Pioneer's SA500 Blowing protection fuse

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Mike H
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#46

Post by Mike H »

Sorry forgot to look at the diagram :oops:

Better diodes yes could do.

CRC well the resistor value will have to be quite small, so would it actually do anything ~ a 3-legged regulator could work, you could afford to lose 4 - 5V :?:


 
 
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#47

Post by colin.hepburn »

Hi All
Well this little pioneer SA500 amp is sounding superb with the new caps in much better than I thought it would be what's the true circuit terminology of this amp it is said to be a SEPP is this correct would explain it addictive sound
To the psu
A little help here to understand a bit more on psu s
1 What are the advantages over a full wave Rec and a Bridge Rec apart from a bit more voltage from a bridge perhaps?
2 Psu Cap uf size
The Amp has a 1000uf 50v original
It was suggested a 10.000uf is this not a bit big for a 10watt amp?
My idea was to replace the 1000uf with say two 3300uf with a resistor between them making a pi filter but I don't want to lose much volts my thinking behind this idea was to have a lower ECR and faster supply
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#48

Post by brig001 »

A bridge rectifier would normally be used with silicon diodes as it makes the transformer cheaper. A full wave rectifier like you have would typically be used with valve gear because the small increase in transformer cost is easily offset by the cost of the rectifier valves. I have no idea why yours is like this, but both methods give full wave rectification i.e. minimum gaps in the supply.

You cannot use a bridge rectifier because you would either use 1/2 the winding and be limited to 1/2 the current, or you would use the whole winding and have twice as many volts. I'm also sceptical there would be any change in sound by changing the diodes.

On capacitors, I personally am not a fan of really huge values, so I would probably just try 3300uF if you already have one, or the two in parallel if you have two. If you have a few different values lying around, try them and see if you can tell the difference. If you were really keen, you could build a high spec. regulated supply and try that.

HTH, Brian.
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#49

Post by Mike H »

It wouldn't be half the current, either one half does all the peak current on every other half cycle or it does it in both directions for every half cycle through a bridge.

An advantage of more modern rectifier diodes may be that they're faster and have less reverse leakage. Or just better made.


 
 
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#50

Post by colin.hepburn »

brig001 wrote: I'm also sceptical there would be any change in sound by changing the diodes.


On capacitors, I personally am not a fan of really huge values, so I would probably just try 3300uF if you already have one, or the two in parallel if you have two. If you have a few different values lying around, try them and see if you can tell the difference. If you were really keen, you could build a high spec. regulated supply and try that.

HTH, Brian.
When i build my Valve headphone amp when i changed out the 1Nxxx diode for Mur 820 and there was a big improvement is the sound giving a inky black background letting more detail thou :)

i will try the two 3300uf caps and Mur Diodes first and see how it gos and i may try a regulated supply latter Capacitance Multiplier perhaps
is this circuit as claimed a SEPP :) 8)
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#51

Post by brig001 »

Mike H wrote:It wouldn't be half the current, either one half does all the peak current on every other half cycle or it does it in both directions for every half cycle through a bridge.
You are correct that the peak current is the same, but the average current for the centre tapped transformer is half. The winding may only be rated for this average current, hence you may only get half (or 60% or whatever) before the winding expires. I'm not sure how big a problem this would be in practice though...
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#52

Post by Mike H »

Oh average, OK. :)

Not sure a transformer winder would risk choosing a wire gauge on that basis though. Also, you have to consider that peak currents are quite considerable for cap input, albeit short in duration


 
 
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#53

Post by colin.hepburn »

Well today I noted a slight Hum and vibration from to psu transformer in the pioneer SA500 After checking it out no visible sign of any shorting or heat damage I just remounted the transformer on some felt backed rubber I have which seems to have damper out some of the vibration so will do for now until I can get a suitable replacement


The Transformers spec is 36-0-36 volts 0.6 amps which is stamped on it with the transformer in circuit I put the DMM on its secondary's and get 30.6 volts AC and get 41.2 volts DC at the amp side which is the correct voltage for the amp can the transformer lose 6 volts when tested in circuit the idea was to replace it with a 120VA 18-0-0-18 toroidal connection to give 36 volts
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#54

Post by pre65 »

colin.hepburn wrote:

The Transformers spec is 36-0-36 volts 0.6 amps which is stamped on it with the transformer in circuit I put the DMM on its secondary's and get 30.6 volts AC and get 41.2 volts DC at the amp side which is the correct voltage for the amp can the transformer lose 6 volts when tested in circuit the idea was to replace it with a 120VA 18-0-0-18 toroidal connection to give 36 volts
Something sounds wrong there. :?

How can you replace 36-0-36 with 0-18 + 0-18, or am I missing something ?
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#55

Post by colin.hepburn »

pre65 wrote:
colin.hepburn wrote:

The Transformers spec is 36-0-36 volts 0.6 amps which is stamped on it with the transformer in circuit I put the DMM on its secondary's and get 30.6 volts AC and get 41.2 volts DC at the amp side which is the correct voltage for the amp can the transformer lose 6 volts when tested in circuit the idea was to replace it with a 120VA 18-0-0-18 toroidal connection to give 36 volts
Something sounds wrong there. :?

How can you replace 36-0-36 with 0-18 + 0-18, or am I missing something ?
By Connecting the centre taps
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#56

Post by Nick »

But then you have a 18-0-18 not a 36-0-36
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#57

Post by colin.hepburn »

Nick wrote:But then you have a 18-0-18 not a 36-0-36
Of course what was I thinking? :oops: Ok so we need two 0- 9v 0-9v transformers wired in series but why is a 36volt TX test at 30.6volts
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#58

Post by pre65 »

colin.hepburn wrote: but why is a 36volt TX test at 30.6volts

Poor regulation ?

Just be careful you don't end up with too many volts if the replacement transformer (s) is bigger VA or better regulated..
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#59

Post by Nick »

Of course what was I thinking? Embarassed Ok so we need two 0- 9v 0-9v transformers wired in series but why is a 36volt TX test at 30.6volts
You need two 0-18, 0-18 in series.

But for your target voltage 30-0-30 is what you want.
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#60

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