Bridging the X-Can V2

[themystical]

I am so impressed by this amp that I am considering using 2 of them as in a bridged mono format for my current/power hungry AKG K1000 headphones. Does anybody know whether the V2 is bridgeable and what I might have to do to make it work?

[thegreatroberto]

Intresting question ( and not one i have the answer to)..........But someone will have to explain amp bridging,'cause I know my X-as100 says it can be "bridged".The MF blurb says it turns it from a 100W /ch (35A) into a 100w/ch (60A).Surely this should read 200w/ch (60A) ? Otherwise where is the gain in bridging.oh, and are there any downsides ?

[rickcr42]

First question-Xcans for K1000 :

Off hand I would say not do-able.The AKG K1000 is called an "earspeaker" for a reason and needs serious power on the order of a 7W amplifier.The X-Can V2 as in most headphone amps is an "amp" in name only and should be considered more of a high current line stage than a true power amp

Question 2-balanced bridge amps :

what you do when you "bridge" a stereo amplifer for more power is add a phase splitter to the input so that a positive version of the signal drives one input and a negative (inverted) version of the signal drives the other input of the stereo amp which means you now need 2 stereo amplifers since both haves of the former stereo amp are now sued to drivea signal channel in a "balanced bridge".

This NEW output no longer uses a common ground but instead uses the POSITIVE side of the amp for HOT (+) and the inverted side for the former GROUND (-) which is now floating.The end result of this is a doubling of the available output power but the cost is also doubled.

When can this NOT be done ? When an amp is already configured as a balanced brided amplifier and the literature will always tell you this because if by accident you hook up any device to the output that uses a common ground (all speaker switches,power meter add-ons,normal headphones,etc) you will blow up the output ubnless it has a good protection circuit-something rare in high fidelity audio equipment

[themystical]

Thanks for that Rick!
First of all having tried a vast number of amps with the AKG's, including EAR V20, Linn Classik, Electrocompaniet etc., some of these costing many thousands of pounds, the best sound quality comes from the humble X-Can V2!!! Yes....hard to believe but factual!!!! Now if only I could get a bit more power, it would be out of this world! Hence my quest for bridging!
Now I believe that one can do what you are suggesting which increases the voltage swing or alternatively do a parallel connection of the outputs which would increase the current. What I was wondering was whether anybody had tried connecting the left and right inputs and outputs together and whether it was safe to do so. I was also wondering whether there was a device (bridging adapter) available commercially to provide the inverted input in the series bridged option you suggest.

[rickcr42]

Now I believe that one can do what you are suggesting which increases the voltage swing or alternatively do a parallel connection of the outputs which would increase the current. What I was wondering was whether anybody had tried connecting the left and right inputs and outputs together and whether it was safe to do so. I was also wondering whether there was a device (bridging adapter) available commercially to provide the inverted input in the series bridged option you suggest. I believe

you have no need for additional current just pure voltage swing (in fact best reports so far i have read are with the 30WPC Aleph) so parallel connection would not be your best option.

If you DO want to try your hand at a balanced amp there are two simple paths you can follow here

1-Active Phase Splitter using one of the Burr-Brown/TI DRV chips or one of the Analog Devices SSMxxx driver chips

2-Passive Phase Splitter using a 1:1 line input transformer-one of the 10K/10K loaded on the secondary side with a 10k resistor.Available devices are the usual supects from Sowter,Lundahl,Jensen,CineMag or for a true bargain from Edcor USA (X-series)

Option 1 is cheaper in that the chips cost little but then when you consider adding a power supply and chassis plus all the hardware that goes with active (lne cord,fuse and holder,power switch.power on indicator) the passive method begins to look like a bargain......plus it SOUNDS better

[themystical]

Will investigate both the passive and the active options but your suggestion of the passive one sounds good to me especially if transformers sound better! What do the 10k series resistors do?

[rickcr42]

What do the 10k series resistors do?

loads the secondary of the transformer.

BTW: both options pretty much eliminate any possibility of using the current volume controls.You will need to make a "new" volume control in the external interface box and set the present controls to "wide open" full volume.
The "10K' trafos resistor can then be a dual 10K pot for each channel,a quad pot for a single volume control (tough to find a quad pot that tracks well for all four sections until you get to a stepper) or maybe something like this from the Raleigh Audio Balanced Line Stage :

[Stormy]

thegreatroberto said:

oh, and are there any downsides ?

The only thing I can think of from my experience with big PA power amps is that when you run them in bridged mono mode the minimum load impedance has to be double what it is per channel in stereo mode.

I can't find any info on minimum recommended loads for the X-Can, but basically I wouldn't suggest using anything less than 64 ohm headphones with a bridged setup (just to be safe). But as the only reason you are doing this is to run AKG K1000s, and they appear to be 120 ohm, that's almost irrelevant.

