Connect two amplifiers to one output

[Guest]

Gday! I have a Fosi v3 class d amp and am looking at getting a second to run two pair (4 speakers) of speaker from the same output source which is a dac. 

 

My question: what are some options to connect the rca input from two amplifiers to the output of my dac? 

Would this work? cheers!

Edited April 9, 2024 by F M

[stereo coffee]

1 hour ago, F M said:

Gday! I have a Fosi v3 class d amp and am looking at getting a second to run two pair (4 speakers) of speaker from the same output source which is a dac. 

 

My question: what are some options to connect the rca input from two amplifiers to the output of my dac? 

Would this work? cheers!

Yes, but you can build one for much less.  Sharing output of your stated source, you are likely to be disappointed as the integrated circuit in the amplifier does not match to normal levels   https://www.ti.com/lit/ds/symlink/tpa3255.pdf?

 

The result i am sorry to say,  is likely to be insufficient audio level caused by insufficient sensitivity.

[Guest]

Thank you for your reply! I had a look through the extensive, detailed pdf and realized how much i don' t know. 

9 hours ago, stereo coffee said:

the integrated circuit in the amplifier does not match to normal levels

I don't understand what you mean by this could you please explain further, are you referring to the Fosiv3 / TPA3255 or fundamental factors effecting the sound?

Cheers! 

[stereo coffee]

43 minutes ago, F M said:

Thank you for your reply! I had a look through the extensive, detailed pdf and realized how much i don' t know. 

I don't understand what you mean by this could you please explain further, are you referring to the Fosiv3 / TPA3255 or fundamental factors effecting the sound?

Cheers! 

The figures to observe are what Texas Instruments quote as Peak to Peak level on page 26, as 3.9v , which means the amplifier provides its stated output with that level of input,

 

Now compare to actual everyday levels that sources output which is peak to peak 0.894V , which is caused by the media being played and not the devices capability.  Calculating then we find on page 8 , what appears as impressive output of 315 watts into 4 ohms, until we factor the input level that media outputs which is 4.36 times than the specification  , less , which as a result  is now just 72.24 watts , and making matters worse is at 10% Total harmonic Distortion. Also factor the source output is dividing in half and 36 watts with 10% distortion is 1000 worse than amplifiers manufactured in 1959  .

 

To give you hope, compare to this amplifier that matches near perfectly the actual level of media being played so no power is wasted and does so with 50 watts output and distortion of 0.03%  https://www.hifiengine.com/manual_library/quad/306.shtml

 

Edited April 9, 2024 by stereo coffee

[georgehifi]

11 hours ago, F M said:

My question: what are some options to connect the rca input from two amplifiers to the output of my dac? 

@F M

You need a volume control on your dac if it has one, so you have a "master volume control"??

If so all you need is two of these on the L&R outputs of your dac to both Fosi V3's  https://tinyurl.com/266929bt 

Then you can set the Fosi's volume to the loudness you want on that pair of speakers and use the dac volume as the master for all.

 

This will work if your dac has a low output impedance, most do save for tube ones. 

 

Cheers George

 

 

Edited April 9, 2024 by georgehifi

[Guest]

12 minutes ago, georgehifi said:

You need a volume control on your dac if it has one, so you have a "master volume control"??

I am currently using an Asus Xonar essence one which has a speaker volume control nob. 

 

Awesome thanks for the info Georgehifi! I'm familiar with Selby and will have a further look into what you've said. Cheers!

[georgehifi]

31 minutes ago, F M said:

I am currently using an Asus Xonar essence one which has a speaker volume control nob. 

 

Yes that'll be fine it has a nice low 100ohms output impedance at all frequencies, and with output volume control,  using the 2 x dual rca's I linked to above. then set your volume  where you need on the V3's. and use this as the master.

So your up for $10 for the dual rca's and another set of interconects.

 

 

Cheers George

Edited April 10, 2024 by georgehifi

[Guest]

27 minutes ago, georgehifi said:

Yes that'll be fine

Thanks again Georgehifi! 

