Carver M-1.5t THUMP at Power Off

[bob p]

Seeing the complexity of Carver's designs, I'd be sorely tempted to stuff in a relay-based anti-thump and DC offset protection board. Trying to modify the existing circuit could open such a can of worms.

I had thought about something similar -- just building a box that would go between the amp and the speakers, and switch from the speakers to a dummy load during power-on/off. It could have a manual switch, or a time delay relay might work, and it could be an external device that would not require any mods to the amp.

I heard about the "Magnetic Field" power supply years ago and always wanted to know how in hell it worked. But from the literature you guys posted, it looks like it's just a triac lamp dimmer with a heavy coat of marketing BS. I still want to know more though, maybe I should be looking for a 2nd hand Carver to take apart

There's also a magnetic coil in there that stores some energy and releases it on demand. Last night I was digging through an old file of stereo manuals that I hadn't seen in 20+ years. In it I found the complete 20-page Carver brochure from back in the day, and there are a couple of pages that explain how the mag field patent works using schematic snippets and block diagrams. I'll scan it and post the relevant pages here.

[Mark Black]

I just found where some kind soul has scanned & uploaded the entire PM1.5 service manual, complete with all pages. Missing only the service bulletin on power supply diode upgrade (you replace all 8 of the main rectifiers with 6A10 type). It's 10MB in size.

http://www.raindogindustrialarts.com...ual_PM-1.5.pdf

From this discussion:
http://www.diyaudio.com/forums/showthread/t-81446.html

I love it when people do that!

Now if you want to get into something REALLY different go out and find a Peavey DECA-series amp to poke around in...

[bob p]

Holy Cow! What a great find!!! Mark, you ROCK!

Just in case anyone's interested in looking at that vintage brochure that I mentioned earlier, I've scanned the first few pages (the amplifiers section). The problem is that it wouldn't scan at anything less than 600dpi so the file is pretty big at 9.3 MB. Its too big to attach here. If your email can handle something that big, lemme know and I'll send it your way, otherwise I'll need to find a location where I can upload it.

[Mark Black]

Hey Bob - do I remember correctly you run Mac OS?

If so there is a wonderful graphics tool called Graphic Converter available as shareware here:
http://www.lemkesoft.com/xd/public/c...lkPTE5Mw_.html

The thing is a great toolbox with almost Photoshop abilities, and will let you change file sizes via the "Save a copy as..." feature.

Super reasonable price too...

If you are not on a Mac I'm afraid I can't help there ('cause I don't do windows).

[bob p]

Not a Mac user -- Linux and Windows.

[Enzo]

Cool, I am on a dial up, so downloading a 10Mb file is not gonna happen. Let me know what it looks like.

[bob p]

Cool, I am on a dial up, so downloading a 10Mb file is not gonna happen. Let me know what it looks like.

actually, it looks like a can of worms.

[bob p]

on a more serious note, 81 pages, 12 chapters. the schematics are fragmented into one page pieces, and that makes it hard to get a big picture of what is going on. the quality of the scan looks like a scan of a xerox of a xerox -- low contrast gray on white, and fuzzy in some places. the pages aren't numbered, and some of them are obviously out of order. some of the ordering seems very disjointed -- almost as if somebody went into the room of two college kids and shoveled a disorganized mess of papers into a scanner. finding information is kind of like looking for a needle in a haystack. The service bulletin section only has 3 service bulletins in it:

# PM-1.5A-4 (drive balancing)
# PM-1200-5 (replacement board for discontinued dual caps)
# PM-1200-2 (to reduce noise in outputs)

The rest of the TSBs seem to be missing.

ITS GREAT!

i'd really love to get my hands on the blueprint though.

regarding dial-up, i switched over to DSL because it was actually cheaper than dial-up for me, because i sit in one location and i don't need to pay for a mobility premium. of course, if you use the internet from several locations and you need mobility, a hard-wired line to one location can't help you. but at $14.95 for a fast direct connection, i'd still consider it if i was only working out of 2 locations. its just so much more convenient than dial-up that its worth the money to me. DSL allowed me to get rid of a 2nd voice line that i used for data. by eliminating that second phone line and the dialup fee, a fast connection costs me about half of what i used to pay for a slow as molasses dialup connection. its a definite improvement.

if you'd like to compare the PM-1.5 manual to what you've got and 10 MB is too big for you to download, just PM me with your mailing address and I'll burn it to CD for you.

