| ptah |
| HTPC incorporating Leach LOW TIM amp. I'll post more as things progress if anyone's interested, thanks. |
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| janneman |
Wow! details?
Jan Didden |
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| pinkmouse |
| What a tease! Of course we want more info! :) |
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| bernhix |
| so nice, more info please.... |
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| ptah |
My goal is to incorporate a PC into an amplifier for the purpose of managing music playback. I did not want amplified speakers. The Leach amp design appealed to me because the instructions are well documented and I like the sound of transistor amps. I'll admit I have limited electronics experience, as I demonstrated in my first post, but I like to learn new things.
I decided to build the exterior of the case from wood because I love wood working and the cost, for me, would be low compared to metal (I always stop to look at antique radios, some of the case work is fantastic). I designed with ventilation in mind, because of the PC components, and wanted to stay within typical amplifier dimensions. I struggled with layout for a couple weeks trying to balance proper component placement, weight distribution and aesthetics.
Another new thing for me was working with Plexiglas As the layout came together it became advantageous to have the chassis completely removable in order to have easy access to the electrical. Allot of "PC moders" use Plexiglas for decoration but it is also very strong and easy to cut and glue. The first go-around I made the mistake of using epoxy for plastics. After three days the joints got brittle and it fell apart. Methylene chloride is glue of choice because it bonds by melting the joints together and hardens very fast.
I noticed that Plexiglas can build up static charge. Sanding the surface eliminates this problem and makes a good surface for spray painting.
I have no explanation for the hatch in the top. Seemed like the thing to have if you like to fiddle.
The front view in the previous post shows the drive bays. One DVD/CD burner, two hot swap SATA drives and one USB/Memory card port.
The amp heat sinks mount on the left and right side of the drive bay and are recessed flush with the same. It gives it a funky look but front mounted heat sinks were the best fit in terms of layout.
I still have to mount the main board (micro ATX) and do the final wiring.
This pic shows chassis out of the case ready for wiring.
Thanks for your interest, it's nice to have a forum to chat about this sort of thing. More posts as Frankenstein progresses. |
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| TomWaits |
| quote: | Originally posted by ptah
...to incorporate a PC into an amplifier for the purpose of managing music playback....Thanks for your interest, it's nice to have a forum to chat about this sort of thing. More posts as Frankenstein progresses. |
I can't see any Frank, it looks great. I am wondering would there be concern with a lack of sheilding? Most PC cases are ugly but the metal provides an almost essential layer. Perhaps you could add some in strategic areas? 2Cents...Can't wait to see your progress.
Shawn. |
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| CBS240 |
Maybe you could line the inside with a fine mesh metal screen for shielding?
just a quick thought:smash: |
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| ptah |
Some pics with power supplies installed before wiring things up. Cut access for micro ATX board and painted front panel.
Checked into shielding and should not be required because the mother board is grounded through the PSU. |
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| ptah |
| And the other pic that did not attach - |
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| FastEddy |
Pardon my intrusion, but I've built a few thousand computers myself and I could not help but notice that you might be using the wrong PC power supply ... For an audio oriented PC, I always recommend getting the largest, highest watt PC power supply you can find, and if you can get one of those "special" audio/PC supplies = better yet.
(Having a power supply about twice as heavy duty as you think you need is good, more is better. If you think you need 200 watts for the PC, get a 450 or 500 watt supply. The basic reason is that a 200 watt cpu, motherboard & drives will be loading the last filter stage of the PC supply to within 80% of its maximum and the capacitors will let a lot of noise through to your analog audio equipment by way of the cabling & radiation. ... with a 500 watt supply the PC supply caps are "only" stretched out to ~40% of power rating = better filtration of switching supply noise, etc.)
