Please, help me choosing amp project for my speakers

[Drummer 35]

Hi all,

I want to build an stereo amp for my speakers.

They are 8ohms impedance and rated at 96db/1w.

I've been drawing a pcb for Lm3886s running in parallel but I doubt I'll get any benefit with that config since the speakers are 8ohm mpedance.

I'm afraid those 50-60 watts won't be enough for playing at loud listening levels.

Tda7293 offers more power but I have read on the forum that it's sound is not as detailed as 3886s

Please, let me know if I'm wrong thinking I'll run short on power with the parallel 3886s or if I should look for other chip amps.

Thanks for your help.

 

[mrWagner]

96dB is good sensitivity, with 50W, you will get quite loud.
Unless you plan to use it in a big hall or smg.
In a living room even 1W will be decent listening level.

 

[Drummer 35]

Thanks for your answer Wagner.

Tested the speakers with a 80w/8ohm rated Rotel amp and at around 80% volume it gets too loud and begins to distort.

I think it's the amp and not the speakers since they are rated for 250w continuous.

Never worked with 3886s amps and don't know how do they work when pushing them hard.

That's why I thought I should go for a parallel solution. (and also because I'd like to have an amp that could drive 4ohm speakers)

I'll wait for more comments before starting with the project.

Thanks!

 

[mikejennens]

I'm with mrWagner; you don't typically need a lot of watts for speakers rated at 96dB. Another option to consider is a tube amp. There are some that shouldn't be much more expensive than a decent 3886 amp. One option is S5 Electronics- Untitled or TubeDepot- https://tubedepot.com/t/diy-central/kits-tube-amp/hifi-tube-amp-kits

With your speakers, even 8 watts should be more than enough.
Mike

 

[AndrewT]

80W+80W into a pair of 96dB/W @ 1m speakers gives a maximum loudness at the 2.5m distant seating position of ~110dB
That is loud and most Builders would be satisfied with half that power capability.
Some listeners would be very happy with a quarter, i.e. 20W per channel and never reach clipping on the loud passages.

A chipamp of around 20W to 50W will probably be plenty loud enough with those speakers in a domestic listening environment, (too loud for your neighbours?).

But chipamps can be too noisy. You must design for low noise to suit these speakers.

 

[Drummer 35]

Thanks for your answers.

Mike, I don't want to go with tubes. They sound amazing but never worked on those amps...I'd like to make my own pcb design and I don't feel confident enough to draw a tube amp pcb.

Andrew, I think you are right and a good gainclone will be enough, but, what are you referring when you say I must design the amp for low noise?

I plan on adding an input filter, dc blocking cap and a zobel network at the output.

Please, let me know if I'm missing something.

Thanks again.

 

[AndrewT]

Read the lm3886 specification, it shows the input referred noise as typically 2.0uV and max as 10uV
Note the ratio of 5 (+8dB) between typical and max.
Next line: SNR typically 92.5dB ref 1W into 4ohms (=92.5dB below 2Vac) and max could be upto 8dB noiser than this.
With mid 80s dB speaker, this would be virtually inaudible.
A max noise chip could be 84.5db below 2Vac

With a 96dB speaker the noise will appear as ~10dB louder.
That combined with a noisy chip or a topology that does not minimise noise could end up with noise at the listeneing seat whenever the audio goes quiet.

All the National noise figures are filtered to the standard A-weighting. When you meausre a real amplifier filtered to pass 10Hz to 20kHz you will measure between 2dB and 6dB louder than the A-weighted figure.

That's why you need to build for low noise.

 

[mrWagner]

Also where are you listening to that speaker? And how loud was it with that 80W amp?
I use a 91dB speaker in my room with a 20W chipamp and I don't think I ever bumped it over 10W. Once I tested the speakers with a 70W amp and it was terribly loud near max power. Normal listening levels I guess is somewhere 0.1W, but probably you listen to music lot louder. So you know what 80W can do, you can calculate what power you need. Was that 80W enough?

 

[Drummer 35]

Wagner, I tested the speakers in a large room. At around 6 meters from listening position. I tested them at "party level" but It's not a normal listening volume.

You're right and I will be happy building an amp not as powerful (don't need to blow the windows) but with better attack and treble detail.

Andrew, as you say, those speakers reveals all the noise and bad recordings.

I thought I should go with the 3886 because of it's simplicity and good reviews but maybe it's not the best choice.

What about a composite Lm3886 amp? More complex but could that solve the noise problem? Should I go other route with other amp project?

Thanks again for your help.