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Old 15th February 2006, 12:32 PM   #1
beppe61 is offline beppe61  Italy
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Default Request of kind help.

Dear Friends,

I am here to ask for your help.
I have a power amp at hand.
In a last attempt to extract more juice from it I would like to replace its single transformer (supplying the two channels) with a bigger one.
The big problems for me are:
1) which type is suitable;
2) how to connect the secondary windings.
I am attaching a picture of the amp where you can see the single transformer with two bridges, one per channel.
Which kind of transformer do I need?
How many secondaries?
How can I form the ground?

I am completely confused.

Suggestion will be very welcome and appreciated.
Kind regards,

beppe
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Old 15th February 2006, 12:49 PM   #2
beppe61 is offline beppe61  Italy
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I am attaching a schematic of the Talema Nuvotem I can get from RS dealer here.
Is it possible to use a single transformer like this to power both the two channels?

Please excuse my silly question but I really do not know how to do it without bad consequences.

Thank you very much indeed.
Kind regards,
beppe
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Old 15th February 2006, 01:03 PM   #3
edl is offline edl  Hungary
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Hi,

A trafo with higher winding voltages wouldn't be suitable. I think you know this fact, so you wuould like to change the present one to a higher VA-rated type. Have you deliberated that the transformer replacement will only give you +1dB - at best? +3dB is so far hard to hear...
The alteration made by a such transformer-changing can be caused by only a better speaker placement.
So this change is absolutely unnecessary and beyond reason.
+6dB rise would be hearable, but for this you would need to quadruplicate the power of your amplifier, or pick up a new speaker with higher sensitivity.

Best regards,
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Old 15th February 2006, 01:15 PM   #4
beppe61 is offline beppe61  Italy
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Quote:
Originally posted by edl
Hi,
1) A trafo with higher winding voltages wouldn't be suitable. I think you know this fact,
2) so you wuould like to change the present one to a higher VA-rated type.
3) Have you deliberated that the transformer replacement will only give you +1dB - at best?
4) +3dB is so far hard to hear...
The alteration made by a such transformer-changing can be caused by only a better speaker placement.
So this change is absolutely unnecessary and beyond reason.
+6dB rise would be hearable, but for this you would need to quadruplicate the power of your amplifier, or pick up a new speaker with higher sensitivity.
Best regards,

Dear Sir,
thank you so much for your extremely kind and valuable reply.
Let me please answer hereafter.
1) Yes
2) Precisely. I am thinking of a very big 800VA with 5% regulation.
3) Honestly not. I am completely ignorant of this.
4) I did not know this as well.

I would like to be more precise anyway.
This amp should give 150W/4 ohm RMS (from specs).
My speakers are 4 ohm average.
The woofer is a Dynaudio 23W75 (or a 24W75 in another speaker).
Is it possible that this kind of power is not enough for those woofers?
It seems impossible to me.
At first I thought that something was wrong with it.
But I cannot hear any noise at all.
Only a very weak and uncontrolled bas, in my reasoning caused by a lack of current from the amp

Maybe replacing the filter caps could be beneficial?
Thank you so much for your kind support.
Kind regards,

beppe
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Old 15th February 2006, 01:41 PM   #5
edl is offline edl  Hungary
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Quote:
I would like to be more precise anyway.
This amp should give 150W/4 ohm RMS (from specs).
My speakers are 4 ohm average.
The woofer is a Dynaudio 23W75 (or a 24W75 in another speaker).
Is it possible that this kind of power is not enough for those woofers?
It seems impossible to me.
At first I thought that something was wrong with it.
But I cannot hear any noise at all.
Only a very weak and uncontrolled bas, in my reasoning caused by a lack of current from the amp

Maybe replacing the filter caps could be beneficial?
Hi!

You gave us so beneficial and important informations.
The weak and uncontrolled bass can be caused by a transformer with high winding resistance! So I suggest you to remove the trafo for a measurement. Than if the resistance of the secondaries are unadmittably high, than transformater swapping become truly right.
From that matter filter caps replacement would be benefical - if they are dried yet. Their value - 10.000uF×2 per channel as I see in your photo - otherwise enough.

What is the rail voltage? It need to be 48-50V, if the amp can push out 150W-RMS on 4ohms indeed.

On the margin: a 150W rated amplifier with using Dynaudio speakers means very high volume and sound pressure when the system is used for home-listening. Or you're using it for PA?

