Input sensitivity match

[Trustful6061]

That sounds problematic. I'm planning on connecting amp and pre-amp with RCA cable, not XLR. Would that make any difference? To be clear, I ordered this Nord NC502 which has RCA-inputs.

Is there any good solutions to fix the problem with my equipment? I've read that Art Cleanbox would help with the voltage, but it would also add distortion so it kind of defeats the purpose of adding the whole power-amp. The whole purpose of this endeavor is to get more clean power than I would ever need (maximize headroom and quality).

There is ofcourse the fact that 60-ish watts of power with my speakers is more than I've ever used and probably ever will, but I would be a tad disappointed if I can only use 25% of my amps output.

Is there more sophisticated alternative to Cleanbox? I own a ground loop isolator (actually it might be exactly this one) if that would help with the noisiness of the pre-amp signal. Again, I am no electrical engineer

E: I am also a bit confused with the information about Denons pre-out voltages. According to Audioholics X3300W had ample amounts of pre-amp output before clipping (4.5 V if I recall correctly), but here X3500H had just about 1.5 V before SINAD went down hard. X3400H should be internally pretty much identical with X3300W. So if X3300W clips at 4.5 V couldn't we extrapolate that 2.0-2.5V output could be somewhat clean?

 

[Julf]

That sounds problematic. I'm planning on connecting amp and pre-amp with RCA cable, not XLR. Would that make any difference? To be clear, I ordered this Nord NC502 which has RCA-inputs.

Did you have a specific reason for that? Balanced connectors (XLR) and cable are better even if the source is unbalanced/RCA.

Is there any good solutions to fix the problem with my equipment? I've read that Art Cleanbox would help with the voltage, but it would also add distortion so it kind of defeats the purpose of adding the whole power-amp. The whole purpose of this endeavor is to get more clean power than I would ever need (maximize headroom and quality).

Yes, don't go for active boxes. You can change the gain of the amps, but it is not entirely trivial.

There is ofcourse the fact that 60-ish watts of power with my speakers is more than I've ever used and probably ever will, but I would be a tad disappointed if I can only use 25% of my amps output.

You still have the extra power there as headroom and reserve. Remember that 25% of the power is only 6 dB down from full power.

Is there more sophisticated alternative to Cleanbox? I own a ground loop isolator (actually it might be exactly this one) if that would help with the noisiness of the pre-amp signal. Again, I am no electrical engineer

I would only worry about it if it turns out noise really is a problem. Ground loop isolators are a bad idea unless you know what you are doing.

 

[ririt]

According to other threads, RCA to XLR from either Benchmark or March Audio are properly wired to ensure optimal connexion between an AVR (RCA output) to Hypex or Purifi amps with balanced XLR inputs. Wiring is done according o the scheme provided by Julf in this thread

 

[Trustful6061]

Did you have a specific reason for that? Balanced connectors (XLR) and cable are better even if the source is unbalanced/RCA.

Nothing really, I was just asking if it might make a difference. I've just thought that if I can use the power-amp without adapters, I might aswell. I never really thought that there would be anything to gain by using an adapter from RCA to XLR.

Yes, don't go for active boxes. You can change the gain of the amps, but it is not entirely trivial.

Roger that, glad I dont need yet another box in the AV-rack. Since it's not trivial it's unlikely I will even try but... How can you change the gain of the amps? And are we speaking of pre- or power-amp?

You still have the extra power there as headroom and reserve. Remember that 25% of the power is only 6 dB down from full power.

Yes I know the scale is logarithmic, but I also know the fact that there is 75% more to get will bug me a bit. Although if the system sounds good, I really could't care less about a little hindrance like that.

I would only worry about it if it turns out noise really is a problem. Ground loop isolators are a bad idea unless you know what you are doing.

I shall not worry about it in that case. I'll keep my ground loop isolator out of my system.

Thanks for the explanation! I'm new to this forum and although I know some of this stuff I really have much to learn.

Since there are many bad RCA-XLR-cables could you give your opinion on this one https://www.cordial-cables.com/en/products/cfu-fc. That just happens to be one cable that I could just go and pick from a store near me. I happen to live in Finland so availability of American manufacturers cables might be limited.

 

[Julf]

Since it's not trivial it's unlikely I will even try but... How can you change the gain of the amps? And are we speaking of pre- or power-amp?

Power amp. There is a feedback resistor that determines gain, but it is a surface-mounted component so desoldering it takes dexterity.

Yes I know the scale is logarithmic, but I also know the fact that there is 75% more to get will bug me a bit.

Don't think of it as 75%, think of it as a minor level difference - or even better, think of it as "ample headroom and reserves". My main systems are active Linn Isobariks with an aggregate of 1200 W per channel of amplification, but anything much above 100W will fry them.

Since there are many bad RCA-XLR-cables could you give your opinion on this one https://www.cordial-cables.com/en/products/cfu-fc. That just happens to be one cable that I could just go and pick from a store near me.

Not how I would do it.

I happen to live in Finland so availability of American manufacturers cables might be limited.

