Line out (for sub) from T-amp

[Xor]

Im thinking about getting me some subwoofers to try out..

I now have a T-Amp with modified input-filter and power-cap..

If I whould like to add line out thats controlled by the pot, what is the best method?

Iv heard suggestions about OPAMPs but I cant figure out how to use them... (this is my first steps into DIY-audio).

Im pretty good with soldering but not with audio-theory..

[Pano]

I see you've gotten no answers to your question.

The best method is to use an opamp buffer. Splitting the signal without a buffer just isn't going to sound good.

Op amp circuits are not difficult, you will find a wealth of information on the web. All you want is a unity gain circuit. But for best results, you'll need a seperate power supply.

Starting to get complicated, isn't it?

[DcibeL]

If you are using a pre-amp of any kind with your t-amp, it should have a low impedance output with high current capabilities allowing you to simply split the output of the preamp into 2 signals using a y-cable without any problems.

The best way to use a preamp with the SI t-amp would be to remove the volume pot so the volume is completely controlled by the pre.

[sx881663]

The following assumes you are using a preamp and have made a direct line in connection in the T-amp box. (jumpering out the original volume control) Also assumed is that you have a Y feed from the pre to the sub and T-amp.
You must have some means to adjust the bass. This means you should have a volume control in the bass amp. If you are using a factory plate amp or factory powered sub it should have all the means necessary to get a proper adjustment. I highly recommend using a warble tone that extends to both sides of the crossover to get the first approximation of the settings. I would imagine that you can find a file to download and burn with Google
If you are not using a preamp and want to do a set of outputs off of the T-amp you must insure that the sub has high input impedance. (Greater than 99Kohm) Look at the existing volume control connections and you will see wires coming from the T-amp input jacks and wires going to the amp. These wires to the amp you want to duplicate, connecting from the same pins on the volume control to the new RCA’s you will be adding. Make sure the polarity is right when you are done by measuring low ohms between all the outsides of the RCA’s. These new outputs will now track the signal going to the T-amp. These new outputs are also high impedance and can’t drive a heavy load including cables. The added cables to the sub should not be more than around 3 foot long. If you must have longer cables you will have to build the op-amp buffer described earlier.
Roger

[Xor]

Originally posted by panomaniac
I see you've gotten no answers to your question.

The best method is to use an opamp buffer. Splitting the signal without a buffer just isn't going to sound good.

Op amp circuits are not difficult, you will find a wealth of information on the web. All you want is a unity gain circuit. But for best results, you'll need a seperate power supply.

Starting to get complicated, isn't it?

No. Not that complicated yet any way

I just need some pointers... like a basic scheamatics and a suggustion on a suitable op-amp..

And im not using a pre-amp.. Just a good av/input selector.

[BWRX]

How much are you willing to spend? Use a DIP socket so you can swap out the op amp. I'd suggest you start out by trying a TL072. Good quality at a good price.

[Pano]

Have a look at any recent dual opamp from Analog Devices or Burr-Brown. Read the application notes and look for a simple circuit.

I hesitate to give you a schematic, because you won't lean much that way. Opamps are very easy to use, you just need to do a little reading. That's how I learned!

Google is your friend, and read the device notes. When you find a circuit that you are sure of, post it here and we'll let you know. It won't take you long.

[Xor]

Originally posted by panomaniac
Have a look at any recent dual opamp from Analog Devices or Burr-Brown. Read the application notes and look for a simple circuit.

I hesitate to give you a schematic, because you won't lean much that way. Opamps are very easy to use, you just need to do a little reading. That's how I learned!

Google is your friend, and read the device notes. When you find a circuit that you are sure of, post it here and we'll let you know. It won't take you long.

Okey.. now I have done some reading.. And I figured that Burr-Brown OPA2134 should be a good choice..

So I think I need to build a "Voltage follower" aka "buffer amplifier" (http://en.wikipedia.org/wiki/Operati...r_applications).

Now.. do I understand it correctly if I assume that I only need the op-amp without aditional components?.. Or do I need some filter to reduce RF?.

I plan to connect the inputs to the output from the pot. So split the signal before the caps. (http://www.michael.mardis.com/sonic/inputmods_F.html)

What is the reason that I cant use the same SLA-Battery that drives the T-Amp as power-source?


(This feels like beeing back in school.. But in a fun way )

[BWRX]

Originally posted by Xor
Okey.. now I have done some reading.. And I figured that Burr-Brown OPA2134 should be a good choice..

So I think I need to build a "Voltage follower" aka "buffer amplifier" (http://en.wikipedia.org/wiki/Operati...r_applications).

The opa2134 is a very good choice and you have found the correct circuit

Originally posted by Xor
Now.. do I understand it correctly if I assume that I only need the op-amp without aditional components?.. Or do I need some filter to reduce RF?.

What is the reason that I cant use the same SLA-Battery that drives the T-Amp as power-source?

You will also need some capacitors for the supply rail(s) for filtering and bypass of the power supply. Most people use larger electrolytics for filtering and small ceramic/film for bypass.

You can also include RF filtering if you wish.

You can use the same 12V SLA, but you will also need input and output coupling capacitors to prevent a DC voltage from showing up at the output.

[cpemma]

The Wikipedia circuit is for a dual-rail power supply (eg, +6V, 0V, -6V). Running from a single-rail supply like your SLA gets a bit more complicated. Apart from the input & output caps, you need to create a "virtual earth" at half the supply voltage so the op-amp can follow both positive- and negative-going sides of the signal (the coupling caps are there to block the DC component at each end).

If you want to use the SLA, Texas Instrument's SLOA058 is a good reference. There are also chips available to provide the virtual earth popular with the battery-operated headphone amps brigade, example using BUF634 here but more common op-amps can be used.