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PostPosted: 17 Sep 2008, 13:16 
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Location: Boston
I posted about this in the in the intro forum and gmilitano suggested I post smoe pictures of what i've got, so here they are, along with some links to schematics and part numbers. I'm looking to build it back to what it used to be: a sweet analog amp for my home theatre system. gmilitano suggested I salvage as much as I can, and being a cheapskate, I think that's a splendid idea.

I think the amp circuits are good, and it was the power that had a a blow-out. I don't understand why these things are so complicated!! I gave up on fixing the power circuit and I think I'd rather just wire something up that will supply the correct power to the amp circuits along with inputs, outputs, volume control, etc. The original unit had this digital control box crap which i think might be the reason for all the complicated stuff. Clearly I'm not a fan.

So here goes the onslaught of info:

First the important bit; this is the board with the amp chips, and heatsinks. The high-gague ribbon on the left is for power in, low-gague header on the left for signal in, the red/black wires coming out go to the speakers. This view shows the 3 bash amp units (stero, i assume. There are 2 sets of speaker out matched to each chip, 5 chips in all, with 3 channels going to the sub (this i'm not really sure why, maybe for the extra power)

Image
Part numbers on the BASH amp chips are:
STA575
N220K0429
MALTA

reverse angle: there are 2 other transistors attached to another heatsink. maybe MOSFETs? one has 2 leads connected, one 3. The heatsink assembly blocks the top of the chip so i can't get a part number off of it without taking it apart and losing the goo.

Image

Here's a chip on the board that bears the BASH logo, i figure it's important. Controller of some sort? BASH amps are digital, no? I'd be interested to know how they work. Seems like the 20-odd pins they have are a little excessive for a stereo component.

Image
In case you can't read the part number, it's STABP01D, H91030311

Can't quite glean any more useful information from the boars. The rest is a bunch of resistors, capacitors, etc that seem silly to list

2 amp boards, as i mentioned earlier


Here's the power board:

Image

reverse shot of some beefy capacitors:

Image

Can't get much info off these transformers. Can't read what the heatsinked transistors on the power board are but i have a hunch their role is pretty arbitrary? Since the info here is a little thin, look what i found: Sweet!. These units are notorious for overheating and failing so there's a lot of info about them. I haven't been able to justify the time commitment, but there's a 91-page forum post about how to fix them. I thought coming here might be a bit more efficient, since that's a lot of damn reading. Here it is if anybody wants to read up. if you do you're far more dedicated than I specifically, some schematics of the power circuit.

So there we have it.

If there's any grunt work I can do to figure this out let me know and I'll get back with it.


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PostPosted: 18 Sep 2008, 10:09 
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It would be nice if you could reuse the amp modules. The problem is that the power supply is not simple at all. It supplies +24, +12.9, +9, +4.4, -8V, and 70V. So it will not be all that simple to just replace the power supply (assuming that is where the problem is).

I would take a look at seeing if you can track down the problem on the power supply.

If not, you can look at building 6 channels of amplification and using your computer to drive them. 41hz.com and chipamp.com offer some kits that would be suitable.

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PostPosted: 18 Sep 2008, 17:22 
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That's what I had envisioned for the project from the beginning. Like I said I have an external decoder and a surround sound card. Would it really be very difficult to build a power supply (from scratch) that supplied those voltages and just hook it up to those modules?

Or, if I want to just dump the parts altogether, do you have a recommendation for which kit from those sites I might want to try in order to get the output i want?


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PostPosted: 18 Sep 2008, 19:34 
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The kits at 41Hz have a good spread of power output. The AMP9 basic gives you 4 channels at 100W each. Then perhaps two AMP11 or an AMP10 to get you the last two channels. Some of the kits are SMT which can be tough so take a good look before you decide.

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PostPosted: 20 Sep 2008, 15:37 
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quick question about wiring:

I realize this might be an issue and I'd like to nip it in the bud before I build my amp.

