Max peak current deliverable by a power amp.

[beppe61]

Dear Sirs,

I have a question (maybe trivial but I am quite ignorant) about peak current output for a power amp.
Seldom in the specifications I see this value.
My question is, does this value dipend mostly on:
1) the type and number of the output devices used or
2) the VA of the transformer or
3) the amount of filter capacitance ?
I ask you this because I have an amp with a single pair of 2N5886/2N5884 per channel.
How much peak current can I expect from this amp with these output devices?
Is there a way to measure it ?
Can I replace this pair with something more powerful to get an higher current output?
You can insult me if this question is too silly.

Thank you very much indeed anyway.

Kind regards,

beppe61

[darkfenriz]

Hi

I have a question (maybe trivial but I am quite ignorant) about peak current output for a power amp.

First it depends on whether the amp has a short-circuit protection or not.
If it has a simple one-bjt protection around output transistor, than the borderline of protecion is Vbe-on-drop (0.7V) divided by emitter resistor of output transistor.
If not, then max current is a value on which output transistor explodes.

Is there a way to measure it ?

If they explode at 7A, then max current is (was) around 6.5A
Seriosly, one could say that max collector current is a max current of an amplifier, however it is wiser to look at safe operation area ratings to answer at which current and which voltage it can brake.
It gives you no simple answer, rather the function of both I and Vce.

Can I replace this pair with something more powerful to get an higher current output?

Yes.

You can insult me if this question is too silly.

No way, there are no silly questions.
regards

[darkfenriz]

How much peak current can I expect from this amp with these output ?

datasheet says 50A amx peak current

[Nigel Goodwin]

I have a question (maybe trivial but I am quite ignorant) about peak current output for a power amp.
Seldom in the specifications I see this value.

Why do you want to know?, I would have thought it's of very little interest?.

Personally I would say that the limiting factor (in the amplifier) would probably be the supply reservoir capacitors - it's those that are responsible for delivering short peaks of current. However, it's the load that's responsible for drawing the current, and that would probably be the largest limiting factor (assuming no limiting in the amplifier).

[peranders]

... but only under certain circumstances which you don't have in your case.

[beppe61]

Originally posted by Nigel Goodwin

Why do you want to know?,
I would have thought it's of very little interest?.
Personally I would say that the limiting factor (in the amplifier) would probably be the supply reservoir capacitors - it's those that are responsible for delivering short peaks of current.
However, it's the load that's responsible for drawing the current, and that would probably be the largest limiting factor (assuming no limiting in the amplifier).

Dear Sir,

thank you so much for your extremely kind and valuable reply.
You have hit the center of the problem.
My load (speakers) are quite demanding in terms of current.
So I wanted to know firstly if the output devices can deliver more current (i.e. they are not a limiting factor).
Now I know they can.
Secondly, if a filter capacitance increase can be beneficial for peak current.
And saying that the supply reservoir caps are responsible for delivering short peaks of current you have completely answered to my question.
Thank you very much.
So I will start doubling the total capacitance ( from 20.000uF to 40.000 uF) and replacing the diodes bridge with a more stronger one.
Then I would like to try another transformer from Talema with more VA, passing from 300 VA to 500 VA.
As you can understand I am experimenting a little here.
But first the caps.

Thank you very much indeed again.
Kind regards,

beppe61

[beppe61]

Originally posted by darkfenriz
Hi
First it depends on whether the amp has a short-circuit protection or not.
If it has a simple one-bjt protection around output transistor, than the borderline of protecion is Vbe-on-drop (0.7V) divided by emitter resistor of output transistor.
If not, then max current is a value on which output transistor explodes.
If they explode at 7A, then max current is (was) around 6.5A
Seriosly, one could say that max collector current is a max current of an amplifier, however it is wiser to look at safe operation area ratings to answer at which current and which voltage it can brake.
It gives you no simple answer, rather the function of both I and Vce.
Yes.
No way, there are no silly questions.
regards

Dear Sir,

thank you so much for your extremely kind and very valuable reply.
Unfortunately your explanation is beyond my ability to understand (I am very ignorant in electronics).
Actually I wanted to know if the output devices can deliver more current, and you answered positively. Thank you.
So in order to get a certain peak current increase I intend to double the filter capacitance and see, well and hear for improvements in sound.
My amp suffers a lack of drive in the part of the spectrum under 100Hz at present.
This experiment will not cost me too much I hope.
And it could be interesting.

Thank you very much again.

Kind regards,

beppe61

[PB2]

Hi Beppe,

This is also a good question but it is complicated. Do you have a schematic for the amplifier?

Does it have output current limiting protection?

It's important to know if the output stage is emitter follower or a CFP.

What impedance does your speaker present to the amp?

Is it 4 ohm but dips lower, or is it strongly reactive?

If you look at the beta or hFE curves for the transistors you might notice that the beta drops at high current, this is called beta droop and was much worse in older transistors.
Take a look at the MJ802, an excellent older transistor but it has a lot of droop, or look at the 2N3055.
This output current can limit due to a lack of drive, usually in older emitter follower designs.

Pete B.

[beppe61]

Dear Pete,

thank you so much for your extremely kind and valuable reply.
Unfortunately I understand that the case is much more complex than I thought.

>

Originally posted by PB2
Hi Beppe, This is also a good question but it is complicated. Do you have a schematic for the amplifier?

Iam really sorry but not, I do not.

> Does it have output current limiting protection?
It's important to know if the output stage is emitter follower or a CFP.

Again unfortunately I do not know.

> What impedance does your speaker present to the amp?
Is it 4 ohm but dips lower, or is it strongly reactive?
If you look at the beta or hFE curves for the transistors you might notice that the beta drops at high current, this is called beta droop and was much worse in older transistors.
Take a look at the MJ802, an excellent older transistor but it has a lot of droop, or look at the 2N3055.
This output current can limit due to a lack of drive, usually in older emitter follower designs.
Pete B.

I understand I lack fundamental info on the topology.
By the way leaving all others things as they are now, do you think that doubling the capacitance in the PS could increase the delivarable peak current ?
On the basis of your very valuable analysis and remarks I doubt a little now.
Are you aware of very easy to build and good schematics (or kits) of low power high current amps ?
This value of the peak current is very seldom stated in the specs.
And in my case it seems a key parameter.
I was lucky with two small but powerful Albarry M408, for instance.
They drove quite easily my speakers with a nice sound.

Thank you somuch for your kind and valuable reply.

Kind regards,

beppe61

[Nigel Goodwin]

Originally posted by beppe61
Are you aware of very easy to build and good schematics (or kits) of low power high current amps ?
This value of the peak current is very seldom stated in the specs.
And in my case it seems a key parameter.

It's of no real concern, which is why it isn't mentioned in the specs - what IS mentioned is the power output, and the maximum current is directly related to that.

There's no such thing as a 'low power, high current' amplifier, high power and high current go together - it's a simple mathematical relationship 'W=IxIxR'.

As has been asked previously, what's the problem with your speakers?, what impedance are they?, and for that matter what make and model are they?.