How to Fix Fender Ultimate Chorus Hum

[@gingercat777]

These Amps were built to be unrepairable....cost wise. I admire your resilience 👍

[@stuartukguitarampguy5830]

Yes they don;t care about maintenance!

[@jtbracknell]

You saved it from the scrap heap for a few more years. Good job Stu.

[@stuartukguitarampguy5830]

Thanks!

[@larrydering1598]

Always a joy to watch you track down and fix these old cheaper amps. I use many of your techniques in my own repair shop.

[@stuartukguitarampguy5830]

Cheers Larry.

[@pda49184]

It lives to be played another day.. Well done for having the patience to find and repair the fault.

[@stuartukguitarampguy5830]

Thanks!

[@upload2352]

Stuart - I suggest that the reason you couldn't replicate the tap/connect issue once the chassis was out of the cabinet was because, while in the cabinet, the board possibly was flexed/held in a way, and with sufficient tension to the board, that allowed/disallowed contact within the bad solder joint. Once the board was removed, that tension was released. Always entertaining stuff - I enjoy the S/S (transistor) amp work vids, as well.

[@stuartukguitarampguy5830]

Yes that's certainly possible.

[@justinjones5934]

Followed this video and got mine fixed up no problem. Cap didn’t have any play but once I pulled the board out it was very obviously cracked. I went ahead and redid all the other points on the caps just to be sure.

[@stuartukguitarampguy5830]

Nice one Justin, well done.

[@JaKeAFC09]

I have that same amp. It's a very nice 2x12 amp which comes cheap. Mine as well, and some other's i've read, have a baseline hum in the 50/60hz range. I did as well parallel the filter caps and no difference. By the schematic, it comes after the pre stage and right before the FX SEND, i 'solved' it with a passive highpass filter in the fx loop as for how i use it i don't need much bass, however would be interesting to find out the cause, i suspect a JFET oscillating somehow...

[@steffenbrix]

interesting! I sold mine because of this...and also two red knob tube Twins...they all have this hum. I was thinking switching noise from the rectifier diodes. But maybe you're on to something?

[@rickkaylor8554]

I admire your technical skills. I've had this amp since 1997 and thankfully had no problems with it despite gigging heavily with it.

[@stuartukguitarampguy5830]

Thanks Rick

[@Bhh-j2s]

I have one that I bought new in the early 90s. It makes thank exact noise. Thank you I think I’ll get the old girl back up and running.

[@stuartukguitarampguy5830]

Tes I like to rescue these amps from landfill!

[@dontuckerjr]

I used to have one of those. Definitely plagued by solder issues after so many years. I still have the sister amp, Princeton Chorus. Great video. Exactly what folks should expect with these amps.

[@stuartukguitarampguy5830]

Thanks for sharing.

[@tjsogmc]

I bought one of these for $30 with that same problem. The issue was a small string of solder hanging off one of the MOSFET legs to a ground. That was it. Took 2 minutes to fix. Been a great amp since.

[@stuartukguitarampguy5830]

Wow well done!

[@wallemon06]

Thank you for sharing your knowledge. I purchased this amp’s predecessor, the Ultra Chorus, new in 1994. That slight background hum is normal, unfortunately. So is the pop and squeal when turning off. (I wonder why Fender stopped selling these?😂) Mine is now behaving badly. Which surprised me because it really doesn’t have many hours on it. However online research indicates that this line had a history of poor solder joints. The filtering caps, or their solder joints, are probably bad on mine due to age. Other users report that reflowing as many joints as possible while the board is off will solve most problems. Thanks again for the video and insight. Cheers from Detroit.

[@stuartukguitarampguy5830]

Thanks for the useful info!

[@sven31415]

For the Chorus to be nice you have to make it slower and not full amplitude.

[@_ROBERT.]

