Gain mismatch? - When to use in-line attenuators?

[tonapo]

Hi there,

I have a Topping D90 DAC which feeds my Musical Fidelity M6si amplifier. There is a fairly small band on the volume control when the volume goes for fairly low to uncomfortably loud very quickly. When the volume control is set to around 9 o'clock its fairly quiet, you can talk but hear the music. If you move the dial to 10 o'clock then it become pretty loud, you are no longer able to talk etc. On another site it had been suggested I might have a gain mismatch between the DAC and amp and that in-line attenuators might be a good solution. I ended up grabbing a pair of xlr Rothwell attenuators to try them out. They are the -20db variety and I have them plugged directly into the amplifier, the XLR cable into the DAC.

They seem to allow me to use more of the volume control but I was unsure if they actually negatively effect the system in any way. So I thought I would put a post up here.

Any thoughts?

 

[DonH56]

Should be fine... The output impedance of your DAC and input impedance of the amp will change the attenuation slightly but that should have no impact on the sound, and as they are simply resistor dividers should not do anything else but attenuate.

HTH - Don

 

[DVDdoug]

Yeah, it should be fine as long as the amp can still go as loud as you want (when you want it louder). Typically, the volume control in an amplifier is just an attenuator at the input anyway.

-20dB seems like a lot of attenuation, but if that's what works you're good!

 

[ADU]

Hi there,

I have a Topping D90 DAC which feeds my Musical Fidelity M6si amplifier. There is a fairly small band on the volume control when the volume goes for fairly low to uncomfortably loud very quickly. When the volume control is set to around 9 o'clock its fairly quiet, you can talk but hear the music. If you move the dial to 10 o'clock then it become pretty loud, you are no longer able to talk etc. On another site it had been suggested I might have a gain mismatch between the DAC and amp and that in-line attenuators might be a good solution. I ended up grabbing a pair of xlr Rothwell attenuators to try them out. They are the -20db variety and I have them plugged directly into the amplifier, the XLR cable into the DAC.

They seem to allow me to use more of the volume control but I was unsure if they actually negatively effect the system in any way. So I thought I would put a post up here.

Any thoughts?

Is this because you're going from the balanced XLR outputs on the DAC to the unbalanced RCA inputs on your amp? If so, then this is probably why you're getting the mismatch. And you might want to consider a different type of arrangement or gear to avoid having to make that kind of connection.

Another possible solution might be a passive balanced to unbalanced line level transformer, like the Radial J-Iso. But that might cost just as much or more than simply making some changes to some of your other gear to enable a better connection between the DAC and amp. And give you no noticeable or appreciable improvement in your sound quality.

I think you were also asking in another topic how transparent devices like the one above might be. And you can probably get some idea of that from Radial's specs and graphs on the J-Iso, which are located here...

J-Iso Specifications - Radial Engineering

The Radial J-Iso is a pro to consumer signal converter. It is designed to take a +4dB balanced line level and bring this down to a -10dB unbalanced format for easy manipulation with computers, hand held recorders and other unbalanced systems. Set and forget controls allow the system tech to set...

www.radialeng.com

 

[sarumbear]

Hi there,

I have a Topping D90 DAC which feeds my Musical Fidelity M6si amplifier. There is a fairly small band on the volume control when the volume goes for fairly low to uncomfortably loud very quickly. When the volume control is set to around 9 o'clock its fairly quiet, you can talk but hear the music. If you move the dial to 10 o'clock then it become pretty loud, you are no longer able to talk etc. On another site it had been suggested I might have a gain mismatch between the DAC and amp and that in-line attenuators might be a good solution. I ended up grabbing a pair of xlr Rothwell attenuators to try them out. They are the -20db variety and I have them plugged directly into the amplifier, the XLR cable into the DAC.

They seem to allow me to use more of the volume control but I was unsure if they actually negatively effect the system in any way. So I thought I would put a post up here.

Any thoughts?

Doesn’t D90 have volume control for its output?

 

[tonapo]

Thank you for the replies, it is much appreciated.

s this because you're going from the balanced XLR outputs on the DAC to the unbalanced RCA inputs on your amp? If so, then this is probably why you're getting the mismatch. And you might want to consider a different type of arrangement or gear to avoid having to make that kind of connection.

No, I am going XLR to XLR fully balanced (at least I think I am!!).

Doesn’t D90 have volume control for its output?

It does, but I run it in DAC mode by-passing the pre-amp. Supposedly this gives the best performance (and I have the volume control on the Musical Fidelity Amp).

-20dB seems like a lot of attenuation, but if that's what works you're good!

I think I went big to ensure I had some kind of effect. I actually also have some cheap JTS balanced in-line attennuators where you can select -10, -20 and -30 but they are in use on my desktop system.

 

[sarumbear]

It does, but I run it in DAC mode by-passing the pre-amp. Supposedly this gives the best performance (and I have the volume control on the Musical Fidelity Amp).

