| rcavictim |
I don't know 'what' this gizmo is so I put it here. Can anyone explain what a Bob Carver Magnetic Firled Power Amplifier is? I have wondered about this for long enough. There is a pair on ebay now here. < http://cgi.ebay.com/Pair-Bob-Carver...1QQcmdZViewItem >
With a name like that I have visions of a saturable reactor being used as the amplifying device. Am I correct? |
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| DCPreamp |
Hi There,
I've worked on a few of these and I've observed the following:
1) Magnetic Field Power Amp = a fancy (maybe even copyrited) name just to stand out among other amps and dazzle (baffle) the uninformed consumer.
2) The only thing related to a magetic field is the use of a TRIAC plus additional circuitry to modulate the primary of the power transformer to limit power/secondary voltage. It doesn't appear to be very well regulated and only seems to "stiffen" the AC line under heavy loads. Not real fancy, not real effective, and can be very noisy due to the low frequency AC lines and spikes caused by high voltage switching.
3) All Carvers I've seen run 'Class G' (rail switching) circuitry in their output stage. They run low/med/high Vcc rails with the 'Class A' drivers running on the highest rails and the additional output devices connected to the higher rails by fast recovery diodes. The entire output stage is controlled by a single op-amp through global feedback. This gives the benifit of lower idle power thus the need for smaller heatsinks, along with high peak-power. The best example of this is their famous little cube amp rated at 200WPC with virtually no heatsink.
Like so much in this world, when you hear exotic names and fantastic claims, think marketing and sales hype, not NASA. |
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| anatech |
Hi Rob,
I'm "Mr. Carver" too. My shop was factory Canadian warranty.
Carver amps use a "mag coil" for the input power control. Normally three tiered supplies for the output section. Some class G, some H. It's a very light efficient amplifier that will deliver devastating amounts of power.
If you want to get these, we are semi close and I can help you out with any problems you may run into. There are a couple threads on Carver amps here somewhere.
-Chris
Edit: Think Nasa, it's valid. :D |
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| rcavictim |
Thanx for the replies guys! Very deceptive marketing name then. Thanx for the offer Chris but I think I'll stick with my 'vacuum tube transfer function programmed' vacuum tube amplifiers.
'vacuum tube transfer function programmed', That's what the seller claimed as though he was just passing on hype from the Carver literature about the product he is re-selling. Geeze what a bunch of c r a p. It is exactly that sort of thing why I now pronounce Bonus as 'BOGUS'.
I'm not making judgement on the amplifier itself of which I have no experience and which Chris spoke well of, just the marketing of it. |
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| anatech |
Hi Rob,
The marketing hype that went with this stuff drove me crazy! That part is cr*p for sure. I have to admit I was a bit surprised by your interest. They are good amps for what they were designed for. Tube amps they ain't.
TFM=Tube transfer Function Modified. There is an added resistance to reduce the damping factor. I don't know of any other changes that may or may not be present.
-Chris |
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| rcavictim |
| quote: | Originally posted by anatech
Hi Rob,
I have to admit I was a bit surprised by your interest. They are good amps for what they were designed for. Tube amps they ain't.
-Chris |
I had no intention of buying, I love my tube amps and highly efficient, very low distortion full range speakers.. The latest Carver auction I spotted just reminded me that I was curious about what they were as I had thought about it ever since I'd heard the hype (it turns out) name and really did think it was some clever applicatiion of a saturable reactor as a audio power amp. I mean with a name like that, what else could it be right? :bigeyes: |
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| Upupa Epops |
| This amp is horrible s... :D |
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| anatech |
Hi Upupa Epops,
You were going to say sand, right? :D
Bob Carver always had a way with advertising. I won't defend that because I found it embarrassing (being the national service center and all). But his engineering was good. He set out to prove a concept and did. The silly TFM came from those famous tests with that magazine.
Having said that, his later amps didn't sound bad, not like the M1.0t. Still there were all those op amps!! Somehow, though all of that, there were much worse sounding amplifiers on the market. His delivered silly power and seldom damaged a speaker when they failed. Now that's an engineering feat!
Would I own one long term - no. Although the Lightstar wasn't bad.
The transformer wasn't a saturable reactor per se, it wasn't used that way. There was no capacitor involved. I've never bothered to sit down and figure out exactly what it was. That was yet another terminology fight. Didn't need or want that.
-Chris ;) |
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| Upupa Epops |
| Chris, BC is probably good engineer, but much more better bussinesman... His machines are tailed-made for american market...No glory parametres, but giant power...Look at measured parametres and somewhere listen it ...You wil know, whatabout I'm talking ;) |
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| anatech |
Hi Upupa,
Yes, I agree. That's basically what I said. I listened to them for years. They got better, but not good to my standards. I listen to a Marantz 300DC and an Eico HF-87a. I am looking forward to building the SymAsym when I can get the boards made.
I've been very lucky to have been able to take home almost every decent amplifier made over the course of 20 years or so. However, in Europe you have an advantage over us in North America. Your industry is rich in two channel audio. Ours is an underground secretive kind of thing. Only a few two channel brands. Tube is even more a rare thing. Most of our good older tube product has been bought and taken to the Orient.
Curious, Upupa, have you listened to the Cyrus product and if so, what do you think? I am referring to the new Cyrus Power.
-Chris |
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| janneman |
| quote: | Originally posted by rcavictim
[snip]With a name like that I have visions of a saturable reactor being used as the amplifying device. Am I correct? |
You are close. It IS a saturable reactor circuit, but in the power supply. Basically it is a form of smps, off-line, but very simple and IIRC it also tracks the signal envelope so he can provide a lot of (music) power and get away with a relatively small output stage.
Jan Didden |
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| anatech |
Hi Jan,
I know this core saturates quickly with a sine wave input, but it is not operated in saturation normally. It's only used to regulate the internal supply voltages. It idles at a very low current.
I guess Mr Carver needed to draw very large amounts of current on demand, and this "transformer" was the way to do it. My thought was that it was a type of current transformer. I don't have a great understanding of how it actually works. I just know what happens when things go horribly wrong. :D When things go wrong with this circuit, it is horrible.
-Chris |
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| janneman |
| quote: | Originally posted by anatech
Hi Jan,
I know this core saturates quickly with a sine wave input, but it is not operated in saturation normally. It's only used to regulate the internal supply voltages. It idles at a very low current.
I guess Mr Carver needed to draw very large amounts of current on demand, and this "transformer" was the way to do it. My thought was that it was a type of current transformer. I don't have a great understanding of how it actually works. I just know what happens when things go horribly wrong. :D When things go wrong with this circuit, it is horrible.
-Chris |
It is some time since I saw it last, your memory of it may be better than mine. I thought that he would short the transformer with the triac to build up a large field that he later recovered when the triac shut off. That's why I mentioned a smps. But at any rate, it WAS clever. And he IS a marketing genius. Kind of like the Amar Bose of amplifiers ;) . Remember the 'Holographic Preamplifier"??
