What in general is the type of circuit used for this commercial in-wall speaker volume control?

Thread Starter

PeteHL

Joined Dec 17, 2014
390
After attempting to design an original volume control with resistors, I find it difficult to see that the commercial volume control that I'm providing a link to has the specifications that it has. Without becoming quite bulky, my design would not be able to handle much more than 15W RMS per loudspeaker and it has only five steps of attenuation. The commercial one handles 60W per speaker (it is a stereo volume control) and I'm fairly certain that it has many more steps of attenuation than five.

So I wonder what the circuit of the below commercial volume control is.

https://www.parts-express.com/Audtek-VR60S-Sliding-Audiophile-Grade-Volume-Control-6-300-554

Is anyone familiar with these in-wall volume controls (by means of inserted resistance) to be able to say generally what the circuit used is?

Thanks if you know,
Pete
 

dendad

Joined Feb 20, 2016
4,109
That has resisters for the control. It may be a "T" network or similar, not just a series resistor. But then again, it may just be the series resistor type.
And the "60W" will be Marketing Division Watts, not real watts.
A lot of the audio stuff is rated as "Music Power" watts, and it seems to be grossly inflated.
I prefer RMS watts.
 
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Ian0

Joined Aug 7, 2020
4,821
Don't forget that loudspeakers are designed to operate from a voltage source with extremely low output impedance - in fact, amplifier manufacturers pride themselves on how low they can get the output impedance (they call it "damping factor" in the specs). If you add an attenuator between amplifier and loudspeakers that output impedance will go from almost zero to about 8Ω, and the damping factor will come down from 100 to 1. The bass will start to boom, as the amplfier loses control over the cone movement at resonance, and the crossovers may no longer operate at the right frequencies.
 

Audioguru again

Joined Oct 21, 2019
4,523
The Audtek "L-PAD" has no audio specs. It says "Max 60W" which is probably peak power that is actually 30W of real power.
Duration is not mentioned so the Max 60W might be instantaneous peaks which might be 10 real watts continuously.

Years ago they were made for vacuum tube amplifiers that used an "L-Pad" so that the impedance was always the same. Then the speaker is missing the extremely low output impedance of a modern solid state amplifier that damps the resonances of a speaker.

L-pads today are made for people who know and care nothing about high fidelity.

I think speakers made many years ago were designed to not make resonating noises when driven by a vacuum tubes amplifier. Speakers designed today have much deeper bass and need a modern extremely low impedance to drive them properly.
 

sghioto

Joined Dec 31, 2017
3,058
L-pads today are made for people who know and care nothing about high fidelity.
Not necessarily. Controlling the volume at the output of an amplifier will always be problematic unless it's maybe a 70 volt system or similar. This pad using resistors vs transformers is arguable the best you can expect.
 

Audioguru again

Joined Oct 21, 2019
4,523
The specs for the audio L-Pad show only its color and weight so you must guess what to drive it with.
The new one called "Pure Resonance" probably makes everything resonate like a bongo drum.
 

Thread Starter

PeteHL

Joined Dec 17, 2014
390
The specs for the audio L-Pad show only its color and weight so you must guess what to drive it with.
The new one called "Pure Resonance" probably makes everything resonate like a bongo drum.
What caught my eye about the Audtek attenuator is that they call it an "audiophile-grade" device. As dendad suggests, this might also be a description from the Marketing Division, but I can't be certain. What I might do is try to find a volume control that is described in detail or buy one to test it.

Thanks to everyone for your comments,

Pete
 

Audioguru again

Joined Oct 21, 2019
4,523
Stores use 70V transformers on each speaker. The amplifier has its own 70V output transformer. The speaker transformers have taps to adjust their power so that their total does not overload the amplifier. Since all the speakers in a store are all in the same room and are all at the same height then they are all set the same, This thread might have a speaker in the garage that needs to have its volume different than the speakers in the house.
 

nsaspook

Joined Aug 27, 2009
9,435
Stores use 70V transformers on each speaker. The amplifier has its own 70V output transformer. The speaker transformers have taps to adjust their power so that their total does not overload the amplifier. Since all the speakers in a store are all in the same room and are all at the same height then they are all set the same, This thread might have a speaker in the garage that needs to have its volume different than the speakers in the house.
As usual the OP doesn't provide that level of detail. We can only see that the OP is talking about a commercial volume control. That implies a commercial 70 volt system but it's just a guess.
 

sghioto

Joined Dec 31, 2017
3,058
That implies a commercial 70 volt system but it's just a guess.
Not necessarily. I had some very similar looking controls in a home I owned several years ago that were connected to a conventional stereo. The control the TS is linking to shows it designed for stereo.
 

Ian0

Joined Aug 7, 2020
4,821
If you want to adjust the volume, place the attenuator between preamp and poweramp. No problem with impedance matching and no problems with power dissipation.
 

Audioguru again

Joined Oct 21, 2019
4,523
The photo of the Audtek volume control guts shows a switch with 20 positions, 20 large resistors and many little resistors.
It does not have a transformer that cuts highs and lows. The speakers determine how much boomy sounds it causes.
 

crutschow

Joined Mar 14, 2008
29,466
Many in-home wall volume controls are autotransformers with a tap for each volume step.
The are thus efficient, have a low output impedance to maintain the damping factor, and can be made small for their power rating.
 

Thread Starter

PeteHL

Joined Dec 17, 2014
390
I intended my thread to be about a volume control where attenuation is achieved by inserting resistance, that is, not the type that use a transformer or autotransformer. I wanted to compare my design to what has been accomplished commercially, because building one according to my design might be just as expensive as some commercial volume controls. So unless my design has some advantage over commercial designs, there is no point in building it.

My volume control is for "standard" stereo amplifiers, not 70.7V or 25V systems. Also this is a volume control for a pair of extension speakers where the control is inserted between the output terminals of a power amplifier and the input terminals of the speakers. In other words, a device for making volume control of the speakers possible in the same room that the extension speakers are located in.

The goal of my design is to keep distortion to a minimum, and thus I avoided one with transformers. Besides, designing one using resistors is more interesting and accessible in my home lab than based on a transformer. I'm not about to get involved with custom making transformers.

I am aware of WIFI and remote controls for amplifiers, but I like the simplicity and potentialyl lower cost of extension speakers connected to a passive volume control.

-Pete
 
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