It may well be but there you are planning to introduce an unknown attenuator to the chain instead of relying on a measured response. Is that logical?

 

[Suffolkhifinut]

Hi there,

I have a Topping D90 DAC which feeds my Musical Fidelity M6si amplifier. There is a fairly small band on the volume control when the volume goes for fairly low to uncomfortably loud very quickly. When the volume control is set to around 9 o'clock its fairly quiet, you can talk but hear the music. If you move the dial to 10 o'clock then it become pretty loud, you are no longer able to talk etc. On another site it had been suggested I might have a gain mismatch between the DAC and amp and that in-line attenuators might be a good solution. I ended up grabbing a pair of xlr Rothwell attenuators to try them out. They are the -20db variety and I have them plugged directly into the amplifier, the XLR cable into the DAC.

They seem to allow me to use more of the volume control but I was unsure if they actually negatively effect the system in any way. So I thought I would put a post up here.

Any thoughts?

How did you decide -20db would give the correct level of attenuation? Tried some Rothwell attenuators a few years back and they did affect system sound. They weren’t linear across the frequency range and higher frequencies suffered the most, they robbed the music of life.

 

[tonapo]

It may well be but there you are planning to introduce an unknown attenuator to the chain instead of relying on a measured response. Is that logical?

No-one has ever accused me of being logical! Joking aside, I suppose I would say it is not an unknown attenuator per se (I know the manufacturer, have read a few reviews, and know what it is supposed to do), although I would like to verify the effects over and above what I think I hear. Which is why I am posting on here to get more perspectives etc.

How did you decide -20db would give the correct level of attenuation? Tried some Rothwell attenuators a few years back and they did affect system sound. They weren’t linear across the frequency range and higher frequencies suffered the most, they robbed the music of life.

Guestimate is the honest answer. I have not noticed much difference in the sound really, just more play on the volume dial.

 

[sergeauckland]

How did you decide -20db would give the correct level of attenuation? Tried some Rothwell attenuators a few years back and they did affect system sound. They weren’t linear across the frequency range and higher frequencies suffered the most, they robbed the music of life.

How can a simple resistive divider affect the frequency response? Unless of course they were followed by some high capacitance due to cable. Resistive attenuators should only ever be positioned at the input of an amplifier, never ever at the output of a source. Then, they can have zero effect on the sound, only attenuate.
S.

 

[Suffolkhifinut]

How can a simple resistive divider affect the frequency response? Unless of course they were followed by some high capacitance due to cable. Resistive attenuators should only ever be positioned at the input of an amplifier, never ever at the output of a source. Then, they can have zero effect on the sound, only attenuate.
S.

Are Rothwell attenuators purely resistive? If so why does it make a difference where you place them in the interconnect, If all they do is increase interconnect resistance?

 

[sergeauckland]

Are Rothwell attenuators purely resistive? If so why does it make a difference where you place them in the interconnect, If all they do is increase interconnect resistance?

Yes, Rothwell attenuators are purely resistive. However, if followed by an interconnect with a high capacitance, the parallel capacitance will roll-off higher frequencies as the series resistance and parallel capacitance for a low-pass filter. What the -3dB point is depends on the attenuator output impedance and the cable capacitance. It's no different to using a resistive passive 'preamp' with long interconnects.

In-line attenuators should always be at the amplifier input, never at the source output unless the interconnect cables are kept short and of low capacitance.

S.

 

[Suffolkhifinut]

Yes, Rothwell attenuators are purely resistive. However, if followed by an interconnect with a high capacitance, the parallel capacitance will roll-off higher frequencies as the series resistance and parallel capacitance for a low-pass filter. What the -3dB point is depends on the attenuator output impedance and the cable capacitance. It's no different to using a resistive passive 'preamp' with long interconnects.

In-line attenuators should always be at the amplifier input, never at the source output unless the interconnect cables are kept short and of low capacitance.

S.

Just been on the Rothwell website and they are selling ‘source attenuators’ as the name says they are plugged into the source not the Amp.

 

[sergeauckland]

Just been on the Rothwell website and they are selling ‘source attenuators’ as the name says they are plugged into the source not the Amp.

Just read that. In the absence of any technical details, and knowing that Rothwell are a sensible company and hopefully wouldn't just build an attenuator the 'other' way round, I have to assume that they're a low-impedance version of the input attenuator.

A source like a CD player or DAC can usually drive 500-1k ohms loads without too much trouble, so an attenuator that presents a, say, 600 ohm input impedance with a correspondingly low output impedance (say 100 ohms) will be able to drive much longer cables than an input attenuator that will present a typically 10kohm input impedance with a something like 1500 ohm output impedance.

However, using an output attenuator on the source requires the source be able to drive the attenuator input without distortion.


S.

 

[Slayer]

How can a simple resistive divider affect the frequency response? Unless of course they were followed by some high capacitance due to cable. Resistive attenuators should only ever be positioned at the input of an amplifier, never ever at the output of a source. Then, they can have zero effect on the sound, only attenuate.
S.