Jan Didden |
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| anatech |
Hi Jan,
They still give me "holographic" nightmares. I keep saying that Bob Carver loves op amps. That circuit reminds me of the old Quad "add with a bunch of amps strung in series" advert. The holographic circuit can be fun to troubleshoot. :dunno:
The primary circuit of a Carver amplifier uses a Triac in series with the mag coil. It varies the trigger phase to allow more or less power into the coil. The coil does not "like" to see a sine wave at all but is perfectly happy getting a chopped wave. This places high demands on the capacitors and rectifiers. They see a very steep waveform on the leading edge like a square wave.
Now for the sickness to show :innocent:, I enjoy working on these amps. The cubes not so much because you can't get to anything while it's together. Once you know what to look for, you don't have to re and re it so often. :bawling: I used to really hate them for that. Not any more. Just takes time.
-Chris |
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| ZGarage |
| quote: | Originally posted by rcavictim
I don't know 'what' this gizmo is so I put it here. Can anyone explain what a Bob Carver Magnetic Firled Power Amplifier is? I have wondered about this for long enough. There is a pair on ebay now here. < http://cgi.ebay.com/Pair-Bob-Carver...1QQcmdZViewItem >
With a name like that I have visions of a saturable reactor being used as the amplifying device. Am I correct? |
If my memory serves me correctly (from about 20 yrs ago) the magnetic field name comes from the ps; the "magnetic field power supply".
In a conventional power supply the mains transformer operates at 60 cycles, that is it charges the storage capacitors 60 times a second.
The magnetic field supply operates it's xformer much higher, above the audible range - usually 50k hz plus. The theoretical advantage is that since the storage bank gets refilled more quicky (50,000 times per second instead of 60 times per second) that the supply won't get "packed down" during large power transients and the amp will always have enough power available. This is also supposed to result in a very well regulated supply.
A side benifit is that the parts for the magnetic field supply are less expensive than for a linear supply.
Soundcraftsman was one of the first (with a patent)...and many japanese designs after about 1985 used this technology.
http://www.soundcraftsmen.com/SR_10_85.jpg
Near as I can tell the "Magnetic Field" name comes from the following (from Wikipedia) "Circuitry is used to pass current through the inductor to store a certain amount of electrical energy as a magnetic field. The current flow is then stopped, and the magnetic field collapses causing the stored energy to be released as current again. This is done rapidly (up to millions of times per second). By carefully metering the amount of energy stored in the inductor, the current released by the inductor can be regulated thus allowing the output voltage to be tightly regulated. A switching power supply incorporating a transformer can provide many output voltages simultaneously, and is typically called a flyback converter. Switching power supplies are typically very efficient if well designed, and therefore waste very little power as heat. Because of these efficiencies, they are typically much smaller and lighter than an equivalently rated linear supply."
http://en.wikipedia.org/wiki/Power_...de_power_supply
http://emcesd.com/tt2001/tt020101.htm |
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| I_Forgot |
Bob Carver put more research and development effort into marketing than into amps and the results show. The marketing BS flowed out of his factory so fast and thick you needed wings to stay above it. The amps were/are unreliable and not especially high audio quality. I would avoid them, in general, but the cube may eventually have some collector value if you get one that is working and put it away so that it stays that way.
I do have and still sometimes use a C-9 "sonic hologram generator" device that actually works as advertised. No power supply gimmicks in this one- just lots of op-amps. It is a speaker crosstalk canceller and provides a very interesting effect depending on the music and the speaker/listener/room placement. I looked into putting some lower noise op-amps in it about 10 years ago and discovered the signature BC design flaw- they used some TI quad op-amp with a non-standard pinout. They probably got a good deal on them because no one else would buy them with that weird pinout. There's no replacing them without making an adapter board. I decided it wasn't worth the trouble.
Soundcraftsmen amps are another story. They are absolutely bullet- proof. I have and still use a 200W/ch PM-860 that I bought new almost 20 years ago. I've connected everything to it, including a lot of experimental drivers and ESLs and it NEVER had any sort of problem. You can get them for <$0.50 per watt on ebay. If you like to experiment with speakers, get one. You can't go wrong.
I_F |
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| anatech |
Hi ZGarage,| quote: | | The magnetic field supply operates it's xformer much higher, above the audible range - usually 50k hz plus. The theoretical advantage is that since the storage bank gets refilled more quicky (50,000 times per second instead of 60 times per second) that the supply won't get "packed down" during large power transients and the amp will always have enough power available. This is also supposed to result in a very well regulated supply. |
No, it ran at 60 Hz and adjusted the firing phase of the triac to control power. It was very well regulated.
| quote: | | The amps were/are unreliable and not especially high audio quality. I would avoid them, in general, but the cube may eventually have some collector value if you get one that is working and put it away so that it stays that way. |
I have to completely disagree with you on that I_Forgot. You are wrong on both counts. Especially with the later models. We did get much service and most was due to people doing rather stupid things with those amps. They are / were very reliable. I just want something better to listen to but wouldn't hesitate to use on for surround. I do use a TFM-6 on my service bench where other amps have blown.
-Chris |
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| SleeperSupra |
I_Forgot,
How did the Carver and Soundcraftsmen stack up sound quality wise? |
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| SleeperSupra |
| My uncle is trying to tell me to get rid of my Soundcraftsmen MA5002A's and buy a pair of Carver M-4.0t's. |
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| anatech |
Hi SleeperSupra,
I don't think I lose the amps you have for M 4.0t's. Not unless you need silly high amounts of power. The later Carver amps sounded better. That and I bet they need service by now.
A TFM 75 would be cool.
-Chris |
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| panomaniac |
| quote: | Originally posted by I_Forgot
It is a speaker crosstalk canceller and provides a very interesting effect depending on the music and the speaker/listener/room placement. |
That's intriguing. How does it work? It is a sort of Dolby type L-C-R matrix that drops out the center? Or does it do something trickier, like flip the center out of phase and fold it back into left- right?
Just curious.... |
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| anatech |
Hi panomaniac,| quote: | | Or does it do something trickier, like flip the center out of phase and fold it back into left- right? |
Like the old vocal cancelers that let you sing to the music. Yipe!
-Chris |
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| I_Forgot |
| quote: | Originally posted by panomaniac
That's intriguing. How does it work? It is a sort of Dolby type L-C-R matrix that drops out the center? Or does it do something trickier, like flip the center out of phase and fold it back into left- right?
Just curious.... |
In your typical stereo speaker set-up, the left ear hears some sound from the right speaker and the right ear hears some sound from the left speaker. This has the effect of reducing the width of the stereo image and "blurring" the localization of instruments/voices.
With cross feed, you send some inverted phase left channel signal to the right speaker (along with the right speaker signal) and vice-versa. Since your ears are on opposite sides of your head, it takes a little longer for the sound from the left speaker to get to your right ear, so you apply a little delay to the cross fed inverted left channel signal that is sent to the right speaker. That way the cross fed signal and the signal from the 'wrong" speaker will arrive at your ear at the same time and cancel each other.
The cross mixing and phase inversion are simple op-amp summing network type stuff. The delays are usually implemented as "all-pass" filters, with op amps and RC networks.
