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Old 15th November 2012, 09:03 PM   #11
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From what I've learned, oversizing the trafo does impact the sound.. But I have no experience of it :P
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Old 15th November 2012, 09:04 PM   #12
sreten is online now sreten  United Kingdom
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Hi,

Like I said, someone will always say go bigger, whatever choice you make.
Why not add bigger caps than you need as well, and while your at bigger
heatsinks and a bigger more expensive case. Why not ? It doesn't hurt ...

Design by oversizing, as bigger is better, but how big
being an openended question, doesn't appeal to me.

rgds, sreten.
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Old 15th November 2012, 10:28 PM   #13
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Quote:
Originally Posted by lausar View Post
Kinda new to chip gainclone amps. I'm looking for a backup amp to my SET 2A3 amp and I'm thinking about going chip amp route. Will I have any problems with these amps with my 16 ohm Altecs?
Have you looked at this? A Test. How much Voltage (power) do your speakers need?

With my 15 OHM speakers hooked up to my 2020 chip amp they only draw 0.4v. Doing the math this works out to .085 watts at serious listening levels.
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Old 16th November 2012, 08:47 PM   #14
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yes i know that.
even so i would prefer have and not need, then need and not have..

There IS a limit where having bigger than needed is useless.
But in this case, 15 ohm speakers are less common than 8 ohm ones i think.
Sure, if this amplifier will surely never need to drive an 8 ohm speaker, then a smaller traffo is okay.
But.. what if not? the chip can handle an 8 ohm load, so why not just size everything to enable it to do so ?
That is what does not hurt at all.
Going for a 400 VA psu would be the pointless thing.
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Old 20th November 2012, 05:16 AM   #15
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From Lenard Audio, a briefing on how to make a chip amp drive like a tube amp:
Click the image to open in full size.

However, if you got droopy treble from using full band current drive above, here is a different option for current drive at only the bass.
From the JLH amplifier schematic of 1969, see component C2, sized to approximately 2500u if driving 16 ohm speakers. Carefully chosen roll-off has a current drive effect potentially useful for bass extension. Likewise, that approach works fine with chip amplifiers too and it installs inexpensive speaker protection, which is not included within the chip. There is no mystery why the update version has ordinary sound but the original has really rockin bass--that difference is C2.
Click the image to open in full size.

Question:
How much output power does "SET 2A3 amp" have into 16 ohm speakers?
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Old 20th November 2012, 05:53 AM   #16
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Quote:
Originally Posted by sreten View Post
Hi,

Higher VA is needed for lower impedance loads. For higher you need less VA.
based on more ampere for low imp speaker load, I would say reality is mostly the opposite
in general you will have to lower VA rating to achieve this
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Old 20th November 2012, 06:45 AM   #17
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Quote:
Originally Posted by sreten View Post
Hi,

Higher VA is needed for lower impedance loads. For higher you need less VA.

rgds, sreten.
you dont need to change VA ratings. you only need to change voltage.

for low impedance load, lower the voltage to get more current.
for higher impedance load, higher voltage. (within specs)
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Old 20th November 2012, 07:06 AM   #18
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Quote:
Originally Posted by lausar View Post
Kinda new to chip gainclone amps. I'm looking for a backup amp to my SET 2A3 amp and I'm thinking about going chip amp route. Will I have any problems with these amps with my 16 ohm Altecs?
or look at ACA
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Old 21st November 2012, 01:28 AM   #19
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VA is a somewhat terrible way to judge transformers, since manufacturers sometimes test with secondaries paralleled (makes cost look lower).

I'd much rather judge the transformer by amperage, which relates directly to bass quality and ripple performance. True enough that 16 ohm speakers need only half the amperage. I certainly wouldn't reduce it--I'd leave it powerful enough to drive 8 ohm speakers and simply enjoy lower ripple performance and better bass when the amplifier happens to drive a lighter load.

Now for voltage, most people max out the chips anyway or come close to it. It is probably because the most popular chips have a limiter we'd like to dodge. Anyway, I don't suggest increasing transformer voltage at all. Most examples are already maxed out.

VA difference? Not practically very different.

Amplifier? Quite different. . .
The 16 ohm speakers of yesteryear have limited power handling capacity and overly tight dampening making a tube amp's low power and current drive (looser electronic dampening) fairly ideal. However, a chip amp with some form of current drive adjustment could do the job. I mention some of that in post 15.

Here's some more.
Parallel amplifiers (with ballast resistors) and bridge amplifiers have looser electronic dampening. You can further help the sound a bit with a CRC power supply.
A bridge amplifier with a big capacitor series to the woofer (or the entire speaker), is a low loss simple way to current drive the bass. Now the impression of a tube amp comes down to whatever you put at the input of the amp.

Okay, here's an option:
Blarebuster or lightspeed attenuator or 6n3p buffer
OP275 Bridge adapter
4 of LM1875 chips or 8 of LM1875 chips for more lavish sound of bridged parallel.
CRC power supply

Simpler option (35 watts per channel):
MooseFet Preamp
Blarebuster
TDA7294 Stereo
CRC power supply

Very simple option (12 watts per channel):
Blarebuster
LM1875 stereo (with 18+18vac transformer)
CRC power supply
*can add the simple clipnipper for headroom management
*could do LM1875 parallel amplifiers (very easy) for a "darker voice" sound; however, you still get only 12 watts per channel when using 16 ohm speakers.
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Last edited by danielwritesbac; 21st November 2012 at 01:30 AM.
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Old 21st November 2012, 06:30 PM   #20
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Quote:
Originally Posted by danielwritesbac View Post
VA is a somewhat terrible way to judge transformers, since manufacturers sometimes test with secondaries paralleled (makes cost look lower).
or in series
VA(watt) rating comes out the same anyway
its always the total of the whole trafo
Ampere rating is each secondary
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