*** The DIY Audio Thread ***

[Dr.EM]

I posted this in the GD electronics forum, but it's more appropriate here I think. My new mini desktop amplifier




Based on LM1875 chips. Uses external PSU this time, to reduce size and noise. Measured at 2x11W RMS output. Full details and build log:

http://www.diyaudio.com/forums/chip-amps/168553-lm1875-miniature-desktop-amplifier-build.html

 

[Dr.EM]

This thread seems to be a bit unpopular now! Anyhow, the speakers to go with the above amp are just finished:

Full details here:

http://www.diyaudio.com/forums/full-range/165604-unusual-design-desktops-wedge.html

 

[Stag]

What's with the wedge shape?

 

[Dr.EM]

Well, to keep it brief, the slim design keeps the speaker (and side ports) near to the rear wall, meaning they get full acousic baffle step (boundary reinforcement), as per studio speakers mounted in the wall. This is important as it's 6dB of bass "free", no expense of driver excursion or power handling, also theoretically less transmission to other rooms as there is less energy into the system for a given low frequency output.

The wedge shaping angles the drivers toward the ears and also reduces parallel surfaces inside the enclosure and hence cuts down standing waves. The driver location on the baffle is chosen for lowest simulated baffle ripple, low Q and low amplitude. Design is ported, about 1.9L internal volume, Monacor SPH-30X driver, a relatively high efficiency driver for this size (3") at 87dB/1W, good for keeping power compression reasonable in those tiny voice coils.

Sound wise, very good actually, a bit like giant headphones at the desk location! I actually get too much low with them next to the wall and EQ improves this, again lowering excursion and power

 

[Founder_film]

I really like them! Good to see something different for a change. I recently gave my Dad my LM1875 amp. Might have to build another one with some speakers. I am completely lost when it comes to speaker design though.

Just ordered the rest of the parts for a Starving Student, hopefully will be building next week. Can't wait, been ages since I have built something.

 

[Dr.EM]

Thanks!

Yes, the LM1875 makes a really rather decent little amp! I was originally going to do a small discrete class AB design, but I destroyed it setting the bias . Cable reading bias had broken inside and I adjusted it to full not realising, typical. Not dissapointed with the LM1875 anyhow, saves space inside too

Keep us updated with your SS build

 

[daz]

Awesome project

What do they sound like in comparison to speakers you've bought?

 

[Dr.EM]

Rather enjoying them actually! Remarkebly detailed sound, probably owing to the lack reflective surfaces nearby/thier close proximity to me; surfaces nearby like the wall are 'designed in' and the driver is a fair height from the desktop. The light cone also helps with resolving fine/fast details and no crossover ensures excellent phase coherency, vocals sound good.

The sound isn't too coloured but is slightly warm, there is no semblance of these being small speakers, which was my main aim. Despite the lack of low bass the lower midrange is very full, whereas in a lot of 2.1 and many small 2.0 setups it isn't. Kick drums still hit plenty hard enough and bass lines (especially electric bass guitar) come accross fine.

Stereo effect is strong and "involving" but at this proximity you don't get much in the way of imaging/3D space, the sound is a bit more like with headphones, very direct, not so spacious.

Comparing to other PC speakers I've heard (various, including the BOSE 2.1s, wasn't keen on those) these are the best overall, don't know if it's a fair comparison though, these sit somewhere between Hi-Fi and PC systems. Just about Hi-Fi quality, but without such deep bass, however also designed to be used at close proximity which 2-way Hi-Fi speakers arn't so good at. It's a nice combination of both worlds for me

 

[daz]

Well that sounds really cool. I did take a look at your thread on that other forum... looks like it took a lot of work to put these together... so i suppose from that perspective you get out what you put in.

 

[Founder_film]

Started work on my SSMH yesterday. Just waiting on the caps I ordered to finish all the soldering:

 

[Yaka]

love that amp, still using mine with my grados.