The effect heard varies a lot with the speaker arrangement in the room, reflections from room boundaries, and the techniques used to mix the recording. With some music the box is absolutely fantastic, with other music it sort of muddies up the bass and doesn't sound right. It often has the effect of enabling sound source localization far from the speakers- it is sometimes a little disturbing, especially if you're nodding off and suddenly something starts sounding like it's behind you.
The only person who can hear the full effect is the one located right in the symmetrically centered listening position. I use electrostatic speakers that don't provide a very wide "sweet spot" and the combination of the speakers and crosstalk canceler is absolutely amazing with the right music.
I_F |
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| I_Forgot |
| quote: | Originally posted by SleeperSupra
I_Forgot,
How did the Carver and Soundcraftsmen stack up sound quality wise? |
In general, an amp that works and keeps working sounds a lot better than one that doesn't. My Soundcraftsmen amp drives any load I connect to it and never suffers component failures or even distorts audibly.
The two Carver amps I have had would both thermal cycle and distort severely if you connected anything but a "standard" speaker to them. Both died when the power transformers burned up. One blew the power fuse before completely destroying the transformer and afterwards it buzzed so loudly I had to throw it away because I couldn't stand to be in the same room with it and it definitely wasn't worth the expense of repair.
I'd say the Carvers were OK when I had them powering the bass drivers in my system when it was biamped. They could not handle driving the ESLs at all.
I_F |
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| anatech |
Hi I_Forgot,
Carvers could not be used to drive mid or high only. That's probably why you blew them up. They would drive bass or full range all day. The other requirement was a good AC supply.
I don't love these amps, but they were very reliable if properly used.
-Chris |
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| I_Forgot |
| quote: | Originally posted by anatech
Hi I_Forgot,
Carvers could not be used to drive mid or high only. That's probably why you blew them up. They would drive bass or full range all day. The other requirement was a good AC supply.
I don't love these amps, but they were very reliable if properly used.
-Chris |
When the amps blew up one was being used for full-range and the other was driving bass only.
I think the problem with them is they are designed with zero margin, anywhere. The power supplies are too small, the heatsinking is too small. The output transistors are right up against their SOA limits. The stability is marginal. There's not much to like about them.
Carver's design philosophy was that marketing rules. He wanted to differentiate his stuff from everything else out there, so he went for small size, light weight, and low cost. The marketing dept was the standard over-promise and under perform outfit. Baffle them with BS and they'll buy... hence "magnetic field" power amps, "sonic hologram" and all the other buzzwords they invented or perverted for their use.
Reducing the power transformer size and minimizing heat sinks takes a lot of the cost, size and weight out of an amp. Unfortunately it also takes out a lot of the reliability and performance. They don't make them like Carver did any more for good reason.
I_F |
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| sam9 |
Re C-9 sonic holography. The name is a tad silly, but if you think about trying to describe it to the general public, that phrase is probably easier to grasp than "speaker cross talk cancellation device" Takes up less space on the front panel. I_Forget's description squares pretty closely with mine. It works. Some times really well. Sometime disconcerting. My favorite example of disconcerting is with a closed miked acoustic guitar recording -- make it sound like the instrument is 10 feet wide. Actually, I think is approximates what you might hear during a guitar recital if you listened with your head 6 inches from the instrument. Sometimes with orchestral pieces it gives a more believable simulation of actually being there than some surround recordings. Finally it comes with a bypass switch if you don't like what you hear.
Re" Magnetic Field....." A purist 2 channel 200W amp, i.e., enough transformer VA rating, PS capacitance, output devices and heatsinkage to run full power indefinately, can be a real pain to deal with from the point of view of weight and physical dimension. Carver's orientation starting with the M400 seems to be to get those capabilities into a more use friendly package. I can't fault him for that. If there are compromises in other aspects that's hardly surprising. Life's like that. |
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| anatech |
Hi I_Forgot,
I did "factory warranty" in Canada for many years, and with many brands. The Carver product was more reliable than most.
Ways to kill a Carver:
Run mids and or highs only (locks the commutators up).
Run an extension cord or poor circuit (voltage falls and supply draws more to compensate).
Run off a small gas generator. (love that, both amp and generator become extinct).
Plug into 550 VAC (flames will cut TO-3 cases and bottom cover)
Let moron service it. (most people refuse to read the service manual).
Carver amps have more protecton than normal amps and normally will simply shut down (except in above cases). I've seen racks operate flawlessly for years. Even Clair Bros. used Carver successfully.
I really have to defend this brand for unjust accusations. If they were not serviced or used properly they could be unreliable. You can't blame the amp for that. But then that means you must read the manual.
BTW, they didn't use a normal transformer at all. It's more a current transformer and that's why it's small. They were very efficient, but not cheap.
If you want to see unreliable, look at a brand called Stewart. Bad design and cheap.
-Chris |
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| I_Forgot |
| quote: | Originally posted by anatech
Ways to kill a Carver:
Run mids and or highs only (locks the commutators up).
Run an extension cord or poor circuit (voltage falls and supply draws more to compensate).
Run off a small gas generator. (love that, both amp and generator become extinct).
|
It looks like you have more fully fleshed-out the list of reasons to avoid these amps.
An amp that dies because the supply voltage is a little low? An amp that works OK full range but dies when used for only the portion of the audio spectrum where the power demand is relatively low?
It is very narrow definition of quality and reliability that overlooks weaknesses such as those.
I_F |
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| Cal Weldon |
I don't think we're going to reach a consensus on this. The original question asked whazzit? not howzit? I really enjoyed the posts that didn't deal with the quality.
EDIT: Spelling |
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| anatech |
Hi I_Forgot,
Everything is in the owners manual. I will not comment further as you seem to have completely missed the importance of some of those things for all amplifiers.
So, operational questions can be answered. If you don't operate these properly, don't blame the amp.
Hi sam9,
Carver's marketing department was brilliant. They drove me nuts, I hated the nonsense they came up with. I pretty much agree with you on your points you've mentioned.
-Chris |
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| Speedz |
anatech, enjoyed reading your responses in this thread. learned some stuff.
i recently picked up a carver PM 1.5 amp.. i will be looking for some schematics for it soon (nice to have on hand) .. just curious your opinion on that amp. i'll be using it to power a pair of Carver Silver edition Amazing loudspeakers.
thanks,
Richard |
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| Workhorse |
| Carver & Anatech in super Harmony:devilr: |
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| gearheaddruid |
I did Carver warranty back in the 1980s. Repaired a lot of them in the 90s out of warranty. I owned one of the 1.5T models for years, never broke it.
If you want to get better sound from these amps. change the rectifiers to HEXFRED soft recovery diodes, change the op-amps to newer designs (Burr-Brown, AD, ECT.). I have modified a lot of them this way and they do sound much better.
I think if used for intended purpose they were fairly reliable as I at one point was doing service for almost every Karaoke company in K.C. and most used these amps because of size/weight/power output ratio. I rarely had to repair the amps, even after blowing speakers with them.
As soon as I had a design of my own working, I sold the Carver to a customer who is still running a pair of Magneplaners with it.
I like the sound of my Mosfet amp much better. Regards all. |
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| anatech |
Hi gearheaddruid,| quote: | | change the op-amps to newer designs (Burr-Brown, AD, ECT.). I have modified a lot of them this way and they do sound much better. |
Oh man!!! Don't do that!