I've just bought a fender ultra chorus pretty much the same as the amp you are working on here i bought it at a online auction cheapish i have no idea if it works even but from what I've seen they all seem to be prone to crackling pots and a hum I've just bought a tin of pot contact i think im going to need it thank you for taking your time to make this video I've learnt a few things cheers 👍

[@stuartukguitarampguy5830]

I hope you manage to get it going Robert.

[@_ROBERT.]

@@stuartukguitarampguy5830 thank you 🎸 🤘

[@wallemon06]

See my comment about my Ultra. It may help. ✌🏼

[@sven31415]

I have two Ultra Chorus in a Stereo rig setup. They have an awesome sound, but I have also the hum and pot crackling. The pot crackling I deal with by just turning the pots many times, but it is not very satisfiying. The hum I am thinking of changing the capacitors. This is why I watched the video and downloaded the schematics.

[@michaelevans3852]

Stuart, it's good information to have. These SS amps are not my favorites but I do have an old Peavey Backstage. I hope the knowledge never comes in handy for that one. I have worked on a Behringer and it seemed quite cheep. Thanks for the tip.

[@steffenbrix]

All red knob Fenders I've had have had this hum problem.... love their sound - but they all sound this way. Both Power/Ultimate Chorus and red knob Twins

[@stuartukguitarampguy5830]

Interesting thanks.

[@jtops3000]

I have a Fender stage 185. It’s similar to this. I had a hum. It turned out to be the effects loop attenuated switch.

[@stuartukguitarampguy5830]

Ah ok interesting thanks

[@dirkfuchser737]

as always... pure enjoyment to watch your videos... T H A N X !!

[@jamjar20049]

I always clean up the ground connection where it joins the chassis from the mains cable. Clean to bright metal and re do the bolt. Oxidation over the years can cause a small resistance build up, only a few ohms, but it is measurable, something like 7 ohms before cleaning and more or less zero ohms after cleaning. Similarly,back of the panel where the pots make contact could be cleaned, there should be zero resistance between the pot casing and the chassis at the connection point as it's screwed on. Worth doing some before and after measurements to see how effective the clean up has been. This might help with the residual hum that this amp has and any others like it that come your way. I have used this technique with good results on my six tranny amps (all Hohner) and the amps don't hum at all, apart from the reverb on one of them when I gun it. Thanks for the entertaining videos Stuart. Ian

[@stuartukguitarampguy5830]

Yes that's excellent advice thank you for reminding me about this.

[@vintageguitaramp_guitarteacher]

Hello Stuart. Another one of those amps which takes longer to to take to bits than it does to repair it. Not the best amp Fender have made, to say the least. A good fix as always. Take care.

[@stuartukguitarampguy5830]

Many thanks.

[@Timthecommenter]

Great vid. I have a fender Power Chorus (sorta the version one of this) and an Ultimate Chorus (the ultimate version). They both have different faults, but I'd really like to fix some of the noise on on the Power Chorus. The chorus effect makes swishy noises when engaged, but the real problem is the stereo effects loop - it just buzzes like crazy if you put anything in there. Might just disassemble and see if I can ID anything obvious. The Ultimate Chorus has a few damaged plastic input jacks. I don't know if that's fixable at all - those jacks look pretty odd.

[@stuartukguitarampguy5830]

Hi Tim Good luck resurecting these!

[@miguelrichartmellado2834]

Well done Stuart ! 👍👍

[@stuartukguitarampguy5830]

Thanks Miguel.

[@markprentice7785]

Quite a thin looking board, which would make it prone to flexing and causing issues with connections

[@katherinemacdonald9909]

Hi Stuart I made a comment asking about my fender stage 100 ,yes I know , well that was on you blues junior video, and then this one came up . Just got mine apart tapped gently everything and found as you said the smoothing pot is the corse cant turn the the buzz off and only happens when played Loud or on Drive / distortion . Many thanks I would not have found it and local repairs busyness wanted £300 just to look at it plus parts , is there a recommended supplier of parts you use and what are the best to fit please.👍🎩🥃

[@stuartukguitarampguy5830]

Well done for sorting it. No, I don;t have a preferred supplier really, I just get parts where I can, quite often on eBay actually!

