[Avro_Arrow]

Here is a little amp I just finished. My first double sided board.
Includes a voltage trigger LED to let me know when battery
voltage is low.
 
Cheers!
 

 

 

 
 

 

[qusp]

 
 
well i've been getting into the breadboarding action. i needed to build an amp to amplify the 1khz sine AC mVrms voltage difference between 2 points in a mosfet matching/testing circuit to get accurate gm transconductance matches, at operating conditions that match the final cct they are going into.
 
one of the points is well above ground so i couldnt use my hp3400a directly, without risking destroying the input with a dc transient and also without loading the circuit under test. my other meters simply arent accurate enough right down low in the ac mVrms range to be useful for this purpose.
 
the 1khz sine signal is fed from my ipad using a signal/tone/noise generator app, sent via a traffo coupled lod (to stop the virtual ground in the ipad from effecting measurements) to what could best be described as a mono cmoy on steroids and this is fed into basically 1 arm of the pass D1 mosfet IV stage (the board these are going into as a tweak from the standard vds matched units i have in there.
 
the measurement amp as you can see is basically an instrumentation amp, i could have just bought a single INAXXX chip, but i wanted to be able to control all parameters. in this case its set for unity gain non inverting input and 100x differential gain in the second stage where the voltage at the mosfet source is subtracted from the voltage at the gate and 100x gain added to the result. i then measure this result with the HP and divide by 100 as part of applying the transconductance equation in the bottom corner. the gate voltage path does not have a cap on it like the source side, because there is no dc to speak of coming from the signal source+amp, the source side does though, so there is a 10u film cap on that side. the HP is AC coupled also
 
i also wanted to work through the whole process of drawing out the schematic on everything and planning it from beginning to end, it also had to meet the condition of being built nearly 100% from my parts bin. by using good chips, measuring the leads out carefully, using chips with good characteristics; low input offset etc. matching the gain setting resistors by hand and using 2 in parallel for each position and decoupling all supplies in a pretty over the top manner; i have been able to get pretty high accuracy, even at 100x gain
 
and it was pretty fun in the end
 
sorry for going on a bit in a gallery thread, but thought perhaps some of you guys might be interested in the details of this one
 



 
but now the not so fun bit
 

 

 

[qusp]

in the pics it was set up with the same 3Vrms signal fed to both inputs to test accuracy, i'll dig out the results if anyone is interested, the grass was in the range of 3mV on the HP with the 100x gain, so 30uV error. i can live with that

 

[Gregoirepat]

Here is my B22 from AMB Lab.
I specify that I'm 18 years old

I built it with an active ground (3-channel)
I didn't finish because I haven't enought money for the chassis and I would realize something really beautiful.

Sorry for the spelling, I'm French
 

 
http://nsa25.casimages.com/img/2011/04/29/110429105901975475.jpg
 

 
http://nsa25.casimages.com/img/2011/04/29/1104291059238056.jpg
 

 
http://nsa26.casimages.com/img/2011/04/29/110429110012737548.jpg

 

[MrDavis]

Very impressive!  I didn't get into DIY until I was 44.

 

[Tinola]

nice build! I wish I can build my own beta 22. I don't have the skills yet. Gonna work my way up before diving in.

 

[mapleleafs]

I just finished undergrad, and so I finally had some time to make a CMOY. Here are a couple pics:
 
 

 

 
I for the most part followed the Tangent tutorial http://www.tangentsoft.net/audio/cmoy-tutorial/.
 
A few remarks:
 
- The amplifying caps that I got from DigiKey were quite a bit larger than I expected them to be. As a result, I had to adjust Tangent's layout slightly, and I wasn't able to fit a pot in my enclosure (well I possibly could but it would be a very tight fit).
- The hardest part of this project (bearing in mind that this is my first DIY of any sort) was probably the soldering on the prototype board.
- The amp definitely seems to make music louder, but its difficult to say for certain that it sounds better. I'm not sure how well PortaPros overall react to amping. (I don't have any high impedance cans to test these out on 

 ). Perhaps in the future, I'll play around with higher capacitance capacitors to see what effect they have on the sound.
 
Overall, it was a pretty fun project. For anyone who's hesistant to make a CMOY (especially if you have limited DIY experience), I say go for it!

 

[Fred_fred2004]

Mucking about with a tin and an Oatley K272A
 
 


 
Cheers
FRED

 

[tranhieu]

Quote:

Here is my B22 from AMB Lab.
I specify that I'm 18 years old

I built it with an active ground (3-channel)
I didn't finish because I haven't enought money for the chassis and I would realize something really beautiful.

Sorry for the spelling, I'm French
 

Nice build! I built my b22 last xmas and I'm nearly 20 now. Time flies 
 

 

[Gregoirepat]

Quote:

 
Nice build! I built my b22 last xmas and I'm nearly 20 now. Time flies 
 

Yes ^^ I built it last year !

 

[mmayer167]

^ that tin is sweet! you should paint it like the magic school bus    cheers, M

 

 

[Avro_Arrow]

Nice one Fred_fred2004!
I wish I had your inventiveness for the "amp in a tin".

 

[El_Doug]

Finished turning my Charlize T-amp into a standalone headphone amp   Sounds very nice indeed with the LCD-2s
 

 

 

 

 
 
Now I just need to put a knob on the pot  
 
 
edit:  I need to learn how to use a camera.  Using my "point-and-shoot" with a flash is showing blemishes that I swear simply do not exist in real life!  The front of the amp looks fine in the "straight-on" photo, but looks like hell in the angled-shots  

 

[MaxW]

Quote:

Finished turning my Charlize T-amp into a standalone headphone amp   Sounds very nice indeed with the LCD-2s
 
Now I just need to put a knob on the pot  
 
 
edit:  I need to learn how to use a camera.  Using my "point-and-shoot" with a flash is showing blemishes that I swear simply do not exist in real life!  The front of the amp looks fine in the "straight-on" photo, but looks like hell in the angled-shots  

Very nice! Where did you get that case? Is it from vt4c? Was the front completely blank when you got it?
 

 

[revolink24]

Here is my B22 from AMB Lab.
I specify that I'm 18 years old

I built it with an active ground (3-channel)
I didn't finish because I haven't enought money for the chassis and I would realize something really beautiful.

Sorry for the spelling, I'm French
 

 
http://nsa25.casimages.com/img/2011/04/29/110429105901975475.jpg
 

 
http://nsa25.casimages.com/img/2011/04/29/1104291059238056.jpg
 

 
http://nsa26.casimages.com/img/2011/04/29/110429110012737548.jpg

You're not the only 18 year old DIYer.