Spot the Design Error

[Phil Allison]

bitrex wrote:

--------------

Was this amp designed to pair with the NS-10s?

** No way.

It's a 30kg beast with large heatsinks designed for live sound applications.

Puts out over 400W per channel at 4 ohms, easily.

Some folk used them for studios monitors cos of having no fan noise.

More likely paired with the famous Yamaha NS1000s.

Look 'em up, best performing 3-way box speaker ever built.

Worth heaps even at 40 years old.



..... Phil





The joke about the NS-10s

is that every studio had a pair because they sounded so unremarkable
that if a mix sounded good on them it would sound good on anything.

 

bitrex <user@example.net> wrote in
news:TKwrF.135842$O_.45328@fx39.iad:

On 10/22/19 1:08 AM, Phil Allison wrote:
DecadentLinux...@decadence.org wrote:

------------------------------------

Hi to all my pals,

a certain "design genius" here called John thinks any clever
engineer can quickly decide if a design is good or otherwise by
assessing only a schematic.

I say that is bollocks, maybe a simple test will make my point.

--------------------------------------------------------------

This schem is for the famous Yamaha P2200 power amplifier sold
in large numbers throughout the 1980s.

http://bilder.hifi-forum.de/max/588660/yamaha-p-2200-schematic_5
025 76.jpg

Nothing very unusual about it, dif pair input with level
shifters, cascode class A stage with bootstrapped load and
complementary Darlington output using paralleled BJTs. All the
semis are well rated for their respective jobs.

Plus the amp meets its published specs easily.

However, within the power stage is a flaw that makes the amp
misbehave terribly. Another bad flaw involves the thermal
switches.

Who here can spot one or both first ?

Use the schem, don't go searching web forums.



Maybe the heat sinks are supposed to be electrically isolated
from
each other and they are not on the chassis?



** The TO3s area all on a large finned heatsink.

The TO220s have individual ones on the PCB.

The design flaws are discoverable from examining the schematic.

" However, within the power stage is a flaw that makes the amp
misbehave terribly. Another bad flaw involves the thermal
switches. "


Obviously, the misbehavior is not evident all the time or Yamaha
would never have sold any.



.... Phil


It's something that they could have not had happen without
spending any (or very little more money), yeah? That is to say
it's surely a design flaw vs a cost-cutting measure that they
figured wouldn't bother with because it didn't happen too often.

Equipment is sold with no protection from plugging an AC adapter
"wall wart" into a DC jack all the time but that can be a "design
flaw" or cost-cutting measure depending on how you look at it, the
mfgr probably does save 50 cents and also fuck you dummy learn to
read the labeling.

General Instrument had a Set top satellite receiver that would, only
after between 20 and 300 hours of operation, start exhibiting noise
in the audio. The audio chip was a custom 68 pin PLCC design by GI
done by Motorola.

Inspection of the chip revealed that Motorola had left out a mask
layet in the chip, and it would, after some time, build up a charge
and start spitting noise into the amp loop. Absolutely verified.
New chip, no noise. Let it run, and it would begin at some point.
Chips with the mask layer had no issue. Motorola was to pay, as
nearly 350k were already integrated into units, and some had even
made it to customer installations. We split the re-work and did
180,000 of them in San Diego, and Puerto Rico did the rest where they
were actually built.

We figured all told, it was going to cost Motorola over $10M for
the goof. Their answer was easy. They bought General Instrument
uplink encoder division.

Training 7 solder assembly folks how to reflow and pull off a 68
pin PLCC without ripping up 1996 tech circuit traces on a commercial
board not meant for rework or rough service was not easy.

They just cannot get that you cannot refow some and pull up and
then hope the rest melt too.

It was all done with MetCal heads sized for the chip. Still.

We did not have hot air rework stations.

Took 'em a while to find that problem's source.

 

[Winfield Hill]

Phil Allison wrote...

This schem is for the famous Yamaha P2200 power amplifier
sold in large numbers throughout the 1980s.

http://bilder.hifi-forum.de/max/588660/yamaha-p-2200-schematic_502576.jpg

I don't understand the input ground connection.
How does input shield-wire "E" get to ground?


--
Thanks,
- Win

 

[Phil Allison]

Winfield Hill wrote:

--------------------

Phil Allison wrote...

This schem is for the famous Yamaha P2200 power amplifier
sold in large numbers throughout the 1980s.

http://bilder.hifi-forum.de/max/588660/yamaha-p-2200-schematic_502576.jpg

I don't understand the input ground connection.
How does input shield-wire "E" get to ground?

** OK - especially for Win, cos he is *such* a nice guy.


1. From point E on the PCB ( mounted on a large heatsink ) it travels via a co-axial cable to an Alps, 21 step attenuator on the front panel.

