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Pre-amp Master Volume with Subwoofer Control

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Mwdepaolo

New Member
Hello, this is my first post on this forum!

I am working with a friend on building a "one-off" audio system for a customer so as to receive feedback on a system we are trying to develop. We are using the following components in the system.

Head Unit: Denon DN300Z - CD/Media Player with B/T AM/FM Tuner
Amplifiers: Niles SI-250 2-channel fully discrete amp 2x50w
Bikes SI-2100 2-channel digital amp 2x100w
Speakers: 4- Jamo IC406FG 6.5" 2-way in ceiling speakers
Subwoofer: 2- JL-Audio 8W3 in custom sealed enclosure

My friend is working on the enclosure and rack for equipment. I am working on a master volume control that will mount on the trim panel of the equipment rack.

I have a 10k ohm ceramic pot already for the main volume control. I am trying to sort out how I would be able to include a subwoofer control as well, all before the amplifiers.

I was thinking about splitting the signal coming off the master volume control, one stereo feed to the SI-250 amp and the other stereo feed through a 5k ohm pot (sub woofer) control. Would this cause potential issues or any kind of feedback in this proposed system?

Additionally, we would like to add a volume/zone control post amp for one of the 4 speakers so as to reduce the volume or mute it for incoming phone calls. Would anyone have a suggestion in this regards?

I greatly appreciate any assistance in sorting out these issues!

Cheers!
 

spec

Well-Known Member
Most Helpful Member
Hello, this is my first post on this forum!

I am working with a friend on building a "one-off" audio system for a customer so as to receive feedback on a system we are trying to develop. We are using the following components in the system.

Head Unit: Denon DN300Z - CD/Media Player with B/T AM/FM Tuner
Amplifiers: Niles SI-250 2-channel fully discrete amp 2x50w
Bikes SI-2100 2-channel digital amp 2x100w
Speakers: 4- Jamo IC406FG 6.5" 2-way in ceiling speakers
Subwoofer: 2- JL-Audio 8W3 in custom sealed enclosure

My friend is working on the enclosure and rack for equipment. I am working on a master volume control that will mount on the trim panel of the equipment rack.

I have a 10k ohm ceramic pot already for the main volume control. I am trying to sort out how I would be able to include a subwoofer control as well, all before the amplifiers.

I was thinking about splitting the signal coming off the master volume control, one stereo feed to the SI-250 amp and the other stereo feed through a 5k ohm pot (sub woofer) control. Would this cause potential issues or any kind of feedback in this proposed system?

Additionally, we would like to add a volume/zone control post amp for one of the 4 speakers so as to reduce the volume or mute it for incoming phone calls. Would anyone have a suggestion in this regards?

I greatly appreciate any assistance in sorting out these issues!

Cheers!
Hy Mwdepaolo, good to see you on ETO.

I see you are from the USA; which State?

There are plenty of audio experts on ETO who could probably evolve a solution for you.

I have an idea of an approach too, but a block diagram of your intended system would be a help- could you post one? In particular can you show where the cross overs are for the subs and L/R speakers.

spec
 

Mwdepaolo

New Member
Hy Mwdepaolo, good to see you on ETO.

I see you are from the USA; which State?https://www.dropbox.com/s/ri2ze94761blpgk/System Diagram.pdf?dl=0

There are plenty of audio experts on ETO who could probably evolve a solution for you.

I have an idea of an approach too, but a block diagram of your intended system would be a help- could you post one? In particular can you show where the cross overs are for the subs and L/R speakers.

spec
I was born and raised in the NW (Portland, OR Metro area) but moved to Las Vegas two years back. I'm enjoying the sunshine for a change!

Here is what I threw together for a diagram. I am mostly interested on getting the main volume control along with sub woofer control assembled. I realize that the zone control (volume adjustment and/or mute) would be more problematic being post amp and in a parallel speaker configuration.

Still any suggestions would be greatly appreciated!
 

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crutschow

Well-Known Member
Most Helpful Member
I seen no problem with controlling the sub amp volume with a pot being fed from the main volume pot, but you want the sub pot to have a resistance value at least 5 times the main pot to minimize loading of the main pot.

