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

[Suffolkhifinut]

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?

What’s the rated input voltage on the Amp? From what I’ve read the formula is, LOG base 10 (output voltage / input voltage). Haven’t verified it and took it at face value.

 

[Slayer]

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.

All i can say is, I agree the xlr attenuators should have No effect on the sound, only attenuate as described. But that's not the case.
I should have added the active pre being used is a Parasound Halo preamp, and the amplifier Anthem MCA.
It's just odd that when adding in the passive volume pot used as an attenuator, it had no effects on the audio quality, it just attenuated as you would expect. Can't say the same for the Rothwells.
I wish i kept the email from Rothwell when i contacted them trying to understand why this was happening. They agreed the Parasound would have no problem driving them into the amp. They were also honest in stating they had others make this complaint before, but could not explain why.
They even still offered to take a return, however it's not worth the hassle of returning them in my case. I'll keep them for down the road when someone needs them. Regardless, i'm not going to say it's a bad product, it just didn't work out for my situation.

 

[tonapo]

socket type for the Amp?

Yes, that is correct.

 

[tonapo]

What’s the rated input voltage on the Amp? From what I’ve read the formula is, LOG base 10 (output voltage / input voltage). Haven’t verified it and took it at face value.

I have been looking at the manual, the specs are attached. I can't seem to see input voltage though.

 

[Suffolkhifinut]

I have been looking at the manual, the specs are attached. I can't seem to see input voltage though.

What Amp are you using?

 

[tonapo]

Its a Musical Fidelity M6si.

 

[ADU]

Thank you for the replies, it is much appreciated.

You're most welcome.

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

Good to know.

 

[ADU]

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).

I'm not familiar with either the DAC or amp you're using. I think using the fixed output on the DAC should be fine though (provided that most of your other gear and connections are in order). AUX1 appears to be the only analog input on the amp designed for variable inputs, with the HT mode enabled on the back.

 

[ADU]

What are you using the amp to drive btw? And do you get the same sensitivity in the volume control if you use an unbalanced RCA to RCA connection between the DAC and amp on AUX2?

 

[tonapo]

What are you using the amp to drive btw? And do you get the same sensitivity in the volume control if you use an unbalanced RCA to RCA connection between the DAC and amp on AUX2?

I am using some Kef Reference 1 speakers.

In terms of the unbalanced RCA, I have not tried, but I will and report back.

 

[Suffolkhifinut]

Its a Musical Fidelity M6si.

Went onto the Musical Fidelity website the only input voltage levels they give are for the MM/MC phono preamp.

 

[Mart68]

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.

FWIW I have also had the same experience with these devices, I agree with Serge there isn't an obvious explanation and many other users declare that they have experienced no such problem. Solved the gain issue by using a passive pre-amp instead, which is also just resistors.

Maybe it was all in my head but there was no improvement over time, they sat on the sound every time I listened. In that situation, whether it is psychological or not, there's no option but to discontinue use.

I tried them both on outputs and inputs. Still have them in a box somewhere.

 

[tonapo]

Went onto the Musical Fidelity website the only input voltage levels they give are for the MM/MC phono preamp.

Oh well, I thought it might just be me not being able to find it.

 

[chips666]

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?

Hello,
Suggestion

For volume control : Adjust M6si amp volume fixed slightly above max listening level and adjust with D90 dac volume control down to desired level
In this case you may not need attenuators
For sound quality : Also check sound with your JTS attenuators

Keep it simple If you dont hear any change there is nothing wrong with your setup

Enjoy...

 

[Suffolkhifinut]

FWIW I have also had the same experience with these devices, I agree with Serge there isn't an obvious explanation and many other users declare that they have experienced no such problem. Solved the gain issue by using a passive pre-amp instead, which is also just resistors.

Maybe it was all in my head but there was no improvement over time, they sat on the sound every time I listened. In that situation, whether it is psychological or not, there's no option but to discontinue use.

I tried them both on outputs and inputs. Still have them in a box somewhere.

Went onto the WEB looking for information on interconnect attenuators, one suggested getting two potentiometers 100 kohms and
10 kohms. Connect the 100k pot in series with a signal lead and the 10k across both signal leads. Start with both at zero and gradually adjust both until you get the optimal setting, providing his resistance values are correct seems a good way to go?
If you’ve got a multimeter any chance you could measure an attenuators series and parallel resistances? Just to satisfy my curiosity.
Thanks,
Ron

 

[Mart68]

Went onto the WEB looking for information on interconnect attenuators, one suggested getting two potentiometers 100 kohms and
10 kohms. Connect the 100k pot in series with a signal lead and the 10k across both signal leads. Start with both at zero and gradually adjust both until you get the optimal setting, providing his resistance values are correct seems a good way to go?
If you’ve got a multimeter any chance you could measure an attenuators series and parallel resistances? Just to satisfy my curiosity.
Thanks,
Ron

sorry I don't have a multimeter. Did have but leant it out and never got it back.

