*** The DIY Audio Thread ***

No, i dont have any plans for the soha II. It is a step backwards from the Bijou.

If i build anything in the near future it will be a kt88 valve amp for my speaker setup.
 
Just been playing with my own DAC OPA2132 output stage. I've managed to get it sounding brilliant, apart from a small backrgound buzzing. It's small enough to not be audible at low volumes, but when I touch the volume knob or turn it up I can hear it... slightly.

I understand this could be a grounding issue, any tips for how to eliminate it?

I've decoupled the op amp's +-12V supplies to ground with 100nF caps.
 
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^ What amp are you using?

I stuck my Amp9b and SMPS into a chassis today, and found I'm getting something similar when using my DAC as a source - lots of background noise. When I use my mp3 player from batteries I get no noise at all, so it's probably some sort of ground loop between amp9 and dac.

I've connected the chassis to mains earth, but I'm still getting it, next I'm going to try shorting the audio in ground to the chassis and see if this helps. PA amps have something similar (a "ground lift" switch), so hopefully this will eliminate ground noise.
 
I'm using the OPA2132 as a headphone amp. It's on a separate breadboard.

It seems to have fixed its self now though...
 
I've just figured out my source selector. It's a 3 pole-4 position rotary switch.

The first two poles (A and B) are used for the 2 sound channels feeding the main amplifier. The 4 sources are:

1: Aux in
2: Line in (front panel)
3: DAC
4: DAC

3 and 4 are common - the DAC only has one output.

2 DAC positions are needed because the DAC has two inputs: coax and optical, which I'd like to select between. This is where pole C comes in. The switch below represents position 3 and 4 on the C pole:

dacsourceselectab4.png


The jumper on the left is the source selector on the DAC's PCB.

The LEDs show which source is being used. The 10k pull-down resistor selects COAX when the COAX LED is lit up. Otherwise pin SB is pulled high and OPT LED lights up.

It works perfectly.:)

I spent ages trying to figure this out, and it turns out that all it needed was a logic high or logic low on the SB pin...

edit: a photo of my current testing.

dsc06339mediumzj4.jpg
 
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Nice, looks like a lifty solution, as it will be neater than having a extra switch that toggles between optical and co-ax.

I've found the source of my noise on the amp9b - the heatsink! Well, the chassis and heatsink is grounded to mains ground, but I forgot the amp9b's chip has the heatsink connected to audio ground. I removed the heatsink and no noise at all.

So either I need to electronically isolate the chip from the heatsink, or isolate the heatsink from the chassis. Good job I've got lots of tape. :D
 
I've been thinking about the heatsink issue too. I'd like to stick the Tripath IC and regulator to the side of my cases, but I'd like to keep the chassis as an Earth connection, isolated from the amp's ground.

Mike, what tape were you thinking of? Surely it'd be a pretty good thermal insulator...:p
 
The only tape I have right now is bog standard electrical tape but I think there's something called kapton tape which is supposed to be good.

Right now I almost have my entire heatsink isolated, I'm hunting around for some coated screws as the current ones are the only thing making the connection...
 
Been working hard so the projects have taken a back seat. even now I'm posting on the iPhone.
p4radox you look like you are making some good progress there, what happens to the amp10?
oh adam that tube amp looks damn sexy, how much did that set you back?
 
kit cost £90
case £30
transformer, knobs and rcas £45
bits and bobs £45.

but i now i have enough wire last a lifetime (silver plated copper, teflon covered - really good stuff and i have 150ft).
 
I was playing around yesterday trying to get the LCD part of the volume control kit i bought to work when i made a big mistake - i accidentally shorted two pins on an IC whilst using a multimeter to check supply voltages, resulting in no fewer than two smoke sources and some burnt out tracks... :(. I had a last go at getting it to work today, and connected jumpers between the points, which still gives nothing, so im pretty sure that (at least) one of the ICs is dead, and i dread to think what other bits of the circuit are gone. Not a good way to finnish the holidays, but im still considering buying another and giving it a second go (but that will be it!).

Im seriously considering a gainclone too, although there does seem to be quite a bit of choice. Damian, i am right in thinking yours was the lm3886 from chipamp.com? How does it sound?
 
MikeHunt79 said:
The only tape I have right now is bog standard electrical tape but I think there's something called kapton tape which is supposed to be good.

Right now I almost have my entire heatsink isolated, I'm hunting around for some coated screws as the current ones are the only thing making the connection...
Click to expand...

What about Nylon screws? That's what I was planning on using. Kapton tape looks promising, if a little expensive. I might get it off the bay rather than the fast shop - seems a lot cheaper.

damian666 said:
Been working hard so the projects have taken a back seat. even now I'm posting on the iPhone.
p4radox you look like you are making some good progress there, what happens to the amp10?
Click to expand...

The AMP10 has been abandoned. There was always something dodgy about it, and I didn't feel I could waste any more of my life on it. I've got an AMP10 basic on the way, which should be here tomorrow I hope.

Chrissy - I've made that mistake before. As a general rule - never use a meter on IC pins.:p
 
ChrissyT88 said:
Im seriously considering a gainclone too, although there does seem to be quite a bit of choice. Damian, i am right in thinking yours was the lm3886 from chipamp.com? How does it sound?
Click to expand...

great, its a simple amp with a decent sound. very inexpensive and well worth a go for the new and experimental alike alike.

@p4radox, its a shame, a great shame. keep it close to hand though as in the near future you may have a eureka moment and it will all fall into place.
 
I'll definitely keep hold of it, if only for component scavenging. I'm really upset at having to give up on it, but I think it's the best thing to do really.:(
 
@p4radox - mm.. definately learned from it... pain because it wasnt particularly cheap and took ages to get here. Still, once bitten... (well, hopefully that will hold true!). The worst thing was the smell - i could not get the smell of burnt silicon/copper/pcb out of my nose for hours.. a constant reminder that i messed up! Im really annoyed that i did it - i should have just left it alone - but its too late now...

@Damian - cheers for the quick reply. Im thinking about giving one a go - as you say, they seem quite cheap when buying bits from america. Did you use all the stock parts from chipamp or did you do a recap?
 
p4radox said:
What about Nylon screws? That's what I was planning on using. Kapton tape looks promising, if a little expensive. I might get it off the bay rather than the fast shop - seems a lot cheaper.
Click to expand...
I've got some nylon spacers but they are too small (m3) :( I've ordered some larger ones and they should work.

Yep that kapton tape tends to be pretty pricey, it's a shame they don't sell it in metre lengths.

I've just gaffer taped my heatsink in place for now, ghetto but it works, no more noise or hiss. :) :o I also just got a jolt of 240v plugging my DAC in a minute ago, I really need to put this in a case! :eek: My finger is still tingling! :o

EDIT: Bah, channel one seems to be muted or something, looks like I'll have to sort that when I get rid of the gaffer tape.
 
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you really need to get these things cased up! 240v is enough to kill if you are unlucky. when working on the bijou i wrote a note saying "1 hand only".

330vdc kills, not many second chances at this voltage
 
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