Dominique,
Thanks for this post.
Glad I found this, I just powered up the amplifier only to blow the 1a fuse immediately, twice in a row, UK mains 230/240v. I have some 1.6A fuses coming now.
It is important that mains fuse is "slow blow" type. Often, you can read "T" (for "temporised") on it.
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T and slow blow are basically the same.
They survive longer when an overload is applied.
T = time delay/ed
T1A, or ordinary 1A, will allow ~240VA of continuous power into the transformer.
T1A will not allow a 240VA transformer (or motor) to start up reliably. You would need to fit a soft start to get reliable repeated start up behaviour.
I have found that limiting the start up Primary current to 2Aac (2.8Apk) allows a T1A to give reliable start ups.
You could extend this experiment to see how much current can pass and NOT blow a T1A fuse during repeated start ups.
It would be nice to have data for a series of T fuses. The manufacturers do not give this in the datasheets.
For 240Vac and 2Aac you would need ~120r of limiting resistance. i.e. I use 100r to 110r of added resistance for a T1A fuse.
They survive longer when an overload is applied.
T = time delay/ed
T1A, or ordinary 1A, will allow ~240VA of continuous power into the transformer.
T1A will not allow a 240VA transformer (or motor) to start up reliably. You would need to fit a soft start to get reliable repeated start up behaviour.
I have found that limiting the start up Primary current to 2Aac (2.8Apk) allows a T1A to give reliable start ups.
You could extend this experiment to see how much current can pass and NOT blow a T1A fuse during repeated start ups.
It would be nice to have data for a series of T fuses. The manufacturers do not give this in the datasheets.
For 240Vac and 2Aac you would need ~120r of limiting resistance. i.e. I use 100r to 110r of added resistance for a T1A fuse.
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Thanks Dom,
I had already ordered the 1.6 slow blow fuses (max recommended by Tom for 220/240) before I read your post. However it is nice to get some confidence boost after seeing your post.
Of course that doesn't rule out some other issue.
Yes I probably should've done that first time!
No drama though, not even a popping sound.
Hi Tinman,
Was that question aimed at me?
If so, it has infinitely quiet inky black silences. Mostly because I am waiting for new fuses.
I will certainly let the group know how it performs with my Dad's speakers.
But you must play a good record, with high DR (dynamic range). FLAC or similar. Orchestral mass if it is possible, please.
-> Album list - Dynamic Range Database
Something like this:
Dynamic Range Meter - foobar2000
ComponentFree Downloads | DYNAMIC RANGE | pleasurize music!
-> Album list - Dynamic Range Database
Something like this:
Dynamic Range Meter - foobar2000
ComponentFree Downloads | DYNAMIC RANGE | pleasurize music!
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Actually, I think he must fix the blown fuse first... No fuse. No sound.
A 1.6 or 2.0 A slow-blow fuse should work. The inrush current will depend on the exact transformer and supply caps chosen, hence, the fuse needs to be selected for each individual case. I generally find that Ifuse = VA/Vmains, where VA is the VA rating of the transformer is a reasonable starting point. Remember, the fuse is there to protect your house from burning down. The fuse is not intended to protect any circuitry.
For smaller transformers, say <=200 VA, a soft start is usually not needed as the transformer has enough internal resistance to limit the current to a reasonable value. Larger transformers, could benefit from a soft start circuit ... or a larger fuse. Either approach is valid.
~Tom
DC servo
One question,
One question,
Does the use of a DC servo offer better sound than a well implemented DC?
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Using a DC servo allows you to eliminate DC blocking capacitors in the signal path, which many find desirable.
A well-designed DC servo has no impact on the sound quality. A well-chosen DC blocking capacitor has no impact on the sound quality either. Key word here: well-chosen, well-designed - i.e. apply engineering, do the math, take the measurements.
Rather than asking "does this impact the sound", I suggest reading up on the purpose of the various circuit blocks. Bob Cordell's book, "Designing Power Amplifiers" is a worthwhile read. As is Douglas Self's "Small Signal Audio Design", actually. I'd recommend it over his power amp book.
~Tom
If dual bridge rectifier and 5x3300uF per rail, 150VA~250VA per channel, or
If single bridge rectifier and 22,000uF per rail, 250VA~300VA per channel.
Notably, the center-point of that latter figure is 275VA.
Yeah, quite close to 277VA.
For a stereo Modulous86, a 22+22vac 500VA transformer seems adequate, since the capacitive load wasn't doubled--it is still pushing 22,000uF per rail.
On the board, I think that I see some power filter at the LME, and since those are individualized per right and left channels, crosstalk distortion is gone, so the stereo amp may have the same stereo separation as dual-mono. Right?
I found it interesting to notice my woofers fluttering around 5Hz when one section of a record rotated under the stylus. The music played loud and clear while the 5Hz came and went on each rotation. The DC servo did not affect music playback at all, even allowing a 5Hz signal to pass. I couldn't hear any difference in SQ with or without the 5Hz flutter. I was surprised to see such a LF signal get past the DC servo, but it did.
Rich
Rich
Thanks Tom,
So right on the edge at 225 VA then.
I will get some 2A fuses too.
It might be nice to have but I really don't think a soft start is needed with a little amplifier like this having use numerous much larger amplifiers. This is a dwarf transformer compared to those in many high power Audiophile monstrosities.
5Hz !=DC. I can't recall the frequency of Tom's servo but likely to be around 0.1Hz
Hi BrianL,
Yes, perhaps a 2.5A will be required, to avoid random fuse deaths.
First job is to get it going, check the circuit is working happily. I will have to investigate for further potential causes if the 1.6A fuses blow immediately.
A higher dynamic range does not automatically mean a better recording. I have some orchestral recordings with the same DR from that plugin as the new Led Zep remasters. Which is a better test record is up to the person listening as its a personal experience. As time goes on I trust that plugin less and less