Some Carver amps are sensitive to the op amp type. Play ever so carefully there. The Lightstar and a few others will not like that game at all.| quote: | | If you want to get better sound from these amps. change the rectifiers to HEXFRED soft recovery diodes |
I have my doubts there. Simply replacing the caps going open and changing the PCB mount filter caps will do that. There are far more serious things going on that hexfreds will not fix. Keep in mind that the amps are slightly underbiased (do not increase over spec). There is also a commutating transient on the output. Never mind the hash from the mag coil. Hexfreds in this case is only dressing on the window. As long as they make you feel good. Yes, been there, tried that. Everything sounded, measured and looked the same.
-Chris |
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| phase_accurate |
I still have a Carver PA amp somewhere (PM1400, was there something like that ?) that is used for a small disco PA once in a while.
I don't trust those double electrolytics that much anymore that are used in the PSU. Are they still made or is it better to replace them by normal types (altough one could run into problems with space) ?
Regards
Charles |
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| anatech |
Hi Charles,
Those were replaced by a PCB assy that fit in where the old dual units were fitted. They are single caps now. If you see any old dual units, they are most certainly bad.
I have heard of some members here fitting singles in on long leads. I don't think that's a secure way of doing this, but it is an option I guess.
-Chris |
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| gearheaddruid |
Chris, I was reffering to the older Carver Amps, I have been out of the service field for over ten years. The HEXFREDS seemed to help some of the commutating noise generated in the power supply. The op-amps I installed were OPA2604 and such. Did not have any stability problems with them.
I just have to add: "Run for the hills folks, or you'll be up to your ears in Martians"
Regards, Steve |
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| anatech |
Hi Steve,
LOL, you're sooooo right!
So, you put the new diodes in the commutator position, or the rectifier banks for supplies 1 and 2? The top rails have a bridge as you know.
I still would be careful with the op amps. They ran into problems when the new designs started using FET input op amps and other high bandwidth devices. They may misbehave in the 200KHz to 1 MHz region. It's like redesigning the front end of a normal amplifier and not looking at the stability. You may have been lucky so far.
-Chris |
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| jacco vermeulen |
| quote: | Originally posted by phase_accurate
don't trust those double electrolytics |
Manuel says : Que ?
If you don't mind the dummy asking, what kind of capacitors are that? |
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| phase_accurate |
| quote: | | If you don't mind the dummy asking, what kind of capacitors are that? |
In order to save space they used double electrolytics for two of the three rail voltages (IIRC, I would have to open the thing to be sure which rails used those). Just think of a lower-voltage and higher-capacity version of the ones that were once fashionable in older tube gear.
Regards
Charles |
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| anatech |
Hi jacco,
Charles' explaination is right, but I'm going to try and make it more clear.
A dual section cap as in those Carver amps was like an old time multi section capacitor. They use the common outer case as ground and had two sections inside. From the outside it simply looks like a radial can capacitor, but has two positive terminals and case ground terminals.
I wonder what the capacitance between sections was. In a Carver, it may have allowed noise to bleed between supplies.
Hi Charles,
The lower two rails. 31 V and 60 V. The 118 V rails used the large can caps on their sides.
All, be careful with the supply voltage adjustment on these. The supplies ran close to the maximum voltage rating on the supply caps. The adjust control can get intermittent. Do not attempt to adjust unless you know exactly what you are doing and are prepared if the supply goes high. You do not want the supplies to go high!
-Chris |
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| mobyd |
The dual cap used in the PM1.5 is certainly a rare bird - one section is 2200uF@50v and the other half is 2200uF@80v. Total unobtanium, and after kludging many with messes of hotmelt glue,cable ties and more standard caps, I finally made a little PCB to retrofit. Other Carvers seem to have unobtanium bits as well - The PM1400 has a little regulator/triac driver board that catches fire and uses a little Harris offline reg chip called a HV2405 and a half opamp/half comparator chip called an MC3405 - both gone the way of the dodo. The PT1250 used a couple of obtainable but bloody expensive BJTs in the SMPSU - luckily you can rip them out, along with the drivers and a pile of other bits and use a couple of modern IGBTs (4PC50UD or whatever) and they work fine. The cheesiest thing in the PM1.5 is the little $2 model shop motor that drives the fan (and whines like crazy when it whacks out its bearings).
M |
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| anatech |
Hi mobyd,| quote: | | The cheesiest thing in the PM1.5 is the little $2 model shop motor that drives the fan (and whines like crazy when it whacks out its bearings). |
That motor isn't too bad. A lack of maintenance will allow the bearings to fail. I note that several other devices use a similar fan.
That thing is the easiest to replace. Small computer type fan without a speed regulator. The caps may go open in the fan supply. Don't forget how old these units are, they are allowed to fail.
-Chris |
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| tomtt |
10 or so years ago, there was a Bob Carver interview,
in Audio magazine.
told them , that the first amp he made, was in a coffee can.
Said he had no money for a transformer, just ran the electric,
from the wall to the diodes , to the output devices-
Also had the nerve, to take his amp to the McIntoch clinic.
the Mc man told him
"this is the most powerful amp i have ever tested".
(350+ watts)
most of Bob's inovations, can be found in,
books about electronic instruments-
2360 |
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| Kahuna |
| Does anyone care to comment/share opinions on a Carver A-760x amp? |
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| jacco vermeulen |
Here's an example of Yamaha's X-Power circuit, an infringement of Bob Carver's patent.
The piano motorcycle company used the "X-Power" in a few 1981 amp models, stuff i saw and heard at the time. (although a 21 year old marine knows squat didly about hand-to-circuit combat)
The triacs are switched by a Sanyo manufactured ig04080, the transformer primaries and ground connections are in the upper and bottom corner on the right side of the centre board.
150 watts in 4 ohms from only two 120 watt Pd output devices.
These amplifiers were only available for a short while, Bob Carver sued Nippon Gakki successfully, afaih.
Notte bade for a commercial marketing guy. :clown:
I remember a Carver amp you can rip dozens of green and black Toshiba 2SA1302/2SC3281 out. |
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| anatech |
Hi Kahuna,
The A-760x is a good amp. A later design, it sounded better. The casework was less expensive to make.
Hi Jacco,
You may be thinking of a 500 or something early along those lines. Almost all plastic transistors in a Carver were 2SA1302A and 2SC3281A. Even the Lightstar. Earlier metal outputs were replaced with MJ15024 and MJ15025 types.
-Chris |
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| solderhead |
| quote: | Originally posted by anatech
Ways to kill a Carver:
Run mids and or highs only (locks the commutators up).
Run an extension cord or poor circuit (voltage falls and supply draws more to compensate).
Run off a small gas generator. (love that, both amp and generator become extinct).
Plug into 550 VAC (flames will cut TO-3 cases and bottom cover)
Let moron service it. (most people refuse to read the service manual). |
Chris, can you explain the failure mode that ensues when a Carver amp gets hooked up to a small gas generator? It would be interesting to know the mechanisms of failure for both the amp and the generator.
Thanks. |
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| anatech |
Hi solderhead,
That's easy if you consider how a Carver amp operates.
