jonclancy
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Post by jonclancy on Feb 16, 2013 11:31:33 GMT
Just my 2p:
How about finding out the mounting holes so this board can be dropped into the Altronics chassis?
Also, an esteemed member commented that, in his opinion, there may be some thermal benefit from moving the output devices further apart.
Just comments, though, from me. I built up 4 channels on the "Rocky" boards, so my Class A pre/headphone amp needs are well and truly met!
Cheers
Jon
PS Cutting metal on the PSU box today!
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Deleted
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Post by Deleted on Feb 16, 2013 11:44:52 GMT
Hi Jon There may be some thermal benefit if you wear gloves when you hold your fingers on the heatsinks after winding up the bias to double current.  With many power amplifiers, the bias setting transistor is mounted on the same heatsink as the output devices to give thermal coupling. To move the output devices further apart would likely affect it's thermal tracking ability. I would recommend that the output resistor holes are made to take .9mm PCB pins to facilitate resistor replacement when using with different headphones. Will's suggested changes are all quite worthwhile changes. Regards Alex |
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jonclancy
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Post by jonclancy on Feb 16, 2013 14:39:29 GMT
Just passing the suggestion on...  |
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Post by Deleted on Feb 16, 2013 14:52:31 GMT
Another thought.
Would folks like to see the output devices moved to the edge of the board to allow a single large heatsink to be used a la power amp stylee. Saves messing with internal sinks or would this also interfere with thermal tracking?
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Will
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Post by Will on Feb 16, 2013 15:35:15 GMT
Out of interest, does anybody else's heatsinks get very warm like Jon's when set to the normal bias setting? (Happy 1000+ posts, BTW  ) Mine, here  never got warmer than 'Hi, I'm a class A headamp, and I'm working' warm andcould touch them for extended periods if the fancy took me. The OP devices could be moved further apart if different heatsinks were used; and moving them to the edge would remove the need for on-board sinks all together, perhaps reducing pcb size. Do like the idea of on-board heatsinks though, personally. Anyhoo, the original changes are easy to do, but the other stuff requires a bit more surgery. I'm happy to go with group consensus, but more changes = more time. |
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Post by Deleted on Feb 16, 2013 16:10:02 GMT
''I would recommend that the output resistor holes are made to take .9mm PCB pins to facilitate resistor replacement when using with different headphones. Will's suggested changes are all quite worthwhile changes.'' Hi all Yes I’d go along with the above and TBH my heatsinks don't really get all that hot @ 100ma bias so no need to change the location of the OP devices. moving the OP devices to the edge of the board may be good to save a little space but not a deal breaker IMHO. still plenty of interest tin Alex's class A but no big surprise on that this is one hell of an amp  so Marc put me down for a set of LS devices per board thanks.  take care |
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pingu
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Post by pingu on Feb 16, 2013 16:37:13 GMT
Wow, I'm off to sleep and come back to see we've already reached the threshold. Nice. Alan, I'll definitely count you in for the LS devices. I presume everyone else wants one each(LS 352 and LS313) per PCB? Will, could you send the artwork over as it is right now? I've only made presumtions about size (extrapolated on T0220 size), and many PCB makers only quote when they receive gerbers. I'll send you an email that you can reply to. What benefit do you see, bringing the pre/HA in line with the PA? You still won't be able to turn one into the other, right? Cheers, guys, keep'em coming, the more the merrier. Yes pls count me in for any GB of bits ...enough for 4 boards Cheers Martin |
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Post by Deleted on Feb 16, 2013 21:48:15 GMT
''I would recommend that the output resistor holes are made to take .9mm PCB pins to facilitate resistor replacement when using with different headphones. Will's suggested changes are all quite worthwhile changes.'' Hi all Yes I’d go along with the above and TBH my heatsinks don't really get all that hot @ 100ma bias so no need to change the location of the OP devices. moving the OP devices to the edge of the board may be good to save a little space but not a deal breaker IMHO. still plenty of interest tin Alex's class A but no big surprise on that this is one hell of an amp so Marc put me down for a set of LS devices per board thanks. take care Hi Shaun Originally, the heatsinks that I used were a little smaller than the taller ones many of you appear to be using. At 100mA bias they didn't get excessively hot, even in our much warmer climate, with days hotter than 40c occasionally. I liked Jeff C's idea of bolting 2 heatsinks together, in case I decided to markedly increase the bias, so I did that much later on, but not because I felt the need to. Even when used as a preamp with much better speakers than mine ,(david2vk) there does not appear to be any real benefit from markedly increasing bias, but you guys have much younger ears than mine. Kind Regards Alex |
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Post by Deleted on Feb 16, 2013 21:56:44 GMT