Good luck :smash: |
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| ptah |
| Yeah, I wrestled with that dilemma too. I really had to decide the purpose of this build. Did I want a multi-media machine or a simple play back platform. I selected the latter because I did not envision doing a bunch of media manipulation. After considering one of VIA's mobo's, I selected a micro ATX instead w/ acceptable onboard graphics and sound and mobile AMD processor. Hopefully that won't eat too far into the little 300W supply. I was intrigued by VIA's offerings but chickened because I don't have experience with them and they are high priced. I think the way I plan on routing the amp input wires should keep me clear of noise, but like you say, I may have to shield or go up in size on the PSU. I'll let you know in a month or so how it stands up, thanks for the pointer! |
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| ptah |
| This is alot of work. I think I have about 100hrs here, several due to inefficiency. These are the last shots for a few weeks. Waiting for the mainboard. I blew two MJ15003's due to inattention to wiring on the upstream side of the binding posts, ouch. These are getting hard to find. The plans call for one resistor and one cap, in series, per channel from positive to negative. I had it crammed tight enough to cause a short. Anyway, the plan is to install the mainboard and load Linux (that should keep me occupied for week). |
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| groov |
It sure looks very nice and very creative of you....my concern will be with those transistors sitting on the front and the possibility of having yhey shorted out since their collectors are hot (voltage wise). It sure gives me some ideas.
I was planning on using plexi-glass for some of my amp cases.
Thanks for the pictures. :D |
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| ptah |
groov,
that's a good point, i did not think of this. if one is shorted to the the other that would be a problem. what should i do? do they make covers or maybe they could be coated? |
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| groov |
ptah,
The only thing that I can think of is to use some plexi and cover the area where the transistors are with some holes on the plexi in order to provide some ventilation.
You should be able to attach the plexi piece onto inner fins somehow so aestitically would not ruin your excellent construction.
And yes if you short one transistor it maybe possible that you will affect the other on the same line.
Cheers :D |
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| davidallancole |
I am not sure were to get them but there is covers that are made for covering TO-3 transistors. We have some on the transistors on some power supplies at the place I work at.
Also I was wondering what you are doing for monitor/keyboard/mouse, that kind of thing. |
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| groov |
ptah
Yes, I agree with david there are these plastic TO3 covers than can be use to ccover those tin cans.
You should be able to find them at your prefered electronic store (ie. digikey, mouser, etc) they should be very inexpensive. As I remeber there use to come in white and black colors.
Cheers:D |
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| ptah |
| quote: | Originally posted by davidallancole
I am not sure were to get them but there is covers that are made for covering TO-3 transistors. We have some on the transistors on some power supplies at the place I work at.
Also I was wondering what you are doing for monitor/keyboard/mouse, that kind of thing. |
| quote: | Originally posted by groov
ptah
Yes, I agree with david there are these plastic TO3 covers than can be use to ccover those tin cans.
You should be able to find them at your prefered electronic store (ie. digikey, mouser, etc) they should be very inexpensive. As I remeber there use to come in white and black colors.
Cheers:D |
Thanks, I'll look for those covers. David - My initial plan was a 7" Lilliput touch screen that would mount on an internal hinge and fold out of the top of the case (then relplace the grating). If I go that route, windows xp would probably have to be the operating system because of touch screen driver support and the ability to use the on screen keyboard (Start > Programs > Accessablity). I need to check the driver thing out closer. Option two would be Geexbox, a Linux distro, that boots from USB or CD. Its sole funtion is a media center interface however it does not support a mouse. Here I would be limited to wireless keyboard and tv screen. Option three would be Suse or Ubantu, wireless mouse and keyboard and tv screen. The best of both worlds would be the Lilliput and some form of Linux. I don't want the windows overhead. |
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| Workhorse |
Hi PTAH,
Your Creation is Immaculate!
Cheers,
K a n w a r |
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| ptah |
I really like the way this turned out. The sound of the Leach amp is good and it is nice to have it integrated with a modern (at least for today!) storage and interface. The video is superb. It is hard to beat software rendered video sent over a DVI-D link. It runs in dual head mode (DVI-D to TV, VGA to touch screen monitor). There is no hum or thermal problems. I decided to leave the TO-3's naked since the chance of shorting is remote.
