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AIYIMA A07 TPA3255 Review (Amplifier)

dr_mick51

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Now YOU are the one relying on test tones! Sure, if you want to maximize SINAD or any other spec at one specific wattage, you can vary the input level until you get the amplifier operating at its sweet spot for that measurement. But as soon as you play music that all goes out the window. However, you can continue to write whatever you want. I'm done on this topic. I still maintain that using a preamp for any reason other than having a very low level analog source will measurably and perhaps audibly degrade the sound in most cases, especially if it uses tubes. Anyone who understands math and basic electronics can read the conversation and decide for themselves what they want to do. Enjoy the music.
You are right. Everything has been shown and said already. People are smart to realize and decide by themselves what they want to do.

I'll keep enjoying my setup and my music in the meantime.
 

arancano

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I'm fascinated by the many ways that we ascertain value. A four figure price for something that small? No way! What if it came in a much larger and heavier case with a lot of extra parts that do nothing and it could not be opened for inspection without destroying it? I own the unit and would gladly pay $1,000 based on sound quality alone. Perhaps I'm easily duped, but satisfaction comes out ahead in my book.
 

Joe Smith

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I don't need more volume with the A07, but I do seem to have one of the A04 amps that has the lower gain. I did a test this week with my old NAD 1020 preamp inserted between sources (cassette, CD) and the amp. Didn't push it hard, but adding the solid state preamp with that unit allowed for a more satisfactory higher volume. Just an experiment as I am mostly using the A04 amp for small room and lower volume level listening. But putting a preamp in the chain with the A04 would allow for a more room filling level, particularly if like me, you have one with that lower gain build.
 

Walter

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I don't need more volume with the A07, but I do seem to have one of the A04 amps that has the lower gain. I did a test this week with my old NAD 1020 preamp inserted between sources (cassette, CD) and the amp. Didn't push it hard, but adding the solid state preamp with that unit allowed for a more satisfactory higher volume. Just an experiment as I am mostly using the A04 amp for small room and lower volume level listening. But putting a preamp in the chain with the A04 would allow for a more room filling level, particularly if like me, you have one with that lower gain build.
Yeah, inexpensive CD players often have pretty low output, I believe. Plus, of course, you need the ADC for the cassette player, as well as multiple inputs with a selector. In your use case, a preamp makes sense.
 

Timstunes

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has anyone confirmed how many watts the 07 or 08 is really outputting at 8ohm?

also curious about the mono block question guy above asked
In Amir’s testing of the A07 with 32v5a psu max 48w @8 ohms. With 48v3a psu max 61w @8 ohms.
 

Elitzur–Vaidman

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Does anyone here know what the gain curve of the A07's volume knob is? I swear that I previously found someone who measured the volume control, but I can't find it again.
 

375HP2482

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I don't pay much attention to the Volume knob. I have a Clip indicator in my preamp, so I set the preamp level a few dB below where that will light up and adjust the Volume knob to my loudest listening levels, ending up around 11 o'clock. Lower knob settings tend to minimize system noise.
 

Elitzur–Vaidman

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That's fair. I use a Topping d50s at -40dB to -30dB with my volume knob around 11 o'clock. Do you think I'd have any appreciable difference lowering the knob and running at -10 to 0dB?
 

375HP2482

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The Volume knob, like most volume knobs, is not a Gain adjustment, it's an input attenuator, knocking the input signal down which improves the received input signal's noise levels. Lowering the volume knob is practical if you know that your source signal is not clipping when it is increased.
 

Elitzur–Vaidman

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Isn't that just a matter of semantics? If I put in 2V and get out 20V then the overall gain is 20dB. If I put in 2B and get out 2V then the overall gain is 0dB. I understand that the amp has a fixed-gain circuitry, but is it incorrect to say the overall system from input -> output has variable gain?
 

375HP2482

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Consumer gear is "standardized" to -10 dBv, which is why consumer amplifiers usually run at more than 20 dB -- strange, as most op amps can put out well over 2 volts, which is +6 dBv. Call it conservatism.