2. From the same attenuator it also travels to the rear panel and meets up with a two pairs of metal XLRs ( male and female) plus two 1/4 inch jack sockets.

The *jack sockets* are firmly grounded to the aluminium metalwork.

The centre point of the two of 22,000uF, 100V filter caps also goes to chassis.

FYI:

Though the input is unbalanced, it is supply hum free and RF proof.

Note the use of two AC fuses, main and spare ;-)

Despite having an 800VA toroidal transformer and NO soft start system, it has a mild inrush surge.

Now, what is wrong with the two thermal reed switches ?

Surely a man of your experience can figure out that at easy one.



..... Phil

 

[Arie de Muynck]

On 2019-10-22 03:00, Phil Allison wrote:

Hi to all my pals,

a certain "design genius" here called John thinks any clever engineer can quickly decide if a design is good or otherwise by assessing only a schematic.

I say that is bollocks, maybe a simple test will make my point.

--------------------------------------------------------------

This schem is for the famous Yamaha P2200 power amplifier sold in large numbers throughout the 1980s.

http://bilder.hifi-forum.de/max/588660/yamaha-p-2200-schematic_502576.jpg

Nothing very unusual about it, dif pair input with level shifters, cascode class A stage with bootstrapped load and complementary Darlington output using paralleled BJTs. All the semis are well rated for their respective jobs.

Plus the amp meets its published specs easily.

However, within the power stage is a flaw that makes the amp misbehave terribly. Another bad flaw involves the thermal switches.

Who here can spot one or both first ?

Use the schem, don't go searching web forums.
.... Phil

D112/D113 seem upside down. This way they decrease the current limit
when there is less voltage over the output transistors, the reverse of a
SOA protection.

There is something very strange about the EUROPE (220V/240V) and
AUSTRALIA (240V) transformer connectionss in the bottom of the diagram.
Looks like a drawing error. Must have been been noticed on testing...

Also, a connection is missing from anode D308 to D306/C301.

More to be found, probably...

Arie de Muijnck

 

[Arie de Muynck]

On 2019-10-22 14:04, Arie de Muynck wrote:

On 2019-10-22 03:00, Phil Allison wrote:

Hi to all my pals,

a certain "design genius" here called John thinks any clever engineer
can quickly decide if a design is good or otherwise by assessing only
a schematic.

I say that is bollocks, maybe a simple test will make my point.

--------------------------------------------------------------

This schem is for the famous Yamaha P2200 power amplifier sold in
large numbers throughout the 1980s.

http://bilder.hifi-forum.de/max/588660/yamaha-p-2200-schematic_502576.jpg

Nothing very unusual about it, dif pair input with level shifters,
cascode class A stage with bootstrapped load and complementary
Darlington output using paralleled BJTs. All the semis are well rated
for their respective jobs.

Plus the amp meets its published specs easily.

However, within the power stage is a flaw that makes the amp misbehave
terribly. Another bad flaw involves the thermal switches.

Who here can spot one or both first ?

Use the schem, don't go searching web forums.
....  Phil


D112/D113 seem upside down. This way they decrease the current limit
when there is less voltage over the output transistors, the reverse of a
SOA protection.

Correction --> they _increase_ the current limit when the voltage is
lower. Should be OK, unless wrongly dimensioned.

There is something very strange about the EUROPE (220V/240V) and
AUSTRALIA (240V) transformer connectionss in the bottom of the diagram.
Looks like a drawing error. Must have been been noticed on testing...

Also, a connection is missing from anode D308 to D306/C301.

More to be found, probably...

Arie de Muijnck

 

This feels like an episode of Batman where the riddler has them in an imminent death situation and starts asking Batman riddles to get out of their predicament.

 

bulegoge@columbus.rr.com wrote in
news:e9d7366b-c40f-45e9-b411-6629043faf2e@googlegroups.com:

This feels like an episode of Batman where the riddler has them in
an imminent death situation and starts asking Batman riddles to
get out of their predicament.

Then...

That was a Holy Dumb Post, Robin.

 

[John Robertson]

On 2019/10/21 10:11 p.m., Phil Allison wrote:

bitrex wrote:

------------

C125 is too small


** No issue there, the output stage is quite stable.

You need to know about good power amp design in some detail.

The thermal switch issue is pretty glaring though.


.... Phil

You mean where either of the THERMAL READ Switches do nothing but turn
on LED 'PR'? They don't actually appear to cut any power to the amp if
it warms up a bit much...

The power switch on the General Model version appears to be missing the
point of having a second 220 winding in the primary transformer. Except
for the Australian version where it appears to be wired correctly.

John :-#)#

--
(Please post followups or tech inquiries to the USENET newsgroup)
John's Jukes Ltd.
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."