Ah, should have guessed it from your username. I am a (swedish-speaking) Finn, but been living in Amsterdam for 23 years now.

 

[Trustful6061]

Power amp. There is a feedback resistor that determines gain, but it is a surface-mounted component so desoldering it takes dexterity.

Ok, I might just ask Nord if they have done such modifications to NC502MP. But as said, this seems pretty far fetched. I suspect there will be some trade-off with the higher gain on the power-amp's side?

Don't think of it as 75%, think of it as a minor level difference - or even better, think of it as "ample headroom and reserves". My main systems are active Linn Isobariks with an aggregate of 1200 W per channel of amplification, but anything much above 100W will fry them.

Ok, that is a constructive way to think about it. I think my woofer can take about 150W before it reaches it's xMech so getting the full power really is not a necessity.

Not how I would do it.

I see. Would you have any go-to recommendations for European buyer?

Ah, should have guessed it from your username. I am a (swedish-speaking) Finn, but been living in Amsterdam for 23 years now.

Ha, what a coincidence. This planet sometimes feels pretty small.

 

[Julf]

Ok, I might just ask Nord if they have done such modifications to NC502MP. But as said, this seems pretty far fetched. I suspect there will be some trade-off with the higher gain on the power-amp's side?

Yes, you would decrease the negative feedback.

Would you have any go-to recommendations for European buyer?

Not really - I tend to make my own cables, and usually try to stick to fully balanced. Problem is that if your amp has a RCA, there is no way to keep the "-" signal and ground separate.

Ha, what a coincidence. This planet sometimes feels pretty small.

Indeed.

 

[dajoe]

Hello all,

this is my first time posting here, so, hello again.
I am in a similar position as Bahamies. I consider getting a sensitive power amp to confine my NAD T758 v3 DAC to the "cleaner" 1Vrms (per Amir's review) using the RCA pre-outs. Since at a later time I might upgrade the source to a more "professional" ~4 Vrms one, I'd prefer some configurable input gain, e.g. the audiophonics purifi builds. There I can remove a jumper and configure an input sensitivity from 2,25 Vrms (25,3 dB gain) to 4,2 Vrms (20 dB gain).

Now, my speakers are 6 Ohms and 89 dB at 2,83 Vrms (~1,33 Wrms), 1 m and rated at a max. SPL of 110 dB.

According to my calculation, 1Vrms output level would give me ~56,5 Wrms (113 W peak) into 6 Ohms and per speaker 105 dB SPL. At my listening position (2 speakers, 3m away) that would be 101,7 dB, which is good, I think. Ideally though, I'd want the ~5 db of speaker SPL headroom within the 1Vrms window of my NAD. And why would I buy a ~400 W amp of which I'd only plan to use 50?

My Idea now, other than selecting a different amp (Apollon configures theirs at 28 dB gain but without the nice jumper option), I could use a RCA to XLR adapter that , instead of setting pin 3 to ground would make it symmetric (-pin2), adding 6 dB. That way, I would have an effective gain of ~31,3 dB and utilize 224 Wrms at 1 Vrms (450 W peak)...

Now my questions
1) am I calculating it right?
2) am I making sense?
3) can you point me to an adapter that does what I want and nothing I don't want or understand?
4) does the fact that I am using an active sub crossing over at 60 Hz anyway render my considerations invalid?

 

[laidick]

Hello all,

this is my first time posting here, so, hello again.
I am in a similar position as Bahamies. I consider getting a sensitive power amp to confine my NAD T758 v3 DAC to the "cleaner" 1Vrms (per Amir's review) using the RCA pre-outs. Since at a later time I might upgrade the source to a more "professional" ~4 Vrms one, I'd prefer some configurable input gain, e.g. the audiophonics purifi builds. There I can remove a jumper and configure an input sensitivity from 2,25 Vrms (25,3 dB gain) to 4,2 Vrms (20 dB gain).

Now, my speakers are 6 Ohms and 89 dB at 2,83 Vrms (~1,33 Wrms), 1 m and rated at a max. SPL of 110 dB.

According to my calculation, 1Vrms output level would give me ~56,5 Wrms (113 W peak) into 6 Ohms and per speaker 105 dB SPL. At my listening position (2 speakers, 3m away) that would be 101,7 dB, which is good, I think. Ideally though, I'd want the ~5 db of speaker SPL headroom within the 1Vrms window of my NAD. And why would I buy a ~400 W amp of which I'd only plan to use 50?

My Idea now, other than selecting a different amp (Apollon configures theirs at 28 dB gain but without the nice jumper option), I could use a RCA to XLR adapter that , instead of setting pin 3 to ground would make it symmetric (-pin2), adding 6 dB. That way, I would have an effective gain of ~31,3 dB and utilize 224 Wrms at 1 Vrms (450 W peak)...

Now my questions
1) am I calculating it right?
2) am I making sense?
3) can you point me to an adapter that does what I want and nothing I don't want or understand?
4) does the fact that I am using an active sub crossing over at 60 Hz anyway render my considerations invalid?

I am not sure if using RCA to XLR could add you 6dB....

