Line Attenuators

[eldarvanyar]

Hi,
I have a Rotel RC 1080 preamp going into a Quad 606 preamp

Here is the Rotel RC-1090

https://uploads.tapatalk-cdn.com/20200316/b4849a53ba0316e7d350799e19059019.jpg


https://uploads.tapatalk-cdn.com/20200316/3ddc34a542816d8958546f8c6dce8e3b.jpg




Quad 606 power amp



Quad 606 Power Amplifier Specification
Power Output: 140 watts per channel (8 ohms)
Distortion: < 0.01%
Input Sensitivity: 500mV
Input Impedence: 20Kohm
Crosstalk: -100db (100hz), -85db (1 khz) and -65db (10khz)
Hum and Noise: 105db
Voltage Rating : 220-200V AC (110-120V via simple power board modification)
Dimensions (WxHxD): 321 x 140 x238 (mm)
Weight: 12kg

The preamp out is 1v and the power amp input is 500mv

What level attenuator would I need to buy to match the preamp to the power amp
-10db or -20db or some other figure?

Thanks

Lee

[walpurgis]

Why, is it causing you problems? It's only a 3db difference, I'd have thought that would be OK.

I don't like line attenuators. They've compromised the sound every time I've tried them.

[eldarvanyar]

I thought that because the output voltage from the preamp being 1v is twice that of the input voltage 500v of the power amp, that it would distort or clip.

I also thought a better matched level would enable greater use of the volume control.

I don’t know too much about pre and power amp matching.

I have a Quad 44 preamp which has a 500mv output and am hoping that the Rotel RC -1090 would be an upgrade.

Thanks for all or any advice

[walpurgis]

I have a Quad 44 preamp which has a 500mv output and am hoping that the Rotel RC -1090 would be an upgrade.

It may well be. The 44 is not one of my favourite pre-amps.

If you're using the Rotel into the 606 and there are no audible issues, I'd not worry.

[Pharos]

Why, is it causing you problems? It's only a 3db difference, I'd have thought that would be OK.

I don't like line attenuators. They've compromised the sound every time I've tried them.

Times 2 is 6dB.

6dB is not that greater difference to the volume pot which probably has a range of 50dB+.

[Barry]

Agreed. For normal listening levels, ideally the volume control should be about half way round its range (say at 12 o' clock, if the range is 7 o' clock to 5 o' clock). With a doubling of input voltage this will move the position of the volume control back to, say, 10 - 11 o' clock)

[eldarvanyar]

I am finding I can only listen up to 11 o’clock maximum otherwise it is too loud. The 606 has a lot of power.

[walpurgis]

I am finding I can only listen up to 11 o’clock maximum otherwise it is too loud.

Probably about right then.

(3db increase is what you get with a doubling of power by the way, 6db increase is a doubling of loudness, not the same thing)

[Pharos]

I am finding I can only listen up to 11 o’clock maximum otherwise it is too loud. The 606 has a lot of power.

My normal listening level is about 60 dB - as a background, and the vol pot is at 9 O'clock for that.

When listening seriously I only raise the levels to 70 to 75, which is a rotation to about 11 O' clock.

The position of the vol pot has nothing to do with the capabilities of the 606, it is an indication of how much voltage is being delivered by your pre to the 606.

It is generally thought that 10dB represents a doubling of loudness.

[Barry]

It is generally thought that 10dB represents a doubling of loudness.

Correct.

Using a sound level meter, I found for normal listening the level was 55dBA. For serious listening the level would be increased to 60dBA. And at 75dBA, I was shaking the floorboards.

[eldarvanyar]

Correct.

Using a sound level meter, I found for normal listening the level was 55dBA. For serious listening the level would be increased to 60dBA. And at 75dBA, I was shaking the floorboards.

Can you recommend a sound level meter or would my iPhone 11 be good enough?
Thanks

[eldarvanyar]

My normal listening level is about 60 dB - as a background, and the vol pot is at 9 O'clock for that.

When listening seriously I only raise the levels to 70 to 75, which is a rotation to about 11 O' clock.

