Pioneer's SA500 Blowing protection fuse

For the three and more legged things
User avatar
colin.hepburn
Shed dweller
Posts: 2294
Joined: Sat Jun 02, 2007 1:24 am
Location: Scotland Aberdeenshire

#91

Post by colin.hepburn »

Mike H wrote:Yep can do, need to get on with finishing some web pages first then can have a look
OK thanks mike
no worries no rush just when you have got the timer :)
Colin
The Blues man ImageImage
User avatar
Mike H
Amstrad Tower of Power
Posts: 20157
Joined: Sat Oct 04, 2008 5:38 pm
Location: The Fens
Contact:

#92

Post by Mike H »

Problee Saturday at a guess, maybe even late tomorrow afternoon, won't take long once I get going :D
 
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
User avatar
Mike H
Amstrad Tower of Power
Posts: 20157
Joined: Sat Oct 04, 2008 5:38 pm
Location: The Fens
Contact:

#93

Post by Mike H »

OK here we go ~ it's a bit big!

As you got 2 x 10,000uF I thought of using a separate bridge rectifier for each channel. :?:

Sorry presets for the regs had to get involved for a couple of reasons:

1. can't assume V-ref will be exactly 1.24 Volts.

2. even if it was, would mean resistor values will include fractions, difficult to source.

3. can't assume actual resistor values will be accurate.

Top half is for power amp, bottom half is for pre-amp, where says 'DUPLICATE FOR OTHER CHANNEL' it means what it sounds like, need two lots :D BR2 only shown as the 'start' of the duplicated other channel stuff.

Note as transformer is 300VA bridge rectifiers need to be rated at 10 Amps or something like just to be on the safe side.

Hope that helps.
Attachments
Pioneer-SA500-PSU1.gif
 
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
User avatar
colin.hepburn
Shed dweller
Posts: 2294
Joined: Sat Jun 02, 2007 1:24 am
Location: Scotland Aberdeenshire

#94

Post by colin.hepburn »

Hi Mike
Just seen this have had computer problems so have been sorting it out all weekend
So any way looks great thank you for your time on this
I was abit puzzled how you get 42 volt out from a 1.5v to 32 volt Reg :o thou
Looks the job though much appreciated :D :D
Thanks again
Colin
Colin
The Blues man ImageImage
User avatar
Mike H
Amstrad Tower of Power
Posts: 20157
Joined: Sat Oct 04, 2008 5:38 pm
Location: The Fens
Contact:

#95

Post by Mike H »

That's only across in to out, according to the sim it peaks at only 25V at switch on. Datasheet says 40V
 
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
User avatar
colin.hepburn
Shed dweller
Posts: 2294
Joined: Sat Jun 02, 2007 1:24 am
Location: Scotland Aberdeenshire

#96

Post by colin.hepburn »

Hi All
Just out of interest and to help understand this circuit better what would be the result of disconnection of the feedback loop
And what is the function on part 22D45 thermistor given its name and placement near the heatshink I guess it has something to do with the amps temp control as a safety cut-outs is this part strictly nessaray for the amp too work or could it be omitted from the circuit if not what would be the modern equivalent part number so I can get spares
Image
Colin
The Blues man ImageImage
brig001
Old Hand
Posts: 550
Joined: Sat Nov 13, 2010 9:56 pm
Location: Back home in Preston now

#97

Post by brig001 »

It's a bit hard to read the values but, since Q1 and Q3 are AC coupled, and the output is AC coupled, the rest of it must be DC stable. This means that the output isn't going to run off to one supply rail or the other. Apart from that, there would be more gain, more distortion, more noise, higher output impedance, lower input impedance... I'm not sure why you would want to do it to be honest.

The thermistor is to compensate for the negative temperature coefficient of the output transistors vbe. So as the transistors get warm, they will tend to conduct more. This will if course make them get warmer and conduct even more etc. leading to thermal runaway. The thermistor reverses this, keeping the bias current more or less constant as the temperature varies.

HTH, Brian.
User avatar
colin.hepburn
Shed dweller
Posts: 2294
Joined: Sat Jun 02, 2007 1:24 am
Location: Scotland Aberdeenshire

#98

Post by colin.hepburn »

brig001 wrote: Apart from that, there would be more gain, more distortion, more noise, higher output impedance, lower input impedance... I'm not sure why you would want to do it to be honest.


