DIY Analog-to-Digital Converter project.Audio measurements tool

[klewis]

Originally Posted by jackinnj

Here's mine:

Jack,

I'm thinking of making one myself. Did you use the +-7.5 volts to run the opamps as well? The ap note isn't clear on this point.

Thanks

Ken

[luvdunhill]

One more thing, I know Frex is busy but perhaps this will help others. The Tent clock doesn't really fit very well. You need to move the 10uF capacitor off-center of its pads, and tilt the clock to avoid an inductor and capacitor. See pictures.

Regardless, the clock will make contact with the metal casing of the input transformer. I'm hoping this is okay, as there is no other way around it that i can see. Anyone know for sure if this is okay?

[jackinnj]

Originally Posted by klewis

Jack,

I'm thinking of making one myself. Did you use the +-7.5 volts to run the opamps as well? The ap note isn't clear on this point.

Thanks

Ken

I used "D" cells, a pack of 5 on each side.

In my case, it was very important to shield the oscillator, so both batteries and the PCB were housed in a big Danish cookie tin.

[klewis]

Originally Posted by jackinnj

I used "D" cells, a pack of 5 on each side.

In my case, it was very important to shield the oscillator, so both batteries and the PCB were housed in a big Danish cookie tin.

Thanks Jack. I get the strong sense that you love Danish cookies .

[EUVL]

Just finished my oscillator.

Battery powered, Lemo2B for balanced output. Rest is standard.
At the moment -130dB H2 limited by noise floor of spectrum analyser.
Shall measure again in 2 weeks when I have access to an AP.


Thanks for the PCB work,
Patrick

[luvdunhill]

Patrick, looks good! Do you anticipate any problems due to the two halves of the battery pack not discharging at equal rates? Or is the on board regulator enough to deal with this?

[EUVL]

a) The oscillator has pure AC output. My test with lab supply suggested that consumption was equal for positive and negative rail.

b) 20 AAA alkaline batteries cost 3 Euros and will last me for hours. So even if they are discharged unevenly, just replace new.

c) I don't think I'll be switching them on very often.

Too many advantages with batteries IMHO.


Patrick

[PB2]

Originally Posted by ghg

Hi Frex

Impressive pcb work, fine.

Maybe you are looking for something readymade, and possible unbeatable, take a look at TI's PCM4222EVM ( US $ 149,-- +shipping ).
You just need a dual 15V and single 5V powersupply.

Here a FFT; source Krohn-Hite 4400A, both units SLA battery driven, PC interface RME-PAD via AES/EBU.

Does your KH4400A have any mods since most people quote .0001 - .0003% distortion for that unit?

[ghg]

Well, let's remember:

1. SLA driven, to get rid of 50Hz artefacts and cross IM.

2. Calibration of the AGC fet section according to the service manual,
available at Jan Dupont's great site.

3. Replacement of the output level pot, got a 10 turn Bourns there.

Getting the 4th zero in THD was the "sweet spot" in connecting the KH4400A to the TI ADC eval board. So, even a slight change of the volume level increases THD to 0.000x. At least this is THD, not THD+N; did 10^6 FFT points to minimize the noise part.

BR

Gary G.

[PB2]

I see, makes sense, thanks.