Ron's Carv M1.5T Recap

[laatsch55]

Why 250 volt Jer? Those 15K-150's would fit wouldn't they?

 

[jbeckva]

Hey Jer, what's the voltage at the rails by chance (if you had a chance to check). The WOPL700 hits 1000w at around 107 right? Just wondered what this one was at or if that measurement would even apply to this type amp. Would love to know exactly what this baby pushes

Not exactly... From what I can decipher, the mag field amps actually have 3 "rails"... sort of... +/- 50, 80, and topping it out at 122 thereabouts. Can't really compare.

Hmm... so one thing.. you said ya heard a "subdued buzz"?? I can hear it .. but that's only if I am a good 6 inches or closer to the tweeters. We'll have to see if the main caps help that any, but if not hmmm... well, we'll "see". Just noticed in my email the caps are being shipped so it should be 2 days til we get those in.

 

[jbeckva]

Why 250 volt Jer? Those 15K-150's would fit wouldn't they?

The one's we spec'd for the 700's??? No.. those are 2.5 "around". The originals on the carv are 1.75 in diameter, so these I am getting (2 inches around) are pretty much as big as there is room for ... I'm probably going to have to do some working in that area to get them to fit.

 

[Phase Linear Phanatic]

Apologies good sirs; I have no business to butt in here; but in my ventures in trying to dig up research on my fathers gear; I thought maybe the Carver site could be of some use to you? I did not see it on the forum here in suggested links. There seems to be rebuilds for each individual amp, even this one. Perhaps this could assist you in some kind of way? If not be a fun read? I shall depart now with narry another word on this topic......

http://thecarversite.com/yetanotherforum/default.aspx?g=topics&f=100

 

[Northwinds]

Not exactly... From what I can decipher, the mag field amps actually have 3 "rails"... sort of... +/- 50, 80, and topping it out at 122 thereabouts. Can't really compare.

Hmm... so one thing.. you said ya heard a "subdued buzz"?? I can hear it .. but that's only if I am a good 6 inches or closer to the tweeters. We'll have to see if the main caps help that any, but if not hmmm... well, we'll "see". Just noticed in my email the caps are being shipped so it should be 2 days til we get those in.

Jer, try flipping the polarity of the plug. Yep, that sub-dued hum is why I sent it to you. Everywhere I read said the 50/80 deal would correct it but who knows. I really think a 3 prong plug is needed these days. That hum has to be some sort of ground issue BUT I have also read that the mag coil needs to be tightened down in some cases but that's something you might want to read up on at the Carver site. Something about a vibration that is transferred to the cover???

"Are you certain that the noise is coming from the speakers?
Disconnect the preamp inputs and speaker cables and power it up.
If you still hear the buzz it's probably caused by magnetostriction in the mag field coil.
Voids in the windings allow the wires to rub against each other as the magnetic fields reverse.
All transformers do this to some extent and mag field coils seem to be more prone.



Unfortunately there is no "cure", however, there are a few things that may reduce the magnitude:

• tighten the bolts that hold the mag field coil to the bottom panel
• install fiber washers on both sides of each of the mag field coil feet to isolate it from the chassis
• add a piece of insulation to the cover directly above the coil (both my M-1.5t's came that way from the factory)
• line the cover with Dynamat or a similar sound-deadening material (DO NOT BLOCK THE VENT HOLES!)

 

[Northwinds]

Apologies good sirs; I have no business to butt in here; but in my ventures in trying to dig up research on my fathers gear; I thought maybe the Carver site could be of some use to you? I did not see it on the forum here in suggested links. There seems to be rebuilds for each individual amp, even this one. Perhaps this could assist you in some kind of way? If not be a fun read? I shall depart now with narry another word on this topic......

http://thecarversite.com/yetanotherforum/default.aspx?g=topics&f=100

There is no such thing as bad advice, thank you! The Carver site though is filled with speculation and constant warnings that more of these amps are destroyed while fixing them by people who are not familiar with them but no direct answers. I have great confidence that Jer and our other experience fixers will get this baby up, done right and reliable. Some of the most knowledgeable people that I know of are on this board and my faith is in them, not a bunch of doomsayers who feel the only way to do it right is to send the amp to them LOL

 

[Phase Linear Phanatic]

There is no such thing as bad advice, thank you! The Carver site though is filled with speculation and constant warnings that more of these amps are destroyed while fixing them by people who are not familiar with them but no direct answers. I have great confidence that Jer and our other experience fixers will get this baby up, done right and reliable. Some of the most knowledgeable people that I know of are on this board and my faith is in them, not a bunch of doomsayers