The Carver type power supply does not hold a huge amount of energy in reserve. It holds just enough to do the job. Therefore the standby current is very small, little heat being dissipated. Once a signal comes along, the required energy is almost immediately draw from the AC supply. This is because the energy is regulated right at the AC input. As the regulating circuits sense a supply voltage drop, they increase the conduction angle on the triac which results in more current being draw. It does this very quickly in time with the music. The fans on a PM 1.5 sit on their own winding and unregulated power supply, so are speed controlled by how hard the triac is turned on. You can hear them going to the music.
What I'm getting at is that the current demands are very immediate from the AC supply. Most times people load these amps down at 4 ohms or lower (even though they shouldn't). Now, a gas generator's output is controlled a little by changing the field current in the generator. The problem is that it can't track the Carver's current demands because they are so quick. The generator overshoots (voltage too high). This tends to cause a decrease in current in the Carver. The generator then undershoots (voltage too low) so the Carver draws more current. The cycle is like a low frequency oscillation - depending on the generator.
At some point the voltage gets high enough to damage the Carver, or low enough to damage the Carver and generator (at low voltage the Carver draws much higher than normal current). How would you like to have a mixer on the same circuit for that ride? All source devices get severely abused as well. Anyway, anything can happen once this gets out of control. I have no doubt that there are generators that can put up with this. The problem is that everyone buys the least expensive generator they can find.
Extension cords are also very bad for these amps if they are too thin or the run is too long. High voltage drop = high current = blown fuse at some point. A possible shorted triac means that when the fuse is replaced the amp may go full current with extremely high voltages inside. This is not pretty.
-Chris |
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| solderhead |
thanks! i am familiar with the immediacy of the current demands caused by these sorts of amps (i've seen them dim the lights to the music), and the dramatic effects on voltage that a subtle change in line resistance can cause under extreme current demands (why extension cords are a very bad idea).
yes, its easy to see why undervoltage/overvoltage inputs are so dangerous to the amp. i'm still trying to wrap my mind around how its bad for the generator though.
thanks again. |
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| anatech |
Hi solderhead,
Most generators can not deal with Carver sized fault currents. There may be a regulator burn out issue trying to excite the field under high voltage and extreme load conditions. Don't forget they are attempting to track each other. The generator would be outside it's design envelope at some points.
I've never seen the dead generators. They went elsewhere. I'm sure their guy has only heard of the Carver amps, never saw one.
-Chris |
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| sam9 |
A PA or pro amp that doesn't interact well with a generator could be serious grounds for concern. But I can't get too upset with that when the amp is clearly intended for ordinary consumer in the home use.
Failure when bi-amping (described earlier) was not much of a worry ca. 1980 when the M400 hundred appeared since bi-amping in a home environment was relatively rare. Also in 1980 power amps were more common among average audio consumer. Today, what with AVRs, iPods and so on I think power amp owner is much more likely to be a serious (fanatic?) audiophile. And that category is likely to make more demands on the equipment. |
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| anatech |
Hi Sam9,
In professional audio, you would use real generators. These are Caribana (Toronto Festival) guys using cheap Honda (and others) gas generators and cranking them into 2 ohms.
I have no pity for them, just their equipment.
-Chris |
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| imix500 |
| The number of those small honda 2 cycle generators used in the various parades in this city where people turn a float into a mobile pa is kinda scary. That's also one reason why the shop I work at demands a large deposit before we rent pa for a parade float. |
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| anatech |
Hi imix500,
I know you've seen this.
Now imagine Caribana, it's completely unreal!
These guys come from all over the world so they can destroy amps - again! Like, every year! And they are mad at the rental companies, the manufacturers and the generator dudes. Everyone but themselves. I am convinced that many just can't accept responsibility at all.
Right after Caribana, it's a fix fest. Some write-offs.
But nothing burns like a powerbase man! :D We're talkin' flames out both sides. :devilr:
No normal festival or nightclub can do this kind of damage. These guys do it all during this short festival. Oh yeah, some of them like to shoot each other as well. :rolleyes:
-Chris |
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| jleaman |
| I'm curious to see what is inside one of these amplifiers ? Any one got a inside shot ? |
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| imix500 |
| It even worse with the shop I'm at. We're the second largest Meyer Sound renter/retailer in the US. With a 15" driver costing $600 (there are 4) and it's accompanying amp at about $4200 in an M3D Sub, the repair bill adds up quickly with this brand. Hence the deposit. |
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| anatech |
Hi Jason,
What, the Carver or Powerbase?
No pics of a Powerbase (Amcron or Crown in the USA). For the powerbase, imagine a chassis divided mid way to make two shelves. There is a fan placed in the middle (brilliant!). The bottom is dirt and some soot. The top half is a couple rows of transistors (no mica) and lots of carbon on the PC board. Blast marks too! Lots of fun. Replacing the boards is the best option is you really want to repair one. They blow for keeps.
I may have a shot of an okay Carver. Yes, found it. This is a working M 1.5. I don't happen to have any in right now, but most look very close to this. What is not shown are the power supply board (along left side, front to back) and the input PCB where the XLR jacks would go (left side on rear panel close to the supply board).
-Chris |
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| anatech |
Hi imix500,
Wow, you get nailed on two ends then. You must see some beauty destruction come back. Innocent faces behind the burned gear. Or, likely there are some you just never see again.
Just do not rent for Caribana in Toronto - ever! Not that you would.
-Chris
Edit:| quote: | | the repair bill adds up quickly with this brand. Hence the deposit. |
I imagine you recone them. Still a pain (labour) and some cost. It's not as bad as an entire driver, motor, frame and all.
How are the amps for service? Do they lose many components or is the damage very limited as in a Carver? |
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| jleaman |
| Oh, i thought these were switch mode PSU or somethng, I remember using one at a dj, and it weighed less than my school binder. |
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| jacco vermeulen |
| quote: | Originally posted by jleaman
or somethng |
Jase,
the PS uses a switching triac and a transformer is somewhat of a coil, so Mr Carver can be viewed as a pioneer of switch mode powersupplies for Oddio.
Or something. |
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| imix500 |
Hey Chris, yeah we've seen some innovative ways to blow up a cabinet. Mostly subs get damaged from being driven too hard. The amps have decent protection and the drivers are pretty stout, but if pushed hard enough you can hurt a Meyer product. It's usually the input board, which is mostly passive, the amp section when mosfets get shorted, or the power supply when input voltages are funky- many cabinets use 48v switching psu's. I either case we don't repair them. We bill for a new assembly and send the bad to Meyer to be rebuilt. I don't think they do component level repair either.
If I ever see a bid for Caribana I'll advice the bosses. Besides, there's a huge Meyer rentel house up there, I forget the name.
We actually don't recone. We bill for a new driver and the old ones go into the dumster. Diving in our dumpster can be a fruitful experience. |
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| phase_accurate |
| quote: | | Hey Chris, yeah we've seen some innovative ways to blow up a cabinet. |
One of my mates runs a small dealer/rental company for PA equipment.
He once sold an Audio Perforance PA to a small local music club. Audio Performance - a small Swiss manufacturer- used the same principles as early Meyer systems (the owner being a buddy of John Meyer).
