yuka42

Yamaha P2200 power amp - Speaker protection
« on: December 21, 2017, 11:34:19 AM »
Good Day! 

I recently took on the task of putting new capacitors in my old Yamaha P2200 amplifier and at the same time I'd like to add some speaker protection to it.  The speaker protection relay board requires 12V AC to operate.  I was curious if I can steal this AC power from the amp itself rather than adding a wall wart?  There's a convenient point on the driver board that is 13V AC straight from the power transformer. 

My questions are:

Is this a safe thing to do?
Will it affect amp operation?
Would the chassis be ground?
Will the 1V difference matter?


Khron

Re: Yamaha P2200 power amp - Speaker protection
« Reply #1 on: December 21, 2017, 11:59:18 AM »
You'll have to check the datasheet for the relay(s) you intend to use - they should have at least the required current mentioned, and perhaps even some power-dissipation-versus-voltage graphs.

That being said, since that 13VAC winding seems to only be used for basically some biasing in the front end of the amp, it may very well not be capable of much over a few dozen mA or so. If at all possible, you'll wanna use as low-power relays as you can get / afford (in order to present as small of an additional load as possible).
Khron's Cave - Electronics - Audio - Teardowns - Mods - Repairs - Projects - Music - Rants - Shenanigans

yuka42

Re: Yamaha P2200 power amp - Speaker protection
« Reply #2 on: December 21, 2017, 12:28:50 PM »
Thanks Khron.  That's a good point about the current draw.  I'm very much a beginner when it comes to the theory.  Here's the datasheet, and a pic of the board itself.  It seems it will take anywhere from 12-18VAC or 12-24VDC.  The mA draw if I read the data sheet correctly would be roughly 40mA/relay. 

I would rather have it mounted inside the amp, nice, clean, and hidden...but if I have to use a separate power supply it wouldn't be the end of the world.  Thanks again.


yuka42

Re: Yamaha P2200 power amp - Speaker protection
« Reply #3 on: December 21, 2017, 12:29:49 PM »
Pic of the board.

Gene Pink

Re: Yamaha P2200 power amp - Speaker protection
« Reply #4 on: December 21, 2017, 12:54:18 PM »
There's a convenient point on the driver board that is 13V AC straight from the power transformer. 

And it is referenced to the -79V rail, through the bridge rectifier.

Gene

Khron

Re: Yamaha P2200 power amp - Speaker protection
« Reply #5 on: December 21, 2017, 01:10:26 PM »
You might be slightly mis-reading the datasheet ratings.

The 12V-rated relay coils will (only) take up to 15.6V or so (according to that 130% figure in the "Max allowable voltage" column at the far right).

If you apply AC to the coils of these, they'll just chatter, as they turn on and off with the sine-wave.

If relays have "AC-compatible" coils, that'll be clearly specified. If that's not mentioned, they're DC-only.




Thanks Khron.  That's a good point about the current draw.  I'm very much a beginner when it comes to the theory.  Here's the datasheet, and a pic of the board itself.  It seems it will take anywhere from 12-18VAC or 12-24VDC.  The mA draw if I read the data sheet correctly would be roughly 40mA/relay. 
Khron's Cave - Electronics - Audio - Teardowns - Mods - Repairs - Projects - Music - Rants - Shenanigans

gswan

Re: Yamaha P2200 power amp - Speaker protection
« Reply #6 on: December 21, 2017, 05:33:40 PM »
How are the relays going to be used for 'speaker protection'?
Is it just a delayed turn-on or are you planning on detecting excessive DC to the voice coil and disconnecting?

You should be aware that if you are using the relays as a switching device during fault conditions (eg full DC to driver) then under load an undersized relay will have its contacts welded or burnt up. Switching DC at full load is not trivial.

Re: Yamaha P2200 power amp - Speaker protection
« Reply #7 on: December 21, 2017, 06:00:56 PM »
I recently took on the task of putting new capacitors in my old Yamaha P2200 amplifier and at the same time I'd like to add some speaker protection to it.

you do know that the P2200 has protection circuitry ?


gswan

Re: Yamaha P2200 power amp - Speaker protection
« Reply #8 on: December 21, 2017, 06:25:22 PM »
The circuit posted does not appear to have any.
The supply rails to the OP devices come directly from the rectifier, and the OP devices appear to be connected directly to the speaker terminals. If an OP device goes short you will get 80VDC across the speaker, until maybe the fuse blows. However the damage may be done by then.

yuka42

Re: Yamaha P2200 power amp - Speaker protection
« Reply #9 on: December 21, 2017, 08:41:15 PM »
Hi All! 

Thanks for the replies.  The Yamaha P2200 does not in fact have any built in speaker protection.  The later models that came out after it....I don't remember the model number,  had speaker protection added.  I have this amp powering some late 70's JBL 4311B's and I'd like to add SOME sort of protection for those speakers as they are getting rare. 

The protection circuit pictured above is one I purchased off eBay specifically for this purpose.  The Velleman K4700U is the same type circuit although it does look a little beefier.  I kinda figured if DC dumps across the speaker outputs it would destroy the relay, hopefully saving the speaker in the process.  Looking at the data sheet, would they be able to handle 80VDC?  Should I look at a beefier circuit instead?