[surprisetech]

2 hours ago, stereo coffee said:

The figures to observe are what Texas Instruments quote as Peak to Peak level on page 26, as 3.9v , which means the amplifier provides its stated output with that level of input,

 

Now compare to actual everyday levels that sources output which is peak to peak 0.894V , which is caused by the media being played and not the devices capability.  Calculating then we find on page 8 , what appears as impressive output of 315 watts into 4 ohms, until we factor the input level that media outputs which is 4.36 times than the specification  , less , which as a result  is now just 72.24 watts , and making matters worse is at 10% Total harmonic Distortion. Also factor the source output is dividing in half and 36 watts with 10% distortion is 1000 worse than amplifiers manufactured in 1959  .

 

To give you hope, compare to this amplifier that matches near perfectly the actual level of media being played so no power is wasted and does so with 50 watts output and distortion of 0.03%  https://www.hifiengine.com/manual_library/quad/306.shtml

 

 

This is all based on just the output chip specs, not the product specs.  The Fosi V3 has an input buffer stage (2x TI NE5532) & a volume control before the power amp chip, so your concerns, I'm sorry to say, are a red herring.

 

Pics of the internals and more product details are in this link where it gets a very good rap.

https://www.audiosciencereview.com/forum/index.php?threads/fosi-audio-v3-amplifier-review.45757/

Manufacturer site with features, specs, etc:

https://fosiaudio.com/pages/2-channel-amplifier-v3

 

From another thread, the OPs speakers are 90dB sensitivity and he is already very happy with the drive level and clean sound from the Fosi V3.

[surprisetech]

4 hours ago, stereo coffee said:

Also factor the source output is dividing in half

 

Sorry to seem pedantic, but no, it isn't. 

That would only be the case if the input impedance of the amp was the same as the output impedance of the source.  (Impedance ratio of 1:1)

Even driving both amps in parallel, the input to output impedance ratio in this case is 100:1 (10,000 Ohms to 100 Ohms).  The source's 100 Ohm output will happily drive the high impedance inputs on the amps with virtually no loss in level.

Basic Ohms law stuff.

[stereo coffee]

The reasons have been provided objectively, but as it seems not understood , but happens to also agree with the subjective opinions as well

 

"With the volume turned up to 3 quarters it's not particularly loud at all."  Audio karma forum

"it's starting to make sense why some people said the FOSI V3 has "not enough power." It's not the output watts, I think it's the line's input level." Audio Science Review

 

 

 

[surprisetech]

22 minutes ago, stereo coffee said:

The reasons have been provided objectively, but as it seems not understood , but happens to also agree with the subjective opinions as well

 

"With the volume turned up to 3 quarters it's not particularly loud at all."  Audio karma forum

"it's starting to make sense why some people said the FOSI V3 has "not enough power." It's not the output watts, I think it's the line's input level." Audio Science Review

 

Yes, the gain in the Fosi V3 input buffer is less than what we typically see, meaning the volume control needs to be set higher than we are used to.  I've noticed this in a few products in recent times.  A new generation of designers unencumbered by previous norms?  Just a guess )

 

The product still delivers the required amount of clean power, but the volume setting creates a perception that the amp is lacking because of the unusually high position.

 

I accept there might be cases where an input source level is so low that the volume control may run out of range altogether, in which case another amp will be better suited.  Has that been reported?  My guess is that it is more of a perception of lack of power due to the volume control setting.

 

OP does not have this problem, nor do the majority of reviewers/users.

 

For decades we've been used to amps with high gain input buffers followed by a volume pot, that then cuts that amplified signal almost back to the level that appeared at the input, in order to achieve our desired listening level.

We've got used to never setting the volume control higher than about 10 o'clock with about 2/3 of the pots travel never used.

 

If there's no need for all that extra gain (no active tone controls, loudness circuits, etc.) it just makes sense to me to lower the gain of the input buffer and set the volume pot to let more of that signal level through to the power stage.

Same end result.  Same sound quality.  Less waste!