Can I create a volume controlled 'line out' in my integrated amp

[bumpy]

My integrated has four switchable phono inputs (only one of which is used) but no line level out (volume controlled).

Is it practical to isolate one of the pairs of phonos and rewire them so they become a volume controlled line level. To a novice this seems an easy thing to achieve. :)

This would be to feed a DSP subwoofer amp which almost exclusively need a line level input.

[Light Dependant Resistor]

My integrated has four switchable phono inputs (only one of which is used) but no line level out (volume controlled).

Is it practical to isolate one of the pairs of phonos and rewire them so they become a volume controlled line level. To a novice this seems an easy thing to achieve. :)

This would be to feed a DSP subwoofer amp which almost exclusively need a line level input.

Hi Chris
Line Level out, sort of by definition does not involve routing audio through a volume control. If you need a volume control from one source
the way I would do this is to arrange a small jiffy box ( or more formal if you wish ) to have two or more pairs of RCA, one as LR input from your source(s) and the other
adjustable in level to connect to your subwoofer amp.

The most common form of volume circuit is called a L pad and has what is called series resistance ( from your source ) and at the same time shunt resistance to signal ground
A purist method would see signal paths not being wiped by mechanical contacts, rather NSL32SR3 LDR's can be arranged both as an attenuator and as a contact less switch.

This way you are not changing your rather unique amplifier from its original specification.

[Firebottle]

Yes you can, the only thing you need to be careful of is that the input impedance of the subwoofer amp isn't particularly low.

I'm guessing that the input impedance of the Transcription Audio is quite high, most probably the impedance of the volume control.

[bumpy]

Yes you can, the only thing you need to be careful of is that the input impedance of the subwoofer amp isn't particularly low.

I'm guessing that the input impedance of the Transcription Audio is quite high, most probably the impedance of the volume control.

Good advice thanks.

[bumpy]

Hi Chris
Line Level out, sort of by definition does not involve routing audio through a volume control. If you need a volume control from one source
the way I would do this is to arrange a small jiffy box ( or more formal if you wish ) to have two or more pairs of RCA, one as LR input from your source(s) and the other
adjustable in level to connect to your subwoofer amp.

The most common form of volume circuit is called a L pad and has what is called series resistance ( from your source ) and at the same time shunt resistance to signal ground
A purist method would see signal paths not being wiped by mechanical contacts, rather NSL32SR3 LDR's can be arranged both as an attenuator and as a contact less switch.

This way you are not changing your rather unique amplifier from its original specification.

Just for clarity, is this 'volume control' fed from additional wires from the speaker terminals of my main amp. What the subwoofer people refer to as high level. Thanks

[Lawrence001]

This is starting to get into worrying territory is everyone else happy with the advice here?

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[bumpy]

This is starting to get into worrying territory is everyone else happy with the advice here?

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What concerns you Lawrence? I want to run a separate amp and active DSP low pass filter to my bass drivers whilst leaving my mid range driver and tweeters to run unhindered from the main amp.

BUT I cant use commercially available stuff with DSP as they are mostly line level inputs and a) I don't have one b) I need to have just one overall volume control for the whole system.

So I may need to find a way of
a) Using the high level speaker output and knocking it back to approx 2v max, much as seems to be done in most subwoofers.
b) Tapping into the 'line level' after the volume control of my main amp

I am ambitious in what I wish to achieve, but not being skilled at electronics I am at the mercy of others, so would be more that pleased to hear your concerns. :)

[Lawrence001]

That's exactly my concern, you're not experienced (and neither am I) but you're being told it's simple to isolate the variable pre out signal inside your (unknown) integrated amp and connect it to one puff the RCA pairs on the back. To me this sounds like a high risk change that could seriously damage the amp or other equipment even if you were experienced.

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[bumpy]

That's exactly my concern, you're not experienced (and neither am I) but you're being told it's simple to isolate the variable pre out signal inside your (unknown) integrated amp and connect it to one puff the RCA pairs on the back. To me this sounds like a high risk change that could seriously damage the amp or other equipment even if you were experienced.

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Fear not Lawrence, I am one of the most risk averse people you might meet. All I am doing at present is background research so I approach all jobs from a position of knowledge.

If it steps over the line of 'DIY' I will default to getting an expert to do it, but as a scientist I am always hungry for knowledge so I can select the best option both from a safety and sound quality perspective.

[StanleyB]

My integrated has four switchable phono inputs (only one of which is used) but no line level out (volume controlled).

Is it practical to isolate one of the pairs of phonos and rewire them so they become a volume controlled line level. To a novice this seems an easy thing to achieve. :)
It depends on whether your integrated amp is old enough to have a RECORD monitoring option on it. If it hasn't then you don't stand much chance. If it does, you can then take the signal from the REC monitor output to a passive volume control.

[Edward]

Chris, suggest you have a chat with the guys at Transcription Audio and ask them. Essentially you want a preout and I would imagine that you can, as you already suggested, tap into the line level after the volume control. Perhaps Transcription Audio can send you the schematic for your amp and also (as Alan mentions) take care about impedance matching etc.

