Dx Blame MKIII-Hx - Builder's thread

[vargasmongo3435]

Yep, canonnica is right, take the caps out, plus your heat sink are good enough you want to see what I'm using? is just a plain piece of aluminum bar. lol and is good for now before I order the amplifier chassis, good luck my friend Byron. but you do what ever is the best for you bro.

regards
vargasmongo

[ByronInLawrence]

Originally Posted by Woody1911a1

rule of thumb is to put the heat (mosfets in this case ) 1/3 up from the bottom .

Is that because hot air travels up? I never thought about it. I guess that makes sense.

The fans are to blow air across the surface of the board, including the on-board heatsinks. I am also planning on replacing the heatsinks with taller (50mm) ones. The aluminum dividers channel the air across the board, and shield the board and signal wires from RFI from the power supply. The problem with the fans is that they are 8cm X 8cm, so if I kept them and the dividers, I can only move the dividers about 1cm each. But even without the fans, the tall capacitors and on-board heatsinks will limit how far I can move the dividers. Also, note that there are no vents in this case at all. With the fans, I would only need to cut a few vents near the front of the chassis. Without the fans, I would need to cut a lot more vents to keep cool air coming into the chassis.

Now, if I got rid of the dividers, that would free up a lot of space (with board parallel to heatsinks) and I could keep my fans.

I'm loathe to remove my filter caps, largely because I paid so much for them! They're super low ESR, low ripple, low inductance etc . . . On the other hand, they are overkill, and I just bought 12 LM3886 chips and some monster torroids from the swap meet. Help! I'm out of control!!

I think I'll put the board parallel to the heatsinks, with transistors on the bottom and play around and see what I can do. I can always bend those dividers if I need to. And I can probably get away with 1/2 the filter capacitors.

Thank everyone for their input,

-Byron

[a.wayne]

Originally Posted by ByronInLawrence

I bought what I thought was a pretty large chassis but, as you can see from the photos, I doubt that I will be able to fit all the parts inside of it. The stuff sitting outside the chassis are the bridge rectifiers, the soft start, and two fans.

You can see from the photos that much of the space is taken up by the boards, and all that space above and below the boards is wasted. I'm considering bending the transistors and putting the board parallel to the heatsinks, but that would put the transistors at the very top of the heatsinks, which is not as efficient for heat dissipation as is putting them in the center of the heatsinks. Do people think that this will work?

-Byron

Byron flip the boards upside down and keep the caps, you will appreciate the difference. Myself had to go to monoblocs, due to space issues and heat sink requirements..

[ByronInLawrence]

Originally Posted by a.wayne

Myself had to go to monoblocs, due to space issues and heat sink requirements..

Please post pictures! Monoblocks sounds really cool, and I don't think we have anyone building monoblocks!

My concern is the cost. I already bought this chassis with heatsinks on both sides. I have considered an external power supply - or maybe part of the PS, like the transformers and soft start external.

So many options! But none are obviously best. I don't do well with too many options. I can't juggle them all in my head at once.

I'm glad someone thinks I should keep as least some of my filter capacitors. I think I have bonded, emotionally, with my filter caps.

-Byron

[vargasmongo3435]

He he he that is funny stuff lol "emotionally, with my filter caps"

vargasmongo3435

[meanman1964]

Byron,
What a nice case, can you tell me the dimensions of the heatsinks?

[destroyer X]

About bias adjustment:


- When you cannot decrease the current you should increase the resistor value you have in series with the bias adjustment trimpot

- When you cannot increase the current you should decrease the resistor value you have in series with the bias adjustment trimpot

- Depending the transistor gain and also the supply voltage, you may need to adjust the resistor you have in series with the bias adjustment trimpot.... values suggested worked into the simulator and also worked real life...but replacing transistor model, or replacing transistor by other with different gain, we have to tweak the adjustment once again.... usually the trimpot has range enough to "cover" or compensate these variations...but if you face troubles and cannot adjust....if current is too much high even increasing the trimpot resistance...or if the current is too much low and you cannot increase the current decreasing the bias trimpot resistance adjustment..them proceed to replace the resistor that is in series with the trimpot in order to make it work to your special case.

regards,

Carlos

[AndrewT]

Originally Posted by ByronInLawrence

I bought what I thought was a pretty large chassis

it looks like you developed and built the amplifier while of after you were procuring your chassis.

I suggest you build up an amplifier on a piece of board. Add on all the nice to have options. Look at how it can be packaged. Mimic that package and particularly the way the inter wiring will end up and test again for hum and noise and oscillation. Then decide what size chassis is required.

The fans should not be needed.
DX PCB near but not touching the heatsinks and vertical will save a lot of space. Throw away the internal aluminium panels. They are not achieving anything useful. You can measure their effect before you discard them.

High quality PSU comes before anything else in a power amp. Keep the good caps, all of them. Keep the PSU very compact. Transformer to rectifiers to smoothing cap wiring should be very short. Before you cut the transformer wires. Experiment with rotating the transformers to minimise hum in the two channels. Then cut to final length.

[canonnica]

Back in july while waiting for the boards to arrive, I made a paper model to see how everything could fit inside a given box... Yes, I took an evening "rolling" paper caps and transformers ... But it gave me this (see pic), and now everything is going as planned. Within a week I should be done and I will posts the end result. It's gonna look mucho like the paper model... a tad heavier though.

[vargasmongo3435]

Today I will try that changing the resistor that is close to the pot to see how it react so the adjustment can be acomplish I hope so .

regards
vargasmongo3435