One more comment: it can be that simply the amp design causes that nasty sounding. Then the only arrangement that can solve your problem will be swapping the amp boards with new diy-ones.

All the best,
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Old 15th February 2006, 01:48 PM   #6
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Hi Beppe:
Quote:
One more comment: it can be that simply the amp design causes that nasty sounding. Then the only arrangement that can solve your problem will be swapping the amp boards with new diy-ones.
...like Hypex' UCD180 or UCD400, as I told you before

Good luck.
Mauricio
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Old 15th February 2006, 02:11 PM   #7
Eva is offline Eva  Spain
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Note that a poorly designed or placed (room acoustics are evil) speaker will not produce enough bass, no matter how much power is fed to it. Most people blame the amplifier in these situations, but what they should do is just to get bigger better more efficient speakers.

A 12" or 15" light paper cone woofer (with proper mid and highs) placed in a proper enclosure will sound kind of loud with just 150W, even if the amplifier is lousy (and I think that yours isn't).
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Old 15th February 2006, 04:22 PM   #8
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by beppe61

Is it possible that this kind of power is not enough for those woofers?
It seems impossible to me.
At first I thought that something was wrong with it.
But I cannot hear any noise at all.
Only a very weak and uncontrolled bas, in my reasoning caused by a lack of current from the amp

Maybe replacing the filter caps could be beneficial?

beppe
Hi,

Your problem is very unlikely to be caused by lack of amplifier current,
as it would only show up at very high levels.

If it is, the probable cause would be overenthusiastic protection
circuits, and upgrading the power supply will not help at all.

For some amplifiers (my Audiolab for example) the manafacturer
recommends reducing the current sensing resistor for permanently
connected low impedance speakers, in my case the protection causes
a relay to drop out, so it is easy to hear the protection operating.

/sreten.
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Old 15th February 2006, 05:36 PM   #9
beppe61 is offline beppe61  Italy
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Location: torino
Quote:
Originally posted by edl

Hi! You gave us so beneficial and important informations.
1) The weak and uncontrolled bass can be caused by a transformer with high winding resistance!
So I suggest you to remove the trafo for a measurement.
Than if the resistance of the secondaries are unadmittably high, than transformater swapping become truly right.

2) From that matter filter caps replacement would be benefical - if they are dried yet.
Their value - 10.000uF×2 per channel as I see in your photo - otherwise enough.

3) What is the rail voltage? It need to be 48-50V, if the amp can push out 150W-RMS on 4ohms indeed.

4) On the margin: a 150W rated amplifier with using Dynaudio speakers means very high volume and sound pressure when the system is used for home-listening. Or you're using it for PA?

5) One more comment: it can be that simply the amp design causes that nasty sounding.
Then the only arrangement that can solve your problem will be swapping the amp boards with new diy-ones.
All the best,
Dear Sir,
thank you so much for your extremely kind and valuable support.
1) I have a friend who can measure the impedance (I do not know the exact name of the instrument).
He uses it for his DIY speakers. I will ask to him.
2) They should be made in 1991 or something like that.
3) It is +/- 56V after the filter caps.
4) Before going on, I must precise one thing.
The amp has been left unused for about two years.
Could this mean anything?
Maybe the caps need sometime to become working again.
But I really do not know.
I use it only for home listening at reasonable level (not very high indeed).
5) The amp is not nasty sounding at all.
It is just that the bass is quite weak and consequently the sound is "thin", without body.

I will follow your precious suggestion anyway.
Kind regards,

beppe
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Old 15th February 2006, 05:42 PM   #10
beppe61 is offline beppe61  Italy
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Join Date: Feb 2005
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Quote:
Originally posted by maxlorenz
Hi Beppe:
...like Hypex' UCD180 or UCD400, as I told you before
Good luck.
Mauricio
Hi Mauricio,
how do you do ?
I am very pleased to hear from you again.
Maybe this would be my last "conventional" amp before switching to UcD amps.
I understand that a lot of commercial products, based on UcD modules, have been on show at the last CES with great results.
So the technology is mature.
If this restoring will not have success I will take the DIY route without further hesitation and UcD modules will be high on my list.
But there are also other very promising more "conventional" kits like the SKA (see solid state forum).

I wish you all the best.
Kind regards,

beppe
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