[@NoSeAsuste]

Please make videos about ALL kind of circuits and repairs. THANKS.

[@Irkennalpha]

I just bought this amp, but it's on a rough condition I use the Stereo Loop, but the input jacks are so cheap and made of plastic. They work but are broken, I though replacing those jacks could be easy but now I don't think so.

[@stuartukguitarampguy5830]

I expect you'll manage to get it going.

[@Irkennalpha]

@@stuartukguitarampguy5830 yes, thank you. With that video I know have an idea of how feasible that is

[@katherinemacdonald9909]

Hi Stuart, took your advice with buying caps for my fender stage, they did Hum then buzz so load no control from switch panel . The caps in it are nichicon but ended up going direct to them as now one had them they are obsolete , tried F&T couldn’t find anyone selling them and £1.000 min order from F&T. Very difficult spent hours searching internet ended up at cricklewood electronics got two 3300uf 63v 105c caps when they turned up today they are correct legend but are a third smaller , question is can I use them or will they fail due to size . Many thanks Craig Macdonald.

[@stuartukguitarampguy5830]

If at least the same boltage and at least the same uF then the size doesn't matter. I get F&T from HiFi Collective.

[@katherinemacdonald9909]

@@stuartukguitarampguy5830 well that’s strange I ordered two F&T from HiFi collective and they sent 40c ones not 105c and when I question it they said they don’t stock SHI 105c so I sent them back . ,Do you have stock of F&T 105c you would sell me.

[@terrywebb5380]

Shame you have to take board out on most guitar amps. Wouldn’t life be simpler if there was a chassis plate that you unscrewed to expose solder joints. My Cambridge p60 amplifier had this arrangement and life was made a lot easier to rectify component faults. Keep these videos coming Stuart and thanks for sharing.

[@stuartukguitarampguy5830]

Hi Terry Yes it would! However most manufacturers do not even think about maintenance when designing equipment. There's absolutely nothing in it for them to do so.

[@irishplucker]

Hello Stuart.great fix.I have the Ultra Chorus which was the forerunner to this one and it has the same problem.Is it save to reflow the solder joints without discharging the caps?I have previously replaced both input jack sockets so have had the board out before.All help appreciated.thanks Michael.

[@stuartukguitarampguy5830]

Hi Michael Probably a bit late now but always discharge the caps first. Good luck with the fix.

[@irishplucker]

@@stuartukguitarampguy5830 Thanks Stuart...any quick way of doing this?..I haven't tried the fix...amp is currently plugged into the wall with the power off at the wall and the amp switched on....will this drain them to earth?....thanks

[@stuartukguitarampguy5830]

Hi. I assumed you were going to remove the chassis to reflow the joints? At that time just short out the large HT caps with a length of wire. The longer you leave the amp the lower the voltage on those caps. After a day or so it's unlikely to have mych vltage but it's always best to check with a metyer and/or short them out. Good luck.

[@irishplucker]

@@stuartukguitarampguy5830 Thanks Stuart.Yes the chassis will be out to do the work..really appreciate that and keep up the great work on the channel..thanks Michael.

[@carlmccarty6470]

Hi Stuart, I'm enjoying your video and have a quick question. I did not see you discharge the capacitors and was wondering if these are safe to service without doing so? I believe tube amps have much larger capacitors? Thanks

[@stuartukguitarampguy5830]

Hi Carl. Yes you should discharge the large electrolytics before working on an amp as they can store a large amount of charge even with the amp switched off.

[@carlmccarty6470]

@@stuartukguitarampguy5830 Thanks for the reply. I was able to fix my Ultimate Chorus by cleaning the volume pots.

[@stuartukguitarampguy5830]

@@carlmccarty6470 Great well done.