If you run your DAC right up to its 2-volt max output, you will get the maximum system dynamic range (lowest noise) by lowering the amplifier's input attenuator ("Volume" "Gain"), as then the amplifier will rarely "see" the dither/LSBs of the DAC. In pro sound this is known as balancing the gain structure of the system, which in pro sound also involves microphone-level preamps operating anywhere from 60 dB to 0 dB gain. The practical issue: it is often not possible to monitor the DAC's precise output level.
 

Sangram

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I can't see why anyone cares about the position of the volume pot. In fact, you generally want to be able to use nearly the full range.
This is correct, and the reasoning of higher drive at lower volume is a fallacy. Excess gain = excess noise. You want an amp that reaches its maximum output level when the volume is set to maximum. That is correct gainstaging.

Unfortunately much modern material has very low dynamic range, and older material has higher dynamic range. It is not possible to have one gainstaging strategy that will cover both satisfactorily. Then there's the problem of multiple sources, with output levels that can vary quite wildly. Thus commercial offerings usually tend to be compromised in one direction or the other, and this is usually intentional.
 

MarcosCh

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This is correct, and the reasoning of higher drive at lower volume is a fallacy. Excess gain = excess noise. You want an amp that reaches its maximum output level when the volume is set to maximum. That is correct gainstaging.
Well, yes, but in most cases, the gain is fixed, so i would tend to think that it is often better leave the signal not very attenuated in the digital domain and apply most of the attenuation in the analog domain with the volume knob of the amp. I guess it depends on the case, but as a general rule...
 
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Sangram

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I wouldn't know about that. We often make preamplifiers with at least two, maybe three different output levels relative to input, so I guess it depends. Not all sources are digital, and not all digital sources have the same output level.

As to digital vs analog, digital SNR is usually relative to FS output and it might be possible to achieve lower noise floor with digital attenuation rather than analog. I use both and have a bias towards neither, but usually prefer no additional electronics at all - which automatically precludes analog attenuation in any form.
 

375HP2482

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This is correct, and the reasoning of higher drive at lower volume is a fallacy. Excess gain = excess noise.
Quite true that excess gain = excess noise. However, that big Volume knob, like most of them, is NOT a Gain knob (even if it is referred to as "gain"). It is in fact an input level attenuator. The actual Gain of the unit is fixed, which is necessary to optimize the feedback loop compensation.
 

Sangram

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The noise floor of the amplifier is fixed and depends on its gain.

Even with no input, the input referred noise will be multiplied by the amplifier's inherent gain.

Thus, an amplifier with higher gain will always have higher noise floor (more noise at output) than that with a lower gain. This is counting with zero signal input, i.e. attenuator at maximum attenuation.

There are ways to reduce input referred noise, for example by running higher bias currents (which reduces input stage transconductance and creates other issues), but only to an extent. You can't avoid the laws of physics. This is before we even consider the noise sources within an amplifier and yes, every component generates noise when current passes through it. This is unavoidable and they add up.

For those interested, Bob Cordell has a (very technical) explanation of noise sources in an amplifier in his design handbook. There are no known ways of removing noise once added to a signal. Noise can be divided into three basic types - voltage, current and thermal. This noise is inherent to the amplifier and power supply design, and cannot be removed even with your volume control at zero position.
 
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375HP2482

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Not sure what running higher bias current means in this Class-D amplifier. This one specs at 35 mA, which would be on the low side for a Class AB amplifier.

At the specified gain G of 21.5 dB, Texas Instruments shows 85 uVolts (-86 dBv) noise output (A-weighted), which at a 4-ohm 86 dB/w/m speaker works out to around -6 dB SPL/1m (close up at 9 inches or so that would rise to 12 dB SPL). Of course, the noise levels will measure higher with no A-weighting.
 

Gaspar74

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Building another TPA3255 amp, robbed the motherboard of another A07 stuffed it in this case, had to modify it remove rca's from board, wire new RCA and also speaer terminals. I decided to remove the DC jack off the board and route it for now where the AC mains would be. Id like to somehow take the 120 AC and step it down to 48v with 7-10 amps. trying figure out eASIEst way to do that WITH space left in chassis. Oh also removed the Toggle switchand wired in a push button from the chassis. Its backwards right now but Ill fix that. Tested it out and it sounds somehow even better than before. Now togo through it tidy all the solder jobs and such etc.
 

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