So one of the guys at this venue once found out that there was a significant rise in bass at high loudness levels if certain links from the woofer box to the controller were removed. Well - they did indeed have more bass - but not for long (and not for cheap either). :hot:
Regards
Charles
Edit: Forgot to mention: It is impossible to make anything foolproof because fools are much too inventive. |
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| anatech |
Hi Charles,| quote: | | It is impossible to make anything foolproof because fools are much too inventive. |
:D
Yes, you learn that after a few years in the service business. Self proclaimed experts are the best at being stupid.
I had a policy of charging a$$hole tax to those people. I still didn't break even.
Hi mixi500,| quote: | | Besides, there's a huge Meyer rentel house up there, I forget the name. |
Long & McQuade or Steve's?| quote: | | Hey Chris, yeah we've seen some innovative ways to blow up a cabinet. |
I wish digital cameras were available way back when. What a gallery we could put together between all of us! :D Might be a good idea to start.
Hi Jason,| quote: | | Oh, i thought these were switch mode PSU or somethng |
As djk mentioned, the triac controlled the amount of energy soming in - thus regulating the power supply rails. The transformer was a special type that liked chopped, partial sine waves. It was called a "mag coil" and will draw extremely high current if you apply a full sine wave all by itself. It was more of a current transformer I guess. We always had technicians short these triacs out (to force it on! :rolleyes: ). They would call to order a mag coil then try to tell us it was defective. I started refusing returns on these pretty quickly. We always tried to explain to these guys that that wasn't the problem.
I wonder how many unrepaired Carver amps there are due to these idiots. Must be a lot of them.
-Chris |
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| wrenchone |
| The weird pinout opamp referred to in this thread is most likely the old RC4136. It was a dual version more or less of the 4558, a cheapo workhore opamp from the '70s. TI made the TL075, a quad TL071-type opamp with the same pinout, but it was never very popular. The rest of the world instead standardized on the LM324 pinout for quad opamps, and left the 4136-type devices in a historical backwater. |
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| anatech |
Hi wrenchone,| quote: | | The weird pinout opamp referred to in this thread is most likely the old RC4136. |
This chip was in use by so many manufacturers for so long, it's hard no to bump into one of these. The TL075 was an improvement in many circuits, but didn't work in all of them.
-Chris |
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| wrenchone |
| Nevertheless, despite their use in some circles, the 4136-pinout opamps went bye-bye. In their day, firms like Exar, Raytheon, and TI (among others) made them. I should have laid in a stock of TL075s when I had the chance. I still have some 4136s in my parts bin. They may still be there when they bury me.... |
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| dangus |
I have an "unrepaired" M1.0t glaring at me. When I first got it, it was intermittent turning on, although after a while it settled down. It was awesome for home use running a couple of NHT1259s. When I began doing parties, I found it wasn't quite so great. Running it off a generator, it ate fuses, until I had to give in and turn the volume down. After that I got a Peavey PV8.5C for the subs, and used the M1.0t for the mids/high cabinets. It still got very hot, so I made a cardboard shroud with a fan that duct-taped to the cover.
It finally gave up the ghost at a party where the generator voltage was unusually high. Nothing happens when it's switched on.
Any tips on what might have failed? |
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| solderhead |
Now this is an interesting case of bad timing. Some of you might remember that I've been looking for an M-1.5t Service Manual, just because I thought it would be good to have one around.
Well, today my amp started misbehaving. Its been playing fine without any audible symptoms or any warning lights, but when I powered it down today I ran into a status lights problem.
Normally, when I power down the amp (with the preamp turned all the way down) a soft "thump" is emitted from the speakers which is presumably a voltage transient. Then the red LEDs in the power bar slowly trickle upward and the amp goes to sleep. This is the way that the amp has worked for 20+ years since I bought it new.
Today when I powered down the amp things were different. As soon as I turned off the power, both yellow "Headroom Exhausted" LEDs came on and stayed on, and a whirring noise came out of the speakers. After a few intimidating seconds of yellow lights they finally went out, and I got the soft "thump." Then the red LEDs trickled upwards as normal and the amp went to sleep.
The new onset of the yellow LEDs at power down and the whirring noise coming out of the speakers scares me. The amp has never used the protection lights or made this sound before. |
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| anatech |
Hi solderhead,
There is a thread where I posted some "go over" instructions. Read it again please. Reread this thread too. PM me please.
Hi dangus,
Read the threads where I've posted on Carvers. Everything you need to know is there. Including this thread. PM me if you can not service it yourself.
You did exactly everything in your power to blow up your Carver. It put up with a lot of abuse from you. I understand that you didn't intend to kill it, but you did a great job. ;)
Hey Jeff - Thank you for posting those.
-Chris |
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| sam9 |
| quote: | | You did exactly everything in your power to blow up your Carver. |
I wonder if the M400's were a little tougher. I've know a couple of people who used them in bridged configuration to drive subwoofers. On the other hand, perhaps the low duty cycle that's usual with sub protect them. |
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| sam9 |
Anatech wrote:| quote: | | I still would be careful with the op amps. |
I had been thinking of someday substituting TL071s for the TLo81's in the M400. From the datasheet they look pretty compatible, almost like the TL07x's are TL08x's with better common mode rejection and better supply rejection. I wouldn't expect to hear much diiference except maybe a slightly lower noise floor. |
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| anatech |
Hi sam9,| quote: | | I wonder if the M400's were a little tougher. |
No. it's more a question of power output. The M 1.0t puts out a great deal more power, therefore the current demands are higher and the generated heat is much higher.
| quote: | | I had been thinking of someday substituting TL071s for the TLo81's in the M400. |
The TL071 is a superior part. You could try a more modern Fet type op amp, but you may run into stability problems. I'd just leave the originals in there unless you want to put newer ones of the same number. Processes are better today. If you feel really daring, try a new style Fet op amp. Might be fun and that might improve the performance, who knows?
-Chris |
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| solderhead |
| quote: | Originally posted by mobyd
The cheesiest thing in the PM1.5 is the little $2 model shop motor that drives the fan (and whines like crazy when it whacks out its bearings).
M |
| quote: | Originally posted by anatech
That motor isn't too bad. A lack of maintenance will allow the bearings to fail. I note that several other devices use a similar fan.
That thing is the easiest to replace. Small computer type fan without a speed regulator. The caps may go open in the fan supply. Don't forget how old these units are, they are allowed to fail. |
Chris, I have picked up a PM-1.5 that's got the noisy grinding bearings in the fan. What's the best solution, to buy a replacement fan from CarverPro? (if they're still available) Other sources? |
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| sam9 |
| quote: | | Chris, I have picked up a PM-1.5 that's got the noisy grinding bearings in the fan. What's the best solution, to buy a replacement fan from CarverPro? (if they're still available) Other sources? |
There are some very qiet fans made for PC's that are extemely quiet such as those from Silenx. Can anny of those be adapted to this use? |
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| anatech |
Hi solderhead,
First try to remove the fan and inspect it. Clean out all debris and clean the blades. Then run it with a variable power supply and listen to it. They draw a lot of current. Oil the front and rear sleeve bearings with a light, no additive machine oil. Sewing machine oil will not work over the long haul. 3-N-1 and WD-40 are not what you want to use either. Run it at low RPM to work the oil in. Then run it higher to see if it's still noisy.