I don't have a lot of experience with relays to be honest so any education is welcome.  Thank you all again.  Here's the ebay add for interest sake.


gswan

Re: Yamaha P2200 power amp - Speaker protection
« Reply #10 on: December 21, 2017, 08:56:52 PM »
Those relay contact are only rated to 30VDC and 10A.
If your 80VDC is applied across the 4 ohm load (say), your relay needs to be able to *break* 20A at 80VDC.
Breaking DC at load starts an arc, which does not extinguish unless the armature is highly sprung and the contact distance is large.
With small relays like the one shown either your contacts will weld shut (providing no protection) or the relay will catch fire in a fault condition.

PRR

Re: Yamaha P2200 power amp - Speaker protection
« Reply #11 on: December 21, 2017, 09:08:03 PM »
The 10VAC winding "V1" will rectify-out to about 13V DC, seems to be fully floating, and already powers eight lamps.

_I_ think the 30V 10A relays will break this amp once or twice. They are actually rated to break the full audio power; but a short-to-rail is indeed pure DC and hard to break. As gswan says, failure may be no-break which is bad.

yuka42

Re: Yamaha P2200 power amp - Speaker protection
« Reply #12 on: December 21, 2017, 09:15:42 PM »
Okay.  After some searching, the circuit in hand works in conjunction with an IC called uPC1237HA...which is essentially built for the purpose of speaker protection (dc detection) and driving the relays (at least what I can figure).  Here's a description and block diagram.

Re: Yamaha P2200 power amp - Speaker protection
« Reply #13 on: December 21, 2017, 09:20:23 PM »
The Yamaha P2200 does not in fact have any built in speaker protection.  The later models that came out after it....I don't remember the model number,  had speaker protection added.
The later PC2002 features output relays.

Over two hundred Yamaha P2200 amplifiers can crossed my path in 25 years,
not once have I seen full output offset with an intact power line fuse.
Not to say it could not happen, but never observed full offset due to a shorted output transistor.
Which I summarize as the fuse blowing before the woofer seizes up.

As to effective output relay control circuitry,  consider the Marantz 250.
Powers from the rails, no extra AC winding necessary.
Look at the amplifier cross-eyed,  the relay kicks in, saving your loudspeakers.

gswan

Re: Yamaha P2200 power amp - Speaker protection
« Reply #14 on: December 21, 2017, 10:11:53 PM »
Okay.  After some searching, the circuit in hand works in conjunction with an IC called uPC1237HA...which is essentially built for the purpose of speaker protection (dc detection) and driving the relays (at least what I can figure).  Here's a description and block diagram.

It can be done with a few diodes and a couple of transistors.
No fancy IC needed. :)

yuka42

Re: Yamaha P2200 power amp - Speaker protection
« Reply #15 on: December 21, 2017, 10:59:29 PM »
It can be done with a few diodes and a couple of transistors.
No fancy IC needed. :)

Indeed.  Here's the Marantz 250 protection circuit.  Anything over 4.5VDC will turn on Q301 and ground the base of Q303 which shuts off the relay.  Man I'm learning all kinds of stuff today.   :D  Cool stuff.  Thanks.

gswan

Re: Yamaha P2200 power amp - Speaker protection
« Reply #16 on: December 21, 2017, 11:56:40 PM »
You can learn a lot from Rod Elliot too.

http://sound.whsites.net/project33.htm

JW

Re: Yamaha P2200 power amp - Speaker protection
« Reply #17 on: December 24, 2017, 05:12:23 PM »
I was faced with almost exactly the same situation with P2200 and JBL 4412's.
Although the amp is really great sounding, I eventually decided that the effort I was putting into researching/verifying that various speaker protection circuits were actually going to work wasn't worth it, and bought one of the newer crown amps. Oh well. Lot's of power and my speakers shouldn't  die because of amp failure. Hard to break 80V!

Also, just to add to the info here, I have 3 P2200/P2100 amps with at least one shorted output transistor each. I bought them that way, so don't have the broken coils  to lament about, but I'm guessing somebody did at some point. Just saying it can't be THAT un common. I have 3 of them.

yuka42

Re: Yamaha P2200 power amp - Speaker protection
« Reply #18 on: January 11, 2018, 11:49:25 AM »
Interesting info JW thanks.

Okay so maybe a bit of side topic but still the same amp.

Please excuse my lack of knowledge in the area. I need confirmation on some oscilloscope readings.

I’ve attached (albeit a cheap) oscilloscope to the outputs of the amp.

I see a 60 hz hum (which I could hear). The Vavr is reading +15mV on the left channel. Would that be the DC offset?  Do I have the scope setup correctly as far as you can tell?  I just built the thing and am learning as I go. Thanks for any clarity you can lend.

yuka42

Re: Yamaha P2200 power amp - Speaker protection
« Reply #19 on: January 11, 2018, 11:58:29 AM »
Here is the right channel. Both channels set to minimum.