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Old 24th September 2010, 04:27 PM   #171
EUVL is offline EUVL  Europe
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I have not published the circlotron circuit.
But you can take the same Mosfet / Jfet building block and apply the standard circlotron follower topology.
Plenty on the net. Very easy, and helps you to understand how it works.

Am pushing for time, so no time to tidy up a proper circuit to publish.
Hope you can manage.


Patrick
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Old 25th September 2010, 12:25 AM   #172
njepitt is offline njepitt  United Kingdom
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Hi Guys,

Well, my DAO amp is finished, and playing... I've posted some photos below, some with it half-built, so things are a bit more visible, and others when all wired up. The last two show the completed amp from the front, and from the back together with the PSU. One cable from the PSU is for DC and ground, the other is for low-voltage AC for the muting circuit. Obviously, that's the perfboard construction on the botton of the amp. Fifth photo shows testing for DC offset - as you can see on the DMM, -6mV on the one channel, the other is similar, and it doesn't seem to change much as the amp heats up. Bias is about 300mA (1.23V across the 3.9R source resistors). I ended up putting the tantalum caps in - we'll see about playing with others later. I may also try to shorten some of the wiring a bit, but so far it doesn't seem to be giving any trouble, so maybe I'll not bother.

One thing I regret is that using these old heatsinks, which had loads of screwholes already, the height of the caps on the perfboard meant I had to put the pcbs higher on the heatsink than I wanted, but after a couple of hours the amp only gets up to around 45 degrees, which is fine. (Measured by pushing the probe into the heatsink somewhere behind the pcb.)

I haven't weighted it yet, but amp and power supply together should be between 4 and 5 kilos, which is more than I hoped but less than I feared.

I'm listening to it this evening using a cheap pair of ipod-type headphones. I picked them up cheaply mostly to test the amp - they're 32R impedance, but aren't really a fair test. They sound much better than I expected, although much too trebly, but I'll have to borrow something better to try out before posting anything about the sound of the amp.

Any comments on the build are most welcome, and of course, many thanks to Patrick for posting his circuit.

Cheers

Nigel
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Old 25th September 2010, 04:03 AM   #173
qusp is offline qusp  Australia
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Quote:
Originally Posted by EUVL View Post
I have not published the circlotron circuit.
But you can take the same Mosfet / Jfet building block and apply the standard circlotron follower topology.
Plenty on the net. Very easy, and helps you to understand how it works.

Am pushing for time, so no time to tidy up a proper circuit to publish.
Hope you can manage.


Patrick
yeah Patrick, I think I must have just misread or misunderstood one if your posts as indicating there was a published circuit somewhere. turning it balanced seems to me to be not all that much more than a source and load connection issue, along with the accompanying changes to CCS etc. I have become frustrated in the past with such circuits for GB's for PCBs etc starting out with balanced and then changing to pseudo balanced. some go ahead and make it much more clear cut SE for both amp and PS sections, but this circuit is differential in pretty much every way, so very little should need doing, especially given I would most likely be breadboarding it, or enlisting the help of a friend and getting a batch PCB job made up (with your permission of course) for my own use, I have no desire to become on of the legions of perpetual GB holders.

if I go ahead and build one (and i'm pretty certain I will when time allows), i'm sure there is enough info around for me to do that without issue. I just need to read up on the circlotron and your posts on the subject as your aims often seem to be similar to mine. I just wish I had the skills and equipment to make up a PCB for myself. i'm not against P2P for prototyping, but really for finished builds I would much prefer a PCB.

thanks again

Jeremy
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Old 25th September 2010, 05:24 AM   #174
EUVL is offline EUVL  Europe
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When you are that far and you have all the parts and understood the circuit, you can contact me for more info.
I have a board layout that you can use for one offs.
I just don't have time to publish things here right now.

And, you have to drive it with a balanced source, without saying.


Patrick
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Old 25th September 2010, 05:29 AM   #175
EUVL is offline EUVL  Europe
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Nigel,

Congradulations.

Hope you get a proper phone soon for testing.
Pretty housing costs money, so make sure you like the sound first.

If you find the sound too trebly, you might have to increae the cap across the ZD Iam afraid.
Try to use some of those low ESR conductive polymer caps. They are small and have low voltages.
I would consider 330uF 10V or even 560uF 6.3V.
You need to play around to suit your taste.


Patrick
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Old 25th September 2010, 04:39 PM   #176
njepitt is offline njepitt  United Kingdom
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Quote:
Originally Posted by EUVL View Post
Nigel,

Congradulations.

Hope you get a proper phone soon for testing.
Pretty housing costs money, so make sure you like the sound first.
Apparently I'm not going to be able to draw any conclusions with the pair of phones I have, so I hope so too...