Specs:
Amp and Power Supply- Leach 4.5, to his spec
Main Board - DFI Infinity RS482 w/ ATI Radeon onboard sound/video
CPU - AMD Opteron 144 (1.8 Ghz, not over clocked), Socket 939
RAM - Kinston Valueram, 512 Mb
PSU - FSP300, 300 Watt, Micro ATX
HDD - 2 - Seagate Baracuda, 320 Gb, SATA 3.0
Optical - Liteon DVD RW
OS - WinXP Pro (I could not stomach a Linux install and did not want to fork for Media Center)
Human Interface - Lilliput, 8", touch screen
Here are a few pics - |
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| groov |
Great looking system ptah.....it seems that you put a lot time and effort into finishing this one up....:bawling:
groov:D |
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| megajocke |
It looks really nice! I like the front panel with drives and heatsinks.
I'd be more worried about giving someone a shock than shorting out the transistors... The cases are 60V above and below ground. If you touch a PNP and NPN at the same time its 120V DC... kind of dangerous don't you think? |
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| ptah |
Mega,
Thanks! I took your advice and "sealed" them with clear epoxy paint. It is was fairly easy and is durable and did not require removing them from the sinks.
Can anyone advise me on how to tell if the audio out from the main board is driving the amp to its full potential. Is it sufficient to check the rms voltage of the audio out from the motherboard with a multi meter? Using this type amplifier what would be a realistic maximum input voltage? |
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| groov |
ptah,
It depends on the mains transformer 2ndary Voltage.
If you are using an original Leach, meaning there is no mods to the feedback resistors, the closed loop gain is 21 (or 26.44dB) and using +/- 58V as power supplies as per Leach's specs then I believe that Dr. Leach designed it to have a ~1.7 Vrms max input which translates to 2.4 V peak, before it becomes non-linear. 21 x 2.4=50.48V with an 8ohms load. I would not suggest to drive this amp that hard, it is illustrated as a max number. Therefore I would suggest a realistic max input of 2V peak assuming you have the right transfromer to handle the power.
I am not sure what is the max output of your PC audio card but I bet it is not more than 2V peak then you should be alright. BTW with 2V peak you will be putting close to 220W into 8ohms load with 5.2 Amps into the load. Hottt damn.
If you want to tested you will need a dummy load of 8ohms with at least 200W capacity on a heatsink.
If your mains transformer secondary output is less then you will have to adjust the numbers accordingly.
Hope it helps.
groov |
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| ptah |
Well I've had this box in my living room for a month now using the motherboard's on-board sound. I was not satisfied with the volume (power) available so I measured the on-board sound voltage with the software volume at maximum using a 1 Khz mp3 file (thanks Groove) and measured 0.5 Vrms. I decided to add a sound card and chose an Auzentec "Mystique" based on reviews, price and a reported 2.5 Vrms output. It is interesting to note that they are the only maker that reports this data (that I could find, any way). I measured 1.9 Vrms using same source file and DTM. The performance increase was fantastic. Much louder playback and the sound definitely improved (the foundation is cracking). As a side note, I measured 0.2 Vrms on a cheap Creative Audiology sound card in my PC.
I guess I really don't have a handle on how to determine the maximum voltage allowable to drive the Leach amp (or any amp for that matter). |
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| EchoWars |
| quote: | Originally posted by ptah
I guess I really don't have a handle on how to determine the maximum voltage allowable to drive the Leach amp (or any amp for that matter). |
Very much depends on the amp. The figure you are concerned with is the one that produces full output. Some may get there with 1.0V input, some may take 2V to produce rail-to-rail swings, some more.
Just depends. I don't think I'd sweat it much. Enjoy the tunes!
(amazing work, BTW) :eek: |
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| ifrythings |
Nice work!!! keep it up :)
BTW having the transformer so close to the board and not shielded woundn't that cause problems? (EMF/EMI) |
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| ptah |
| I have not detected any problems with EMI. Toroids are supposed to produce allot less interference than EI types. |
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| TomWaits |
It has been said before but I just thought I'd remind you...this is an amazingly cool project. Well done and very unconventional.
Can you make me one? :D
Cheers,
Shawn. |
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| ptah |
Thanks for compliment! It's great to get feedback and this site is a wonderful resource. Working on the second build for a friend with significant changes, mainly in the case design and main board selection in order to drive down the overall size (height and depth). I sure have learned allot (since my background is not EE) but have much more to learn.
I have been reading my old EE textbook and Randy Slone's high power amp book. I am looking for a www resource that gives a better explanation of BJT and MOSFET operating principles, circuit design and component selection. |
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