[@bobparker4989]

Well done Stuart you cracked it

[@stuartukguitarampguy5830]

Cheers Bob

[@michaelsteenson7915]

Hello Stuart.Can you tell me the value of the filter caps?and are they the same as the ones in the ultra chorus ?...can you supply them to me also..thanks Michael.

[@stuartukguitarampguy5830]

Which amp do you have? Is it the ultimate chorus? Can you not just read the values off the existing caps?

[@irishplucker]

​@@stuartukguitarampguy5830Hello Stuart..Ultra Chorus...I have sent a message to your website.

[@electrolytics]

Cool video. Thanks Berkshire Amp Repair.

[@stuartukguitarampguy5830]

Glad you enjoyed it!

[@okmokmqazqaz]

Hi Stuart, I have a similar one, a 1992 "Ultra Chorus" with a mid pitch noise that starts on switching it on and decreases in pitch until it disappears after 5-7mins. I have reflown the smoothing capacitors and the same noise persists every time I switch it on as described before. I checked the rest of the board for dry solder joints and all seem OK, Would you please have any suggestions on what to check next? Thanks a lot!

[@stuartukguitarampguy5830]

Ugh that sounds like some sort of oscillation. They can be very tough to sort out. No simple suggestions, sorry.

[@JaKeAFC09]

the ultra chorus should be exatly the same as the ultimate chorus under a different name. You can find the schematic of the ultimate. To troubleshoot it i guess you have to go thru the entre signal path to find the source of the noise.

[@stuartukguitarampguy5830]

Thanks Jake.

[@dennismasterton3834]

Well done Stuart.

[@stuartukguitarampguy5830]

Thanks Dennis

[@Phantom_dave]

Just question: You don't use your scope looking for noise, curious why not?

[@Phantom_dave]

Not queting your method, jut curious.

[@stuartukguitarampguy5830]

@@Phantom_dave Hi David Loike most people who repair gear, it is SUPER rare for me to have to get a scope out to trace things. 99% of the time simpler methods suffice.

[@steffenbrix]

So...no fix :(

[@indierocks7624]

No need to unload those black caps? or is thayt only in tube amps? Have the same prob so is my next project...

[@stuartukguitarampguy5830]

Mostly tube amps but they can certainly go in transistor amps but I usually only replace if faulty. Good luck with yours!

[@indierocks7624]

@@stuartukguitarampguy5830 Thx I see a lot videos when they unload the voltage of the caps first before they resolder them. So this voltage in the caps in a solid state is lower than in a tube amp? Dont want to be electrocuted... :)

[@stuartukguitarampguy5830]

@@indierocks7624 Hi,. Yes the cap voltages in solid state are WAY lower than tube amps. Typically they are +/- 50V. Tube amps are +450V!

[@paulsto6516]

Good show! Thanks for posting.

[@stuartukguitarampguy5830]

Thanks Paul.

[@richardmills6505]

Is that hum at 100Hz ? ie 2 x 50Hz mains ?

[@stuartukguitarampguy5830]

I can't recall I'm afraid.

[@SIXSTRING63]

At first listen it sounds like a bad solder joint on a cap. I will see if I’m right after finishing the video.

[@stuartukguitarampguy5830]

Good call.

[@toneelectronix]

Ahh!!! can be used as a morse code transmitter huh?? ;) Thank you Stuart!

[@seanhoward5562]

Looks like the amp was exposed to some type of dampness by the rust on the handles

[@stuartukguitarampguy5830]

Yes this is not uncommon. It's amazing where people store their amps!

[@sven31415]

I have it on my amps

[@cobar5342]

Well done

[@stuartukguitarampguy5830]

Thank you!

[@motokev2727]

Great video. Why would the owner pay big bucks to fix it. I'm guessing $150 USA

[@stuartukguitarampguy5830]

He didn't. I charged about $70. I don't have expensive premises and don't need to make a living at this so I can be reasonable in my pricing.