I'm going to want to have it accept many many inputs. That is, I want to make something of a reciever out of it, but rather than switching inputs, I want to mix them..

Currently I have a 1/8" splitter going into the back of my 2.1 and I plug computer, surround decoder, ipod, etc. into it simultaneously. Having 2 devices at once causes wierd problems. For example, if my computer is plugged in but muted, or not playing anything, the decoder etc has to be turned up alot and when i unplug something the other thing gets really loud.

I assume the issue is because the ground wires of each device are at different potential levels, but I know there must be a way to avoid this problem.

Would I have all my inputs in the device sharing a common ground. Doesn't teh spliter essentialy do that anyway?

I'm sure its a simple thing, but I'm also sure I'd run into issues just wiring it the "straightforward" way I would make up on my own.


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PostPosted: 21 Sep 2008, 09:31 
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What happens when you share an input like that is the signal goes to multiple input devices and some of the signal is lost in each of the sources which have some output impedance. This will likely be a problem even if it is turned off. Try and see.

The easy way to get around this is to use switched inputs.

Cheers

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PostPosted: 23 Sep 2008, 07:38 
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You could build your own pre-amp as well then, as Gio said, used switched inputs. Just a dial to select each one. There is a SUPER easy pre that you can build that will give you HIFI sound. Its the B1 PreAmp by audio electronics guru Nelson Pass. I think it cost me a little more than 12 bucks to build. But I have no enclosure on it and only one set of RCA inputs and one set of RCA outputs so if you want multiples you might be looking at more like 20-30 bucks. It retails for $1000. :)
Do you know what your budget is for the amps? The transformer on that thing never gave 560W... ever. So, while the fuse could handle it the transformers would have burnt. So you know, transformers are the most expensive part of this. We should probably evaluate how much power you actually do need.
So a few things we need to do..
1. Get an idea of a budget.
2. Check the speakers and get back with us on the SPL, or, efficiency or the speakers. Hopefully they will say so on the back but maybe you will just get a P/N as a place to start. If you want to build your own speakers then :) we really have a lot of leeway on which amps and how much power since you can select extremely efficient speakers which will NEVER need half a kilowatt of power to blow the dorms down.
My guess for an amp budget is $280 including transformer if you use your miserly ways to find great prices on good components. Guess for speakers is quite a bit more. Probably $100 each for something very economical. Of course if you want you could go for much less on the speakers if you give up a lot of quality in the drivers, but the plywood is going to cost you the same no matter what quality drivers you go with.
Its worth the investment. Really you can make something incredible for cheap. Cheap compared to the same sound out of something store bought, that is.
Ri

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PostPosted: 23 Sep 2008, 09:25 
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I'm almost certain the speakers are 8 ohms. It doesn't say on the units themselves, but on the amp outputs the label says (speakers 8 ohms) I assumet the sub is as well. If I just take my multimeter and test the resistance across the speaker will it give me the right info?

I don't think I want to build my own speakers (yet). Part of my motivation here is to be able to re-use as much of what I already have as possible. Like I said I was quite pleased with my system and wouldn't mind re-building something similar.

Like I mentioned earlier, about the pre-amp, I want to avoid switching the inputs. I want to be able to mix inputs (maybe even surround inputs) together so I can, for example, play Halo and listen to music from my Ipod or computer. With the creative card I have (and it's digital input) I could presumably do so on the computer, but since Creative has horrible, horrible support such a function has been disabled since I bought the card.

Anyway this is beside the point.

I really like what I found here:
http://www.ampslab.com/hx100_dan.htm

If that guy bought the kits from the site at full price, he paid $800+. I don't want to do that, but the design seems perfect for me.

From 41hz.com, the AMP9 (4 channels, 50W@8ohm) is close to what I want to make, but I think compared to what I'm used to that might end up being a little weak.

Ideally I'd like to put something like 5 channels of 70-100W and 1 channel of 150W+ in the same enclosure, preferably off the same power supply.

