Guide to install pre-outs on an AVR - AVS Forum
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post #1 of 68 Old 07-13-2012, 06:01 AM - Thread Starter
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Does anyone know of a guide to install pre-outs on an AVR that does not have pre-outs? I searched google for hour and couldn't find anything. It seems that it would be relatively easy though.
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post #2 of 68 Old 07-13-2012, 06:19 AM
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+1....I'd like to know as well....but this might be more appropriate in another forum.
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post #3 of 68 Old 07-13-2012, 06:32 AM - Thread Starter
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Originally Posted by miahallen View Post

+1....I'd like to know as well....but this might be more appropriate in another forum.

I figured that DIY speaker guys would have more experience than the AVR forum :P
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post #4 of 68 Old 07-13-2012, 06:41 AM
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Quote:
Originally Posted by WagBoss View Post

It seems that it would be relatively easy though.
With point to point wiring, yes. With an analog volume control (tap it on the input side) yes. With modern electronics, using wave soldered SMCs and VCA volume controls, not easy at all.

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post #5 of 68 Old 07-13-2012, 01:41 PM
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I've worked in electronics for decades and am confident in most gear, but this is not a job I would willingly take on without a schematic and layout and design will vary between brands and models so anything done will be case specific.

I'd look to find the input to each amplifier channel internally, as that would be the easiest place to take signal from and would be the natural pre out point anyway. If you're lucky, that will be a cable or cables that connect the line level section and power amp boards where you can break out the signal.

Best of luck. Considering how easily an amateur can damage something like this, I'd suggest just buying an AVR with pre outs.
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post #6 of 68 Old 07-13-2012, 08:15 PM - Thread Starter
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Quote:
Originally Posted by A9X-308 View Post

I've worked in electronics for decades and am confident in most gear, but this is not a job I would willingly take on without a schematic and layout and design will vary between brands and models so anything done will be case specific.
I'd look to find the input to each amplifier channel internally, as that would be the easiest place to take signal from and would be the natural pre out point anyway. If you're lucky, that will be a cable or cables that connect the line level section and power amp boards where you can break out the signal.
Best of luck. Considering how easily an amateur can damage something like this, I'd suggest just buying an AVR with pre outs.

ha yea, i didnt really think about it when I bought it, and i got it for really cheap so meh. I have the rx-v671, which is basically the rx-v667's newer model, and the 667 has pre-outs and the 671 does not. so for a schematic or layout, it should be identical to what the 667 does.
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post #7 of 68 Old 07-14-2012, 07:22 AM
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In a pinch you could build or buy some level converters from the world of car stereo. A quick google found this russound piece.

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post #8 of 68 Old 07-14-2012, 07:26 AM
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Originally Posted by petew View Post

In a pinch you could build or buy some level converters from the world of car stereo.
The problem with those is they're slaved to the output level of the amp. Depending on the OPs application that may or not be an issue.

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post #9 of 68 Old 07-14-2012, 10:43 AM
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Quote:
Originally Posted by WagBoss View Post

ha yea, i didnt really think about it when I bought it, and i got it for really cheap so meh. I have the rx-v671, which is basically the rx-v667's newer model, and the 667 has pre-outs and the 671 does not. so for a schematic or layout, it should be identical to what the 667 does.

If you're lucky, it's quite possible that they use the same pcb, and just change which components get installed - in which case it's just a matter of adding parts.

That said - even being a professional audio engineer, I think it's more work than just buying the right product. If you got a good deal, it should be easy to break even selling your unit and then not a huge cost to step up to the one with preouts.

Have you ever designed a circuit before, or is this your way of trying to learn? I definitely don't want to discount the hobby side of things...

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post #10 of 68 Old 07-14-2012, 10:45 AM
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Check out the DI4000 by Behringer. I used this to convert the line out from my avr into a pro amp to drive my mains. Worked flawless and didnt add any additional noise that i noted. For about $100 it was perfect to do what i wanted, it was also able to +20db to the sub output to work perfect to drive a pro amp for that as well.
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post #11 of 68 Old 07-14-2012, 11:19 AM - Thread Starter
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Quote:
Originally Posted by MBentz View Post

If you're lucky, it's quite possible that they use the same pcb, and just change which components get installed - in which case it's just a matter of adding parts.
That said - even being a professional audio engineer, I think it's more work than just buying the right product. If you got a good deal, it should be easy to break even selling your unit and then not a huge cost to step up to the one with preouts.
Have you ever designed a circuit before, or is this your way of trying to learn? I definitely don't want to discount the hobby side of things...