Another thought. Would folks like to see the output devices moved to the edge of the board to allow a single large heatsink to be used a la power amp stylee. Saves messing with internal sinks or would this also interfere with thermal tracking? Hi Chris When used as a preamp as well, due to extra circuitry such as a delay PCB, which can also be used to switch between RCA Out and headphones, you are likely to find that even with a 1U rack case, things will become a little cramped. Unless the bias transistor is also clamped to this large heatsink as well, then yes, it is likely to affect the stability of the bias current. Kind Regards Alex |
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Post by Deleted on Feb 17, 2013 0:25:54 GMT
''there does not appear to be any real benefit from markedly increasing bias'', Hi Alex Yes I’ve not tried increasing the bias and not felt any great need to do so. I suspect that you statement above is correct and well you know my thoughts on changing things for the sake (heat) of it. Nope IMHO it’s a well proven design that’s good to go as is. I suspect that from the number of people here who have built already and still would like another seems to confirm that also. And it goes on  take care |
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Post by gommer on Feb 17, 2013 19:36:29 GMT
Hi guys,
Just adding that I wouldn't mind adding all the active parts in the group buy, so more than just the LS devices alone. There's not really a hurry, as it seems that Will is going to need some time to change the layout.
Cheers, Marc
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Will
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Post by Will on Feb 17, 2013 21:03:32 GMT
.....There's not really a hurry, as it seems that Will is going to need some time to change the layout. Cheers, Marc Top Gear didn't really grab me tonight  I've left the heatsink side of things, as it really was too invasive, and didn't want to spend too much time on this, holding things up. |
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Will
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Post by Will on Feb 17, 2013 21:08:09 GMT
Also meant to say that I've removed the smaller ls device pins, it's just not in the picture above.
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jonclancy
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Post by jonclancy on Feb 17, 2013 22:52:35 GMT
Sorry guys - I think it was the Power amp I was talking about for the device spacing.
As you were... Carry on, etc.
Doh!
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pingu
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Post by pingu on Feb 17, 2013 23:01:39 GMT
Hi guys, Just adding that I wouldn't mind adding all the active parts in the group buy, so more than just the LS devices alone. There's not really a hurry, as it seems that Will is going to need some time to change the layout. Cheers, Marc Yes sounds a good idea add me in if you have a GB for all active bits seems better value that way. If not enough intrest well just the LS thingies (tech legal term  ) will be OK Martin |
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Post by Deleted on Feb 17, 2013 23:12:50 GMT
Sorry guys - I think it was the Power amp I was talking about for the device spacing. As you were... Carry on, etc. Doh! Hi Jon A small problem to some, but a major problem to others, is that the original SC design saw that the spacing of the output devices coincided with the fin spacing in many commercially available heatsinks of the right dimensions. It is much easier to drill mounting holes right through clear areas of the heatsinks than tap 3mm thread going into the fins. Frequent removal and re-installation of the PCBs may see these fragile tapped threads damaged. Some may even manage to snap off the taps, and be unable to remove the remainder. That is more likely to happen when tapping say 4mm threads in the top of the heatsinks for mounting covers. It would appear that I am not the the only klutz that has done that.  Kind Regards Alex |
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pingu
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Post by pingu on Feb 17, 2013 23:41:12 GMT
Frequent removal and re-installation of the PCBs may see these fragile tapped threads damaged. Some may even manage to snap off the taps, and be unable to remove the remainder. That is more likely to happen when tapping say 4mm threads in the top of the heatsinks for mounting covers. It would appear that I am not the the only klutz that has done that. Kind Regards Alex [/quote] Thanks for that Alex I thought I was the only klutz that broke taps  . I was told that it was because I was taught to repair my cars with a club hammer and long handeled bar for the sockets .... ooops ther goes another exhaust stud  Martin |
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Post by Deleted on Feb 18, 2013 0:21:47 GMT
.....There's not really a hurry, as it seems that Will is going to need some time to change the layout. Cheers, Marc Top Gear didn't really grab me tonight I've left the heatsink side of things, as it really was too invasive, and didn't want to spend too much time on this, holding things up. Hi Will looking good those changes will make for |
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Post by Deleted on Feb 18, 2013 0:22:53 GMT
Top Gear didn't really grab me tonight I've left the heatsink side of things, as it really was too invasive, and didn't want to spend too much time on this, holding things up. Hi Will looking good those changes will make for a nice smooth build. thanks take care |
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Post by Deleted on Feb 18, 2013 0:28:53 GMT
Shaun
I think that the inner pads for T2 and T3 have also gone.