[Enzo]

I spread out those blueprints. Three of them are the power supply, and one is a channel card parts layout. I don't have the whole amp in plan size. The letter size I have is what the factory sent us when we did sevic on them. it is a copy of a copy too.

I know about the DSL, but for various reasons, I don't want to change right now. DOn';t feel like looking for free install, the telco wants some bux to install. Prolly wants $$ for interface. I do have two lines, one mainly for computer at night, but it is also my ring over line during business, so not sure I can lose it. Also don't want to get stuck with 1 or 2 year commitment with a soak you early out charge when I am not sure I will be at this location for that long. I should have gone for it when I moved the business here a few years ago. The telco was falling all over them selves to get me into it. Free this free that. ANd I would not be able to keep my email addy. The ISP's idea of "taking care of that" is to send a blanket email to everyone on my contact list. BFD. It is in a lot more places than my list. Last time I changed phone numbers I paid the telco bux to get an extra year of forward number message to those calling old #. Yes, I know I would like it, because ther are things I just don't do now - streaming video, audio, large files, etc.

On to the Carver:

I don't find the multipage a problem. One page is an amp channel. Both are the same, so only need one. Got a block/wiring diagram. And a power supply. All the rest is layout drawings or schemos of odd things like the input card or the fan or the VU. Some of it is duplicated for 240v versions, I can skip those. Then a bunch of tyoed pages with circuit description and troubleshooting. Most anything I do to it will be looking at the channel card or the PS.

There is a bull about changing the gain of the amp - the sensitivity really - how much signal does it want for full out. Change R3 on each channel card.


Meanwhile, how does it stack up against your amp itself?

[bob p]

i don't really care about streaming video or streaming music either. its nice to be able to process the occasional large file when you need to, but in the big scheme of things i find that DSLs biggest benefit for me is to make web surfing less painful. the Ampage experience is a LOT better on DSL than it was for me on dialup -- much less waiting for pages to load. but you're right -- the thought of changing ISPs and emails is a real PITA. two ways around that are to use web-based email like yahoo or gmail, or to buy your own domain name and have someone handle the back office work to make enzo@enzo.com a reality. the second option is really just another way to spend money for people who think it is cool to have their own domain name.

i'm sure that you don't find multipage schematics to be a problem because your mind is better than mine at reading those sorts of documents and keeping it all in your head. you deal with lots of complex circuits and you're practiced at the whole compartmentalization concept. i'm just a self-trained tube hack who gets nervous any time he has to look at a circuit that's more complicated than an AB763.

i don't know how the PDF file I've downloaded stacks up against the amp itself. i haven't yet pulled the amp out of service and opened it up to compare it to what's on my computer screen. need to clean the desk off to make room...

[bob p]

There is a bull about changing the gain of the amp - the sensitivity really - how much signal does it want for full out. Change R3 on each channel card.

by any chance, would that have a bulletin number that matches the first one i described? it sounds like the same one, and i only have a total of 3 service bulletins for the PM-1.5.

[Enzo]

It doesn't have a number, it is a typed page with a drawing. If they issued it under a number later, I don't know it.

Here is the gist:
just near the TL081 is R3. Look straight down from pin 2 of IC1. It sets the gain. Here are some options for overall amp gain, input sensitivity for 450 watts into 8, and R3 value -

26db 3.0v 910 ohms
29db 2.0v 620 ohms
32db 1.5v 470 ohms

Do not attempt to have fain outside the range of 26-32db.

[bob p]

i don't have that.

[Enzo]

Well, now you do. That is about the extent of it. SOme paragraphs of palaver, and a little drawing to locate the part. One on each channel card. If you have a channel card layout drawing, you'll spot it.

[zbyszekskibinski]

loud thump in speakers on turn on/off

I looked up at your threads on annoying thumps in loudspeakers when turning off the amp and I seem to have the same problem with my Marshall MG 15 DFX.
It's brand new and on warranty, so I'd better not mess up with it now, but I was thinking about incorporating some delay speaker switching circuit. Anyway, do you guys think these thumps can cause some damage to the amp or the speakers? Cheers, Paul.