I am an electrical engineering student 4th year. so.. yes i have designed a circuit :P

It's actually about $400.00 for virtually the same receiver, but with pre-outs. It's actually ridiculous.

http://www.amazon.com/Yamaha-RX-V671-7-1-Channel-Network-Receiver/dp/B004QR56SE

http://www.amazon.com/Yamaha-RX-V773WA-7-2-Channel-Receiver-wireless/dp/B007JF85SS/ref=sr_1_1?s=electronics&ie=UTF8&qid=1342290294&sr=1-1&keywords=rx0v773
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post #12 of 68 Old 07-14-2012, 11:20 AM - Thread Starter
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Quote:
Originally Posted by Bill Fitzmaurice View Post

The problem with those is they're slaved to the output level of the amp. Depending on the OPs application that may or not be an issue.

Yeah and it's just wasting the all the power through the voltage divider.
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post #13 of 68 Old 07-14-2012, 11:21 AM - Thread Starter
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Originally Posted by noobzorta View Post

Check out the DI4000 by Behringer. I used this to convert the line out from my avr into a pro amp to drive my mains. Worked flawless and didnt add any additional noise that i noted. For about $100 it was perfect to do what i wanted, it was also able to +20db to the sub output to work perfect to drive a pro amp for that as well.

I'm looking for a cost of... 4 bucks :P I bought some rca chassis mounts for 50 cents each

and that behringer unit you linked is not what I want at all, I do not have a line out on my avr. I want to install a line out.
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post #14 of 68 Old 07-14-2012, 12:05 PM
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Quote:
Originally Posted by WagBoss View Post

I'm looking for a cost of... 4 bucks :P I bought some rca chassis mounts for 50 cents each
and that behringer unit you linked is not what I want at all, I do not have a line out on my avr. I want to install a line out.
If it gives you the same result without having the possibility of ruining your AVR then why not?

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post #15 of 68 Old 07-14-2012, 12:22 PM - Thread Starter
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Originally Posted by flyng_fool View Post

If it gives you the same result without having the possibility of ruining your AVR then why not?

yes, and the post I was commenting on was telling me to buy a line-out amplifier lol.
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post #16 of 68 Old 07-14-2012, 12:38 PM
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Quote:
Originally Posted by WagBoss View Post

I'm looking for a cost of... 4 bucks :P I bought some rca chassis mounts for 50 cents each...
Easy part done, then. I think you need to get ahold of the schematics unless you can find someone who has made the change you want to the very same AVR. In days long past, what you want to do was easy. All you had to do was pick up the signal at the output of the volume control. Today it is more complicated. CE manufacturers typically use designs which combine rotary encoding for the volume control, source selection, tone control, volume control and other functions into a single LSI chip. You will at least need to identify the chip and its pinouts to be able to do what you want. Failing that, I guess you can always trace back from the output transistors.
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post #17 of 68 Old 07-14-2012, 02:03 PM
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Originally Posted by WagBoss View Post

Yeah and it's just wasting the all the power through the voltage divider.
What power?
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post #18 of 68 Old 07-14-2012, 02:27 PM - Thread Starter
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Originally Posted by A9X-308 View Post

What power?

what do you mean? most of the power from the signal is being wasted as heat in the resistor in the voltage divider. If I can take the signal before the amplifier then it's not wasting the power of the amplifier as it is not being amplified.
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post #19 of 68 Old 07-14-2012, 02:32 PM - Thread Starter
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Originally Posted by Colm View Post

Easy part done, then. I think you need to get ahold of the schematics unless you can find someone who has made the change you want to the very same AVR. In days long past, what you want to do was easy. All you had to do was pick up the signal at the output of the volume control. Today it is more complicated. CE manufacturers typically use designs which combine rotary encoding for the volume control, source selection, tone control, volume control and other functions into a single LSI chip. You will at least need to identify the chip and its pinouts to be able to do what you want. Failing that, I guess you can always trace back from the output transistors.

can't I just trace the line from the amplifier channels back to the chip... then google the chip pin layout and find where the + out is, and just take a wire off of that to the rca chassis mount?

or even just take it from right before the amplifier for the channel, where the line goes into it?
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post #20 of 68 Old 07-14-2012, 03:02 PM
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Quote:
Originally Posted by WagBoss View Post

I'm looking for a cost of... 4 bucks :P I bought some rca chassis mounts for 50 cents each
and that behringer unit you linked is not what I want at all, I do not have a line out on my avr. I want to install a line out.

The unit takes line-level (speaker out) and converts into line (rca type) output.
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post #21 of 68 Old 07-14-2012, 03:09 PM
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aren't there high level to line level convertors for about $20?

would this work:

http://www.manventureoutpost.com/products/FUSION-HL%252d02-High-to-Low-Level-Converter-(HL%252d02).html?google=1

btw, i like your initiative, its just that i've never even heard of somebody wiring up their own line level outs to a factory receiver. if you can do it...great!

