Carver M1.5 Crackle Noise - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 22nd March 2013, 06:53 PM   #1
diyAudio Member
 
Join Date: Sep 2011
Default Carver M1.5 Crackle Noise

Hello all,

I've recently acquired a Carver M1.5 and upon listening have found that there is a faintly audible crackle sound.

Diagnostic indicators:
  1. It's definitely worse when the interconnects are unplugged.
  2. It actually seems to get better when the amplifier has been on for a while.
  3. The crackling becomes louder with an increase in volume, but not in direct proportion.
  4. The crackling isn't constant... It comes and goes quite frequently.

Pretty weird. DC offset on both channels is below 15mV.

Any ideas?

Cheers,
Chris
  Reply With Quote
Old 22nd March 2013, 10:20 PM   #2
Tajzmaj is offline Tajzmaj  Slovenia
diyAudio Member
 
Join Date: Mar 2011
Location: Ljubljana
Hi.
I have some experience with PM 1.5 which is basically the same amp. My advice would be recap it and properly adjust it again. It is an old amp. But of course good one. Funky unit. If you need I have service manual for PM1.5. It can be used for some guidance. Email me if you need it.
And it is also important amp is properly grounded.
That buzzzz or putputput...or something like that is generated by ''dimmer'' psu , that ''magnetic field coil''.
Cheers, Taj
  Reply With Quote
Old 26th March 2013, 07:36 PM   #3
diyAudio Member
 
Join Date: Sep 2011
Update:

The crackle definitely comes from both channels - but is worse in the left channel.

I found two burned resistors on the right channels board (you can see the same resistors on the left hand board), picture here: http://imgur.com/XZFtVvP

Otherwise the amplifier looks pretty good under the hood. It's a bit dusty, but none of the other components look burnt and none of the capacitors are bulging.

The crackle is definitely worse when the interconnects are not plugged in - might this be an indicator that the power caps are fine? I'd like to replace them in time, but I'd rather not replace them now unless I know they're the problem.

Cheers,
Chris
  Reply With Quote
Old 26th March 2013, 09:52 PM   #4
diyAudio Member
 
indianajo's Avatar
 
Join Date: Jan 2010
Location: Jeffersonville, Indiana USA
Small crackles probably won't be the power supply caps. Shorts in those would be huge crackles.
I've found small crackles in tantalum coupling caps, that I bought new with the crackle in them. Before the internet, you bought at the store and had to be "happy" with what was available. Having the right numbers on the outside was as far as the store was prepared to guarentee their parts.
The best way to isolate would be with an oscilloscope. Or, you can listen with a sound probe (amp with a DC blocking capacitor on the input and a zener across the input after the cap to reduce huge pops when the DC level changes in the input. If going though the stages, the crackle is only after a certain stage but not before, the problem is somewhere around that stage. Be careful, this amp has dangerous voltages in it, use only one hand at a time and clip the negative of the meter or probe to frame. Wear safety glasses, exploding parts can damage your eyes.
Good luck. If you use google the right way, the carver schematic diagram has been uploaded on this forum before.
__________________
Dynakit ST70, ST120, PAS2,Hammond H182(2 ea),H112,A100,10-82TC,Peavey CS800S,1.3K, SP2-XT's, T-300 HF Proj's, Steinway console, Herald RA88a mixer, Wurlitzer 4500, 4300
  Reply With Quote
Old 26th March 2013, 10:22 PM   #5
diyAudio Member
 
Join Date: Sep 2011
Thanks indianajo.

Could this not be a grounding issue?
  Reply With Quote
Old 27th March 2013, 12:35 AM   #6
diyAudio Member
 
indianajo's Avatar
 
Join Date: Jan 2010
Location: Jeffersonville, Indiana USA
Crackles can be bad solder joints, whether on the ground or the hot side. They can be oxidized pressure connections between brass/tin parts, as the ground lugs to case. Also any push in connector that is not gold/palladium/rhodium plated or soldered. (Almost every connector in commercial amps). The scope or sound probe may focus your eyes on just where. Or you can look at every solder joint or connection and hope you spot it. Can also be bad connections within a transistor, resistor, diode, or capacitor. Some guy with a Peavey bass amp on I&A thread just paid 50E in Portugal for an "expert" to find a crackle, which turned out to be the leg corroded off a zener diode at the solder joint. Poorly washed flux can do that in 30 years. Knowing which part or joint is the cause takes analysis.
__________________
Dynakit ST70, ST120, PAS2,Hammond H182(2 ea),H112,A100,10-82TC,Peavey CS800S,1.3K, SP2-XT's, T-300 HF Proj's, Steinway console, Herald RA88a mixer, Wurlitzer 4500, 4300