 

[Julf]

I am not sure if using RCA to XLR could add you 6dB....

Usually it is the other way around. Balanced outputs often have double the voltage swing.

 

[dajoe]

According to my understanding, balanced XLR has three lines: 1 is shield, 2 is +signal, 3 is -signal (floating). What Balanced -> RCA unbalanced would do is shorting the -signal to ground, grounding the shield and providing +signal vs ground. This effectively halves the amplitude or reduces the input by 6 dB. I want to do it the other way round: Convert the unbalanced RCA output to a true balanced XLR input - if this can be achieved with a passive adapter. Using just a RCA->XLR cable would give my +signal on line 2 and ground on line 3.

 

[Julf]

According to my understanding, balanced XLR has three lines: 1 is shield, 2 is +signal, 3 is -signal (floating). What Balanced -> RCA unbalanced would do is shorting the -signal to ground, grounding the shield and providing +signal vs ground. This effectively halves the amplitude or reduces the input by 6 dB. I want to do it the other way round: Convert the unbalanced RCA output to a true balanced XLR input - if this can be achieved with a passive adapter. Using just a RCA->XLR cable would give my +signal on line 2 and ground on line 3.

The "passive adapter" is called a cable.

There is no problem (apart from the signal level) in driving a balanced/differential input from an unbalanced input. See variation #17 here:

Rane Application note 110

 

[dajoe]

Thanks, Julf.

I think I still have difficulties to understand what these cables actually do to the output level. Balanced XLR -> unbalanced RCA actually doesn't change the level at all, right? 4 Vrms between pin red and black become 4 Vrms between red and ground on RCA.

 

[Julf]

I think I still have difficulties to understand what these cables actually do to the output level. Balanced XLR -> unbalanced RCA actually doesn't change the level at all, right? 4 Vrms between pin red and black become 4 Vrms between red and ground on RCA.

Balanced to unbalanced can result in -6 dB (half the voltage), if you take the signal from "+" or "-" ("hot" and "cold") and ground instead of from between "+" and "-", but that is not an issue when you go the other way around (unbalanced to balanced/differential).

 

[DonH56]

Note you can usually connect the XLR input signal (-) and shield to an RCA's output ground. In general you should not short the XLR (-) output to ground as you are shorting one side of the differential driver's output.

A differential (XLR) output has twice the voltage swing of a single-ended output using only one side of the differential output. Not using one side of the differential output means only half the signal swing into the single-ended (RCA) input.

You may (or may not) find this useful: https://www.audiosciencereview.com/...d-balanced-unbalanced-and-all-that-jazz.1352/

HTH - Don

 

[Julf]

You may (or may not) find this useful: https://www.audiosciencereview.com/...d-balanced-unbalanced-and-all-that-jazz.1352/

And that thread has your excellent recommendation to use a balanced cable even if the source is unbalanced.

 

[bigguyca]

According to my understanding, 1) balanced XLR has three lines: 2) 1 is shield, 2 is +signal, 3 is -signal 3) (floating). What 4) Balanced -> RCA unbalanced would do is shorting the -signal to ground, grounding the shield and providing +signal vs ground. This effectively halves the amplitude or reduces the input by 6 dB. I want to do it the other way round: Convert the unbalanced RCA output to a true balanced XLR input - if this can be achieved with a passive adapter. Using just a RCA->XLR cable would give my +signal on line 2 and ground on line 3.

Balanced and Differential Connections are not the same!

1) In a balanced connection the impedance from each signal line, lines 2 and 3 is the same to ground. That is why is it call balanced. The use of the lines is not included in the definition.

2) You discussing differential signaling with your + and - examples. Differential signaling and balanced lines are two different things.

3) What is your definition of floating in this context? What should be floating?

4) Shorting the (-) line to ground puts an unnecessary load on the electronics that are driving the (-) line and is not recommended by many manufacturers. Why are you advocating it?

 

[dajoe]

Balanced and Differential Connections are not the same!

1) In a balanced connection the impedance from each signal line, lines 2 and 3 is the same to ground. That is why is it call balanced. The use of the lines is not included in the definition.

2) You discussing differential signaling with your + and - examples. Differential signaling and balanced lines are two different things.

3) What is your definition of floating in this context? What should be floating?

4) Shorting the (-) line to ground puts an unnecessary load on the electronics that are driving the (-) line and is not recommended by many manufacturers. Why are you advocating it?

Thanks for all the feedback. I am still learning about signal transmission electronics so sorry if my terms are not accurate.

My understanding is that +/- or hot/cold are floating, meaning they don't have a defined potential vs the shield (or ground). In a balanced connection, the ground does not play a role for the signal. Thinking about it, an XLR/RCA cable connecting pin 3 and 1 is in fact no short then.

 

[Harmonie]

Balanced is not always an advantage ....
https://www.audiosciencereview.com/forum/index.php?threads/balanced-vs-unbalanced.12684/post-500334

 

[Julf]

Balanced is not always an advantage ....
https://www.audiosciencereview.com/forum/index.php?threads/balanced-vs-unbalanced.12684/post-500334

So when would it be a disadvantage?