Regards
Alex
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Post by Deleted on Feb 18, 2013 0:33:54 GMT
Shaun I think that the inner pads for T2 and T3 have also gone. Regards Alex Hi Alex Yes i noticed that Will mentioned that's also be useful. also noticed the extra large pads for OP resistor for experimenting. all good stuff and the usual high standards from Will take care |
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XTRProf
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Post by XTRProf on Feb 18, 2013 3:35:42 GMT
Sorry, what have the new parts done to the amp as I don't have the old layout to compare.
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Post by Deleted on Feb 18, 2013 3:59:06 GMT
Sorry, what have the new parts done to the amp as I don't have the old layout to compare. Chong A few people had problems with the 78L15 blowing up. This is a known problem with this VReg , and S.C. even reported about it. Some brands of the more bullet proof 7815 and 7915 , need a minimum load current to properly regulate. That is the function of the additional 3.3K resistors. Replacing the originally specified AD744 or TL072 of the Offset Corrector with an OPA134 will reduce the noise component from the Offset Corrector I.C. itself, that appears at a reduced level into the feedback network.The 2.2nF to 4.7nF across the 1 Megohm in the offset corrector, helps to further reduce wideband noise generated by , and amplified due to the high gain of the offset corrector I.C. This further improves the S/N ratio of the amplifier and makes low level detail sound a little cleaner and more obvious. It also helps to further improve the 3D sensation when used as a preamp and high quality power amplifier. Do the same to both preamp and Class A power amp and you gain even more.. Regards Alex Jon This may help for starters. I believe that this new project should be Marc's baby, with assistance from Will who designed the original and new PCBs for this project. Marc is free to start a new thread which can be stickied as required. I can assist with anything additional, as well as the deletion of any posts needed to tidy up things on request. Regards Alex |
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jonclancy
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Post by jonclancy on Feb 18, 2013 5:34:11 GMT
Morning Alex! Will, We NEED a list of these mods as a separate MkII (locked) thread linked in your sig - pretty please!! Some, at least, can be retro-fitted to current boards. Cheers Jon |
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Post by Deleted on Feb 18, 2013 5:48:02 GMT
Morning Alex! Will, We NEED a list of these mods as a separate MkII (locked) thread linked in your sig - pretty please!! Some, at least, can be retro-fitted to current boards. Cheers Jon Hi Jon I am pretty sure that Will would cover that in his existing links. The only change for existing people with the Class A HA/ preamp will be the addition of the 2.2nF capacitor across the 1M resistor of the Offset Corrector. All the new builders will need is to replace the 78L15 and 79L15 with 7815 and 7915 and fit 2 x 3.3K resistors as a load for the 7815 and 7915, plus the 2n cap. I will see what I can do , but no promises as I have a new PC to put together before this one stops wotrking completely, and get a new tyre for the car's passenger's side rear, rego inspection and possible repairs AND find the money to pay for it all after the elecectricity mob take $1,050 out of my savings for the last quarterly bill ! Kind Regards Alex |
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