Adding pre-out to Teac A-H300 possible?

[biggzy]

Hi all, im slowly getting my bedroom system sorted (Teac Reference 300) and just wondering if it will be at all possible to add a Pre-out on my Teac amp, i have the service manual in PDF HERE

Any info/help would be great as im looking to do this over the next few weeks, i can add the pre-out sockets to the back easily but not sure where i would wire them from and if i need to add any capacitors etc to get it to work, and not sure how hard it would be, from what i have read i would need to take a connection from the pre-amp section after the volume control, thats all i know. The amp is from around 1999 and is stereo only.


Thanks,
Adam.

[biggzy]

If i can get any help with this, here is how the mod should look...




Adam.

[Reid Malenfant]

Hi Adam, give me a few minutes & i'll have a picture up of where to connect to

Ok, first up here is the best part of the amplifier PCB so you can see the connector in relation to the output transistors along the bottom

Amp PCB.jpg

Next up you get it a bit closer

Amp PCB close.jpg

There should be two connections in the centre, both of these are grounds. Connect the ground to both phono sockets & make the connection to the outer ring of the phono sockets. The others are marked Left & Right for you they obviously connect to the phono socket centre pins

[biggzy]

Hi Adam, give me a few minutes & i'll have a picture up of where to connect to

Thanks Reid, your a star

[Reid Malenfant]

Done, edited in to my last post

[biggzy]

Done, edited in to my last post

Thanks mate, i will open her up tonight and have a look for the section i need to run the wires from, then buy the bits etc, do i need any resistors or anything and will it put any strain on the teac at all? will i be able to use the power amp i add and the A-H300's speaker outs to bi-amp some speakers or do i have to match the amp carefully? thanks very much, i will update this topic as i go along with this mod.

Also (sorry for all the Q) will this allow the tone controls etc to work with the power amp also or is it just a flat direct out?

Thanks,
Adam.

[Reid Malenfant]

Those connections will be made to the output of the pre amplifier before it gets fed to the power amp itself. Sensitivity of the pre outs will be the same as the the gain of the power amplifier, in other words if you use another power amplifier (as standard) it'd need to have the same gain as the Teac power amp.

You could fit a 47K ohm or 50K ohm dual potentiometer & connect it in between the connector & the phono sockets in which case you'd be able to balance the sensitivities assuming the external power amp is more sensitive

If it wasn't then you'd be in the doo doo

The pre amp should have no difficulty driving an extra 50K ohm per channel. If it did have it really must be a piece of junk I'd expect any pre amp to have an output impedance of 100 ohms or less, though there are a few oddities that have a 1K ohm output impedance

Also (sorry for all the Q) will this allow the tone controls etc to work with the power amp also or is it just a flat direct out?

The tone controls will work for either the built in power amp & the pre outs at the same time

[biggzy]

Those connections will be made to the output of the pre amplifier before it gets fed to the power amp itself. Sensitivity of the pre outs will be the same as the the gain of the power amplifier, in other words if you use another power amplifier (as standard) it'd need to have the same gain as the Teac power amp.

You could fit a 47K ohm or 50K ohm dual potentiometer & connect it in between the connector & the phono sockets in which case you'd be able to balance the sensitivities assuming the external power amp is more sensitive

If it wasn't then you'd be in the doo doo

The pre amp should have no difficulty driving an extra 50K ohm per channel. If it did have it really must be a piece of junk I'd expect any pre amp to have an output impedance of 100 ohms or less, though there are a few oddities that have a 1K ohm output impedance


The tone controls will work for either the built in power amp & the pre outs at the same time

Sounds good, but how would i find out the gain of my amp? i would rather leave it standard (no potentiometer) and hope it works lol, also what sort of wire would be bast to use for this mod?

Will probably use the pre-outs to drive a Teac A-L700P power amp but only use 2 channels (its a 3 channel amp).

Again, thanks loads i appreciate it alot.

Adam

[Reid Malenfant]

For wire i'd use two short lengths of screened audio cable, it doesn't need to be anything spectacular

If you happened to buy another Teac unit with a built in pre amp, similar to what you have there it'd be dead easy to adjust the gain & not fuss with the variable resistors. All you'd need to do is connect to say the CD input on the new amp, switch to CD (obviously) & then adjust the volume on the new amp to balance the pair. At that point you leave the new amps volume control alone & simply use the one you have there already

If you buy just a power amp then you'll have to find some way of balancing it with what you already have which will be impossible if it's less sensitive & need variable resistors as already mentioned if it's more sensitive

[biggzy]

For wire i'd use two short lengths of screened audio cable, it doesn't need to be anything spectacular

If you happened to buy another Teac unit with a built in pre amp, similar to what you have there it'd be dead easy to adjust the gain & not fuss with the variable resistors. All you'd need to do is connect to say the CD input on the new amp, switch to CD (obviously) & then adjust the volume on the new amp to balance the pair. At that point you leave the new amps volume control alone & simply use the one you have there already

If you buy just a power amp then you'll have to find some way of balancing it with what you already have which will be impossible if it's less sensitive & need variable resistors as already mentioned if it's more sensitive

Thanks Reid, it sounds like i need these resistors then, is it just a simple task of soldering these just before the audio cable gets to the pre-outs? or am i missing the plot somehow lol, any chance of a quick mock-up of what it would need to be like to work.

Thanks,
Adam.