The position of the vol pot has nothing to do with the capabilities of the 606, it is an indication of how much voltage is being delivered by your pre to the 606.

It is generally thought that 10dB represents a doubling of loudness.

Thanks that’s very helpful in understanding what is going on.
Does the pre increase the voltage as you turn the volume up to the 606?
Also does increased voltage into the 606 lead to increasing the wattage?
If the 606 is 140w, is that continuous or does it increase according to the pre volume?
Thanks

[Pharos]

Thanks that’s very helpful in understanding what is going on.
Does the pre increase the voltage as you turn the volume up to the 606?

# Yes it increases the pre O/P voltage provided to the power amp.

Also does increased voltage into the 606 lead to increasing the wattage?

# The pre O/P wattage increases slightly, but is not a consideration, the preamp power being minimal; it is a device designed to provide voltage gain.

The pre when providing a higher voltage to the power amp, drives, ('instructs') the power amp to apply a higher voltage across the speakers, which then draw more current, and dissipate a higher wattage. More wattage - higher sound O/P.

If the 606 is 140w, is that continuous or does it increase according to the pre volume?

# That is a maximum capability, (potential ability) which is only reached if it is driven hard enough, and very unlikely.
You could think of the pre as a water tap handle, that controlling the water flow, the latter caused by the water pressure provided by the water suppliers.
Thanks
# Hope this helps.

[Mr.Ian]

Is this on cd/dac Whst happens with non digital sources - update for clarity - I mean the excessive volume ?

[Barry]

Can you recommend a sound level meter or would my iPhone 11 be good enough?
Thanks

Lee,

The sound level meter I used was bought from Maplin. It belonged to a friend of mine, and I borrowed it out of curiosity. Can't comment on the accuracy (the meter was not expensive), however it was 'interesting' to see just how uneven the response of my speakers/room was.

[Pharos]

I was also going to mention that I had a Maplin one, fairly cheap but quite heavy, and criticised by Alan Shaw for being cheap.

Actually I have been impressed with mine but I have not compared it with a serious one.

It cost about £30, and was on offer for £15 when introduced.

Instinctually I feel it to be quite good.

[Haselsh1]

I can only speak from my own experience but back in 2009 I had a Croft pre/power combination and used Golden Jacks attenuators to over come the ridiculous over sensitivity of the amps. As a by product I also noticed a marked improvement in sound quality.

[Mike Reed]

My limited experience in using attenuators to tame the 3.4 V output of my CDP into my valved pre is that the less attenuation you use (at the pre. end in my case), the less it affects s.q.

Despite learned technician types on another forum recommending -20 dB attenuation or more, I tried a friend's -10 dB and -15dB ones, which were too much. Ended up buying a Goldenjacks -6 DB. Absolutely no perceivable detrimental affect on s.q,., but made all the difference in making all my sources show within the VU meter range.

[Light Dependant Resistor]

I am finding I can only listen up to 11 o’clock maximum otherwise it is too loud. The 606 has a lot of power.

Passive attenuation therefore is the answer needed. Less components that are potentially altering the audio signal between your source and power amp,
with a passive - will bring beneficial result.

There are many forms of passive, that are all worthwhile auditioning.

[Lawrence001]

Passive attenuation therefore is the answer needed. Less components that are potentially altering the audio signal between your source and power amp,
with a passive - will bring beneficial result.

There are many forms of passive, that are all worthwhile auditioning.

Really?? I thought there was only one type of passive attenuation worth auditioning [emoji38]

[Light Dependant Resistor]

I agree with you :), ... but for some, the path of discovery they seem to always strangely insist on, is therefore longer.:violin:
requiring self discovery and awareness, before naturally returning to what you are referring to.

[Pharos]

And that principle, of discovering relevant and irrelevant factors represents growth.

[Light Dependant Resistor]

The history of patent no 1,357,773 November 1920, do you think would infer perhaps too much time with growth ?

One could say dwelling on the wrong product, getting well misled and in despair clinging on to upholding, what was never
intended to pass audio signals,.... but still some like to take their time.

[eldarvanyar]

Passive attenuation therefore is the answer needed. Less components that are potentially altering the audio signal between your source and power amp,
with a passive - will bring beneficial result.

