Basic Technical measurements for Amps ?

Hiten

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Hi all,
Are there any basic technical measurments required for DIY made amps or vintage amps ? I read some where in this forum that Distortion analyser is basic measurement. Are there any other basic/critical measurements to see 'efficiency' of circuits/amps ?
Thanks
Hiten
 
Kaushik Thanks a lot

Cranky, The reason for asking is ...
I already have a vintage system running. But I plan to build a moderately good system. Budget constraints and lack of audiophile ears have made my choices very easy. F5, Tripath and Gainclone got me interested and I am leaning towards gainclone more despite knowing they may have few shortcomings, because I like minimalist approach very interesting (less complicated the audio signal travels ~ less problems). So my query was for if I may build one I was curious to see if basic things required by amp is fulfilled or not, if not can they improved a little bit ? And also that knowledge would be handy for vintage amps.
I think a perfect amp meeting all specification/criteria is not possible. If possible they would be dull and lifeless. Only circuit design idea implemented as work of art ignoring or compromising few things which are not important can be a good amp.

Few more questions Cranky & Kaushik :D
1) Is gainclone class a amp ?
2) Is this hack/DIY possible ? (Aim is to discard CD Player/Hard Drive based source)
Taking technical information from data sheet of microprocessor used, can Digital out be taken from Portable Touch Screen Media Player by opening it.
Thanks
 
hitensitapara ,

unless you are not opening an audio company or writing a book stay away from measurements. simple tests of a variety of signals you can see on scope and determine how the amp is handling them.

you can check the respnse of different power regulators... and decide on the best one.


On more reason is measurements does not always indicate
final SQ .Measurements will distract your mind from listening to music too !

However you can plan a speaker setup and do some measurements,(did not explore what can be done)
A diy interface for soundcard is here Soundcard Interface

the DIYA thread:Test & Measurement interface for Soundcard - diyAudio

Nice analysis of gainclones here ADX Electronics - Why Gainclones work
 
unless you are not opening an audio company or writing a book stay away from measurements. simple tests of a variety of signals you can see on scope and determine how the amp is handling them.
you can check the respnse of different power regulators... and decide on the best one.
Hi Kaushik, :) No No I am not opening a co. nor am I that finicky about measurements, just few basic things like you already have mentioned.

I did not understand what you meant by eliminating source - where is the music going to played from?
Sorry Cranky, I did not made my self clear. What I meant was since Portable media player can play wav/flac files can Digital out be taken from inside bypassing internal DAC. Because I have seen portable Media player with line out but no digital out... Idea was to store all music files in wav format in media player take digital out and feed it in to external ~DAC to amp.
You will need some sort of attenuator to control the volume if you don't already have a preamp.
Why cant a high quality pot be used instead of attenuator ?
 
So yes, you can make it work if you know what you're doing.
A used chinese cheap touchscreen player is accessible, will be interesting to look inside.

You can also use a SPDIF transmitter chip to convert I2S to SPDIF, and then stream to a readybuilt DAC of your choice. The CS8404 does this pretty well to about 24/96KHz, newer chips will even do 24/192.
As most players have USB interface I was wondering if with some firmware/software it can be used as digital out ?
On the net I have seen some DIY guys take digital out (I2S ?) from SD Flash memory chips but were too technical.
dsPIC33 and SD Card WAV to I2S, SPDIF Player "Ultimate
 
1. Output power into 8/6/4 and if possible, 2/1 ohms

2. For Class AB amps, crossover distortion

3. Harmonic distortion - 2,3,5,7,9,11 minimum across entire bandwidth at various power levels. THD = sum of 2HD + 3HD usually at 1KHz, not sufficient indicator.

4. Intermodulation distortion

5. Slew rate

6. Bandwidth

7. Output impedance/damping factor

There are lots of others, but the basics are right here. If I was finicky, I would look at graphs of THD versus power for different loads, as well as clipping behaviour and THD as a function of frequency.

Measuring all of this is a little difficult for the average DIY'er and most of it has to be interpolated.

I'm curious to know why you asked...

Hi Cranky,
Allow me to go a bit off topic here... It is commonly known that AVR amps costing 25k do not have the same SQ as Stereo Amps costing same.

