# Crate V18 ( I know, I know) noise issue



## buckaroobanzai (Feb 2, 2006)

Hi all, having a noise issue with a secondhand Crate V18 my brother picked up cheap. I said I would see if its fixable, if not it'll likely become an extension cab.

Amp is massively noisy above 12 o'clock on the Gain and Level controls, even with no input. I have disconnected the reverb - same. I have swapped in a set of tubes from my Classic 30 - same.

The amp appears to have had some mods done, they seem to be the common mods done to this amp from various threads on GearPage and TDPRI. Switch of R4 and R10, changed the slope resistor in the tone stack (r18) to a 100k. Also looks like R5 bypassed with a 4.7uF cap. Looks like it was done pretty well, not a hack job.

Here's a Youtube link. 




All ideas welcome. Thanks!


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## keto (May 23, 2006)

Clean the input jacks, all of them. I can’t remember if these have a loop, that needing cleaned is worth the time. Beyond that, post gut shots, we have several great techs that often chime in on these threads, theyve solved lots of cases.


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## cboutilier (Jan 12, 2016)

The previous generation of Crates, the Vintage Club series, had a ton of issues with their input jacks and the channel switching relay circuit. Don't know if these amps are similar at all.


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## buckaroobanzai (Feb 2, 2006)

Thanks guys. Have cleaned the single input jack with no improvement. There's no loop in this amp. It's single channel and has a weird switching power supply. It's a cheaply made amp but I'd like to save it if I can. BTW, the hiss does not seem to affect the sound of a guitar when I plug one in, the guitar sounds clean up to about 12 o'clock and then gets dirtier as I turn the gain and level up. So I guess you could say that the hiss is "background noise", it's just really loud.


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## keto (May 23, 2006)

Tried tube swapping?


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## buckaroobanzai (Feb 2, 2006)

keto said:


> Tried tube swapping?


As mentioned, I pulled the tubes from my (quiet) Classic 30 and put them into the Crate. Noise level is the same as with the V18 tubes.


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## Alan Small (Dec 30, 2019)

that is noisy alright....pull all the preamp tubes and see if the noise comes from the power section only...if quiet then 1 preamp tube at a time back in place...closest to power tubes first(phase inverter)...all tube sockets and pins cleaned with proper spray...you might get lucky with a single dual triode replacement only....sounds a bit like a screen resistor is burnt up too but one thing at a time....


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## buckaroobanzai (Feb 2, 2006)

Here's some gut shots - looks to me like at least one cap in the power supply has gone. One of the green ones next to the transformer. It doesnt help that Crate put some kind of glue/sealant over parts of the board that has now turned brown. I will pull the power supply board out and try changing these caps and possibly a couple of other components connected to them.


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## nonreverb (Sep 19, 2006)

Looks like someone's been messing with the first gain stage. Try and pull that first 12AX7, the noise might be greatly reduced if not disappear.


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## Latole (Aug 11, 2020)

Replace this cap, it is dead and why not the other close to it ? Its you noise issue IMO
Some burn spot on circuit board, copper trace may need some soldering.


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## Latole (Aug 11, 2020)

Schematic here; 

https://www.thetubestore.com/lib/thetubestore/schematics/Crate/Crate-V18-Schematic.pdf


Blow cap is C116 , 470 mfd 25 volts


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## Paul Running (Apr 12, 2020)

It sounds like shot-noise to me and without a scope you are guessing where it originates. Semi-conductors can be notorious for it's effects. Scope the power supply lines first.


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## nonreverb (Sep 19, 2006)

Latole said:


> Replace this cap, it is dead and why not the other close to it ? Its you noise issue IMO
> Some burn spot on circuit board, copper trace may need some soldering.
> 
> View attachment 345543


That is glue


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## Latole (Aug 11, 2020)

nonreverb said:


> That is glue



You may be right. Why glue over there ?


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## nonreverb (Sep 19, 2006)

If you turn all the volume/tone pots to zero and it's quiet, it's most likely a preamp problem and from the video you posted, that seems to be the case. My first guess is, there may be a certain level of line white noise inherent in the amp to begin with but whoever was in there has modified the circuit causing an elevated level. Like I said, try removing the first tube....if it goes away, that's a good place to start....if not let's carry on and eliminate the next potential cause. There's no sense flying from one end of the amp to the other trying all kinds of stuff....that will only get confusing. It has to be methodical.


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## nonreverb (Sep 19, 2006)

Latole said:


> You may be right. Why glue over there ?


To keep the radial caps in place.


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## Latole (Aug 11, 2020)

nonreverb said:


> To keep the radial caps in place.


Look very thin to be useful IMO


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## Latole (Aug 11, 2020)

nonreverb said:


> If you turn all the volume/tone pots to zero and it's quiet, it's most likely a preamp problem and from the video you posted, that seems to be the case. My first guess is, there may be a certain level of line white noise inherent in the amp to begin with but whoever was in there has modified the circuit causing an elevated level. Like I said, try removing the first tube....if it goes away, that's a good place to start....if not let's carry on and eliminate the next potential cause. There's no sense flying from one end of the amp to the other trying all kinds of stuff....that will only get confusing. It has to be methodical.