Last edited by indianajo; 27th March 2013 at 12:40 AM.
  Reply With Quote
Old 27th March 2013, 07:25 AM   #7
Tajzmaj is offline Tajzmaj  Slovenia
diyAudio Member
 
Join Date: Mar 2011
Location: Ljubljana
Hi. Those 2 resistors are R42, R43. They are part of ''+ rail commutator''. Once more I'm offering service manual. Amp boards are the same as in PM1.5. If you are not sure how to repair it, please get some experienced technician. This amp is more complicated because of it's triple rail design and ''magnetic field'' power supply. I doubt there is some exotic oxidation present. It's been probably shorted at full power and/or there is some dry small cap. I agree that crackling is not coming from smoothing cans. My guess is that something happened to that commutator circuit and it might be behaving quite randomly now. You will need scope, generator and chunky dummy load. Be aware there is very high voltage present. I don't know which version of PM1.5 is but even at ''L'' version there is some +-70V and +-124 at ''normal version. Please be careful.
Cheers
  Reply With Quote
Old 27th March 2013, 08:03 AM   #8
diyAudio Member
 
Join Date: Sep 2011
Hello gentlemen.

Thank you for your responses!

My electronics experience is severely limited, and I don't have access to a scope.

I think that I may take this amplifier to a professional.

Tajzmaj - thank you for the offer, but I actually already have the service manual for the M1.5.

I checked the DC rail voltage at the 130V filter caps and it's currently at 110V rather than 124V. Could this be the problem? I doubt so.

Chris
  Reply With Quote
Old 27th March 2013, 08:56 AM   #9
Tajzmaj is offline Tajzmaj  Slovenia
diyAudio Member
 
Join Date: Mar 2011
Location: Ljubljana
I don't think it's the problem. Of course you can try to adjust properly. It will probably change the '' rhythm '' of noise if it's related to psu ''pumping''. But still you have those burned resistors. I would strongly recommend to take it to some tech. I have several PM1.5 and it is definitely worth to recap it (completely-even all those small caps), maybe you can leave those 2 big filter cans. If you still have installed 2 smaller dark blue double caps there are substitute boards available on ebay. Than everything should be readjusted. After all this it will show how good it is. Very powerful and quite decent sounding. Maybe little on the ''hard'' side but still ok. And of course almost unlimited power for home use.
Cheers
50 80 V Capacitors to Repair Carver M 1 5 M 1 5T PM 1 5 | eBay
  Reply With Quote
Old 27th March 2013, 10:32 PM   #10
diyAudio Member
 
indianajo's Avatar
 
Join Date: Jan 2010
Location: Jeffersonville, Indiana USA
Good technician training is to purchase a 24 to 48 v power transformer, some filter caps and rectifiers, a junk car speaker, a heat sink (or old aluminum scrap) and an LM3886 amp IC, and build a sound probe. Check the chip amp thread for schematics etc, or download the LM3886 datasheet from datasheetcatalog.com. The amp plus a blocking cap (.47 uf @ 600v) on the input, and a back to back zener diode (2.7 v) from input + to ground, makes a sound probe. Then you can look for where the popping sound starts in the schematic. The Carver is a very difficult amp to learn the basics on. the triple power supply is tricky, and the voltages could be lethal. I learned solid state amp repair on a dynakit St120, a very simple 14 transistor amp with one power supply. In those days I had no schematic diagram or service manual or help, I had to draw my diagram and guess at a lot of things that had been burned away.
__________________
Dynakit ST70, ST120, PAS2,Hammond H182(2 ea),H112,A100,10-82TC,Peavey CS800S,1.3K, SP2-XT's, T-300 HF Proj's, Steinway console, Herald RA88a mixer, Wurlitzer 4500, 4300
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Caps for Carver M1.0T Original Burnedfingers Solid State 2 18th March 2011 11:07 PM
carver m1.5t joepro Solid State 4 22nd January 2007 07:30 AM
Help with Carver M1.5t oldsthunder Solid State 2 22nd June 2006 02:02 AM
Carver M1.0t Loud "tong tong" noise Visigoth Solid State 9 4th January 2006 01:17 AM
Carver M1.5t Transistors jeffgilb Parts 1 15th August 2005 03:22 PM


New To Site? Need Help?

All times are GMT. The time now is 04:13 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2