Okto Research dac8 Stereo custom output voltage for FirstWatt F5

[Jaje]

Hi there,

what custom output voltage should I request from Okto Research for connection from OktoResearch dac8 Stereo to FirstWatt F5 and how XLR pins should be connected to RCA ones? I know it is not ideal to connect XLR to RCA but that's what I need.

Thank you for an answers

 

[abdo123]

So @8Ohm (Nelson did not provide rated power @ 4Ohm) you will need ~2.47 Vrms to drive it to the advertised 25W power @ 8 Ohm

the measurements he shared shows that the amp begins to clip with 0.3% THD+N @ 50W @ 2 Ohm. To drive it to that output you need ~1.74 Vrms.

you're free to make an informed decision at this point.

 

[helsington]

I think F5 has a gain of 15dB. That makes the voltage to be ~2.5V based on the equation.
This is unbalanced signal. Okto Research custom output voltage can be in range from 1 to 12V RMS. But they have balanced output!
@abdo123 Does that mean that Antti needs a 5V custom voltage (because of the balanced voltage being double)? Or should he go with 2.5V?

 

[abdo123]

I think F5 has a gain of 15dB. That makes the voltage to be ~2.5V based on the equation.

I'm a little sick and i divided over 10 instead of 20 for some reason, i edited the post.

It is not disclosed at which wattage the amp actually clips, so i'm not going to recommend any specific values for them just rough guidelines.

@abdo123 Does that mean that Antti needs a 5V custom voltage (because of the balanced voltage being double)? Or should he go with 2.5V?

.yes if he's going to use balanced output and only use one of the two pins then he needs to double whichever value he picks by 2.

maybe more experienced members like @restorer-john and @solderdude can comment on that though as i'm not exactly sure.

 

[Jaje]

.yes if he's going to use balanced output and only use one of the two pins then he needs to double whichever value he picks by 2.

Thank you. In fact I have to use balanced output as there is no unbalanced output available.

maybe more experienced members like @restorer-john and @solderdude can comment on that though as i'm not exactly sure.

Can either of you @restorer-john or @solderdude confirm that please?

 

[solderdude]

The F5 starts to clip at 20V RMS
amplification = 5.82x so you need 3.43V to clip it.
When driving it from the + side of a balanced connection the output voltage (balanced) should be 6.86V.

Now there is the practical matter when listening to music.
Not all recordings reach 0dBFS so a little extra gain can be very useful.
As the power amp has no volume control it has to be done digitally.

So I would recommend for the Octo to reach at least 12V out (balanced)
This will give you the opportunity to add 5dB gain for recordings that need it.
When you hear the sound getting less smooth at high levels you just dial back.

 

[abdo123]

The F5 starts to clip at 20V RMS
amplification = 5.82x so you need 3.43V to clip it.
When driving it from the + side of a balanced connection the output voltage (balanced) should be 6.86V.

Now there is the practical matter when listening to music.
Not all recordings reach 0dBFS so a little extra gain can be very useful.
As the power amp has no volume control it has to be done digitally.

So I would recommend for the Octo to reach at least 12V out (balanced)
This will give you the opportunity to add 5dB gain for recordings that need it.
When you hear the sound getting less smooth at high levels you just dial back.

wouldn't the amp clipping aggressively damage the tweeter? Is this a risk worth taking?

 

[solderdude]

When you hear the sound getting less smooth at high levels you just dial back.

That will only be the case at maxed out volume (owner will know the volume is set at max) with recordings that are reaching 0dB.
The owner will know that when the volume control is set above -6dB he should be more careful.

In most cases his volume control will be between -40 and -10 at best.

 

[Jaje]

The F5 starts to clip at 20V RMS
amplification = 5.82x so you need 3.43V to clip it.
When driving it from the + side of a balanced connection the output voltage (balanced) should be 6.86V.

Now there is the practical matter when listening to music.
Not all recordings reach 0dBFS so a little extra gain can be very useful.
As the power amp has no volume control it has to be done digitally.

So I would recommend for the Octo to reach at least 12V out (balanced)
This will give you the opportunity to add 5dB gain for recordings that need it.
When you hear the sound getting less smooth at high levels you just dial back.

As I am usually listen to classical music where 0dBFS is quite rare and I listen currently via Burson Conductor 3P (I guess unbalanced 2V RMS) at 2 o'clock at most, I'll opt for 12V out balanced (max. they offer as custom output voltage). Thank you both @solderdude and @abdo123 for answers!

 

[dped90]

As I am usually listen to classical music where 0dBFS is quite rare and I listen currently via Burson Conductor 3P (I guess unbalanced 2V RMS) at 2 o'clock at most, I'll opt for 12V out balanced (max. they offer as custom output voltage). Thank you both @solderdude and @abdo123 for answers!

But when I asked about ordering the DAC8 Pro with the optional higher voltage output range, Pavel Krasenky did make plain that there’s no free lunch:

There is no change in how the volume works with various full-scale voltage settings. What changes when we configure the custom output voltage is the gain of the analog circuits. The noise floor changes proportionally with the full-scale output voltage, meaning that the dynamic range is preserved. If you were to raise the full-scale output voltage to 12V, you would see the noise floor increase by around 9 dB. Also, it's common for harmonic distortion to increase slightly with higher signal voltage in analog circuitry.

But have you or anyone you know who ordered this DAC with the 12 volt output range noticed any noise during the quietest passages of your music tracks, and/or what sounds like audible (third harmonic?) distortion?

Also, please make/model of amplifier fed from the Okto Pro DAC and your speakers' sensitivity.