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post #22 of 68 Old 07-14-2012, 03:27 PM
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Quote:
Originally Posted by WagBoss View Post

what do you mean? most of the power from the signal is being wasted as heat in the resistor in the voltage divider.
I haven't looked at the specs of your AVR, so lets assume 100w/8Ω for a channel which is 28.3Vrms before clipping. The end to end resistance of the voltage divider shown in an earlier post is 4k2Ω. P=V²/R = 28.3²/4200 = 190mW at full power, and lower most of the time.
In a class AB amplifier, which almost all AVRs are, every stage except the output will be class A, so the current draw will remain the same irrespective of signal (or none), so no power saved here, and as shown, only a trivial amount actually dissipated in the output stage and into the voltage divider load.
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Originally Posted by WagBoss View Post

If I can take the signal before the amplifier then it's not wasting the power of the amplifier as it is not being amplified.
How does plugging into a pre out (an RCA connector) stop the pre signal from also going to it's respective power amp stage? The pre out and the power amp in are in parallel (in an AVR with pre outs).

Using a voltage divider after the amp is hardly optimal, but it would work and use a trivial amount of power.
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Originally Posted by WagBoss View Post

can't I just trace the line from the amplifier channels back to the chip... then google the chip pin layout and find where the + out is, and just take a wire off of that to the rca chassis mount?
or even just take it from right before the amplifier for the channel, where the line goes into it?
There is no guarantee that the chipset doing the VC will be a typical line item like a PGA2310 or CS3318 but if you're lucky it might be. Tapping the signal at the power amp input is what I suggested in post 5.
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post #23 of 68 Old 07-14-2012, 03:41 PM
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Originally Posted by LTD02 View Post

btw, i like your initiative, its just that i've never even heard of somebody wiring up their own line level outs to a factory receiver. if you can do it...great!

Like this:  http://www.epanorama.net/circuits/speaker_to_line.html


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post #24 of 68 Old 07-14-2012, 04:56 PM
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Quote:
Originally Posted by WagBoss View Post

can't I just trace the line from the amplifier channels back to the chip... then google the chip pin layout and find where the + out is, and just take a wire off of that to the rca chassis mount?
or even just take it from right before the amplifier for the channel, where the line goes into it?
Of course you can reverse engineer if you want.

FWIW a simple voltage divider, like the one Kal provided a link for, and others have suggested, across the speaker outputs is probably quicker and easier, if not as elegant. There will be very little power wasted because of the large (relative to speaker impedance) value resistors used. By using high value resistors, we limit the current, and thus the power loss. The high impedance input of whatever downstream device you add takes almost no current to drive. It just has to be the right voltage.
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post #25 of 68 Old 07-14-2012, 07:15 PM
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"Like this"

neat! that looks simple enough.

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post #26 of 68 Old 07-14-2012, 07:27 PM
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Quote:
Originally Posted by WagBoss View Post

what do you mean? most of the power from the signal is being wasted as heat in the resistor in the voltage divider..
Not if the resistors are a high enough value, which they must be to adequately reduce the voltage. Besides, if they did dissipate a lot of power they wouldn't be half watt resistors.

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post #27 of 68 Old 07-14-2012, 08:35 PM
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Quote:
Originally Posted by WagBoss View Post

I am an electrical engineering student 4th year. so.. yes i have designed a circuit :P

Did it work? :P smile.gif

I guess if your time is worth less than $400 then it's worth exploring. It shouldn't take too long to reverse engineer a schematic of what's in your AVR - which is where I'd start. I would be very surprised if you could find a node to just tap off and wire directly to an RCA output and work well enough to sound better than the speaker level converter. Gain structure and output impedance would be two areas of greatest concern...

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post #28 of 68 Old 07-14-2012, 08:40 PM
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Quote:
Originally Posted by Kal Rubinson View Post

Like this:  http://www.epanorama.net/circuits/speaker_to_line.html

900ohm output impedance is pretty high for a line level signal - I would try to scale the resistor values back so that the shunt resistor is more like 100ohms. Also, it's not uncommon for speaker amplifier stages to have a little DC offset - I personally would add a series cap to prevent any potential offset from transferring down stream.

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post #29 of 68 Old 07-14-2012, 08:53 PM - Thread Starter
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so... there is no disadvantage to just use a voltage divider? Since I already bought RCA chassis mounts, mideswell build my own line-level converter instead :P So I'd use just a 1k and a 100 ohm resistor as the divider... or a 4k and 400 ohm? Should I just grab some 1 W resistors to be safe or would 1/2 be fine?

or should I do what http://www.epanorama.net/circuits/speaker_to_line.html says and do a 33k ohm to 1k ohm as its possible for my receiver to output 105 wpc?

Or the best bet seems to be like a 10k and a 470 ohm..?
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post #30 of 68 Old 07-14-2012, 08:56 PM - Thread Starter
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so the behringer DI4000 will take a speaker-level out and convert it to balanced line-level outputs? Or does it only take line-level outs? It looks like it only takes line inputs, but it says it takes up to 3000 watts per channel into it?

is there any advantage to use this over just a standard voltage divider? other then the fact it has balanced outputs.
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