Carver M-1.5t Noisy and weak one channel - diyAudio
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Old 29th January 2013, 01:15 AM   #1
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Default Carver M-1.5t Noisy and weak one channel

A friend brought me his Carver. Says it has a weak and crackly channel. I don't even have sp[eakers here that I can run it hard enough to replicate. Does this amp have any common areas to look for?
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Old 29th January 2013, 08:03 AM   #2
Tajzmaj is offline Tajzmaj  Slovenia
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Hi. M1.5 is quite complicated amp. I suggest you to get service manual and study it. If you need I have one for PM1.5 which is basically the same amp. There are probably quite few dried-out caps. Be aware there is VERY HIGH VOLTAGE present. Hi rail is +-125V so please be careful. If you don't have much experience repairing such amps you better find experienced tech.
Cheers
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Old 29th January 2013, 08:12 AM   #3
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I would really appreciate the manual. Thanks. Voltage was down to 119VDC. I adjusted slightly to 123.5. I don't think that would cause one channel to be out. I cheched input bias with meter. They both measure within a couple of points from one another. Aside from poking around and looking. I have done nothing. He said he'd like to recap it any way so I'll do all the electrolytics. I would like to know what brand to use for replacements.
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Old 29th January 2013, 08:22 AM   #4
Tajzmaj is offline Tajzmaj  Slovenia
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I'm not very ''audiophile'' guy so my advice about capacitors. Go with something decent like Panasonic, Elna, Vishay....I wouldn't buy any too expensive things. I'm not sure if you have still those nasty double capacitors inside. There are 2 big cans on the chassis and 2 smaller blue on the psu board. Later they replaced it with some sort of auxiliary board on which 2 capacitors were installed. Well luckily you can buy such board on the ebay. Try something like ''carver replacement capacitors''
It is also good idea to replace all 3 trimmers. 2 for idle adjustment and the one for psu voltage.
Email me and I will send you the manual.
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Old 29th January 2013, 08:30 AM   #5
Tajzmaj is offline Tajzmaj  Slovenia
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50 80 V Capacitors to Repair Carver M 1 5 M 1 5T PM 1 5 | eBay
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Old 29th January 2013, 05:05 PM   #6
djk is offline djk
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Be sure and replace the input cap, it's a small mylar type. The copperweld leads go intermittent.

Also be sure to replace the cap in the feedback loop to ground, that would make it sound weak.
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Old 29th January 2013, 05:12 PM   #7
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Could you please provide location or description of these components. This amp looks a little foreign to me but I am going to take my time and follow all of the instructions.
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Old 29th January 2013, 06:46 PM   #8
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Quote:
Originally Posted by argonrepublic View Post
He said he'd like to recap it any way so I'll do all the electrolytics. I would like to know what brand to use for replacements.
All brands sell a 1 year life cost cutter capacitor. Some brands also sell a 10 year life (10000 hours @ 105 deg C). capacitor. Check the datasheet and buy the latter. I go as low as 3000 hours sometimes, but not below.
Crackling can be bad solder joints or components that open up under stress. Not particularly a sign of bad e-caps. Can be a shorting film or ceramic cap. You need to probe through with a scope, or at the minimum a fast VOM or VTVM with a 20 VAC and 2 VAC scale. You will need to put a .047 or .1 uf cap in series with the probe on a VOM, they read DC on the AC scale otherwise. Unless you bought a RF probe for it. I exercise the amp with a battery radio tuned to a rock station so you can see the beats of the music on the meter face. DVM's average over 4 seconds or so, are useless for debugging AC problems. DVM's are useful for proving that you are not going to kill yourself on a charged up (over 25 VDC) cap. At the end of the repair I load test the amp into 8 ohm 225 watt resistors, or 10 ohm 450 watt resistors in pairs. I clip lead 4 ohm car radio speakers, protected by >4700 uf back to back electrolytic caps, across 5 ohms of the 10 ohm resistor, so I can hear the music during the load test. Check your DC out on speaker and bias current on OT's before finishing.
I don't believe in the experts only theory of repair, but I do believe in sharing the knowledge. One hand at a time around high voltage- over 25. Electricity across your heart can stop it. Don't solder or work with tools with the amp plugged in. Don't touch any metal over 25 VDC. Use a clip lead to analog ground on the minus of the meter to facilitate one hand debug. No jewelry- 3 V can burn your finger off with a ring. Don't work alone with the power on. Discharge any caps or other metal over 25 VDC with a resistor tool like detailed under "high voltage" safety thread of the tube amp forum. Unslolder with safety glasses on, solder splashes. Use them for tests too, there is enough energy in this amp to blow capacitors through the ceiling if they short. If you have any DC out on speaker at any point, put the amp in series on a wall heater element with the mains voltage to keep OT explosions limited in size. This amp is too big for a light bulb box, IMHO. Make the AC connections securely and in a gounded box, no bare ac wires flying around. My 1.3k wouldn't get the op amps to +-15 v on a light bulb box.
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Last edited by indianajo; 29th January 2013 at 07:07 PM.
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Old 18th February 2013, 06:00 PM   #9
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I have been reluctant (cautious) about the Carver amp. I went ahead and bought the Capacitor kit but have not installed it. The amplifier has been hooked up on one channel for a while I have been told. I ran it on two channels and was able to hear sound intermittently on one channel. I have it on my desk. Plugged it and went through it comparing voltages on both channels they are dead on equal.
I then unplugged the unit and checked for impedance at inputs. It appears one the good channel is 0.1 ohms and the bad channel is wide open. I am going to study the service manual and am open to and hopeful for any opinions. This amplifier is out of my league but may find something simple and with help, repair something more complicated.
Thanks
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