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Old 3rd October 2013, 02:52 PM   #1
adason is offline adason  United States
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Default upgrading x-can V1? anyone?

hi, I have not seen many threads about musical fidelity X-cans.
I have V1, first old version, I do not use it much, since I have better sounding headphone amps, and was wondering, if I CAN (pun intended) improve its sound, maybe I would use it more often.
Just last time I put 6H6P in it, I got plenty of those from lampizator projects, and the sound was beefier, but those tubes do not fit inside the box, they are big, so I would need to find new box, so I put the originals back...

Here is my question...it uses two OPAs, one NE5532 per side. Would replacing these with OPA2134 improve the sound?

Last edited by adason; 4th October 2013 at 01:26 PM.
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Old 11th October 2013, 03:28 PM   #2
adason is offline adason  United States
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I guess there is not much interest in an old headphone amp...I do have it on the bench right now, I put sockets in it and OPA2134s, and NOS 6H6P, the sound is great, smooth, and with authority. Now I need to find new box for it, as it does not fit in original box, and I do not like the original box anyway, it was cramped inside.
I am thinking I can add 4 input switch on the front, and besides headphone jack one more output and use it as preamp, if needed.
Is there anything else I can modify? While its on the bench?
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Old 15th October 2013, 12:10 AM   #3
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That's an eccentric circuit to say the least. I'm not sure whether I fully understand it tbh. Some sort of dynamic class A job? In any case I would assume it to have low enough distortion unless running out of current, since the output cathode followers are in the feedback loop.

Are you happy with the amount of gain it provides? Currently it's at 8x or 18 dB, which is mid-highish for a headphone amp.

In any case the gain-setting resistors look a tad too large for lowest noise and distortion. R108 and R109 could be reduced to 1/10 their value while simultaneously increasing the value of C106 by a factor of 10. If you don't have 2k and 14k at hand, 2k2 and 15k should do fine (1/4W metal film jobs). With the stock values, you never ever get equal impedances at +in and -in, not to mention that resistor noise dominates output noise.

As far as further tweaks are concerned, I'm not sure what sort of R115 value the circuit needs to remain stable under capacitive load. 47 ohms generally is low enough for less finicky cans but may be too much for pickier ones (or too little for others that are a bit thin on the bottom). If you've got a scope, try loading the output with 10 nF or so and watch out for oscillation with various resistor values. What would you want to be driving with it?
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Old 15th October 2013, 12:34 PM   #4
adason is offline adason  United States
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I was hoping someone will explain that output circuit to me, I am no expert. Seems like some sliding bias of sort. Currently the headphone amp is plugged directly to azur 640 cd player and sennheiser hd600 headphones. Sound is great, well balanced, smooth yet detailed. Volume pot is at 1/3rd, seems plenty of gain, but I am going to put it in the big box and make it a preamp/headphone amp, so higher gain may come in handy.
At this point I was only thinking if I can replace some caps for better quality while it is accessible. Thanks for the comment.
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Old 16th October 2013, 09:38 PM   #5
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HD600s should be quite happy on this one.
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Volume pot is at 1/3rd, seems plenty of gain, but I am going to put it in the big box and make it a preamp/headphone amp, so higher gain may come in handy.
18 dB is plenty for a preamp, actually. With a power amp of 26-30 dB, you're looking at 44-48 dB total gain, which is a common range for integrated amps (~100wpc units tend to be around 46 dB). Some attention to noise is highly recommended in this application if the speakers are to remain dead quiet. Even when modified as suggested, noise level would still be only average. You're well advised to calculate how much power amp gain you really need.
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At this point I was only thinking if I can replace some caps for better quality while it is accessible.
You could use film (~1) or bipolar for C103, and bipolar for C109. The rest ought to be fine assuming they weren't junkbox quality parts to begin with. (And if they were, I'd swap the 16V ones.)
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Old 23rd October 2013, 01:37 PM   #6
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About an year ago, my colleague asked me to upgrade his X-CAN (not sure V1 or V2).
It accepts 12 AC. So, I replaced the original external transformer to a Nuvotem. This improves the mid to high frequency definition very much. Yet, the sweetness of the X-CAN is retained. I have to admit that I love the sound so much. I even seached for a X-CAN in the second market! Worth to give it a try.

My colleague also tried to replaced the volume pot. Not sure wether he finally used an Alps or a TDK one.

Of course, you can replace caps and some resistor in the signal path.
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Old 23rd October 2013, 08:19 PM   #7
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have you tried Mike (pinkfloyd) on the rockgrotto forum?
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Old 28th October 2013, 03:26 PM   #8
adason is offline adason  United States
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sorry for silence, I was out hiking in Sierra Nevada mountains, did Mt. Whitney and some other peaks, it was beautiful, but cold at night...

@ sgrossklas, yes, 18dB gain might be too much if you use it with normal amp after, but I have few amps with no gain, or very little gain sitting on the shelf... I got Nelson's Sun of zen, I got Andrea's Power follower, and some other class A buffers, which should work nicely with higher gain preamp

@ B&W_arthur, replacing the original wallwart trafo is a great idea, thanks...the original is ok size, but I hate wallwart transformers, alaways take more than one socket, I will definitely change it

I am tempted to change the small alps pot for big stepped attenuator, I just do not have one at hand, but I should be able to get some stuff from ebay

as I mentioned before, it sounds great now with opa's and tube's upgrade
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