There are many forms of passive, that are all worthwhile auditioning.

Can you list some?
Thanks
Lee

[Firebottle]

Standard carbon track potentiomenter.
Plastic track potentiometer.

Switched attenuator. Can be surface mount resistors or any variety of carbon/metal film/tantalum resistors on the larger switches.

Relay ladder attenuator. A series of relays switch resistor pairs (generally) in and out of circuit.

Transformer based attenuator with switched taps. The inductor is usually a single winding, hence technically an autoformer.

Light dependent resistor attenuator.

Solid state volume control chip such as the PGA2310.

[Slawts]

Hi Lee,

What sort of problems are you encountering that makes you feel the need for attenuators?

I have a valve pre and a ss power amp and there was audible hiss. which I found irritating.

I had another amp which was valve but didn't drive the speakers as well as I would hope.

I tried attenuators from members on here and bought a pair of 10db Rothwells from one of them.

The valve power is sold and there is no hiss from the ss amp. I forget the attenuators are there and it is the best my system has sounded. I still end up no more than around 9am on the dial but never ended up more with the valve power amp.

[eldarvanyar]

Hi Lee,

What sort of problems are you encountering that makes you feel the need for attenuators?

I have a valve pre and a ss power amp and there was audible hiss. which I found irritating.

I had another amp which was valve but didn't drive the speakers as well as I would hope.

I tried attenuators from members on here and bought a pair of 10db Rothwells from one of them.

The valve power is sold and there is no hiss from the ss amp. I forget the attenuators are there and it is the best my system has sounded. I still end up no more than around 9am on the dial but never ended up more with the valve power amp.

Hi,
As I stated at the beginning of the thread my Preamp output voltage is 100mv and the power amp input is 50mv. I am not able to use the volume control past 10 to 11 o’clock on the Preamp as it is too loud. My understanding is I am not benefiting from the Preamp as much as I should be. I wonders if attenuators would help and what level.

Thanks

Lee

[Pharos]

Yes, a simple potential divider cutting the I/P by 6dB, using the I/P impedance as the other resistor, and costing the price of two resistors will do it and do it best.

Just place a resistor in series with each I/P. (Which is what the more expensive and clumsy method using attenuating leads will do).

[Light Dependant Resistor]

Standard carbon track potentiomenter.
Plastic track potentiometer.

Switched attenuator. Can be surface mount resistors or any variety of carbon/metal film/tantalum resistors on the larger switches.

Relay ladder attenuator. A series of relays switch resistor pairs (generally) in and out of circuit.

Transformer based attenuator with switched taps. The inductor is usually a single winding, hence technically an autoformer.

Light dependent resistor attenuator.

Solid state volume control chip such as the PGA2310.

Also j- fets used as voltage controlled resistors, observing linearity can be improved with feedback, pages 243-249
"Designing with field effect transistors Second Edition Siliconix inc

[Slawts]

I think your understanding is wrong.

Unless there are lots of problems with the sound you are fine and haven't got a mismatch.

[Mr.Ian]

For fear of showing my ignorance I havent posted before but here goes.

You input 150mv and turn the rotel up to max volume and you get 1v out. You need 500mv to get max power out of the power amp. So inputting 1v might in theory overload the power amp.

But the preamp volume control adjusts the output voltage, so you will only get 1v at maximum volume. Its unlikley that you will be using the preamp (Rotel) at maximum volume so it wont be outputing 1 volt.

BUT what source outputs 150mv ? I am struggling here, I guess some old viintage gear might. 300mv to 500mv is more common and 2-3v for dacs and cds players etc.

The 150mv input 1volt output is merely a guide showing how much gain the pre amp provides. feed in 300mv and at max volume you will get 2 volt out. Use a cd that outputs at 2v and the preamp will output 13v.

But all this is with the volume control at maximum. Turn the volume control down and the voltage drops.

If the sound is really harsh, shrill, agressive, distorted then you might be overloading somewhere, probably on the digital sources only, but my guess is all is fine and you are getting hung up over the specs in the manual when you dont need to.