bpribadi 0 Report post Posted October 4, 2004 (edited) In a different, and more interesting approach Let's see how do we see those specs in 'audio' language... if I say amp, means the whole circuit, if I say op-amp, means only the op-amp (let's start with op-amp basic amp first before going to transistor or tube). Let's start from the input. Amp's input impedance doesn't really have impact in sound quality. As long as it is not too low for the source to drive it. I would say, in common, 22 kohm is the practical lowest impedance eventhough it can go lower than that like 10k. Then why not set it very high? Because too high will cause Mr. Noise become significant. Noise is very low power signal, with low impedance, it is powerless, so less interference of noise. Amp's gain. Should be set as low as possible, but still meet the requirement. Why low? Because of gain-bandwidth product (gbp) of an op-amp is constant. For op-amp, the higher the gain, the lower the bandwidth. For audio application, it is normally not critical, because today's op-amp gbp is normally very high, so it will still within the audio range. And for high speed op-amp, the higher the gain, the more stable the op-amp, so it has to be set correctly. For headphone amp, according to my experience (and calculation) gain of 6.6 is sufficient for 32 ohm headphone. For high impedance can, you will need around 10. Don't set the gain too high, as it will amplified the unwanted noise as well. Frequency response. People say that human hears 20-20kHz, true, but higher frequency harmonic is needed to 'shape' the lower frequency. Confuse? For example, a square wave at frequency 10 kHz. If we pass the square wave to a low pass filter with frequency cut off at 20 kHz, the output is not square anymore, the edges will be rounded. The square wave needs all the harmonic frequencies up to at least 10x it's frequency to have a proper shape. Means, 10 kHz square wave need at least 100 kHz bandwidth to be square. So let's take this as the rule of thumb, 10 times 20 kHz, means 200 kHz. Now we see why SACD and DVD-A has higher frequency respone, because we need those high frequency harmonic. The richer the harmonic, the truer the sound. Means acoustic piano will sound like acoustic piano, and you might be able to notice the difference between two acoustic pianos, or two Stradivarius violins Signal-to-Noise ratio. It is true that noise is annoying, but for me as long as it is not audible, I'm happy. Today's components are low noise, so normally we don't really have problem with noise (in audio application). Just make sure to use low noise components, such as metal film resistor, low noise op-amp, low noise OFC cable/wire, etc. And one more thing, keep every path as short as possible. Slew rate. This is one of the most important factor. It is the ability of the amp to reach high voltage in the shortest time possible. The unit is volt/micro second. The higher the slew rate the better the imaging of the amp. With high slew rate op-amp, we can hear more seperation between the musical instruments and singers, and we can locate their position easily. Output impedance. Should be as low as possible. It will determine the damping factor (load/output impedance). The lower the output impedance, it means the amp has more control over the load. Sound wise, it sounds tighter bass, and more accurate treble. That's all for now, I hope you find those information usefull to start amp DIY. Cheers! Bram Edited October 4, 2004 by bpribadi Share this post Link to post Share on other sites
heady 0 Report post Posted October 4, 2004 Good stuff Bram. Lot's of hardwork there. Share this post Link to post Share on other sites
Q00 0 Report post Posted October 4, 2004 Nice...that post itself should be a sticky! Share this post Link to post Share on other sites
clemo 0 Report post Posted October 4, 2004 Guru Bram, Read it twice, so we select op-amp and components based on above mentioned. what's next. Share this post Link to post Share on other sites
bpribadi 0 Report post Posted October 4, 2004 Alamak... I feel old Don't call me guru lah... I just share my knowledge. You know these days, no company needs EE so I rather share it with you guys before it fades away from my brain Next will be the design phase. I recommend you to read Tangent's guideline to build CMoy. It is very good. http://www.tangentsoft.net/audio/cmoy-tutorial/ Then start to list down all the components, and buy them. After that we can arrange a small meeting for the assembling session Hopefully we can find place and time for it. Share this post Link to post Share on other sites
clemo 0 Report post Posted October 4, 2004 In fact i have tried doing the cmoy but unsuccessful. Therefore need help. Maybe i am not very good at electronics stuffs cos' i'm from a mechanical background. BUT i love music and very much a DIY person. So i would like to try, it just gives me the statisfaction 'HIGH' Share this post Link to post Share on other sites
aaa 0 Report post Posted October 4, 2004 In fact i have tried doing the cmoy but unsuccessful. Therefore need help. Maybe i am not very good at electronics stuffs cos' i'm from a mechanical background. BUT i love music and very much a DIY person. So i would like to try, it just gives me the statisfaction 'HIGH' Don't scare me lah... I have no background of any kind and is building a PPA clone as my 1st time. in fact that's why I choose OPA627 than OPA637. already invested so much into the parts, if later cannot work will die... Share this post Link to post Share on other sites