 

[piglet]

On 22/10/2019 02:00, Phil Allison wrote:

Hi to all my pals,

a certain "design genius" here called John thinks any clever engineer can quickly decide if a design is good or otherwise by assessing only a schematic.

I say that is bollocks, maybe a simple test will make my point.

--------------------------------------------------------------

This schem is for the famous Yamaha P2200 power amplifier sold in large numbers throughout the 1980s.

http://bilder.hifi-forum.de/max/588660/yamaha-p-2200-schematic_502576.jpg

Nothing very unusual about it, dif pair input with level shifters, cascode class A stage with bootstrapped load and complementary Darlington output using paralleled BJTs. All the semis are well rated for their respective jobs.

Plus the amp meets its published specs easily.

However, within the power stage is a flaw that makes the amp misbehave terribly. Another bad flaw involves the thermal switches.

Who here can spot one or both first ?

Use the schem, don't go searching web forums.




.... Phil

I am suspicious of VR101 - if the wiper lifts off the track then TR115
and TR110 will stop conducting and each half of the output stage will rail?

piglet

 

On Tue, 22 Oct 2019 14:07:54 +0200, Arie de Muynck
<no.spam@no.spam.org> wrote:

On 2019-10-22 14:04, Arie de Muynck wrote:
On 2019-10-22 03:00, Phil Allison wrote:

Hi to all my pals,

a certain "design genius" here called John thinks any clever engineer
can quickly decide if a design is good or otherwise by assessing only
a schematic.

I say that is bollocks, maybe a simple test will make my point.

--------------------------------------------------------------

This schem is for the famous Yamaha P2200 power amplifier sold in
large numbers throughout the 1980s.

http://bilder.hifi-forum.de/max/588660/yamaha-p-2200-schematic_502576.jpg

Nothing very unusual about it, dif pair input with level shifters,
cascode class A stage with bootstrapped load and complementary
Darlington output using paralleled BJTs. All the semis are well rated
for their respective jobs.

Plus the amp meets its published specs easily.

However, within the power stage is a flaw that makes the amp misbehave
terribly. Another bad flaw involves the thermal switches.

Who here can spot one or both first ?

Use the schem, don't go searching web forums.
....  Phil


D112/D113 seem upside down. This way they decrease the current limit
when there is less voltage over the output transistors, the reverse of a
SOA protection.

Correction --> they _increase_ the current limit when the voltage is
lower. Should be OK, unless wrongly dimensioned.

Looks to me that if one side swings close to a rail, and current
limits, it increases the current limit on the opposite side, namely
the one with a lot of voltage drop across it.

Luckily, music is AC coupled so doesn't have really long duration
swings.

That is really an ugly variation on the repeated-a-million times
standard audio power amp.




--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

Phil Allison <pallison49@gmail.com> wrote:

Hi to all my pals,

a certain "design genius" here called John thinks any clever engineer can quickly decide if a design is good or otherwise by assessing only a schematic.

I say that is bollocks, maybe a simple test will make my point.

--------------------------------------------------------------

This schem is for the famous Yamaha P2200 power amplifier sold in large numbers throughout the 1980s.

http://bilder.hifi-forum.de/max/588660/yamaha-p-2200-schematic_502576.jpg

Nothing very unusual about it, dif pair input with level shifters, cascode class A stage with bootstrapped load and complementary Darlington output using paralleled BJTs. All the semis are well rated for their respective jobs.

Plus the amp meets its published specs easily.

However, within the power stage is a flaw that makes the amp misbehave terribly. Another bad flaw involves the thermal switches.

Who here can spot one or both first ?

Use the schem, don't go searching web forums.

Hmm, I can see two things which look like errors:

- capacitor C123 seem way too small, bigger (say 1u) would give
better transient response
- filetring of voltage for VAS and input stage is with respect
to negative rail, so it couples variation from negative rail.
Correct way is to filter with respect to ground (would cost
few cents for higher voltage capacitors)

The second rises THD, but it probably still is within specs,
so I would not call it "misbehave terribly".

Schematics is not clear about feedback takeof point. As drawn
it suggest that it may by suboptimal, leading to increased THD.

--
Waldek Hebisch

 

[piglet]

On 22/10/2019 22:12, Phil Allison wrote:

piglet wrote:

---------------


I am suspicious of VR101 - if the wiper lifts off the track then TR115
and TR110 will stop conducting and each half of the output stage will rail?


** The misbehaviour happens in normal use, it has no connection with any faults developing.

Affected uses had no choice but to get a different amplifier.