I'm with you. They should not make any difference on the sound. This has been the stance i have taken since the get go.
However, after much experimentation, my view or stance has changed. While I agree they shouldn't make a difference, yet, In reality, i must admit they do have a negative effect.

When i first bought and tried these a few years back, I thought at first, they seemed to be affecting the high frequencies in a negative way, but my brain told me this can't be true, it's only attenuating all the frequencies.
So, a couple weeks back i decided to experiment a little more. Seeing how it has been a few years since used, I would have a fresh outlook.
First, I tried with the Rothwells (xlr) connected at the amp, Immediately, the sparkle, life, whatever you want to call it seemed to be missing, bass seemed improved. Once again, I thought this must be my imagination. So, I pulled them out and this time i added a passive preamp (xlr) to the mix.
While the passive pre of course did attenuation, there was No obvious reduction (negative effects) in the highs, bass also seemed normal, only attenuated.

So in short, I don't know why they (Rothwells) are affecting the highs as they do, but they are. I suspect, not verified, it is somehow affecting the phasing (pure speculation on my part). Oddly enough, I have tried the RCA version in the past, and noticed No ill effects. Go figure.

Serge, would really appreciate your thoughts on why this may be happening. I'm baffled as to why it is, but it is audible. I know without measurements, it's all purely a subjective observation. But that's my observation. Needless to say, they will not be used again.

 

[sergeauckland]

As you say, without measurements, it's subjective observation, and I would add, speculation as to cause. I've measured any number of attenuators, and have never found any change in frequency response, flat from DC to well above any audio frequency. Eventually, yes, HF rolls off due to the capacitance of any cables connecting to my measuring equipment, but that happens at hundreds of kHz, not anything remotely audible. Similarly, they add no distortion and only thermal noise, so as far as I'm concerned they are totally transparent.

Speculating, if there is a change in audio quality, it might be due to the source not liking the reduced input impedance, which could reduce bass if the source's output capacitor is a bit low, or HF roll-off as already discussed above. It could also increase distortion somewhat.

As to any difference between XLR and RCA attenuators, there should be even less difference with XLR attenuators as every bit of pro kit with XLR outputs will happily drive down to 600 ohms, so the lower input impedance with the attenuators in circuit should have no effect.

S.

 

[tonapo]

Just been on the Rothwell website and they are selling ‘source attenuators’ as the name says they are plugged into the source not the Amp.

Just read that. In the absence of any technical details, and knowing that Rothwell are a sensible company and hopefully wouldn't just build an attenuator the 'other' way round, I have to assume that they're a low-impedance version of the input attenuator.

They are XLR rather than RCA, I read that the source attenuators are RCA although its not very clear. I have been using mine amplifier end anyway. I have also had a look at my receipt to see if it mentions 'source' and it doesnt say, nor on the vendor website I used. I will have a look at the actual attenuators to see if I can see anything.

 

[Suffolkhifinut]

As you say, without measurements, it's subjective observation, and I would add, speculation as to cause. I've measured any number of attenuators, and have never found any change in frequency response, flat from DC to well above any audio frequency. Eventually, yes, HF rolls off due to the capacitance of any cables connecting to my measuring equipment, but that happens at hundreds of kHz, not anything remotely audible. Similarly, they add no distortion and only thermal noise, so as far as I'm concerned they are totally transparent.

Speculating, if there is a change in audio quality, it might be due to the source not liking the reduced input impedance, which could reduce bass if the source's output capacitor is a bit low, or HF roll-off as already discussed above. It could also increase distortion somewhat.

As to any difference between XLR and RCA attenuators, there should be even less difference with XLR attenuators as every bit of pro kit with XLR outputs will happily drive down to 600 ohms, so the lower input impedance with the attenuators in circuit should have no effect.

S.

In my original post on this I asked ‘tonapo’ how he came up with choosing a 20 db attenuator. Mine were also 20 db and have always wondered whether a 10 db would have been better. Subsequently from what I’ve read taking a 2V source output and a. 100 mV input then the nearest match would be 20 db although it’s only approximate.

 

[tonapo]

Mine were also 20 db and have always wondered whether a 10 db would have been better. Subsequently from what I’ve read taking a 2V source output and a. 100 mV input then the nearest match would be 20 db although it’s only approximate.

Thank you for this.

I just had a quick look at the D90 DAC manual and I attach the 'output parameters' - The Line out XLR output voltage is 4Vrms, is that the source output you reference?

 

[Suffolkhifinut]

They are XLR rather than RCA, I read that the source attenuators are RCA although its not very clear. I have been using mine amplifier end anyway. I have also had a look at my receipt to see if it mentions 'source' and it doesnt say, nor on the vendor website I used. I will have a look at the actual attenuators to see if I can see anything.

Surely the XLR attenuators will be pin types for the source or a socket type for the Amp?