I don't think those measurements will tell us anything, if there is something real going on I am speculating that it must be a more complex interaction involving the input and output impedances specific to the connected devices which would explain why it does not manifest in every situation.

 

[Suffolkhifinut]

sorry I don't have a multimeter. Did have but leant it out and never got it back.

I don't think those measurements will tell us anything, if there is something real going on I am speculating that it must be a more complex interaction involving the input and output impedances specific to the connected devices which would explain why it does not manifest in every situation.

Certain you’re right, 10k across the signal conductors in pratical terms would be a virtual insulation short circuit coupled with up to 100k of series resistance which would limit amplifier input current. How could it do anything else but greatly affect the impedance interface?

 

[sergeauckland]

Certain you’re right, 10k across the signal conductors in pratical terms would be a virtual insulation short circuit coupled with up to 100k of series resistance which would limit amplifier input current. How could it do anything else but greatly affect the impedance interface?

Not sure exactly what you mean, but in practice, 100k of series resistance and 10k to deck is a perfectly sensible ~20dB attenuator, which is pretty unlikely to upset any source. The reason it's only approximately 20dB is because the 10k is in parallel with the amplifier's input impedance, and the 100k is in series with the source's output impedance. That's true of all resistive attenuators, which is why if accuracy if attenuation is needed, then the attenuator ratios need trimming.

For very many years (like 50+), sources have had a low output impedance and inputs have had a >10k input impedance, so there's never been an issue with impedance matching. Before then, with valve output stages that didn't have a cathode follower, output impedances were of the order of several 1000 ohms, even as high as 10kohms, so input impedances had to be very high(>1Mohm), fortunately not difficult with valves, but cable lengths between outputs and inputs had to be kept short, typically 1 - 1.5m (3-5ft). Pro equipment almost invariably had cathode follower outputs, and 600ohm outs and ins were normal, although even then, 600 ohm out to 10k in were not unusual.

S.

 

[ADU]

I am using some Kef Reference 1 speakers.

In terms of the unbalanced RCA, I have not tried, but I will and report back.

Thank you for the reply, tonapo.

I am not as experienced with the type of gear you're using. So bear that in mind as you read my comments/suggestions. I think trying RCA to RCA might help to isolate whether the issue is in the XLR connections, or somewhere else in the setup though. (Since RCA is the standard in home setups, I think it might be somewhat less likely to find errors in the implementation of those connections than with the XLR ins/outs. Not sure about that though.)

The specs on the Reference 1 suggest an amp in the 50 to 200 Watt range btw. While your amp is 220 Watts, which is a bit higher. And I saw no way to trim the gain on the amp, other than using the volume control. So perhaps this amp is just a bit too powerful for the speakers you're using?

I wonder if there are any controls on the speakers themselves that will allow you to trim/dial back the gain there. And also wondered if you were using any kind of EQ that could be effecting the output levels on your player or DAC.

 

[Suffolkhifinut]

Not sure exactly what you mean, but in practice, 100k of series resistance and 10k to deck is a perfectly sensible ~20dB attenuator, which is pretty unlikely to upset any source. The reason it's only approximately 20dB is because the 10k is in parallel with the amplifier's input impedance, and the 100k is in series with the source's output impedance. That's true of all resistive attenuators, which is why if accuracy if attenuation is needed, then the attenuator ratios need trimming.

For very many years (like 50+), sources have had a low output impedance and inputs have had a >10k input impedance, so there's never been an issue with impedance matching. Before then, with valve output stages that didn't have a cathode follower, output impedances were of the order of several 1000 ohms, even as high as 10kohms, so input impedances had to be very high(>1Mohm), fortunately not difficult with valves, but cable lengths between outputs and inputs had to be kept short, typically 1 - 1.5m (3-5ft). Pro equipment almost invariably had cathode follower outputs, and 600ohm outs and ins were normal, although even then, 600 ohm out to 10k in were not unusual.

S.

Serge
Surely inserting a 100k series resistance + 10k parallel resistance will alter the impedance quite a lot. If it didn’t what would be the point in inserting them in the first place? Long time since I’ve done anything with valves, were cathode follower circuits used because they were capable of higher current operation, like emitter follower circuits in bipolar transistor circuits? In this case where the original post said the XLR source output voltage is 4 Volts does it suggest an attenuator isn’t likely to solve the problem?