The folks at 41hz seem to be fond of Tripath chips? I know nothing about what chip is what and where to find them, but I'm thinking I'd like to buy the parts separately from the PCB because I think the kits might be a bit of a rip-off? Unless I'm wrong and the amp chip itself is quite expensive, I don't see how a couple of capacitors (even the bigass 10,000 microFarad caps can't be more than a buck or two a piece??), transistors, etc. can add up to $80. Given the power I want I think the 41hz AMP10-BASIC sounds ideal, and I'd want to buy 3 of them to power all 6 speakers, but I'm heasitant to blow the $240 just yet before I totally know what i'm doing.

I'd like to build the amp before the pre-amp. I've been sure that I want them to be separate units (i.e. so I can re-design my input box without having to futz with the amp, which really only has 1 job to do).

thoughts?


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PostPosted: 23 Sep 2008, 10:37 
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sconeman wrote:
I'm almost certain the speakers are 8 ohms. It doesn't say on the units themselves, but on the amp outputs the label says (speakers 8 ohms) I assumet the sub is as well. If I just take my multimeter and test the resistance across the speaker will it give me the right info?

Yes, you can just stick the DMM on the input/output of the speaker to get Ohms. This matters, but not a lot. What matters is the efficiency. For "efficient" speakers, and lets define that at >90db at 1meter with 1Watt, you can get away with...... drum roll... one watt. Seriously. So 560W is silliness and unnecessary. Plus it gets expensive. Lets be fair and say that the speakers they sold you are about 84db per watt at a meter away. For each increase of 3db we need to double the last wattage. So, 87db is 2watts and 90db is 4watts and 93db is 8watts and 97db is 16watts and 100db is 32watts. I think once you hit 32watts requirement you really probably have more power than you need to get some incredibly loud sound out of almost any speakers. Imagine 32watts into a 100db per watt and one meter speaker. The speakers would walk across the floor.
I know one watt sounds crazy, but many many tube amps use less than one watt and you can get very respectable volume into efficient speakers. But, we are not talking about tube amps and we are probably not talking about efficient speakers. We are probably talking about something from Peter Daniels at audiosector.com or chipamp.com or 41hz. There are a few others. Using the LM3886 chip (you can get it for 3.50 each channel at apexjr.com) is a great great choice. The sound quality is spectacular for the price. You can buy boards for, I think, $6 each at chipamp.com. The power supply will be a bit expensive cuz of the transformer. Try to find a cheap 18V toroidal transformer with, for 6 channels, probably a minimum of 600VA. You could give or take a few hundred VA on that but overkill is a positive thing with the transformer and if you can find one that gives closer to 800-1000VA its going to make a nice difference in punch and not a huge huge difference, but a noticeable difference, in price. Try to keep the ouput voltage from minimum 16V to max 24V.

Quote:
Like I mentioned earlier, about the pre-amp, I want to avoid switching the inputs. I want to be able to mix inputs (maybe even surround inputs) together so I can, for example, play Halo and listen to music from my Ipod or computer. With the creative card I have (and it's digital input) I could presumably do so on the computer, but since Creative has horrible, horrible support such a function has been disabled since I bought the card.

I suppose you could switch two inputs "ON" and have a volume pot for each input. GIO does this make sense? I think it could work fine for your Halo plus music option.


Quote:
I really like what I found here:
http://www.ampslab.com/hx100_dan.htm

I looked at that and $800 seems very accurate. The enclosure/heatsinks/transformers alone are going to hit at a minimum of half of that cost. Enclosure probably around 70, heatsinks about the same, transformers maybe 80 each for the biggies and 30 for the little guy. My estimates are probably accurate but I tend to shop for best price ALL the time and find deals. Heatsinks can really add up if you cant find a good ebay deal on them.

Quote:
From 41hz.com, the AMP9 (4 channels, 50W@8ohm) is close to what I want to make, but I think compared to what I'm used to that might end up being a little weak.