C116 is a filter cap for - DC voltages for Op Amps, no good filtering = noise


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## greco (Jul 15, 2007)

I always enjoy these troubleshooting threads and learn something from each one.

However, I fully understand how frustrating all this could be for the OP

@buckaroobanzai Hello my friend. Hope you and yours are keeping well and safe.


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## nonreverb (Sep 19, 2006)

Latole said:


> C116 is a filter cap for - DC voltages for Op Amps, no good filtering = noise


Yes that might be the case for general noise that's present regardless of the volume.. Since the noise can be manipulated with the volume, that would not be the case. IMO


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## nonreverb (Sep 19, 2006)

Latole said:


> Look very thin to be useful IMO


It doesn't have to be thick. The factory stuff is very strong. The reason it's dark looking is because of heat from the diodes changing it's colour over the years. I serviced computer monitors for years and this condition was typical in switching power supplies where hi current diodes were in contact with component glue.


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## buckaroobanzai (Feb 2, 2006)

You guys are awesome. I will be ordering replacements for both caps, I also want to check the other components in the general vicinity. As mentioned, the board is not burned, its the stupid glue that Crate used. I will also pull the main board and check the soldering on the mods that were installed. Might also replace the cheap op amps that are in it. These V18's had a lot of problems but it will be an OK amp for my brother if I can get it sorted. If not, its got a decent Eminence speaker in it ( not original) and I will turn it into a 112 cab. Or maybe build that 18Watt Lite that I have most of the parts for.


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## nonreverb (Sep 19, 2006)

buckaroobanzai said:


> You guys are awesome. I will be ordering replacements for both caps, I also want to check the other components in the general vicinity. As mentioned, the board is not burned, its the stupid glue that Crate used. I will also pull the main board and check the soldering on the mods that were installed. Might also replace the cheap op amps that are in it. These V18's had a lot of problems but it will be an OK amp for my brother if I can get it sorted. If not, its got a decent Eminence speaker in it ( not original) and I will turn it into a 112 cab. Or maybe build that 18Watt Lite that I have most of the parts for.


Good point. Op amps can get noisy


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## Paul Running (Apr 12, 2020)

buckaroobanzai said:


> You guys are awesome. I will be ordering replacements for both caps, I also want to check the other components in the general vicinity. As mentioned, the board is not burned, its the stupid glue that Crate used. I will also pull the main board and check the soldering on the mods that were installed. Might also replace the cheap op amps that are in it. These V18's had a lot of problems but it will be an OK amp for my brother if I can get it sorted. If not, its got a decent Eminence speaker in it ( not original) and I will turn it into a 112 cab. Or maybe build that 18Watt Lite that I have most of the parts for.


There is a lot of potential with those Crate V series amps. I had a V33 years ago. Many people knock the PS however, it is well-regulated for clean playing and if you can keep the noise off it, your laughing.


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## Latole (Aug 11, 2020)

nonreverb said:


> Yes that might be the case for general noise that's present regardless of the volume.. Since the noise can be manipulated with the volume, that would not be the case. IMO



You may be right, I see so many strange thing when fixing amps. You only know what was the issue when amp playing fine


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## Paul Running (Apr 12, 2020)

You can squeeze abit more headroom from these amps by switching to fixed-bias. You can source the bias from the -17VDC line from the PS that powers the negative rail to the op-amps, as indicated on the schematic...just add a divider network and isolation resistor...-14VDC makes this amp sing with Amperex EL84s.


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## buckaroobanzai (Feb 2, 2006)

Paul Running said:


> You can squeeze abit more headroom from these amps by switching to fixed-bias. You can source the bias from the -17VDC line from the PS that powers the negative rail to the op-amps, as indicated on the schematic...just add a divider network and isolation resistor...-14VDC makes this amp sing with Amperex EL84s.
> 
> View attachment 345567


Thanks for the schematic and the suggestions, Paul. In this case, since it is just going to be my brothers play-at-home amp, I will keep the mods to a minimum and just try to get it quiet and functional. Of course, if the SMPS cant be revived, that will be it for the Crate , and i will use the chassis and cab to build something else. Cheers!


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## buckaroobanzai (Feb 2, 2006)

Hi All

Update - some success. I ordered parts from Digi-Key - 2 low-ESR 470uf caps and 2 UF 4004 diodes. Pulled the old components and scraped as much of the brown goo off as I could. Installed the diodes on standoffs for better heat dissipation and glued the caps down with a little bit of latex silicone. I also pulled the main board and re-did the solder joints on the mods. I installed a 5751 in V1, a JJ 12AX7 in V2 and a 12AT7 in V3. Screwed it all back together and fired it up. No appreciable noise until almost the end of the dials - certainly good enough for my brother for home use. It's still not that great of an amp, but I am glad I saved it. Once it dies for good I will have an excuse to build that 18 watt clone I have most of the parts for.

My thanks again for all those who contributed to this thread. You guys are the best!


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