HTH, Brian.
Hi Brian
Thanks for you explanation on this
I was just wondering what the outcome would be :) although different circuit terminology i have see switchable feedback on some valve amps

and so the thermistor is needed then or a bigger heatshink perhaps ??if it ever needs replaced any idea what the new equivalent is for the 22D45
Heres the link to the pdf of the circuit should see it better
http://www.kallhovde.com/pioneer/sa-500om-sm.pdf
Colin
The Blues man ImageImage
brig001
Old Hand
Posts: 550
Joined: Sat Nov 13, 2010 9:56 pm
Location: Back home in Preston now

#99

Post by brig001 »

If one thermistor failed, I would remove the good one and measure its resistance at two temperatures. It should be possible then to find an equivalent. Just hope both don't fail together :)

You could try it without feedback if you wished, but I would have a scope on the output just to make sure it wasn't oscillating - I can't see how it would, but better safe than sorry your tweeters have blown up.
User avatar
colin.hepburn
Shed dweller
Posts: 2294
Joined: Sat Jun 02, 2007 1:24 am
Location: Scotland Aberdeenshire

#100

Post by colin.hepburn »

Both the thermistors are OK it's just seems like a good idea to have spares or if I decide to have a go at building a clone of the amp which I may do as it's a good sounding amp
when used with a good pre amp i also have its bigger brother the SA500A which also sounds good and uses the same 22D45 Thermistors so spares or equivalents would be good to have i feel
Colin
The Blues man ImageImage
User avatar
Mike H
Amstrad Tower of Power
Posts: 20157
Joined: Sat Oct 04, 2008 5:38 pm
Location: The Fens
Contact:

#101

Post by Mike H »

Did you happen to measure what the thermistor's resistance is at normal room temperature?

I notice there's already two diodes in series ('SV-3A') so the thermistor is like "extra icing on the cake".
 
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
User avatar
pre65
Amstrad Tower of Power
Posts: 21373
Joined: Wed Aug 22, 2007 11:13 pm
Location: North Essex/Suffolk border.

#102

Post by pre65 »

You could waste your life away worrying about things that might go AWOL one day. :)
The only thing necessary for the triumph of evil is for good men to do nothing.

Edmund Burke

G-Popz THE easy listening connoisseur. (Philip)
User avatar
colin.hepburn
Shed dweller
Posts: 2294
Joined: Sat Jun 02, 2007 1:24 am
Location: Scotland Aberdeenshire

#103

Post by colin.hepburn »

Mike H wrote:Did you happen to measure what the thermistor's resistance is at normal room temperature?

I notice there's already two diodes in series ('SV-3A') so the thermistor is like "extra icing on the cake".
No I hadn't thought of it until now
it's just when looking at the schematic I figured it would be good idea to get the parts as spares for both this amp SA500 and the SA500A which uses the same parts 22D45 I see my other pioneer amp SA6200 does not have Thermistors in is circuit which is why I was asking if the theristors are really needed in these amps
For the diodes I believe you could use 3 1N4148 connected in series
Colin
The Blues man ImageImage
User avatar
colin.hepburn
Shed dweller
Posts: 2294
Joined: Sat Jun 02, 2007 1:24 am
Location: Scotland Aberdeenshire

#104

Post by colin.hepburn »

pre65 wrote:You could waste your life away worrying about things that might go AWOL one day. :)
theses are good sounding amps so some spares are a good thing to have i am sure you have some spare valves :shock:
Colin
The Blues man ImageImage
User avatar
pre65
Amstrad Tower of Power
Posts: 21373
Joined: Wed Aug 22, 2007 11:13 pm
Location: North Essex/Suffolk border.

#105

Post by pre65 »

colin.hepburn wrote:
pre65 wrote:You could waste your life away worrying about things that might go AWOL one day. :)
theses are good sounding amps so some spares are a good thing to have i am sure you have some spare valves :shock:
Maybe, but most of my amps are built from the contents of my spares box.

Anyway, you know what I meant. :lol:
The only thing necessary for the triumph of evil is for good men to do nothing.

Edmund Burke

G-Popz THE easy listening connoisseur. (Philip)
Post Reply