Yes. I found this as well. Supposedly there is an MKII upgrade that can be done to the M500t's. (sort of like Joe's WOA upgrade) But all the doom and gloom from doing such a task that I read on the posts there had me saying NO to that desire. From the two magnetic field amps I had here; the buzzing seems normal. It sounds as if they come from the amps themselves. That's also normal from what the Carver site says. But I heard it from the speakers once too. Till I did something. Wait........it was when I had the left and right speakers connected; but NO RCA cables into the main in's. The amps were OFF! And the speakers buzzed. So did the amps. All be it faintly. (Until I pulled their power cords). Constant AC into the transformer and the design of the amp? Something I know nothing about. But when I connected my RCA's to the preamp and amp, the buzz from the speakers went away. Still; to have two of them doing the same thing...........I believe this is the intended design of the amp. There is a ground lug on the back of these things? Somone on the site there said they interconnected the two, someone else said they connected it to the pre-amp...blah blah speculation like you said. Mine went away, and at the volumes I listened to, the amp buzz was moot.

Still...............what's all this trickery here? Odd amps these things are................................

 

[laatsch55]

The desigh of the power supply, involves triacs, triacs are noisy.

 

[Northwinds]

The desigh of the power supply, involves triacs, triacs are noisy.

Is this noise what is called Mains-Bourne EMI???? I see that they sell filters for that issue

Seems wierd that I can't find posts about people complaining about the noise when the amps were purchased new or references to Carver amps being noisy like that. I wonder how many people on eBay that have sold these amps and then had a return because of that noise? Only references that I have seen point to some sort of ground loop and the fact that polarity may be an issue

 

[Phase Linear Phanatic]

Jer, try flipping the polarity of the plug. Yep, that sub-dued hum is why I sent it to you. Everywhere I read said the 50/80 deal would correct it but who knows. I really think a 3 prong plug is needed these days. That hum has to be some sort of ground issue BUT I have also read that the mag coil needs to be tightened down in some cases but that's something you might want to read up on at the Carver site. Something about a vibration that is transferred to the cover???

"Are you certain that the noise is coming from the speakers?
Disconnect the preamp inputs and speaker cables and power it up.
If you still hear the buzz it's probably caused by magnetostriction in the mag field coil.
Voids in the windings allow the wires to rub against each other as the magnetic fields reverse.
All transformers do this to some extent and mag field coils seem to be more prone.



Unfortunately there is no "cure", however, there are a few things that may reduce the magnitude:

• tighten the bolts that hold the mag field coil to the bottom panel
• install fiber washers on both sides of each of the mag field coil feet to isolate it from the chassis
• add a piece of insulation to the cover directly above the coil (both my M-1.5t's came that way from the factory)
• line the cover with Dynamat or a similar sound-deadening material (DO NOT BLOCK THE VENT HOLES!)

I can't speak for when the amps were new, but I am only agreeing here with the above answer you gave in explaining the buzz that you said you heard and that apparently that Jerry had heard as well. Since this was also the case with both mine as well , research on the site brought me to the same answers you saw more or less. I think age and inherrent design play a factor. Most complaints i saw of people who were doing overhauls of these amps, was that the boards were brittle and prone to complete catastrophic cracking. They seemed to think the new weight of the bigger caps caused this along with jolting from shipping the upgrade work back. Keep in mind what I read was all in the M500t section. So what i saw may differ slightly from what you saw on your specific amp.

Your speculation of wondering how many ebayers did a return on these things due to such a hum, makes me also ask how many ebayers are SELLING them for this reason? Magnetic field....... The word itself just makes me THINK the work "buzz". Just kinda kidding there but........It sounds like a transformer being a transformer; only the magnetic field being more prone by nature of design. As stated above. Sounds like a very logical answer?

I felt the buzz was faint as you describe and made no more noise than my old plasma tv when it was on. Nature of the design. The dynamat seems curious? I've used that in vehicle applications myself. I cant imagine dynamatting the inside of an amp though? Seems like that would only act as a heat insulator to me ? And you'd want the metal case to extract heat. Especially since the carvers have no external heat sinks ..........

