View Full Version : How to connect external amp with no pre-out?


Infinite Mind
09-14-2004, 02:00 PM
I have a spare inegrated amp that I want to use with an external amplifier. Is it possible for me to connect the external amp if there is no pre-outs?

I.M.

ohskigod
09-14-2004, 02:09 PM
if it were a plate amp for a subwoofer, you could just use the high input (speaker wire) connections, but i have a feeling your talking about a regular power amp. there is no way (al least safe or useful way) to connect them without preouts that i know of. maybe some of the more knowlegable might have an idea, but i doubt it.

Bob
09-14-2004, 02:21 PM
You could use the tape monitor outputs but you lose
volume and tone controls. You'd need a volume control
on the amp or make one.

jpciii
09-14-2004, 04:09 PM
How easy is it to add/customize a set of pre-outs? I have a reciever with a suspect amp section... was thinking of adding pre outs to it to make it into a pre-amp....
thanks

uncooked
09-14-2004, 06:09 PM
if you want to use it with the other amp just use Y adapters from the source into each. if you want to use it as a preamp then there is no real way to do it without preouts

Don C
09-14-2004, 06:35 PM
I have never tried it myself, but I think that you can use a headphone jack as an output.

Ski
09-14-2004, 06:49 PM
About the only way I can think of is to use the tape monitor. You would have to connect the amp to the tape monitor outs and copy from source. If the amp has volume controls, you are set. If not you'll need to put something like an EQ that has full freq. attenuation or possibly a cassette deck. If you use a cassette deck, you would most likely have to put it in Rec/Pause and adjust the recording level.

Good luck and use disposable speakers for your trial efforts.

EchoWars
09-14-2004, 06:54 PM
Originally posted by Infinite Mind
I have a spare inegrated amp that I want to use with an external amplifier. Is it possible for me to connect the external amp if there is no pre-outs?

I.M. You could mod the integrated and add pre-out jacks...

Dynacoman
09-14-2004, 07:40 PM
In most cases wouldn't ya just make a connection to the center volume tap and ground for a pre amp out?

Infinite Mind
09-14-2004, 08:42 PM
Does using the headphone out jack degrade the quality of the pre-amp section?

Also, EW, if I where to add-in permanent pre-outs where would you suggest that I pull the signal from? It is a Luxman L-210 (45W) I'm trying to connect to an external amp.

I.M.

EchoWars
09-14-2004, 09:00 PM
In most cases wouldn't ya just make a connection to the center volume tap and ground for a pre amp out? No...there's no drive capability there.Does using the headphone out jack degrade the quality of the pre-amp section? I wouldn't recommend this. The headphone jack is driven by the amp output stage...voltage levels all wrong for your purpose, among a slew of other reasons why this is a bad idea.Also, EW, if I where to add-in permanent pre-outs where would you suggest that I pull the signal from? Every amp is different, so I'm at a loss to recommend something specific to your Lux. Units I've done this to required a bit of study to determine the best place to break the chain.

Gerrit
09-15-2004, 03:52 AM
IM,

Not a unique requirement whatsover.

You just need to build a simple circuit (the same circuit used in plate amps to convert speaker level to line level).

The parts quality will vary depending on your needs (plate amps use resistors but they only have to do bass so parts quality is negleble). If you have serious intentions it will be better to use transformers.

Chech out this site: http://www.hut.fi/Misc/Electronics/circuits/speaker_to_line.html

or google with "speaker signal to line level" You will find more info than you will ever need

Hope this help, if not post again and I can mebe help with the math.

Best Regards and welcome

Gerrit

DS1784
09-15-2004, 06:41 AM
carver used to make a high level adaptor just for this. it was a small black box about three inches square. had about nine inch pigtails wires to hook up to speaker outputs and rca's for power amp hook up, i had one up till about six months ago. they were $50.00 new. sold mine on the bay for $15.00. i see them come up for auction about every three or four months or so. they worked quite well and didn't really put any noise in the system

EchoWars
09-15-2004, 06:45 AM
Originally posted by Gerrit
IM,

Not a unique requirement whatsover.

You just need to build a simple circuit (the same circuit used in plate amps to convert speaker level to line level).

The parts quality will vary depending on your needs (plate amps use resistors but they only have to do bass so parts quality is negleble). If you have serious intentions it will be better to use transformers.

Chech out this site: http://www.hut.fi/Misc/Electronics/circuits/speaker_to_line.html

or google with "speaker signal to line level" You will find more info than you will ever need

Hope this help, if not post again and I can mebe help with the math.

Best Regards and welcome

Gerrit That's cheating!! ;)

Sure, it would work. But of course the signal travels all the way through the Lux amp before it goes to whatever he wants to power.

I guess without ripping open the Lux and adding a pre-out/main-in jacks (which are very nice to have) this is likely the only way to do it.

But it's pretty Mickey-Mouse.

/me looks at my avitar :yikes:

Gerrit
09-15-2004, 08:33 AM
Hi EW,

It's not cheating that much...

The control amp will see the input of the speaker-to-line-level-converter-thingy at > 15K. So electrically speaking the 4-8 Ohm output inpedance of the control amp will not even "see" that it's "driving" another amp.

You can safely drive speakers and the slave (second) amp from the speaker outputs without worying about impedance problems.

So much so that if the control amp were to be a tube amp, you should put a big 8 Ohm resistor over the +/- terminals if not connected to speakers. This will ensure that the output is loaded as some (all??) valve amps want to see a load while running.

Best Regards

Gerrit

Dennis Gardner
09-17-2004, 01:24 AM
EW has the best approach, by adding preouts before the amp gets ahold of the signal. This is usually the cleanest sounding. In the car audio world using a step down filter is accepted more readily since a car's interior noise starts around 50 db anyway.
In a quiet room, the noise floor is more noticeable.

Unless all components are high quality, you are likely to add more noise than it is worth.

In your integrated, you have a preamp stage and the final amp stage with both adding noise to the signal. When you step the speaker level back down to a preamp signal, you don't lose the noise that has been added by the amp. Regardless of the quality of the final amp being added, it will still amplify the noise from the 2 other amp stages. The fewer stages you have between the source and speakers, is generally considered the preferred method.

Sell the integrated and get a good used preamp. You have the best of both worlds then with a great upgrade path.

d3imlay
09-18-2004, 08:48 AM
Go to Radio Shack and get a 10K, audio taper, stereo volume control. Mount it in a metal box. Solder a cable acoss the two ends of each pot. These two cable will eventually plug into the the tape output of the preamp. Solder another cable between the wiper and terminal of the pot that has the shield of the first cable soldered to it. In other words, connect the second cable between the wiper and ground. Plug these two cables into the power amp input. Verify that turning the pot clockwise increase the volume by touching your finger to the input cable. This will create some hum and buzz, at a low level. Start with the volume control at it's midpoint.

Obviously this isn't the ideal setup. However if you can use a soldering iron ( no small feat) you can at least try your idea for a minimal cost.