Carver M-4.0 ...A/C Hum

Hello... Carver fans... I'm new to this site , but a owner of many Carver components... Trying to figure out the source of a "Nasty" ...A/C hum issue w/ an Carver M-4.0 Amp. This amp is a recent Ebay Gamble.. Ha! I'm an Ebayer! [ DuncanAudio777 ]

What I have tried: When I Isolate the amp w/ a pair of speakers... a loud & horrendous A/C growl... from L & R channels comes forth. When hooked up to the system.. the hum drops considerably ! ?? It is a bit strange that the noise level lowers as much as it does, but it is still present... I know this is NOT normal. My first inclination is power supply caps? One can spend as much $$ on all the caps ... than I paid for the amp, so I do not want to just start replacing 9000 uf caps @ $ 60.00+ each. The unit is in great cosmetic condition so I'm willing to upgrade as needed... May even upgrade signal path caps w/ audiophile grade caps... Any input would be great....[/b][/size]

Hello and welcome to the carver forum. Do you have any fluorescent lights, solid state dimmer switches or SS IR controls for a fan on the same circuit? You may try to flip the plug 180 degrees on the amplifier itself [where it actually plugs into the wall] and get back to us to see if that works.

Hi Julin... thx for welcome & reply... I have tried all of the simple issues... it is not a " ground loop" problem.

"Do you have any fluorescent lights, solid state dimmer switches or SS IR controls for a fan on the same circuit?" ....Nope.

The thing that puzzles me is ... amp w / a speaker load isolated... the hum is more like a... ROAR , which begins to harm one's ears ??? I hooked up a ...Carver PM 175 to same circuit & speakers .... DEAD Quiet... as it should be.
No visible signs of leakage or stress on 4.0 PS caps, but I realize they are aging....

PS... a bit later.. Just finished re-checking....amp w/ a pr. of speakers isolated... using an extension cord , ..went about the house trying other outlets... same exact results & rage.

I've experienced the same thing with an M-4.0t that I had awhile back. If you plugged in the amp to speakers without RCAs hooked up, a very loud hum came through the speakers. I think I discovered it when I was attempting to do an A/B comparison with a different amplifier. The hum wasn't present in the amp at all until I disconnected the RCAs then HHHMMMMMM!! Scared the crap right out of me!! I asked Rita (Carver's old tech) if that was normal and she just asked me why I'd have it hooked up that way in the first place. That amp was refurbished with all new caps and it still did it. Now I unplug everything before I attempt to make changes in my system, something I know I should of been doing anyway but for awhile there it was multiple amplifiers just about every day and I got lazy. Anyway, Welcome!!

Welcome DuncanAudio

So tom, would you like us to start calling you Julian from now on ??? LOL

Sure. You wouldn't mind me calling you TFM-6cb, would you? It's all good. Folks can call me whatever they would like.



Duncan, the hum while the RCA's are disconnected does not surprise me. As jjptkd has mentioned, this happens even on newly refurbed units as well. It wasn't until he mentioned this that I was reminded that this is normal [Mine did the same thing after refurb when I powered up and forgot the RCA input connection on a recently refurbished M4.0t].

Let me ask you this.....when you changed out the 4.0t with the PM amp, is there anything else that changed? I mean anything beyond the PC, L&R SC's and the L&R RCA's?

you need to remove the hair on that avatar tom!!!

TOM ... sorry about that lol

THX ...Everyone ... ALL comments are right on target ! AS ...we all know ... Rita's Comment is true. Why ?
I was swapping out amps while testing the M - 4.0... first noticed a hum while no music was playing. Not... the typical high power hiss. I use multiple amps & speakers @ the same time. Anyway..the , M-4.0 was the only one w/ any A/C noise . I pulled the amp out ..hooked a small set of test drivers to amp ... W/ ..No RCA ..In put. Why? To put a load on the amp & listen to see if the power tranny is humming OR ... hum from speakers only. As stated ... When this girl warmed up! ...she started.. P M S _ing !
I have owned many Carver amps .... still have my 15cb. NEVER... have I heard such a ROAR...from a SS amp. I own & tinker w/ tube amps, have had this happen w/ a tube amp w/ bad caps. Anyway, Having read many blogs & Carver posts... I'm finding out that this is... " normal " ??? However.... Read the Service Notes in the TFM 42/45 - M-4.0 manual last night... Found some great repair/ changes that address the excessive " buzzing " issues of these models.... SO GLAD I READ this info... as stated by others, Changing caps do NOT fix ..ALL ..Hum/buzz issues. There are several changes { by Carver } to power supply & lowering the input ohms... to lower noise ... I plan to try these "factory Fixes"
My personal add on.... Adding some shielding around Power Tranny & down the side of the Right Channel Rail

Really like the sound of the M-4.0.... I'm a Tube Lover , but my Power Hungry... JBL L'7s needed more juice than most tubed amps can deliver...
BTW/. Really like the sound of the TFM's ... Hate the A Series Amps that C. Corp. made. Sound harsh & horrible to me. Bet they would perform better w/ Higher Grade caps... I wanted to hear the M-4.0 ... due to the " tube modded sound" .... Later! D` I "m glad to be a part of this forum.... I do NOT need a $30,000 dollar SNOB Amp.... Give me a Carver..... then trick it out w/ Audiophile Grade caps ....I will let ya know how it turns out!

Duncan, you remind me a lot about LB. Forgive me if you do not know who he is.

Let me ask you this.....when you changed out the 4.0t with the PM amp, is there anything else that changed? I mean anything beyond the PC, L&R SC's and the L&R RCA's?

Could you please answer this one question for us?

You should really give an M-500t a listen. They sound great with JBL's.