Are you using log (audio) pots for these controls? If not you will get a very non-linear loudness response versus pot rotation.

Muting a speaker might be best done with a mechanical relay with contacts in series with the speaker leads.
 

Mwdepaolo

New Member
Sorry, I forgot to include the crossovers. I plan on using Fmod crossovers between the volume controls and the amplifiers, low-pass for the subwoofer and high-pass for the stereo amp. We're using this approach for the initial system as it will allow us to make adjustments easily by swapping them out.
 

spec

Well-Known Member
Most Helpful Member
I was born and raised in the NW (Portland, OR Metro area) but moved to Las Vegas two years back. I'm enjoying the sunshine for a change!

Here is what I threw together for a diagram. I am mostly interested on getting the main volume control along with sub woofer control assembled. I realize that the zone control (volume adjustment and/or mute) would be more problematic being post amp and in a parallel speaker configuration.

Still any suggestions would be greatly appreciated!
Thx- if that is a thrown together diagram, I can't wait to see your pro version.:)

What I have in mind is to mechanically link three log potentiometers (rotary?). I nave done this a few times on hifi amps and it works very well. Although I made the mechanics, I think you can also buy them. If you favor this approach please let us know. I hope I have understood your requirements correctly.

spec

(our posts crossed crutschow)

UPADATE: I think I have misunderstood. You want independent control and you are asking about the electronic aspects. :banghead:
 
Last edited:

Mwdepaolo

New Member
I seen no problem with controlling the sub amp volume with a pot being fed from the main volume pot, but you want the sub pot to have a resistance value at least 5 times the main pot to minimize loading of the main pot.

Are you using log (audio) pots for these controls? If not you will get a very non-linear loudness response versus pot rotation.

Muting a speaker might be best done with a mechanical relay with contacts in series with the speaker leads.
Yes, the 10k pot I have is a log pot. Do you mind explaining or providing a reference on your recommendation for the 5 times value so as not to load the main volume pot? I'm curious to understand further.

Also, with regards a relay for muting the one speaker, since it will be wired in parallel wouldn't this cause an unbalanced load to the amp when muted? How might I avoid this issue?

Thank you for your input!
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
Your like "missing a part". This http://www.goedekers.com/Petra-SSLSX310.html is probably for car audio, but it does have the controls your after. Note, no mention of power requirements.

Generally this falls under "active crossover".

The purpose is to remove the low bass from the L/R outputs at a selectable frequency and combine the low frequencies into a mono output. In some car audio system the sub level could be remote and it is relative.

Active crossovers can be more sophisticated by splitting the woofer, mid range and high ends. Not sure if they can provide a "center channel".

5.1, the new digital terminology suggests LF, RF, FR, RR, center and sub. 7.1 adds two "delayed" channels.
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
You might let the person with the phone have some control of the volume using a local L=PAD. These go in the speaker leads.

Turning off the speaker in a modern amplifier is acceptable for mute.

You would like what I incorporated into my home built amp. I used a VACTROL or a LED/FET Optooupler to turn off the audio on power off. This could be "mute" at a channel level. At the same time, I drove it on with the exponential charge on a capacitor, so you got a gradual turn-on within about 10 seconds.

The series VACTROL acts as a voltage divider between the output and input and its quick to turn off. My design wasn't designed for quick off and ramp ups randomly or periodically, but just on power-up or power down. Not hard to do.
 

crutschow

Well-Known Member
Most Helpful Member
Yes, the 10k pot I have is a log pot. Do you mind explaining or providing a reference on your recommendation for the 5 times value so as not to load the main volume pot? I'm curious to understand further.

Also, with regards a relay for muting the one speaker, since it will be wired in parallel wouldn't this cause an unbalanced load to the amp when muted? How might I avoid this issue?.....
The output of a pot has an equivalent resistance of up to 1/2 the pot resistance, depending up the pot setting, and this will cause a voltage drop from any load impedance connected to the wiper. You want to generally minimize that loading so I suggested an arbitrary value of 5 times the pot resistance (10 times the minimum output impedance), which should cause only a slight loading effect (<1dB).