I'm hoping you can save the bearings. Also check the caps and diodes for the fan supply.
Sometimes the brushes wear out. New motor time from Carver Pro.
Hi sam9,| quote: | | There are some very qiet fans made for PC's that are extemely quiet such as those from Silenx. Can anny of those be adapted to this use? |
Sorry, no. Once you see one of these amps you will understand. They could have used a more efficient fan, but they didn't. Therefore we are stuck with these.
-Chris |
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| solderhead |
| just an update: CarverPro no longer stocks fans for the PM-1.5/PM-1200 style amps. it seems that we're either stuck with repair or replacement. |
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| anatech |
Hi solderhead,
These are very similar to some hairdryer fans I've seen. Try contacting some of those suppliers.
-Chris |
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| I_Forgot |
Would using the wrong fan cause the amp to blow up?
They seem pretty picky about load, input signal frequency range, and power supply. But they are GREAT amps, and very reliable!
I_F |
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| anatech |
Hi I_Forgot,| quote: | | Would using the wrong fan cause the amp to blow up? |
Depending on many things. If the variable supply voltage caused the fan to fail, then the amp would overheat when driven hard for sure. Don't forget the fan speed is variable with the load on the supply.
Sorry I_Forgot, guess you forgot. :D
-Chris |
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| I_Forgot |
| quote: | Originally posted by anatech
Depending on many things. If the variable supply voltage caused the fan to fail, then the amp would overheat when driven hard for sure. Don't forget the fan speed is variable with the load on the supply. |
Actually I was making the assumption that the amp provided proper control for the fan. That was probably a foolish assumption on my part- the fan control is probably no more reliable than the rest of the amp. If you think impure thoughts about it, it will probably die a fiery death.
I_F |
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| anatech |
Hi I_Forgot,| quote: | | If you think impure thoughts about it, it will probably die a fiery death. |
:D
I needed that today, thanks! :)
The output from the mag coil depends on the flux density (or current through it). As the amplifier delivers power, the primary current increases (a lot). All windings connected to the core get more energy, or their voltage rises. Voltage feedback is returned to the error amp from all rails of the amplifier section so that they are fairly stable.
Now, the fans run on their own little winding. If you were to increase the voltage enough, there would be a point where the fans all run slowly. Naturally this is too high for the rails. The fans have almost enough voltage to turn under normal idle conditions. As the amplifier works into a load you can hear the fan(s) speeding up and slowing down to the music. :D You have to hear a wall of these doing this at a big show. It's pretty funny!
So, what's the problem you might ask? Easy. Most DC fans have a speed control circuit inside. This means at low voltage the fan supply is too lightly loaded. I don't know if that matters, except for higher voltages and under load you may over volt the filter caps, the current draw being lower that the originals. If you did away with the rectifiers and used the AC from the mag coil, those fans would tend to want to lock to the supply frequency. I think they would act as a normal transformer and overheat with the chopped wave form.
So, you are basically into uncharted waters there. The amp simply controls the fan with varying voltage as the load increases.
-Chris |
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| Zero Cool |
The soundcraftsmen PCR power supply uses triacs after the transformer and before the PSU Caps to regulate the supply lines. I have never really sat down and figured out exactly how it works. But it does....
Zc |
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| Zero Cool |
| quote: | Originally posted by SleeperSupra
I_Forgot,
How did the Carver and Soundcraftsmen stack up sound quality wise? |
The SC PCR series of amps are great. a little of the mosfet mist on the top end but very warm. They use the good Hitachi Mosfets. 2Sj50/K135's which i think were the best sounding of that series.
The Carvers can be harsh and very annoying. we had them in our studio and i could mark spots on the master fader where the sound would be harsh. presumably from the rail switching in the amp.
The SC are great little amps. the beat out the Adcoms hands down. they are a killer super budget amp.
The MA series and anything with a 4 digit number A2502 etc etc used some form of class H. and are not in the same league as the PCR or PM series or the Pro Power series of amps. all use the exact same circuit.
The Little SC's are still one of my fav amps of all time. I have even accidentally shorted out the speaker cables with out killing the amp. just popped a fuse but the amp still worked. |
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| anatech |
Hi Zero Cool,| quote: | | The soundcraftsmen PCR power supply uses triacs after the transformer and before the PSU Caps to regulate the supply lines. |
Yes, totally different circuit to the Carver product.| quote: | | The Carvers can be harsh and very annoying. |
The early ones - for sure! The late model ones were a completely different animal and sounded very good. So it depends on what you are comparing.| quote: | | The SC are great little amps. the beat out the Adcoms hands down. |
Again, different series and different models had their own sound with Adcom. The statement was too sweeping so as to be inaccurate for all models.
Please PM me. No parts have showed up yet. 2nd request.
-Chris |
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| sam9 |
Mine has been working fine since about 1982. I sent it is once for service to have the triac firing adjusted. It was buzzing quite a bit. But that's about it.
If you don't mistreat it in any of the way previously discussed (dumb human tricks), but just use it like a normal home audio product you should be fine. |
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| sam9 |
| quote: | | The Carvers can be harsh and very annoying. we had them in our studio and i could mark spots on the master fader where the sound would be harsh. presumably from the rail switching in the amp. |
\
I think it is interesting that Doug Self addresses this in his Class-G article and design. He says it results from diode switching noise. He claims to greatly reduce it by using Schottkys. Sounds like a potential fix assuming the rail switching in the unit you mention uses accomplished by diodes (it is in the M-400). But is there a Schottky that is safe to use at the voltages involved? |
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| solderhead |
| maybe i just overlooked it -- got a link to the Doug Self article? |
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| anatech |
Hi Guys,
Carver Cubes (M-400 and variants) are very tricky to service. Most people break the darn sockets. I hate when they do that! Too much grease is another pet peeve I have. Keep these away from most technicians.
The triac firing (uneven) has been an issue with those. The triac had been upgraded. They were the worst sounding models, but they did do exactly what they were designed to do.
Hi sam9,| quote: | | He says it results from diode switching noise. He claims to greatly reduce it by using Schottkys. |
No. I wish people would study things more completely before offering an opinion on them. I have his book, but haven't read it yet.
What I can say is this. The "glitches" on the output are caused by the commutating transistors. Playing with diodes is not the answer.
I am so sick of people "solving" problems with diodes!!!!
What happens is that the next voltage is applied to the output stage as a stepped waveform in the earlier models. What this means is when the signal crosses a threshold, BANG, the voltage is switched suddenly to the next level. This causes a glitch to be transmitted through the output transistor (the step is normally around 30 VDC to 50 ~ 60 VDC) to the output line. Later units then went to a tracking supply configuration which eliminated this glitch to a great extent. The final tier was still a "bang-bang" type. No diodes were played with because they were not the problem to begin with. It was how the supply voltage increases where handled.
So now you know what the problem was. I had countless amps on my bench and investigated this issue on my own. They had it fixed before any comment was made by myself.