clemo 0 Report post Posted October 4, 2004 Better get instructor before starting your project then or try first ...fail try again and again..... I have been in this road before, maybe is that my basic is not good enough. Can handle welding but not solder. Share this post Link to post Share on other sites
bpribadi 0 Report post Posted October 4, 2004 (edited) I have a bad habbit which is doing DIY with Big Bang method. Big Bang is, you solder everything, finish then you try it out. The bad thing from Big Bang is, when it is not working, it will be more difficult to trouble shoot. But I also have good habit to compensate my Big Bang style, which is very long planning. I plan my amp very long, much longer than any other phases. I print out my board layout, look at it again and again, bring it with me to MRT, etc. So, I would say, to avoid failure with expensive components, we can share our schematic and board layout in this forum, probably somebody else may find the fault on it, thus save us from failure Next year I will start PPA clone with 5 buffers per channel Cause soon I will receive free OPA637 and OPA627 from TI I will start the drawing soon. Edited October 4, 2004 by bpribadi Share this post Link to post Share on other sites
Guest drumma Report post Posted October 4, 2004 1) clemo aka Clement - 98298697 2)drumma aka Li Ji - 97656912 3) Share this post Link to post Share on other sites
heady 0 Report post Posted October 4, 2004 (edited) Bram, 5 buffers!!! I am thinking of buying Glassman's buffer which is diy and cost US$40 for a set of 3 with parts included. Only problem is smd parts! I read on the headfi sites that it is just below the LaRococo buffers in sound quality. I will put up the layout for my PPA clone once I finalise it. BTW - I ordered the OPA from TI last Friday night and got them today!! That's fast! Edited October 4, 2004 by heady Share this post Link to post Share on other sites
bpribadi 0 Report post Posted October 4, 2004 Bram, 5 buffers!!! You know why? Because last time, at Farnell, buying 10 and 8 buffers cost about the same I already have 10x HA3-5002. I will use the free buffer from TI for the ground channel. Now it is different, their price group is for 25 pcs, last time 10 pcs or more the price was lower (much lower). Yup, I got mine also Thanks a lot TI! Share this post Link to post Share on other sites
heady 0 Report post Posted October 5, 2004 bpribadi, there is this guy on headfi who posts a lot and seems to be expert, he said above 2-3 buffer chips, the improvement is marginal. I really don't know but we will know if you built your amp, as we can test adding one buffer at a time and listening. I am trying to save space on my PPA board but to put in Glassman's buffer, I need the space from 9 holes square in the perfboard. So I will end up with the ability to test up to 4 buffers as well. But I don't think I will finish mine before you. I am still tinkering with my pimeta, decided it is too good to put into a tin with only one cap. I am working on adding the full complement of caps and putting it into a bigger casing. Good thing I went modular, no problem in changing. Let's have a session end of the month to listen to our pimetas. Also need to collect the adaptors from you. Regards. Share this post Link to post Share on other sites
bpribadi 0 Report post Posted October 5, 2004 I am still tinkering with my pimeta, decided it is too good to put into a tin with only one cap. I am working on adding the full complement of caps and putting it into a bigger casing. Good thing I went modular, no problem in changing. Let's have a session end of the month to listen to our pimetas. Also need to collect the adaptors from you. Hi Heady, I'm glad you finally gave up the mint's tin casing. No point you spent so much on the components, yet you minimize it's performance by space Put more caps please Yes that the good thing of being modular, but the bad thing is, you can't make the paths as short as possible. Must use a very good jumpering wire between the modules. Let's arrange a meeting sometime end of the month Share this post Link to post Share on other sites
huangyong 0 Report post Posted October 5, 2004 In fact i have tried doing the cmoy but unsuccessful. Therefore need help. Maybe i am not very good at electronics stuffs cos' i'm from a mechanical background. BUT i love music and very much a DIY person. So i would like to try, it just gives me the statisfaction 'HIGH' Don't scare me lah... I have no background of any kind and is building a PPA clone as my 1st time. in fact that's why I choose OPA627 than OPA637. already invested so much into the parts, if later cannot work will die... aaa, if that's your first time, then just buy a PPA board from tangent and try out the soldering work.. at least u can get familiarized with those DIY works. Make the first time a succesful one to increase you confidence Then for the second or third amp, you can try your own layout, just like Bripadi's. I am so glad to see there're lots of forumers here interested inDIY cheers Share this post Link to post Share on other sites