50W is going to be great per channel on almost any speakers. The commercial marketers like to WOW you with high wattage that is either unnecessary or NOT there. 50W is not weak by any means.

Quote:
The folks at 41hz seem to be fond of Tripath chips? I know nothing about what chip is what and where to find them, but I'm thinking I'd like to buy the parts separately from the PCB because I think the kits might be a bit of a rip-off? Unless I'm wrong and the amp chip itself is quite expensive, I don't see how a couple of capacitors (even the bigass 10,000 microFarad caps can't be more than a buck or two a piece??), transistors, etc. can add up to $80. Given the power I want I think the 41hz AMP10-BASIC sounds ideal, and I'd want to buy 3 of them to power all 6 speakers, but I'm heasitant to blow the $240 just yet before I totally know what i'm doing.

Hes fond of them because he is good at designing around them and because the other chips that are popular have audiosector and chipamp already doing a better than anyone else job at designing for them. I think a lot of the DIY kit guys try not to step on each others toes since there is not a lot of money to be made selling kits to a very small public.
The chips are not expensive and the caps can be had for 1.99 each 12,000uf 50V at apexjr.com. Best deal on the net per microfarad.
With a kit you really dont have to know what you are doing. You just have to be safe. $240 is a good deal for that much power and that many channels. You will spend that much in time and frustration doing it any other way, however both ways will be fun and rewarding and I dont think that even if you were as frugal as I am that you could get away with less than $240 for that many channels including pcb boards.
Remember that the AMP9 kit does NOT include power supply. You can either use two car batteries to get 24V and recharge them regularly or you can build a power supply which will NOT be cheap even building it on the cheap. Lets see...
If you go with probably the least expensive toroids I can find you would use http://www.antekinc.com and pay about a penny per VA.. Thats cheap cheap cheap. So lets say only $44 for each of 3 AN4218 toroids. Thats 400VA each toroid with double secondaries from each for one set of secondaries for each channel. so $132. You could go with one AN8420 for $84 but it has 4 secondaries. Not a big problem, just a preference for one set of secondaries per channel.
We need caps. At 1.99 each for 12,000uf lets say 16 of them for 32 plus shipping. Luckily you will be buying LM3996 from the same guy. Saves on shipping and overall cost. 6x3.50 gets 21. Rectifiers are 2.50 each from apexjr so we need 6 of them for $15. Various resistors will run a few more dollars and some wire is another few bucks.
On/Off switch maybe $2, plug $2, Fuse holder $1.50, snubber caps for power caps and rectifiers add approx $10 could be lots more or less depending on what quality caps you use, but $10 is nice number :)
Enclosure... maybe build your own but I have been using wood enclosures and if I were using metal I would probably not have so many grounding problems. Premade metal enclosure. I think you could go to the local electricians store and get a switch box that would fit all of this, but it wont be pretty. However, you might get away with $50. Other than that probably upwards to $70-$100 for something pretty to house 3 transformers and closer to $50-$70 for one.
So lets guess that if you do most of this yourself you are into ~$225 for power supply without the enclosure. The kits are dependent on the supplier but we can guess that you are at a minimum of $240 and thats a fair price. You dont need much in the way of heatsinks for each chip, but we need to remember that the kits do not supply enclosures, switches, wires, fuses in most cases, RCA inputs and outputs, speaker outputs, or heatsinks.
So it is entirely possible to run into about $600 for 6 channels.
Somebody correct me if you think my numbers are crazy. They sound fair to me.
Ri

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PostPosted: 23 Sep 2008, 12:23 
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sconeman wrote:
I really like what I found here:
http://www.ampslab.com/hx100_dan.htm

Dan is a member here. I'll bring this to his attention.

For switching if you need just two inputs go with a normal switch. If you need a bunch you can get a rotary switch. I have yet to find a rotary switch that I am happy with.

Cheers

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