Pretty smart cookies over at Carver eh? <------(I'm Canadian, what can I say?)
-Chris |
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| sam9 |
| quote: | No. I wish people would study things more completely before offering an opinion on them. I have his book, but haven't read it yet.
What I can say is this. The "glitches" on the output are caused by the commutating transistors. Playing with diodes is not the answer. |
Since you haven't read the book yet, the section of interest is Chapter 10. In the text around figures 10.7 and 10.8 diode gliches are discussed and the two figures are Spice simulations showing them. They are different from the normal crossover glitches. Sadly, he did not show traces from an actual amplifier before and after using Schottky's.
I felt I was offering a speculation rather than an opinion. Sorry if I wasn't clear on that point. Until such time as I get the nerve to muck around in side the thing I am speculating. If I were ever to try it and report on the results, then it would be an opinion. |
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| anatech |
Hi sam9,
No, I didn't take your statement as your opinion. You clearly stated that you read this in Self's book. I'm okay with that.
What I did was to offer my direct observations and the corporate response from Carver to those problems. So what I stated was exactly what I measured on my bench with my 'scope and THD analyzer. I cued up the glitches with the tracking supply commutation. Newer amplifiers were the commutated supply tracked the audio signal in an analog fashion still had these glitches, but to a greatly lesser degree.
Please feel free to make comments like this. I was unaware of Mr. Self's comments and so sought to set the record straight. I do appreciate this type of input.
I will have a peek later. One thing is correct though, these do not look like normal crossover glitches. Mostly because they aren't.
-Chris ;) |
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| sam9 |
Self's Class G schematic is visually simpler than an M400 and he doesn't say anything about power supplies so I'm guessing they are conventional with voltages taken off the secondary after the appropriate number of windings.
He also does something clever with biasing. Both inner and outer drivers are biased from the outer rail. Apparently biasing the4 inner driver from the inner rail is another source of switching noise. (I don't have the book nearby so my recollection is uncertain.) This hardly looks like a "simple mod" even if it could be don at all. |
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| anatech |
Hi sam9,
I glanced over the example used in Self's book. It's not the same as the Carver. Just related.
In Carver amps, the drivers are run from the top rails to begin with, I'm not sure about the M-400 though. The step voltage is also much higher than is normally used in a Carver. Perhaps that is why there are three rails as opposed to two.
So he is examining a much earlier Hitachi design rather than a Carver design, the differences between the two are important. I'll read that section more carefully once I begin this book.
-Chris |
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| crazygreek |
I love my Carver amps!
I'm a Business and Electrical Engineering student at Lehigh University, and I have been acquiring broken Carver TFM amps over the past couple of years for repair.
I had been using my first TFM-15 amp for deejaying, although it just recently developed an issue (see http://www.diyaudio.com/forums/show...threadid=106952). I just recently repaired a TFM-15CB, which will be used for redundancy with my deejay equipment (repair guide here: http://www.lehigh.edu/~evb209/proje...r2/carver2.html) I also have two broken TFM-25's, which I have been trying to combine into one working unit. I'm sure DIYaudio.com will be a great for these and other projects! |
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| solderhead |
back to the subject of fans:
| quote: | Originally posted by anatech
The output from the mag coil depends on the flux density (or current through it). As the amplifier delivers power, the primary current increases (a lot). All windings connected to the core get more energy, or their voltage rises. Voltage feedback is returned to the error amp from all rails of the amplifier section so that they are fairly stable.
Now, the fans run on their own little winding. If you were to increase the voltage enough, there would be a point where the fans all run slowly. Naturally this is too high for the rails. The fans have almost enough voltage to turn under normal idle conditions. As the amplifier works into a load you can hear the fan(s) speeding up and slowing down to the music. :D You have to hear a wall of these doing this at a big show. It's pretty funny!
So, what's the problem you might ask? Easy. Most DC fans have a speed control circuit inside. This means at low voltage the fan supply is too lightly loaded. I don't know if that matters, except for higher voltages and under load you may over volt the filter caps, the current draw being lower that the originals. If you did away with the rectifiers and used the AC from the mag coil, those fans would tend to want to lock to the supply frequency. I think they would act as a normal transformer and overheat with the chopped wave form.
So, you are basically into uncharted waters there. The amp simply controls the fan with varying voltage as the load increases. |
Chris, I finally obtained some replacement fans for the PM-1.5 from the OEM. I had the problem of spent bearings on an older fan, which had developed an intermittent noise problem. Sometimes the fan would idle slowly and quietly, and at other times it would squeal horribly. I cleaned a lot of dirt out of the fan, but the bearings were shot and it needed to be replaced.
After a lot of searching I found the OEM fan and ordered a batch of them. Upon replacing the original fan, the new fan is quite a bit louder at idle. Compared to the original 20-year old fans which would spin very slowly at idle votlages of 6-9 VDC, the new fan spins a LOT faster and it moves a LOT more air at and idle votlage of 18 VDC. Notice that when the amp is idle the DC voltage across the fan is a lot higher than it was on the original fan that was replaced.
I have to admit I'm a bit surprised by the fact that the supply voltage increased so dramatically upon replacing the fan. It jumped from somewhere between 6 - 9 VDC with the old fan to about 18 VDC with the new fan. As you would expect, the new fan spins a lot faster and moves a lot more air. But it seems far too loud, both at idle and under load.
By any chance do you know the votlage specifications for the fan supply? It would be interesting to know the voltage specifications for operation at load vs. no-load condtions, at both the Low and Hi switch settings. It would also be interesting to know the voltage specs for the fan when the thermal switch bypasses the dropping resistors on the fan board. FWIW the fan is rated 12-32 VDC / 80mA, though at idle the old fans were markedly under voltage at 6-9 VDC. To get to such low voltages with the new fan one would need to sub the dropping resistors, and at those votlages, sometimes the new fan will turn and sometimes it won't |
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| anatech |
Hi solderhead,
The voltage across the fans is determined by both the loading on the fan supply and the load the amplifier is under. They normally turn slowly at idle. Your B+ adjustment will affect how the fans run. Therefore, your B+ adjustment must be set before you can do anything else. That includes bias current. I guess you can set up the meters though.
Do you have a link for the OEM supplier?
Hi crazygreek,| quote: | | I also have two broken TFM-25's, which I have been trying to combine into one working unit. |
I strongly disagree with this practice. What was wrong with the other amp?
-Chris |
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| solderhead |
AFAIK the B+ is only adjustable on the 124 VDC rail by adjusting RP1 on the PSU board. It is adjusted properly to 124VDC, and the OTs are properly biased.
I seem to be missing how to adjust the B+ on the low (36VDC) and medium (74VDC) rails. If you could point that out I'd appreciate it.
The fan circuit supply is actually taken off of the lowest voltage taps on the PT (red wires that supply the 36 VDC rail). There's a set of diodes forming a full wave SS rectifier on the back side of the PSU board, and the rectified unfiltered AC leaves the main PSU board at point C. It travels along a red wire under the chassis to the fan board. No adjustment of the fan supply voltage is available on either the main PSU board or the fan board. The only way to adjust the fan B+ is by swapping out the voltage dropping resistors on the fan PCB. |
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