Generally solid-state amplifiers have a very low output impedance and thus are normally immune to load imbalance, from no-load to full-load.
 

spec

Well-Known Member
Most Helpful Member
Turning off the speaker in a modern amplifier is acceptable for mute.
Keep is right. Just to explain. If you are driving two speakers in parallel from the output of a normal transitor (BJT or MOSFET) audio amplifier: (class A, class AB, class D) that is a voltage drive, in which case, removing one of the speakers will have no effect on the volume (power) to other speaker. Hence the audio volume will be unchanged.

spec

(our posts crossed again crutschow)
 

Mwdepaolo

New Member
You might let the person with the phone have some control of the volume using a local L=PAD. These go in the speaker leads.

Turning off the speaker in a modern amplifier is acceptable for mute.
Would it be feasible to incorporate both an L-pad for attenuation and a relay for muting the single speaker?

Would the L-pad have any issues being in line with a second speaker that is wired in parallel as shown in my diagram?
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
The L-pad presents a constant impedance to the AMP, so if the speakers are 8 ohms, the parallel combination is 4 ohms. the AMP should have a rating for for 4 ohms.
 

audioguru

Well-Known Member
Most Helpful Member
The passive crossovers cannot be fed from a volume control and cannot feed a volume control, they need extra buffers. Since they are 12dB per octave then their phase shifts will create a notch at the crossover frequency.
An L-pad destroys the good damping of an amplifier on the resonances of a speaker.
 

Mwdepaolo

New Member
The passive crossovers cannot be fed from a volume control and cannot feed a volume control, they need extra buffers. Since they are 12dB per octave then their phase shifts will create a notch at the crossover frequency.
An L-pad destroys the good damping of an amplifier on the resonances of a speaker.
Can you explain further on the "notch" that these passive crossovers would create? And if they have this affect then where are these type of crossovers useful or are they just a quick and dirty method?

Does the L-pad destroy the damping factor of the amplifier because of the way it loads it? If you don't see this as a good option, would you possibly recommend anything else for gain control? Or would it be best to either dedicate a small amp to this one speaker where you could control the pre-amp gain or scratch the gain control and just use a relay to disconnect the speaker?

I appreciate the input!
 

Mwdepaolo

New Member
Your like "missing a part". This http://www.goedekers.com/Petra-SSLSX310.html is probably for car audio, but it does have the controls your after. Note, no mention of power requirements.

Generally this falls under "active crossover".
So, after receiving the feedback from everyone thus far, I have decided to take your suggestion.

I just ordered the SSL SX310 as well as Clarion's MCD360 from Amazon. That way I can play with two units for comparison. I'm hoping that by using one of these active crossovers I will be able to avoid what Audioguru mentioned with regards phase shifting and "notching". It also helps simplify the sub woofer control.

My question with regards this approach (using the MCD360 as example) would be:

Will I still be able to utilize a 10k stereo log pot between the head unit and the active crossover for gain control? Or would I need to match the input impedance that the MCD360 is rated for?

Here are the specs for the MCD360:
Power Source: 14.4 volts DC negative ground
Input current: 0.5 amp max
Disortion: 0.01% THD at 1V output level
Frequency Response: 10Hz - 30kHz - 3dB
S/N Ratio: >100dB
Separation: 60dB
Crossover Slope Rate: 18dB per octave 3rd order butterworth
Input Impedance: 20K Ohms
Output Impedance: 100 Ohms
Output Gain: 1:2(+6db)
Output Voltage level: 5 volts max
Dimensions: 152mm x 180mm x 43mm
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
What I would consider doing is to "move the controls" or the ones you care about. i.e. replace the integral control with a panel mounted one and hide it in a "rack case".

Input and output Z of the audio inputs in consumer stuff is generally misunderstood. Commercial audio uses 600 ohms in/out and balanced differential signally with twisted pair cables. The 600 matches the characteristic impedance of the wire. The "right way".

In consumer audio, the output has to be much less than the input Z. 100 ohms vs 10K in the above example. The 100 helps to eliminate ground loops., but there is a slight voltage divider effect with the 100 and 10K..
 
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