Good topic.

[themystical]

I would like to try out the parallel bridging option first as it does not add any additional components to the signal path which could potentially degrade the sound quality and it does not cost any money!!
The circuit diagram for the V2 is located here.http://www.rock-grotto.co.uk/x-canv2.pdf
Would it be safe to try this out? i.e connect inputs and outputs of the two channels in parallel? Any help with this wquestion appreciated!

[rickcr42]

The schematic just looks "wrong"

at first glance a long tailed pair but then it gets wonky and I personally would not trust it as entirely accurate

Still the best way to get to balanced with this amp is phase splitter-volume controls-two X-Can V2 amps with present volume controls wide open-take the signal from the two output jacks and make an external Dual floating TRS-to-DIN "adapter" for the K1000 plug

But that is only if you must.Not having a shared feedback loop is a serious negative and it is usually better to use an amp designed to be a balanced amp than to try and force it to be something it is not.If the amp were a single ended open loop design then it would be different

[themystical]

I really appreciate your help with this Rick! Thanks again!! You are a fountain of knowledge!!!!!
Here is the schematic for the X-Can V3 output stage which I believe is very similar to the V2. (http://www.diyaudio.com/forums/showthread.php?s=&threadid=59577) Do you think it would be safe to try connecting the outputs together?

[rickcr42]

Do you think it would be safe to try connecting the outputs together?

if you are looking for "parallel" connection for each amp try simply strapping the L/R inputs together by using a short RCA to RCA interconnect at the "line out" jacks (left channel to right channel)then make an external adapter that just "mono" connects the output jacks.
Since there is already a resistor in place on the output,hopefully in the 100-120 ohm range ,the output would not be fighting the opposing channel for precedence and should work fine and would be like paralleling opamps or buffers to increase the output drive current while lowering the overall output impedance.

Sound better ? No clue.

But be aware man,this is not a balanced connection,just strapping two amps together as one thus a single ended mono amp in the end.To use this method as a balnced amp you will now need FOUR X-Cans instead of the former two.

Think in terms of channels with a balanced amp having four discrete channels of available amplification

CH 1-Positive Drive Left
CH 2-Negative Drive Left
CH 3-Positive Drive Right
CH 4-Negative Drive Right

There is no common ground connection in a "balanced bridge" amplifier and only the input will have a ground reference.connect one of the four outputs to ground and you short it out,likely blowing that channel.

I realise this can get a bit confusing but to be honest it is damn near as bad trying to explain it ;D

[themystical]

Exactly my thoughts Rick!
The other thing is with the two channels being in phase and equal in magnitude ( circuitry being identical) it is difficult to imagine one channel reverse driving the other. The magnitude of the errors due to component innaccuracies. one would imagine to be small and these would be further attenuated by the output resistors.
It seems like it is worth trying!
I will provide some feedback on the SQ issue.
But first I need to buy another x-can V2. Just saw one on UK ebay which I need to nab!!

[rickcr42]

sure,always worth a shot man ;D

be aware also of the volume control will now be tracking parallel channels,likely with the typical imbalances we have with most pots at any but the very end of the rotation (loudest part).

Nothing is ever perfect and even a stepper has limitations untill they come up with one that costs little and has around 300 positions of 0.1 % tracking.

I personally HATE "ratchety" controls and why I like to use continuous rotation pots instead of the stepped attenuator flaws and all.The other way always seems to give me everything but exactly what I really want.The "tweener" settings

[themystical]

Would you believe that The X-can on ebay dissappeard just as I was going to hit the "buy it now" button. Somebody else beat me to it!!! That means a few days wait whilst I source another one!
I see what you mean by the vokume control pot.....I may try putting them both on max and utilising the pre-outs from my Linn Classik which I use as a source to see how much difference that makes!

[thegreatroberto]

Yeh,a BIN of £85 was never going to hang around long ! I was considering myself,but delayed too much as well !

There's always the one that is going for £155 with days to go !

[themystical]

Got the second x-can a few days ago and have tried out the parallel bridging to run each of them as a mono amp. Basically I have turned the volume control to full to operate each amp as a power amplifier and created a special headphone cable which parallels the left and the right channel outputs in each amp. The input comes from the pre-out of my Lin Classik with the left going to one amp and the right to another. A short phono to phono cable connects the spare left and right input phono connection together.
So what about the all important sound quality?!
Well I have only listened to this set-up for a day or so but the biggest improvement is in the bass quality/quantity/texture and the general sense of real dynamics whilst retaining the already excellent high frequency/midband quality of the single amp. This is a real night and day difference beating by miles all of the other mods put together and the best I have got out of the x-canV2!
With this level of sound quality, (better then amps costing many thousands of pounds) I am not sure whether a bridging adapter whilst running the x-can in balanced mode can make any further improvement!!!!!