 

[mlucitt]

You mentioned the buzz is coming from your tweeters? The infamous 60Hz hum would be most evident in the woofers, being designed to reproduce that frequency band specifically. If the sound is in both woofer and tweeter speakers, I would be temped to use the amp as a boat anchor. If the hum is only present in the tweeters, you have a classic 60 Hz harmonic issue that the circuitry in the amplifier is designed to reject, or your speaker crossover networks are mis-wired. It does not sound like an oscillation or "motorboating" sound?

I am not familiar with the Carver signal conditioning in the front end of the amp nor the filtering in the output section, but if this hum is coming through both L and R channels (I didn't see that in the post) it is likely originating in the power supply section. Obviously, if it is stronger on one side, that would be the side to troubleshoot.

I would start by placing .047/100V poly caps across all large capacitors to see if that makes any difference (easy), then I would place .005uF/250VAC X-type capacitors on both legs of the incoming power line grounded right at the case entry location (harder). Finally, I would install a power line conditioner inside the case and use a three-wire power cord to connect to the power line conditioner and ground the center conductor of the cord to a shiny place on the chassis with a star-shaped lockwasher on both sides of the lug (more harder).

I would love to put the output of that amp on a 250Mhz oscilloscope or audio analyzer with a 2KHz test signal or sweep the spectrum and find the exact profile of the "buzz" you are struggling with. Another thought - if you short the inputs, does it change the hum? That would point to a signal conditioning issue. Maybe front-end signal caps in both channels failed at the same time. Stranger things have happened.


Mark

 

[Northwinds]

You mentioned the buzz is coming from your tweeters? The infamous 60Hz hum would be most evident in the woofers, being designed to reproduce that frequency band specifically. If the sound is in both woofer and tweeter speakers, I would be temped to use the amp as a boat anchor. If the hum is only present in the tweeters, you have a classic 60 Hz harmonic issue that the circuitry in the amplifier is designed to reject, or your speaker crossover networks are mis-wired. It does not sound like an oscillation or "motorboating" sound?

I am not familiar with the Carver signal conditioning in the front end of the amp nor the filtering in the output section, but if this hum is coming through both L and R channels (I didn't see that in the post) it is likely originating in the power supply section. Obviously, if it is stronger on one side, that would be the side to troubleshoot.

I would start by placing .047/100V poly caps across all large capacitors to see if that makes any difference (easy), then I would place .005uF/250VAC X-type capacitors on both legs of the incoming power line grounded right at the case entry location (harder). Finally, I would install a power line conditioner inside the case and use a three-wire power cord to connect to the power line conditioner and ground the center conductor of the cord to a shiny place on the chassis with a star-shaped lockwasher on both sides of the lug (more harder).

I would love to put the output of that amp on a 250Mhz oscilloscope or audio analyzer with a 2KHz test signal or sweep the spectrum and find the exact profile of the "buzz" you are struggling with. Another thought - if you short the inputs, does it change the hum? That would point to a signal conditioning issue. Maybe front-end signal caps in both channels failed at the same time. Stranger things have happened.


Mark

Hi Mark, before the amp left here for Jer's, I heard the subdued hum in both sides only from the woofers, Jer says he hears it in the tweeters now so I don't honestly know. I took it deep in the ass with this trade deal but there is no way I will use this as a boat anchor. I can't afford any other good amps, what I have is what I have unless I am lucky and win Lee's Supercharged PL400 prize and based on my luck, I am certainly not holding my breath. Other then that, I have to use what I already have. The bucks are just not there as I am basically unemployed and have two teenagers in the house who are my priorities. I also will not downgrade just to have another amp in my system. I am so used to the WOPL400 that most everything else sucks in comparison but I had high hopes for this M1.5T

My speakers are not the issue, they are CV E-712's and perform flawlessly with the WOPL. They are very similiar to the D-7's that CV replaced in the E series lineup

I still have a C1 preamp that needs the tone bank looked at... it makes a thump sometimes when engaged and you touch the tones controls, sometimes it does not... but when the tone bank is switched off, it performs flawlessly? I have never been a fan of tone controls so it's not an issue to use it as is. I am still using the CT-24 with the WOPL, the C1 is a decoration in the back bedroom for now along with an Audio Source EQ ONE series II that has a hum. It's nice to own quality gear but the fact that it sits unused because of issues makes it worthless

Personally, the fact that the M1.5T uses a plug without a ground disturbs me, grounds would seem important to make sure there is no noise but Lee says the use of triacs in it mean it's going to be noisy no matter what so a conumdrum indeed. Do these amps really make noise like Phase Linear Phanatic says? The Carver board is a waste of time for me, more people say bad things then good unless I let them "fix" my amp. Jer is deep into it, we will wait and see what he says in his next post. Perhaps the ideas you suggested might help isolate any problem and hopefully will solve any issues. Joe said he was going to look at the schematics but I have not seen him pop on here with his thoughts yet. I imagine his plate is already full so that is understandable