1. Can the factors mentioned in above points, be considered as indicators of SQ. If yes, then can it be safely assumed that AVR measurements for these factors are inferior to Stereo amp measurements?

2. The main definciency that I found in AVR SQ is that some rich harmonics present in source-signal are altogether missing in their speaker-out signal. Is there a measurement-technique that measures how many (%age) harmonics go missing at the AVR amp speaker-out compared to harmonics in source-signnal?

request you reply to above.
Thanks in advance,
Regds,
 
Try some ready solutions like lossless SD card player
QLS QA-550
Yes Kaushik, That looks good.
Discussion:
Lossless SD-card player - diyAudio
Thats good read. Has many extra links also. will read at leisure. Thanks a lot
Hiten
 
inferior to Stereo amp measurements?
It is not so simple. ...

And yes, there is electronics that can go that low or even lower, mostly used in medical applications - where distortion can really be fatal.

Hi Cranky,
Thanks for the detailed clarification. I guess for the regular music enthusiast there's only audition-option to make judgements... numbers may actually mislead... (...as I found belatedly that a Stereo amp having higher THD can actually sound better than the AVR having lesser THD)

Regds,
 
Any element that produces sound, apart from a tuning fork, generates different harmonics along with the fundamental.

Hi Cranky,

Even a tuning fork has higher harmonics in addition to the fundamental frequency. Any energy carrying signal in this physical world necessarily is a combination of pure signals each comprising of a particular frequency. This composite signal travels with what is called the 'group velocity'. In the case of a tuning fork, if it's struck gently, it produces sound conprising of a fundamental frequency and in general many other harmonics. However, because of the construction, the higher harmonics die out to inaudible level (not strictly zero level though) much quicker than the fundamental. That's why when using a tuning fork, one has to wait a short time before actually using it as a refernce frequency.

The experiment and the problem described in this site (tuning fork and harmonics) would actually show also the harmonics. The minimum length for resonance in the air column in the tube will correspond to the fundamental mode. But there will be larger lengths of the air coulumn where there would also be resonances if the expt can be done very quickly before the harmonics die out too much.

Regards :).
 
Kaushik,
Read upto page 15 of the link you gave. After that it was getting more and more technical so stopped reading further.
Post #60 on this page Lossless SD-card player - Page 6 - diyAudio explains what the guy "ecdesigns" wanted to build, he built that thing (solid state media player) from bottom up. While I was thinking of hacking readymade touchscreen media player. Just imagine a memory based touch screen wav source.. how convenient that would be.
But I think CDP Manufacturers and audio Cos. will not allow such product to be commercially available.
 
No, you cannot use the USB connector or the interface. The USB on a media device is a slave, whereas to use a USB DAC you need a host controller.

Host controllers are found on devices like the WDTV or routers like the Asus N13 etc, which can recognise and control a hard disk or printer.

With custom firmware it is possible to get that port to do pretty much anything (it is beyond the scope of my knowledge though), but with a media player you cannot.

And then there is USB On-The-Go - Wikipedia, the free encyclopedia

Wonder how many devices implement this ...

Cheers
 
is there any mean to measure the output of woofer pre out from avr. if i use a multimeter what parameter should i look for to know that avr pre out is working fine.
 
Kaushik,
Read upto page 15 of the link you gave. After that it was getting more and more technical so stopped reading further.
Post #60 on this page Lossless SD-card player - Page 6 - diyAudio explains what the guy "ecdesigns" wanted to build, he built that thing (solid state media player) from bottom up. While I was thinking of hacking readymade touchscreen media player. Just imagine a memory based touch screen wav source.. how convenient that would be.
But I think CDP Manufacturers and audio Cos. will not allow such product to be commercially available.

You can make a easy to use player.. but the hardware for decoding,clock sections must be premium grade as well as the overall design ... how the audio data is picked up and processed .



That is why say creative mp3 player and cowon have drastically different SQ.

Even though the diyAudio SDcard player sells about 5k
but it is not yet exatly replacing audioCD player ...what may be the reason..?I guess the dsPic chip used to do the
decoding(in the SD card player) etc is not that good .
There are many diy flac players with other chip .. but all lack something...
 
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