 

[sketch145]

Some cracking stuff in this thread, you guys have inspired me to have a go at some diy audio gear. I'm going to start with a chip amp and a couple of 2 way cabinets and then go from there I think (it's been ages since I've had a decent audio set up, I'm using logitech x210s at the moment) I'd love to try a tube amp some time in the future too. I'll likely be frequenting this thread to beg advice from you guys when it all goes wrong, I'm a total noob at all this audio stuff .

 

[Dr.EM]

Best of luck with it! Chip-amps are quite straight-forward if you're using bought PCBs (reccomended), but check about grounding, which is one potential pitfall.

http://www.diyaudio.com/forums/chip-amps/128561-chip-amp-power-supply-beginners-guide.html
http://www.diyaudio.com/forums/diya...udio-component-grounding-interconnection.html
http://sound.westhost.com/earthing.htm

Post here or on DIY Audio if you have any questions on it.


A 2-way speaker is still hard to get right. Fortunately, there are many, many existing great DIY designs to choose from:

http://www.zaphaudio.com/
http://www.humblehomemadehifi.com/
http://www.troelsgravesen.dk/Diy_Loudspeaker_Projects.htm

to link just a few pages. Also lots of designs on the DIY Audio forums and HT guide forums

 

[sketch145]

Thanks for the links, I've come across a couple of those sites when googling for info. I've only had experience with DC circuits before now so I'll be enlisting the help of my grandfather who has worked most of his life as an electrical engineer so he should be able to make sure everything is properly grounded and that I don't fry myself in the process.

I've also registered on the diyaudio forums so I'll likely be asking for help there too.

Out of interest what are the main reason you recommend bought PCBs? I was planning to lay the circuit out on breadboard and then solder it permanently onto stripboard. Is the main advantage just the ease of laying things out or are there other benefits (I guess an etched board would be smaller for one thing)?

 

[Oh Ed not again.]

Read through a couple of pages of this thread, and I'm starting to get the itch to build something....

I'm after an amp and a couple of speakers, nothing too crazy but they'll live under the telly. So ideally with 3 RCA inputs, and bass/treble control etc.. Are there any kits out there that meet this criteria?

Also does anyone have any recommended reading/shop links etc..?

Cheers in advance (/goes back to thread for more reading)

 

[Dr.EM]

Out of interest what are the main reason you recommend bought PCBs? I was planning to lay the circuit out on breadboard and then solder it permanently onto stripboard. Is the main advantage just the ease of laying things out or are there other benefits (I guess an etched board would be smaller for one thing)?

I made an LM1875 amp on stripboard (above few posts), it is possible, but any higher power amp (3886 etc) I wouldn't reccomend it. You need high current capacity tracks which stripboard is not, and the pin arrangment isn't really suitable on these devices, it's 2 staggered tiers usually. I could carefully bend the 5 pins of a 1875 to fit, but this is impossible on a 3886. You also have parasitic capacitances to deal with which can cause oscillations or other poor performance.

Options are bought PCB, which is tidy and easy, or point-to-point when using 3886 or other larger package devices (ie, power over 15W needed). Some PCBs here:

http://www.chipamp.com/

 

[Founder_film]

Hi all. Finally got round to finishing my SSMH today after a lot of annoying casework. Here are some photos:

Okay I have turned it on and got some sound out of it. First impressions, it sounds very good. However I have some concerns.

There is a hum coming through my test headphones, it's low and it nearly goes away if when I touch the volume knob and headphone jack. Is this a grounding problem?

Also one of the tubes glows brighter than the other. Is this normal? The brighter one looks a bit too bright to me. Is this bad? What could be wrong?

 

[Yaka]

very nice build,not sure on the brighter tube thing but the for me went away when i grounded the pot on my beta ss board like this

 

[Founder_film]

I have grounded my pot. So not sure where the hum is coming from...

I don't want to run the amp for too long incase the brighter tube thing will damage it.

 

[Dr.EM]

Nice build, I expect those large valve holes were hard to cut? I actually use flat wood bits for such jobs, but it's not reccomended

Is the metal casework grounded? An internal photo may help