Or pop along to Transcription Audio and ask them to provide preouts to your amp. They seem to be only about 30 minutes away from you and I would imagine they can do it while you wait (assuming they don't have to implement an extra buffer stage).

[Jazid]

It would be incredibly easy to make a volume controlled 'line level' output from the speaker terminals. You'd need to know the approx amp power output and speaker impedance, and create a board with two resistors in series with each other and in parallel with the speakers.
So say output was 50W into 8 ohm speakers that is 20V across the terminals full output. To get this to approx. 2V a 10:1 resistive divider such as a 100 and 12 ohm respectively in series from positive to negative, take the output from negative and the junction of 12 ohm and 100 ohm. It gives you what you need, no need to get inside the amp, no loading on the amp, low output resistance for the line level electronics running the bass amp and all controlled by one volune knob. What's the issue?

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[M6NTL]

It would be incredibly easy to make a volume controlled 'line level' output from the speaker terminals. You'd need to know the approx amp power output and speaker impedance, and create a board with two resistors in series with each other and in parallel with the speakers.
So say output was 50W into 8 ohm speakers that is 20V across the terminals full output. To get this to approx. 2V a 10:1 resistive divider such as a 100 and 12 ohm respectively in series from positive to negative, take the output from negative and the junction of 12 ohm and 100 ohm. It gives you what you need, no need to get inside the amp, no loading on the amp, low output resistance for the line level electronics running the bass amp and all controlled by one volune knob. What's the issue?

Sent from my BLA-L09 using Tapatalk50 Watt resistors are BIG, and they get hot!

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[Firebottle]

I'm really bothered about this thread, there is so much mis-information.

Where do you get 20V from for 50W into 8 ohms> the output level at full is 28V peak, or 56V peak to peak.

Also if you are driving a 100 ohm resistor you will get nowhere near 50W into it, more like 4W.

:doh:

[Jazid]

I'm really bothered about this thread, there is so much mis-information.

Where do you get 20V from for 50W into 8 ohms> the output level at full is 28V peak, or 56V peak to peak.

Also if you are driving a 100 ohm resistor you will get nowhere near 50W into it, more like 4W.

:doh:

I got 20V from Ohms law.
I cannot find a way to get any other result than 20V.
Of course this is RMS which is what we are dealing with here since the OP is trying to get a 2V RMS output for a separate woofer amp.
20/8=2.5 amps
2.5Amps x 20V = 50W. Seems simple enough to me.
28V peak or 56V P2P is of course about the same figure as 20V RMS but massively less useful to the conversation. So what exactly are you trying to prove Alan?
20V across 112 ohms is just shy of 4W, these are not expensive resistors, currently a socking 52p (plus VAT) from CPC for 7W versions and less for the 12 ohm one. These resistors won't even get warm unless you are trying to fry your loudspeakers with some weird square waves or summat.

[Lawrence001]

I got 20V from Ohms law.
I cannot find a way to get any other result than 20V.
Of course this is RMS which is what we are dealing with here since the OP is trying to get a 2V RMS output for a separate woofer amp.
20/8=2.5 amps
2.5Amps x 20V = 50W. Seems simple enough to me.
28V peak or 56V P2P is of course about the same figure as 20V RMS but massively less useful to the conversation. So what exactly are you trying to prove Alan?
20V across 112 ohms is just shy of 4W, these are not expensive resistors, currently a socking 52p (plus VAT) from CPC for 7W versions and less for the 12 ohm one. These resistors won't even get warm unless you are trying to fry your loudspeakers with some weird square waves or summat.I think it's 2v peak rather than RMS.

I misunderstood the thread earlier hadn't realised we were taking a signal off the speaker outs in parallel with speakers, I guess it's ok if the voltages are kept below 2v.

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[Blackdog]

I agree with Firebottle, there is some bad info here.
It would be a fairly simple modification to disconnect one input, tap off of the volume control and wire that disconnected input as an output. The subwoofer has a high input impedance, will run just fine running directly off of the volume control.
You're probably looking at a £50 modification.
Forget trying to run off of a padded down speaker connection. You'll waste power as heat, and add distortion. And it will probably cost just as much or more.

[Jazid]

I agree with Firebottle, there is some bad info here.
It would be a fairly simple modification to disconnect one input, tap off of the volume control and wire that disconnected input as an output. The subwoofer has a high input impedance, will run just fine running directly off of the volume control.
You're probably looking at a £50 modification.
Forget trying to run off of a padded down speaker connection. You'll waste power as heat, and add distortion. And it will probably cost just as much or more.Yours is probably the worst information in this thread. What you suggest might be a simple mod in some amps but the OP has already said he is risk averse and not keen to dig inside his amp.
Subwoofers usually have a 10k input impedance. This is low and will mess up pretty much any part of the circuit around a volume pot and likely introduce significant distortion unless a buffer is added as well. That is also simple in theory but what are the power supplies like, how much space is inside, and so on.
Regarding padding down the output with a couple of resistors please explain how you believe this will add significant distortion? Thermal losses are near irrelevant here.

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[paulf-2007]

I'm certainly no expert but I managed to wire a pair of rca sockets after the volume control on my 300B for a subwoofer. It was point to point wired so very easy. As you haven't said what amp it is I would suggest you let someone that knows look at it first.