Help - I've got a gain problem.

[Martinh]

Hi all,

I have a problem with excess gain in my system, which means that the volume is already too high at only 9 o'clock.

I've been playing around with attenuators and have found that I need more than 20 db attenuation to improve the situation.

Using a 10k resistor in series with the signal and 750 ohm across to the ground gives me -23 db (I think). I've put these inside the RCA connectors (neutrik metal) and its much better but not completely perfect. Could do with a bit more i think.

My speakers are sensitive at 90 db and marantz don't publish a gain figure.

I think -23 db attenuation sounds a bit much, don't you?

Any ideas?

Martin

[Reid Malenfant]

Hi Martin, is that with all sources of just one? That is one hell of a lot of attenuation, the problem is you'll also be introducing noise into the system with those 10K resistors in series :rolleyes: As well as that with no defined output impedance (of whatever the attenuator is connected to) I'd expect possible rolloff of low & high frequencies :doh:

[Martinh]

Hi Mark,

Yes it's on all sources:

Dacmagic output imp <50 ohms
Tv analogue out unknown
Tuner 2.2kohms
DVD player unknown.

I was wondering if I should increase the values of the Lpad resistors to increase the overall value, while maintaining the same attenuation? The load on the outputs would then be lower?

Any other solutions?

Martin

[Reid Malenfant]

I'm amazed you have a problem as the Marantz amp won't have gain that is much different from anything else out there :scratch: Just about any other integrated will have a similar gain.

I find it odd that your Tuner is outputting a similar level, or is this a DAB unit?

[Macca]

I notice you are using a sub. That couldn't be a factor could it?

[Martinh]

The tuner output is 600mV , but it sounds nearly as loud as the dacmagic, which is 2.1 V - all very strange.

I'm running -23 db at the mo, and it does not seem to have affected the sound or frequency extremes. But there's always a nagging doubt :rolleyes:

I was thinking of doing a mod of the amp and put the attenuator network between the input selector and volume control. I could then buy some nice expensive resistors, which were shared between all sources. Does that make sense?

The sub is working at a very low level and has the upper roll off set at around 40 hz, so does not affect the overall sound level.

Cheers, martin

[Reid Malenfant]

The tuner output is 600mV , but it sounds nearly as loud as the dacmagic, which is 2.1 V - all very strange.

I was thinking of doing a mod of the amp and put the attenuator network between the input selector and volume control.
That won't make a whole lot of difference in reality.

I'd place any attenuator following the volume control, so it loads that rather than increasing the input noise. In certain respects it shouldn't make any difference.

Effectively what I suggest you'd have the 10K resistor tied to the output of the potentiometer at the wiper & the 750 ohm to ground with the output from the junction of the two.

I reckon it'd result in less noise...

[StanleyB]

Get a less powerful amp and/or less sensitive speakers.

[Martinh]

Get a less powerful amp and/or less sensitive speakers.

Yes, that is the answer.

In the short term, I will need some attenuation.

Just been listening to the results and all sounds great - sounds balanced with no obvious loss at either end of the frequency spectrum.

Do different types/makes of resistor affect the sound? I can pay 10p from maplins up to £10 each from hifi collective.

Martin

[YNWaN]

I'm not quite sure that is the answer as such.

What I mean is, as it stands, your amp isn't particularly powerful and your speakers aren't spectacularly efficient.

It is likely that the law of the volume control you amplifier uses means that full output is achieved with it pointing at approximately 12 O'clock (perhaps less when fed the 2V of a CD or DAC). This would also have the effect of compresing the relative difference between the output levels of different sources.
_________________________

My experience is that resistors do make a difference (depending on the circuit and where they are used) - but in this case I wouldn't use resistors to pad down the output. In other words, does this 'problem' really need addressing, can't you just use the volume control at a lower setting? I mean, it doesn't sound like the amps input is actually being over driven (clipping), so it's working fine. If you really want the volume control to be usable over a wider range I would consider changing the volume control (or buying a different, and better, amp).

[Martinh]

I'm not quite sure that is the answer as such.

What I mean is, as it stands, your amp isn't particularly powerful and your speakers aren't spectacularly efficient.

It is likely that the law of the volume control you amplifier uses means that full output is achieved with it pointing at approximately 12 O'clock (perhaps less when fed the 2V of a CD or DAC). This would also have the effect of compresing the relative difference the output levels of different sources.
_________________________

My experience is that resistors do make a difference (depending on the circuit and where they are used) - but in this case I wouldn't use resistors to pad down the output. In other words, does this 'problem' really need addressing, can't you just use the volume control at a lower setting? I mean, it doesn't sound like the amps input is actually being over driven (clipping), so it's working fine. If you really want the volume control to be usable over a wider range I would consider changing the volume control (or buying a different, and better, amp).

I think you have hit the nail on the head Mark. The amp and speakers are not over powerful/efficient and it's a popular budget combo.

The problem manifests itself because the system is used by the whole family in the lounge and with the remote control for volume. Without attenuation there are only a few volume steps (4-5) between silent and too loud. Therefore, it's difficult to set the volume to the right level. With attenuation, there are around twice that many steps. If it were in a hifi room that would be ok but for general family duties....it's a problem.

I tried some -14 db goldenjacks which improved things but the -23db homemade pad helps a lot.

I've never had this problem before with any other unit, so I'm a bit baffled.

Cheers, martin

[Martinh]

OK, please feel free to call me a plonker...

It seems the problem is with my harmony remote control, not the amp.:doh:

In the default setting, the harmony sends a fixed length "pulse" to the amp for volume. This pulse is longer than the pulse sent by the original remote and therefore the volume pot motor turns for longer, giving larger steps.

A quick(ish) bit of tweaking has now reduced the volume pulses to minimum length and there is now much more fine control. Not perfect, but better.

Im not sure if this type of motorised pot is powered by a std DC geared motor with no position/speed feedback or whether its done by a stepper motor. There are no end stop sensors, as the motor continues to turn with a slipping clutch to avoid damage.

If it's just a dc motor, I reckon a slower speed would have given more precise control, as it's pretty quick at the moment.

We now (almost) have hifi harmony at my place ;)

Martin

[Reid Malenfant]

We now (almost) have hifi harmony at my place ;)

Martin
:) Qudos for sussing the remote control one out :smoking: