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Old 22nd October 2019, 07:57 AM   #251
FauxFrench is offline FauxFrench  France
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Join Date: Dec 2017
Location: The mountains, calm and quiet.
Quote:
Originally Posted by chermann View Post
Hi FF

yes the LM1875 is a very fine sounding amp.
if you mentioned my lab power supply-yes this should be less ripple but the fans are really loud and its not for listening.
yes i like analytical and very important - good sound stages . this gives me the "live" feeling at home ...and once again: with music like Blank&Jones album "relax edition 4" = electronic this amp sounds very good and the power is really enough for at home to shake the house
testing with other speakers - my kef Q100, open baffle 12/5

i am still hoping to get better sound out of the 1875 -
- PSU - less ripple as possible
- check all original kit components
- set the gain down - what should i do?
- PSRR is at the neg.supply worse - frequency depending (figure 7 ) is here something to "help" the chip ?

to be honest - yes if you look at the data sheet you see what that chip can compared to the others.(attachment) i know that its partly nonsense to buy a kit about 2 € add some components (+6€) and expected a fantastic sound but that for me the target to squeeze that out -thats my personal mind setting.

chris

Hi Chris,

Your chip-amp comparison scheme shows your very systematic approach to development. A good way to get an overview. But, I believe your are not fully fair to the TDA7265 on THD (8 Ohm) where you use a worst case value: https://www.google.fr/url?sa=t&rct=j...C6Vf5Qhrhp0d2z
I read values of 0.01% and 0.02% for 8 and 4 Ohm loads.

It makes a lot of sense to start with a very cheap kit and see what you can get out of it. When you finish your LM1875 work, I guess you will agree that the sound is in the better half of what is sold as commercial products, disregarding price. That we can get surprisingly much out of very little (economically seen) is what may inspire youth to continue this intellectual challenge. Did we just end up with a mediocre result, it would be a futile effort. For too long we have gotten into the habit of just buying without caring much about what we get and actually need. I guess you will agree that your perspective changed when you, as a prior audiophile, entered DIY electronics and got an idea how the circuits influence the sound.

As I have a temptation for re-use, I have a number of dual-winding power transformers recovered from old scrapped amplifiers. I then buy (or even recover) good size electrolytic capacitors of decent quality to make unregulated power supplies. To those unregulated power supplies, I add separate (variable) regulator boards typically based on buffered LM317/337. As result, I have silent variable (dual-) voltages with little ripple and surge current capability in the order of 10A. The whole lot does not look pretty but is very useful for testing of amplifiers (single- or dual supply) and didn't cost me much.

Changing the gain of the LM1875 is with R4 (20K) on page 2 of the datasheet: http://www.ti.com/lit/ds/snas524a/snas524a.pdf

I dare not say how much the power supply ripple influences the fine sound details you analyze.

Last edited by FauxFrench; 22nd October 2019 at 08:24 AM.
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Old 22nd October 2019, 10:51 AM   #252
chermann is offline chermann  Austria
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Hi FF


yes you are right the TDA7265 is not correct - i use the worst case - its not fair- copy paste from 3 lists...whatever i will correct that. thanks


chris
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Old 22nd October 2019, 02:56 PM   #253
chermann is offline chermann  Austria
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Hi


something without sound i made some frequency response test on 8R to look at my actual amp1_2 (green caps) at the low level and this phase shift.
the phase shift is still visible - any ideas to that??? 1k is ok. lower freq. are "earlier" and higher as 1k, 20k... its "later"

so different frequencies go with a different phase /time to the output?
yellow 100Vrms in and the blue is on the R channel output terminals


40hz, 100,400,1k,6k,12k, 20k,30k
chris
Attached Images
File Type: png 40.png (52.2 KB, 109 views)
File Type: png 100.png (48.5 KB, 112 views)
File Type: png 400.png (52.2 KB, 115 views)
File Type: png 1k.png (54.5 KB, 115 views)
File Type: png 6k.png (48.8 KB, 109 views)
File Type: png 12k.png (48.9 KB, 2 views)
File Type: png 20k.png (48.6 KB, 3 views)
File Type: png 30k.png (49.6 KB, 8 views)