I have faith in Jer and the other guys such as yourself who have the knowledge to figure this stuff out. I just sit back and try to understand while keeping my fingers crossed

I am so mad that I got burnt on this deal, I could have probably snagged a much better amp but the AK seller said everything worked as it should (except the non-working M200T that came in the deal which I sold for $50 to help finance some parts for this 1.5). This was my shot at a better amp and I guess I just made a poor decision

EDIT: Bottomline I am grateful to Jer for taking it on as my SS Gift, also to Lee and anyone else who has helped with ideas, can't ask for much better then that

 

[jbeckva]

Ah don't count me out yet dudes. Got some polys to ring around the bridges, and the big caps are being replaced.

Really it aint noticeable on the tweeters unless I am 6 inches away (wear headphones, geesh lol). But we'll see... "half full"

 

[Northwinds]

No worries Jer on that account, I have total faith in you. Like I said countless times before, you turned a blown up husk into a firebreathing monster. Your skills are not in question at all and then again, this is a board devoted to Phase Linear amps and this is new ground for a lot of people. You are an explorer heading into uncharted territory like Lewis and Clark and they did pretty damn well

 

[jbeckva]

Long as I don't have to deal with Montezuma's Revenge..

 

[mlucitt]

Your equipment is in good hands with Jer. It will be good for all of us to learn what is causing the hum and how it can be fixed or at least reduced.

Mark

 

[Gepetto]

Your equipment is in good hands with Jer. It will be good for all of us to learn what is causing the hum and how it can be fixed or at least reduced.

Mark

Haven't studied it in huge detail but would hunch that it is that triac regulator circuit on the AC primary attempting to regulate secondary voltages that you hear buzzing. That will throw off all kinds of harmonics that will make its way into your tweeters.

 

[Northwinds]

Haven't studied it in huge detail but would hunch that it is that triac regulator circuit on the AC primary attempting to regulate secondary voltages that you hear buzzing. That will throw off all kinds of harmonics that will make its way into your tweeters.

Joe, what do you think about the magnetostriction angle that the Carver guys spout off about? From what I have read, if it was magnetostriction, then the amp would buzz when no speakers are plugged in and I already checked that before I sent it to Jer. What your suggesting as a culprit seems plausible even with my extremely limited knowledge. This coincides with Lee's assertion that triacs are noisy so could that triac circuit be going bad? I am pretty sure when new that amp did not have that faint hum, the Stereo mags of the 80s would have tore Bob a new ass if it did

 

[Gepetto]

Joe, what do you think about the magnetostriction angle that the Carver guys spout off about? From what I have read, if it was magnetostriction, then the amp would buzz when no speakers are plugged in and I already checked that before I sent it to Jer. What your suggesting as a culprit seems plausible even with my extremely limited knowledge. This coincides with Lee's assertion that triacs are noisy so could that triac circuit be going bad? I am pretty sure when new that amp did not have that faint hum, the Stereo mags of the 80s would have tore Bob a new ass if it did

Not so sure of that Ron. I have run out of rule number ones but close to rule number one is you never put a low frequency switcher on any audio gear. That is what this triac appears to have done.

 

[Northwinds]

A member (Dennis Miller) over on AK saw a comment I made about the hum when I asked a member who is selling a restored M4.0T if he heard it. By PM this morning, this is what he said, not sure but maybe worth a try at least?

"I just recapped 4 M1.5t's this last week. So far I have only rotated one of the amps into my system for a listening test. The others are to follow soon.

I observe (hear) the same hum after powering up the amp and before powering up the pre-amp in my speakers. After I power up the pre-amp there is no hum from my speakers. It is dead quiet.

Does this describe the condition you also observed?

Is this normal? Yes for this amp. The hum is because the input is not terminated leaving the front end of this amp wide open.

Have your tech try this. Have him instal RCA shorting plugs into both the Left and Right inputs. The hum should go away. If it does not then you do have problem. Have him look for a bad ground connections between the boards and the chassis. Two come to mind. The triac has a ground bus from the Regulator board and the triac case and chassis. There is also a ground connection screw from the chassis to the speaker common.

Again if the hum goes away with the inputs shorted you have nothing to worry about. At least in my opinion."