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Thread: 2a3PSE

  1. #21
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    Quote Originally Posted by Chops54 View Post
    You won't get full output with a shunt. No problem if you've plenty of watts to spare.
    Its the pseudo shunted pot I've used in the other WAD amps that I've built so I don't imagine that it'll be too much of a problem in terms of volume.

    The cct shows a 100k log instead of the 50k I'm used to using so that should be interesting to see how it performs.
    "It's ok your comments are noted, so if you want a war you've got one. Watch your back, ya !!!!...." in an email from Marco 3/4/09

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    Quote Originally Posted by davym View Post
    I'm not keen on shunted pots but if I had to, I'd use a cermet linear pot and metal film resistors to shunt it (fake log).

    Better would be a straight 20k log pot. I have 10 and 20k Tokos pot's and although I prefer them to Alps Blue, I find the miniature DACT pots better than all I have tried so far. There is still a bit of a veil with the Tocos pot's and channel balance is not as close as the DACT gets.

    FWIW I paid not much more for my DACT pots than I did for the cheapest carbon one and I prefer the sound of the DACT but it's a personal taste issue as usual. Some folks like a pot to bring a bit of warmth/colouration to the sound, others see that as the enemy.

    Pots - cheapest I could get and no fakes.

    http://www.ebay.co.uk/itm/1908494312...84.m1439.l2649
    http://www.ebay.co.uk/itm/140437348649

    This guy is good for valve amp parts, I got some nice Teflon insulated wire from him recently which would be good for hook-up in your amp.

    http://www.ebay.co.uk/itm/3806618114...84.m1438.l2649

    Yeah, I've used him before. I'll investigate the DACT pots to try once I've got the thing built with the ALPS blue (as standard!)
    "It's ok your comments are noted, so if you want a war you've got one. Watch your back, ya !!!!...." in an email from Marco 3/4/09

  3. #23
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    Well, I think I've just ordered the last of the components I need to build the amp (with the exception of the signal and power valves.)

    I'm going to concentrate on the physical building of the amp first before I turn my attention to turning some control knobs. With any luck I should be ready for valves by Christmas!
    As this is my first tagboard / point to point amplifier build I've got the original kit instructions to give me a hand. there's a lot more wiring that isn't on the diagram (heater connections)

    hopefully I should get some work done this week.
    "It's ok your comments are noted, so if you want a war you've got one. Watch your back, ya !!!!...." in an email from Marco 3/4/09

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    Just realised I've not got enough signal cable for the runs from the bank of phonos to the selector switch. (14 phonos!) seriously considering getting a metre of 16 way studio multicore to do the job....
    "It's ok your comments are noted, so if you want a war you've got one. Watch your back, ya !!!!...." in an email from Marco 3/4/09

  5. #25

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    Just a thought, but that's an expensive build you have going on, if it were me I'd use some of that Teflon insulated silver coated copper wire I linked to. If you keep it away from transformers etc it probably doesn't need to be screened. The best thing (if there's room) would be to mount the selector switch at the rear next to the phono sockets and use a shaft and bush to take a 6mm control rod to the front panel. You could also do that with the volume pot. It's a good way of keeping internal signal runs very short so less chance of loops which pick up noise. This is how a lot of high end amps are laid out. I had a Sonneteer amp years ago which had that layout, it was totally silent when on but no music was playing.

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    to be honest, it's probably about six and two threes in terms of cost. the Van Damme cable is 20 for a metre, and I'll only use half of it so could use the rest for another build at some point in the future. It's professional grade stuff so is of adequate quality for the job.
    since there's two output transformers, a choke and a big mains transformer, avoiding the traffos is near impossible. the phonos are right next to one output traffo anyway so I'd rather stick to screened and build the amp as standard in terms of layout. there's plenty of scope for hum as it is without using non screened wire. the layout means that trying to mount the selector and volume control at the back and using a shaft is going to be tricky on this build. However I agree that it's probably a better solution generally. The other option is a relay board so that there's only one set of audio cables going to the front of the amp.
    "It's ok your comments are noted, so if you want a war you've got one. Watch your back, ya !!!!...." in an email from Marco 3/4/09

  7. #27

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    A relay board can be good but having to rig a separate power supply just for it is what puts me off. I usually settle for an external passive pre in a small enclosure, it keeps things simpler and solves a lot of internal noise issues. I can then muck about trying different pots etc without messing around inside the power amp. So many options but of course not relevant if you want to build exactly to original spec.

  8. #28
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    You don't want a multicore cable unless each conductor is separately screened. You don't even want both channels within one screen like ProPatch for obvious reasons. If you've four inputs and one tape then you need to bring ten screened cables to the selector switch. Of course as Davy says mounting the selector switch near the inputs is always a good idea if you can.
    There is another way and it's what I did with my valve amps. I made them into power amps and put the selector switch and volume pot/s in another box ie just like a passive preamp so now there's just one pair of RCAs on the rear panel. This is how NVA do it and the beauty of this is that your amps have the gain to do this. This is passive done right in my view and it makes for a very flexible arrangement. You'd even be able to use a 0db TVC if you wish.
    Si.

