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Chip Amps Amplifiers based on integrated circuits

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Old 4th June 2009, 07:09 AM   #391
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by bmwpowere36m3
the amp's continuous power rating of 68W at 4 ohms with a 28Vcc. Based on the spec sheet that equates to an Iopeak of 5.8A and looking at trafos of 250VA
two channels of 68W+68W require a transformer between 136VA and 272VA.
Your 250VA is perfect.
The 5.8Apk only applies to sinewave into a resistive (non reactive) load.
The transient peak current into a 4ohm reactive speaker load could be around three times this, i.e. ~17Apk.
That is way in excess of the chipamp specification. The transformer can easily meet this transient requirement.
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Old 4th June 2009, 09:33 AM   #392
tent is offline tent  Germany
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Hi again,
ok all is clear.
Only the exact meaning of:
Quote:
Originally posted by AndrewT
shorted and open circuit input.
is a bit unclear to me.

For the rest I'll do the measurements and see what is the result, also the bulb test result with different rated bulbs.

Now basically I think that next w/e I'll go to take a new toroid with dual secondaries and see if I'll get a good one this time!

Thanks,
tent:wq
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Old 4th June 2009, 05:21 PM   #393
AndrewT is offline AndrewT  Scotland
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open circuit input = the input RCA socket with no interconnect inserted.
shorted input = insert a shorting RCA plug into the input RCA socket.

A shorting plug can be assembled from an RCA plug with the ground tag/barrel soldered to the input/line tag.
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Old 5th June 2009, 08:47 AM   #394
! is offline !  United States
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Quote:
Originally posted by !
Darn, Cal says I have to change my username due to the forum software changes. It'll be....

like a disguise !

well after continued email, Cal is, I feel, unreasonable, so good luck, adios, etc, I'm outta here. Too much BS for what was supposed to be an enjoyable hobby.
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Old 5th June 2009, 10:36 AM   #395
tent is offline tent  Germany
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Quote:
Originally posted by AndrewT
open circuit input = the input RCA socket with no interconnect inserted.
shorted input = insert a shorting RCA plug into the input RCA socket.

A shorting plug can be assembled from an RCA plug with the ground tag/barrel soldered to the input/line tag.
Ok I did all those measurements (and I had to repeat them also for both channels right?!? ) and basically in all situations I can read c.a. 104-107mV DC, no difference if shorted input or not (and I have no volume POT, the volume is anyway ridiculously low): sounds bad, right? Something is probably wrong in the schematic or in my work?
And even worse: the only situation where I can read a different measurement is at power off where I get a spike reaching 1400-1600mV DC, could this be harmfull to the speakers? (I did already test with speakers BTW.. I hear a loud POP at turning the amp off)
While, when turning on, no POPs nor spikes, just quick and smooth rise to the ugly 107mV DC
Any suggestions?


Quote:
Originally posted by !



well after continued email, Cal is, I feel, unreasonable, so good luck, adios, etc, I'm outta here. Too much BS for what was supposed to be an enjoyable hobby.
!: so only because of a nickname change?
Well "escalmationpoint" would be a nice and short nick too, isn't it?
Besides jokes I'd try to see if the databse of the new forum would be directly importable from the old thus maintaining old nicks, or in case if this is impossible, maybe "e!" would also be an interesting idea..

cheers,
tent:wq
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Old 5th June 2009, 11:19 AM   #396
AndrewT is offline AndrewT  Scotland
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I had another look at post371.
The 13Vac transformer outputs a lot of current.
To achieve this current ability they have used a bi-fillar winding rather than a thicker single winding.

You could open up the insulation and separate the two windings to create a 13V+13V transformer. Bring all four wires to the output leads.
Fit flexible output leads at the same time and make them too long initially. You can cut them short later.

What is the mains input voltage when you measure the unloaded secondary output voltage?
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Old 5th June 2009, 12:03 PM   #397
tent is offline tent  Germany
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Quote:
Originally posted by AndrewT
I had another look at post371.
The 13Vac transformer outputs a lot of current.
To achieve this current ability they have used a bi-fillar winding rather than a thicker single winding.

You could open up the insulation and separate the two windings to create a 13V+13V transformer. Bring all four wires to the output leads.
Fit flexible output leads at the same time and make them too long initially. You can cut them short later.

What is the mains input voltage when you measure the unloaded secondary output voltage?

Hi Andrew,
yes you're right the two wires of the secondary coming out of both transformers are in reality made of two wires connected togheter.. (see also a foto of the trafo earlier)
But not so sure what you propose about bringing "all four wires to the output leads", "same time", "too long", etc.
Did you mean connect them (separated and prolonged) to AC1, AC1_, AC2 and AC2_?
But if I separate the two wires from the trafo don't it just be 6 volts or similar? (i.e. 6v-0v 0v-6v)
I'll try it out anyway, would this probably silent the trafo also?

The mains input voltage is at unloaded status: 236V AC

Thanks,
tent:wq

(PS: my english is probably a bit limited.. sorry..)
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Old 5th June 2009, 12:38 PM   #398
AndrewT is offline AndrewT  Scotland
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Hi,
a bi-fillar winding has two separate (insulated) wires wound on the core.
If you separate the wires into two windings, each produces the same voltage but has half the current capacity.

A 10A, 13.5Vac bi-fillar secondary becomes 5A, 13.5Vac + 5A, 13.5Vac when separated.

This will not solve the noise problem. It will allow you to run the good transformer with the voltage you need.

When you have altered the bad transformer, you may discover that it has been wound/wired incorrectly and now operates quietly, but this is unlikely.

When you feed 236Vac into the transformer, what is the secondary Vac when there is no load on the secondary?
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Old 5th June 2009, 01:44 PM   #399
tent is offline tent  Germany
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Join Date: May 2009
Quote:
Originally posted by AndrewT
Hi,
a bi-fillar winding has two separate (insulated) wires wound on the core.
If you separate the wires into two windings, each produces the same voltage but has half the current capacity.

A 10A, 13.5Vac bi-fillar secondary becomes 5A, 13.5Vac + 5A, 13.5Vac when separated.

This will not solve the noise problem. It will allow you to run the good transformer with the voltage you need.

When you have altered the bad transformer, you may discover that it has been wound/wired incorrectly and now operates quietly, but this is unlikely.

When you feed 236Vac into the transformer, what is the secondary Vac when there is no load on the secondary?
Wow, I see, So I'll try to disassemble the trafo and see what happens now..

The secondary output load is 13.4Vac.

Now I tried also with the light bulb tester and curiousely enough the 60W bulb stays on at amp powered on!! not really bright but also not dim.. I'm going to recheck everything again now.. grr..

tent:wq
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Old 5th June 2009, 02:07 PM   #400
tent is offline tent  Germany
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if I disconnect the AMPs and PSU and have only the trafos I also get a light from the lamp but this time a really dim one.. uhm.. ?

tent:wq
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