..... Phil

Thanks Phil. Ok how about C112 being a bit small to bypass a noisy zener
D105?

piglet

 

Phil Allison <pallison49@gmail.com> wrote in news:7b392552-82df-40ae-
9a59-16bb0fce0eec@googlegroups.com:

bule...@columbus.rr.com wrote:

----------------------------------

This feels like an episode of Batman where the riddler
has them in an imminent death situation and starts asking
Batman riddles to get out of their predicament.



.... LOL

You have succeeded in building a better bat trap.

 

[Winfield Hill]

Phil Allison wrote...

Now, what is wrong with the two thermal reed switches ?

What's right with it? The two LED circuit is incomplete
and meaningless, in the drawing, worse than the hidden
input ground connection. Are you saying that SL119B, or
whatever the p/n is, is two reed-relays? If so, where's
the rest of it? If not, what's going on, nothing?


--
Thanks,
- Win

 

[Phil Allison]

bule...@columbus.rr.com wrote:

----------------------------------

This feels like an episode of Batman where the riddler
has them in an imminent death situation and starts asking
Batman riddles to get out of their predicament.

..... LOL

 

[Phil Allison]

John Robertson wrote:

---------------------

The thermal switch issue is pretty glaring though.


------------------------------

You mean where either of the THERMAL READ Switches do nothing but turn
on LED 'PR'? They don't actually appear to cut any power to the amp if
it warms up a bit much...

-------------------------------------------

** OK - the first cupie doll goes to John Robertson !!

The two thermal reed switches, bolted to L & R channel heatsinks and wired to a PCB then a tiny red LED on the front panel, labelled "Thermal" - do absolutely nothing !!

https://en.audiofanzine.com/dual-channel-power-amp/yamaha/P2200/user_reviews/r.18074.html

The Japanese designer did just as required, fitted an over-temp indicator and left it at that.

In practice, the indicator only comes on when output devices are sizzling hot- about 120C on their cases. If nothing is done in the next few minutes the channel fails with massive damage requiring a complete re-build. Sometimes a serious PCB fire breaks out too.

I reckon you are supposed to have a little man, sitting watching that red led all the time and able to take immediate action if it ever lights !!!

The amp PCBs use about a dozen fusible resistors, mostly small WW types in crucial spots with mA ratings printed on them, but still they fail to stop the fibreglass board catching alight.

The nickname I invented for the model is the " 22 oh boom " !

----------------------------------------------------------

The power switch on the General Model version appears to be missing the
point of having a second 220 winding in the primary transformer. Except
for the Australian version where it appears to be wired correctly.

** That is a fascinating issue, I have never been able to get to the bottom of it. Yamaha's schem shows versions with the power tranny's primary dead shorted and power fed to the centre tap. Cannot possibly work as drawn.

My best guess is there are really two toroidal transformers in the aluminium can that hides them, primaries in series wired out of phase to each other.. Doing this reduces the magnitude of the inrush surge so no soft start is required.

FYI:

The general model is factory wired to suit the market while the others have a slide switch inside to select 220/240.



...... Phil

 

[Phil Allison]

piglet wrote:

---------------

I am suspicious of VR101 - if the wiper lifts off the track then TR115
and TR110 will stop conducting and each half of the output stage will rail?

** The misbehaviour happens in normal use, it has no connection with any faults developing.

Affected uses had no choice but to get a different amplifier.



...... Phil

 

[piglet]

On 22/10/2019 22:39, piglet wrote:

On 22/10/2019 22:12, Phil Allison wrote:
piglet wrote:

---------------


I am suspicious of VR101 - if the wiper lifts off the track then TR115
and TR110 will stop conducting and each half of the output stage will
rail?


** The misbehaviour happens in normal use, it has no connection with
any faults developing.

Affected uses had no choice but to get a different amplifier.



.....  Phil


Thanks Phil. Ok how about C112 being a bit small to bypass a noisy zener
D105?

piglet

Another thing I am not sure about is the way the aux -ve rail is ac
bypassed not to ground but instead to the -80v rail bobbing up and down
with signal - could that invite motorboating. Like make C116 a higher
voltage part with anode returned to ground not -80V.

piglet

 

[Phil Allison]

Winfield Hill wrote:

-------------------

Phil Allison wrote...

Now, what is wrong with the two thermal reed switches ?


What's right with it? The two LED circuit is incomplete
and meaningless,

** The circuit shown is complete.

John Robertson has already taken the cupie doll for spotting that it simply does nothing of any use.

A great many amplifiers have similar LED indicators labelled "Thermal" or "Protedct" but do actually shut the amp down or at least disconnect the speakers.

AFAIK, the P2200 is unique in not doing so.

Are you saying that SL119B, or
whatever the p/n is, is two reed-relays?

** No, that's the part number for the tiny front panel LEDs.

If so, where's the rest of it?
If not, what's going on, nothing?

** Hmmmm - the man cannot see the wood for the trees ...



...... Phil