I'm not into spending big money on chassis and housings - I usually dry to dumpster-dive, or equivalent, so I can spend money on parts (and music, of course...) I also find it a fun challenge to make use of trash, like these heatsinks, which came from sawing an old car audio amp in two.

Quote:
If you find the sound too trebly, you might have to increae the cap across the ZD Iam afraid.
Try to use some of those low ESR conductive polymer caps. They are small and have low voltages.
I would consider 330uF 10V or even 560uF 6.3V.
You need to play around to suit your taste.


Patrick
After reading your post I decided to try this. I pulled the 22uF tantalums off, and tried to put the 220uF elna silmics in (the ones I originally bought for this) but it was hopeless. With some difficulty I then put in some no-name 220uF 16v caps I had from old computer PSUs to see what would happen, but they made no difference to the bass. So I think it is most likely just the poor quality of the (cheap) headphones. I'll have to wait to test the amp with better phones before thinking about tweaking.

However, could you post an example of the caps you are referring to? Also, isn't the jump from the 22uF to 330 uF quite a bit? Was there any particular reason to specify these values? For instance I could fit larger tantalum caps in if I wanted to, say 47uF or 100uF maybe, since they have rounded bottoms, and it's easier to poke the soldering iron into the limited space...

Thanks again for all the help

Nigel
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Old 25th September 2010, 10:56 PM   #177
EUVL is offline EUVL  Europe
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No particular reasons, just what I have on hand and what fits.
Conductive polymer caps you can search at Digikey. Large collection.

The cap of the cascode device has an effect on the square wave response, just as the load impedance.

But until you get decent phones, no point to experiment further at this stage.


Patrick
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Old 26th September 2010, 02:29 AM   #178
qusp is offline qusp  Australia
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Nigel, are you able to put the cap across the zener under the board? if so I would suggest the murata SMD D size package low Z polymer caps or the panasonic special polymer SMD. the murata have the advantage of coming in up to 20v for the smaller capacity caps. i'm using the 13v in my IV. hear is a link at mouser for the 220uf the panasonic special polymer are here PCE3270CT-ND for the 100uf 8v SMD and are available in larger values too albeit at lower voltage ratings. should be easier than trying to squeeze it in from the top.

the tantalum polymer and niobium oxide SMD caps are also rather nice. though the noibium are only available in relatively low voltage ratings. but they are a very cool orange
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Old 26th September 2010, 02:38 AM   #179
qusp is offline qusp  Australia
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Patrick, thanks very much for that offer mate. once I get my head around the circlotron and its relation to the DAO, i'll drop you a line. the circlotron and how it works seems a bit counter-intuitive at first glance, but will only take a bit of study as there is plenty of info around.
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Old 26th September 2010, 02:54 AM   #180
njepitt is offline njepitt  United Kingdom
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Hi Guys,

Quote:
Originally Posted by EUVL View Post
No particular reasons, just what I have on hand and what fits.
Conductive polymer caps you can search at Digikey. Large collection.

The cap of the cascode device has an effect on the square wave response, just as the load impedance.

But until you get decent phones, no point to experiment further at this stage.


Patrick
I agree there's no purpose in experimenting without better phones, although due to the immense delay in getting stuff sent to Brazil it's wise to think things through well in advance.

Quote:
Originally Posted by qusp View Post
Nigel, are you able to put the cap across the zener under the board? if so I would suggest the murata SMD D size package low Z polymer caps or the panasonic special polymer SMD. the murata have the advantage of coming in up to 20v for the smaller capacity caps. i'm using the 13v in my IV. hear is a link at mouser for the 220uf the panasonic special polymer are here PCE3270CT-ND for the 100uf 8v SMD and are available in larger values too albeit at lower voltage ratings. should be easier than trying to squeeze it in from the top.

the tantalum polymer and niobium oxide SMD caps are also rather nice. though the noibium are only available in relatively low voltage ratings. but they are a very cool orange
Now I hadn't thought of SMD.... There is certainly space under the board; although the traces are on top the space doesn't allow for a clean surface mount, but wires through to the other side could work... Thanks for the idea!!
(No way to see cool orange caps under the board, though, unfortunately... )

Meanwhile, I am listening to the amp right now. System is Linux PC to "Superpro" DAC (purple cigarette-pack size commercial job) through USB, to diy preamp (juma's BF862 schematic - posted elsewhere on the forum) feeding the DAO, to cheapo ipod-style headphones, which are surely the weakest link. As I mentioned above bass response is poor most likely due to the phones; otherwise first signs are very positive. I'll resist making any report on the sound until I have better phones, but at least I can say it's really nice to listen to, even with the cheap ones...

Cheers

Nigel
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