  9. #29
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    not only is it individually screened, it's balanced as well.
    "It's ok your comments are noted, so if you want a war you've got one. Watch your back, ya !!!!...." in an email from Marco 3/4/09

  10. #30

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    Balanced is good! fairly easy to setup too if your only source is a turntable, most other balanced sources use audio transformers to get a balanced output.

  11. #31
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    I wish I understood more of this thread. I thought the thread title referred to a distant cousin of C-3P0!

  12. #32

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    Nah it's the lovechild of Marvin the paranoid android and R2D2.

    And lo another amp was born!



    I think the solder fumes must be getting to me, i was once content with a pint and a rollup!
    Last edited by davym; 3rd December 2013 at 23:22.

  13. #33
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    Quote Originally Posted by davym View Post
    Balanced is good! fairly easy to setup too if your only source is a turntable, most other balanced sources use audio transformers to get a balanced output.
    wandering slightly off topic, but I run 5m of balanced cable from my turntable to the MC stepups in my phonostage. however it's single ended after that. one of the advantages of MC carts is that they'll drive very long runs of cable. much like a microphone, electrically.
    "It's ok your comments are noted, so if you want a war you've got one. Watch your back, ya !!!!...." in an email from Marco 3/4/09

  14. #34

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    I like high output MC's, way better than any MM I've had. The balanced run will also be excellent for rejecting noise.

    I cant think why all high end kit aint balanced, inexcusable when folk are paying thousands for each box, expensive real estate for your PCB's to live in IMO.

    That's why I like diy, a few hundred quid spent on decent components & well assembled, or a few thousand for an off the shelf equivalent.

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    High output MC are usually high impedance output and aren't much use for longer balanced runs. But I agree, balanced makes much more sense. pretty much all studio stuff is.
    "It's ok your comments are noted, so if you want a war you've got one. Watch your back, ya !!!!...." in an email from Marco 3/4/09

  16. #36

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    Yup, almost all MC carts are low impedance which is good.

    It pays to check though, one example is the DL102 it's an MM but it's impedance is high at 240 Ohms! my DL160 is a high output MC with an impedance of 120 Ohms.

    Not an issue for me though cos my deck is on the same rack as everything else so interconnects are short.

    Any progress on the 2A3PSE build? Just wondering how you are connecting the signal cable screens, I seem to remember from when I built the WD KEL84 it had the screens connected at the socket end but left floating at the switch end. looking forward to seeing some finished pics now

    EDIT - just noticed I said that the DL102 is an MM when I know fine well it's an MC cart
    Last edited by davym; 5th December 2013 at 00:06.

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    no real progress at the moment, still waiting for various bits and bobs to arrive.
    Going to follow the WAD convention with the screens connected at the socket ends only. they act as a drain. should make a start on it in the next week or so. going to butcher the case before I bolt any more bits to it; have to drill a couple of holes to poke the fibre optic through to embed into the wooden volume control and source selector switches for point illumination.
    components are starting to arrive though. got most of the capacitors, a few more resistors to arrive too and then I should be on my way
    "It's ok your comments are noted, so if you want a war you've got one. Watch your back, ya !!!!...." in an email from Marco 3/4/09

  18. #38

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    Could be ready to fire up for new year then eh, nice one!

    That fibre optic indicator thingy sounds like a plan but wont it be kind of stiff when you turn the knob? are you going to cut a circular slot/track in the front panel behind the knob for the fibre optic strand to run in?

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    Not sure yet. the length of fibre optic arrived today. it's certainly stiffer than I imagined it would be. I might use a very short piece of it as a lens and put the LED inside the knob behind the fibre optic. that way the wire can take the strain as it were. (probably going to use screened signal cable for this one) in order to keep it hidden I think I'd probably have to drill out the mounting hole on the 2mm steel chassis and make a bracket to sit behind the space. and I'd have to drill out the brushed aluminium face plate which is 4-5mm thick to a diameter of around 25mm. the knob is going to be around 35mm in diameter maximum, so I've not a lot of space to play with. I've no other way of illuminating the space behind the knob for the fibre optic to pick it up. I'm going to knock a couple of holes through the steel that I can use before I bolt 15+ kg of transformers down.

    in terms of progress for the build, I've started wiring up the o/p trannies to the speaker terminal lugs. it's a start! no more components as yet. I'm still waiting on a number of resistors in the post.
    "It's ok your comments are noted, so if you want a war you've got one. Watch your back, ya !!!!...." in an email from Marco 3/4/09

  20. #40

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    Christ what a storm and now snow! The front in town (Oban, George st) was well under water earlier. We just got the internet back close to midnight!

    Re the LED, Naim do something similar with an LED fitted in the knob but from what I remember, they use two individual single core flex wires loosely twisted and have quite a large cut out in the front panel behind the knob to allow free(ish) movement when the knob is being turned. The knob also has quite a large recess/hollowed out area at the back of it to give plenty of space for the wires.

    All more hassle than I can be arsed with but if you get it sorted it will look good. You'll need to try a few different resistor values to get the brightness right too or it'll be glaring at you.

    Probably a good idea to set things like that up before you bolt all that iron to the chassis, that's a lot of weight to have to heft around eh!

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