[@RonanCantwell]

It looks like someone has been in at that before, judging by the amount of flux residue on some of those pads...

[@stuartukguitarampguy5830]

Yes that's often the case!

[@bluesplayer59]

Smashing stuff !!

[@eugenepohjola258]

Howdy. These friggin' PCB:s in guitar amps. They will fail eventually. Cold solders may look good. The lead may have encircled the component lead yet not truly adhered. Difficult to spot alright. Tubes and PCB:s are a combination of failure even more. Thermal stresses will cause PCB traces to un-adhere to the board. Traces may brake and the split can be really difficult to see. PCB tube sockets are worst. Wired sockets are a little better. My former neighbour complained about her TV set. It had been in for repair several times but in the shop the fault did not show. It worked well. I suggested I might have a look at it. The PCB was fastened to the metal frame by long solders along the sides. I tilted the frame backwards as designed to be done. I tapped around the PCB with the screwdriver handle. With slightly heavier tapping I could get the fault come and go. I observed the framework longsolders being most sensitive. Sure enough. Pushing with the screwdriver on the board side of the solders cracks in the solderwork could be discerned. Using a magnifying glass it was evident that all longsolders had cracked. Quite an effort actually to redo all the longsolders in a zigzag manner. Like welders do longwelds to avoid leaving stresses in the welds. Voila'. I was rewarded with the best dinner of my life with ice cream and chocolate. Best regards.

[@stuartukguitarampguy5830]

Nice repair. Well done.

[@toml7945]

15:08 HaHaHa!!

[@edwardhannigan6324]

Funny but those old Fender amps look very impressive, but sound wise; and I used to have an old Fender tranny; was never the best..Still, interesting video and good fix..Ed..uk.😀

[@stuartukguitarampguy5830]

Thanks Ed. Yes, I hated that chorus effect!

[@10beerman]

To boldly go where someone's gone before.. me thinks

[@ancoraproductions]

You don't like it much... Well, you had the chorus set wrong. Distortion is not great, but the clean is very good.

[@stuartukguitarampguy5830]

Ah ok!

[@mrmanch204]

To set the chorus, left knob 10 o'clock- right knob 2 o'clock. You had far too much depth.

[@stuartukguitarampguy5830]

Ah, ok thanks for the tip

[@cybergyber]

Please put on nitrile gloves before poking about on a live circuit! Accidental groundings hurt at best.

[@stuartukguitarampguy5830]

Hi Yeah, after 50 years I knd of know what I'm doing! Also I'm not sure a nitrile glove would help with 450V DC. Could be wrong, and I'm not experimenting! All the best

[@ancoraproductions]

You've set the chorus wrong, that's all.

[@goodun2974]

Life is too short for tone that bad! Horrid-sounding thing; no surprise since it was built in the late 80's.

[@stuartukguitarampguy5830]

Agreed. Truly hidious. Ugh!

[@jasondorsey7110]

​@@stuartukguitarampguy5830The early 80s ones from the Rivera years were actually pretty good, but they were a little simpler, used better components and real wood cabs...from the late 80s on, fender stopped taking analog solid states seriously, now they're just entry level junk or overpriced unrepairable modellers

[@JaKeAFC09]

It's a nice amp instead, on the clean channel at least. It sounds weird because the chorus is not dialed in properly. Most effect pedals with sound bad at extreme settings.

[@steffenbrix]

This amp sounds absolutely wonderful...one of the best ever. But the hum makes it unusable.... :(

[@wallemon06]

These were built in 1992 with production ending in the late 90s, I believe. The first few years they were called Ultra Chorus. Later renamed Ultimate Chorus. I bought mine new in 1994.

[@alexdeleon7135]

Quite a poser, this one.

[@stuartukguitarampguy5830]

Got there in the end though!

[@_ROBERT.]

He's pretty good at what he doe's i definitely wouldn't say he is a poser a cleaver man yes.