to R11. Pin 10 then would be shorted to pin 9, that is to say grounded, though in reality it doesn't matter what you do with pin 10. So when the channel is live signal flow through R8,R11 and on beyond. When the channel is deselected, the signal path is grounded off between R8 and R11 to prevent crosstalk.

[The8]

52 Bill is referring to C5 being left floating, you could try putting a bleeder resistor, maybe 4.7MΩ from pin 10 to 8 on relay 1C. I apparently meant C7 in my earlier post, you might also try putting a bleeder resistor, maybe 2.2MΩ from the junction of C7&R8 to ground. Anyone have a correction on relay 2C? As drawn, the output from V1-B would go to ground or nowhere, I don't think that's what they meant.

Don't use an internet sampling to decide if there are performance issues with amps. A lot of guys - myself included - wouldn't bother reporting pops in amp because they are so common.

Looking at the unterminated caps being switched by relays, I don't doubt the amp pops.

To terminate C5, 2.2meg or larger should be sufficient, tack the new resistor from the righthand end of R4 to ground. I pick R4 because it will be easier that C5 itself, and they are wired together. You could wire it to the telay, but I don;t find those as accessible, myself.


And do it again for C7. You don't really have to get between C7 and R8 unless it is convenient. A resistor to ground from either end of R8 will be OK.


Relay 2C? Look at the V50 to see how it should have been drawn.

R8 should have gone to pin 8 of the relay, not pin 10. Yes, connected to R11. Pin 10 then would be shorted to pin 9, that is to say grounded, though in reality it doesn't matter what you do with pin 10. So when the channel is live signal flow through R8,R11 and on beyond. When the channel is deselected, the signal path is grounded off between R8 and R11 to prevent crosstalk.

Thanks Enzo and Rob.

I looked around at my stash of parts and don't see anything higher than one M-ohm, and don't feel like stringing 3 or more of them in series. I'm going to have to make a run to get some higher-valued resistors, and will post back after I get this done.

Thanks a lot for your help.

[Enzo]

Got a 1 meg? Tack it in place then and see if it solves the popping. it may or may not have some small effect on the sound, but just as an experiement to see if it helps the popping, try it. I call that "proof of concept." if it works, go back and replace it with a somewhat larger value later when you have the time and materials.

[The8]

I ended up going to Radio Shack yesterday. They had 1 meg resistors and 10 meg ones, but nothing in between. I ended up getting some 10 meg ones, and tried as you said - one 10 meg resistor from the right pad of R4 to ground, and another one from the left pad of R8 to ground. Unfortunately it did not fix the issue - the amp still pops going from the clean channel to overdrive, and thumps (almost like a loud heartbeat type sound) when going from the overdrive channel back to clean (but the thump only happens if I'm playing something while switching channels). Sorry I didn't mention that earlier. I thought I had, but it must have been in another forum that I posted in.

Do you think that 10 megs may be too high of a resistance?

Thanks again for trying to help me out.

[The8]

Just wanted to give an update on this. I wasn't able to completely get rid of the extra noises.

I ended up re-soldering several components. The first ones I to re-did were two resistors with pads underneath some tube sockets (R28 and R17). Previously I had just soldered from the top - but now I removed the socket, soldered the resistor properly, and replaced the socket. I also ended up replacing some other caps with some Mallorys. I'm not sure if it really makes a big difference, but I had spare Mallory caps of the right value, and wanted to touch up solder joints on this board to see if it would help the noise issues I was having.

Anyway, after doing all that, it seems that the noises have been reduced somewhat. When playing loud, it's really not much of a nuisance anymore. In fact, I think part of the problem was that I was playing it at home at very low volumes, which made the channel switching noises a lot more apparent.

Thank you very much to those who tried to help me with this. I'm pretty happy with this amp now.

[JC1]

WHy your amp pops when channel switching

Just wanted to give an update on this. I wasn't able to completely get rid of the extra noises.

I ended up re-soldering several components. The first ones I to re-did were two resistors with pads underneath some tube sockets (R28 and R17). Previously I had just soldered from the top - but now I removed the socket, soldered the resistor properly, and replaced the socket. I also ended up replacing some other caps with some Mallorys. I'm not sure if it really makes a big difference, but I had spare Mallory caps of the right value, and wanted to touch up solder joints on this board to see if it would help the noise issues I was having.

Anyway, after doing all that, it seems that the noises have been reduced somewhat. When playing loud, it's really not much of a nuisance anymore. In fact, I think part of the problem was that I was playing it at home at very low volumes, which made the channel switching noises a lot more apparent.

Thank you very much to those who tried to help me with this. I'm pretty happy with this amp now.

The reason your amp pops when channel switching is because of the large difference in audio levels between the clean & overdrive channels. I have a similiar problem with a modded up JCM800. I created a single input with channel switching between the output of the first side of V1a & input to V1b. I used LDR"s to isolate the input split & recover split & a relay to select either LDR's. I thought the delay time between the LDR's would eliminate any popping..I was wrong! I could have done the same thing with just 2 relays like your amp. The 2 channel recovery happens right before V2a/b & tone stack via the other 2 LDR's (4 total). The popping shows up on the output of the tone stack. Can't see anything on V2a input or any where before that.

I proved it by putting clipping diodes on the overdrive channel before the 2nd LDR junction. The diodes greatly reduce the larger signal that is present on the O.D. The large reduction eliminated the pop. So, I have distortion, diode like a JCM900 & no pop. Unfortuneately, I pefer no diodes tone better so now I search for another remedy.

Your previous post states you were told to at least try 1M resistors that you had on hand and choose to ignore that and buy 10Megs & that didn't work. Hmmm, so looking at the quote above, I'm assuming a few days after to did try the 1 Megs and it still didn't help?

[Enzo]

Hi JC, welcome to the forum.

Considering that last post was three years ago, and the poster has only 5 posts total, I fear he is gone and will not see your reply.