Last edited by chermann; 22nd October 2019 at 02:58 PM.
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Old 22nd October 2019, 11:19 PM   #254
FauxFrench is offline FauxFrench  France
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Join Date: Dec 2017
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Quote:
Originally Posted by chermann View Post
Hi

something without sound i made some frequency response test on 8R to look at my actual amp1_2 (green caps) at the low level and this phase shift.
the phase shift is still visible - any ideas to that??? 1k is ok. lower freq. are "earlier" and higher as 1k, 20k... its "later"

so different frequencies go with a different phase /time to the output?
yellow 100Vrms in and the blue is on the R channel output terminals

40hz, 100,400,1k,6k,12k, 20k,30k
chris

Hi Chris,
Such phase shift is normal. It relates to phase lead- and lag networks. I will not claim to be a specialist in this but until more clever people comment, I will give you a hint.
At low frequencies you seem to have a phase lead phenomenon with the output phase preceding the input phase. My impression is that it relates to the two Nichicon Muse capacitors that cause a lead effect at low frequency where the capacitors have an influence.
At high frequencies you seem to have a phase lag effect with the output phase succeeding the input phase. My guess is it relates to either the inherent phase-lag of the amplifier circuit itself or to the zobel network.

Last edited by FauxFrench; 22nd October 2019 at 11:34 PM.
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Old 23rd October 2019, 07:52 PM   #255
chermann is offline chermann  Austria
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Default ...phase shift with the other board - amp2

Hi


i did this phase shift measurements on the other board (wima 4,7, 22 ES green muse NFB - huge 1000F caps at the rails)

yellow 100Vrms in and the blue is on the R channel output terminals
40hz, 100,400,1k,6k,12k, 20k,30k
chris
Attached Images
File Type: png 40_amp2.png (53.4 KB, 7 views)
File Type: png 100_amp2.png (49.8 KB, 7 views)
File Type: png 400_amp2.png (52.7 KB, 3 views)
File Type: png 1k_amp2.png (49.1 KB, 3 views)
File Type: png 6k_amp2.png (49.4 KB, 2 views)
File Type: png 12k_amp2.png (49.3 KB, 2 views)
File Type: png 20k_amp2.png (48.6 KB, 2 views)
File Type: png 30k_amp2.png (50.5 KB, 3 views)
File Type: jpg 47wima22ES_1000Frail_1.jpg (214.4 KB, 22 views)
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Old 23rd October 2019, 07:58 PM   #256
FauxFrench is offline FauxFrench  France
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Quote:
Originally Posted by chermann View Post
Hi


i did this phase shift measurements on the other board (wima 4,7, 22 ES green muse NFB - huge 1000F caps at the rails)

yellow 100Vrms in and the blue is on the R channel output terminals
40hz, 100,400,1k,6k,12k, 20k,30k
chris

Am I right, there is little difference with the other board?
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Old 23rd October 2019, 08:14 PM   #257
chermann is offline chermann  Austria
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Default ...cap bank ..capacity check...resistor too high.

Good evening
i really thinking about the capacity at my amp and the ripple. therefore i did a check with my LCR meter to "see" the max capacity per rail at my mock up.now with the amp1_2 (ES caps)

remember i have -per rail per amp side:

2x100F at the board
3300F directly mounted on the terminal of the board
1x1000F at the cap bank
0,4 R
and then the 2x2200F-which is the first after the rectifier
200+3300+1000+4400=8900 with tolerance less - i measured 7,5mF so ok or not?


why i do not see with the LCR the other caps to the other amp side? missing
200+3300+1000= 4500 --> 13400F per rail ideal

after searching around i found the problem --> the 0R4 is too high the LCR cant see the caps at the other side. i soldered a 0R1 in parallel to the 0R4 and i did the same measurement agian- now i see 11,6mF a the complete rail. i checked this from the other side too.


a test at 200mVrms 1khz input on 8R load to look at the ripple - 04R and 0R1//0R4 - differential probe
measuring point is at after the rectifier
measuring at the cpa bank last cap
directly on the amp board terminal (where the 3300F caps are)


add the 0R1
measuring point is at after the rectifier
measuring at the cpa bank last cap
directly on the amp board terminal (where the 3300F caps are)


technicaly its getting a little bit worse..sound check not done...

dont ask me why the 100hz ripple signal is scattered



chris

Last edited by chermann; 23rd October 2019 at 08:17 PM.
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Old 23rd October 2019, 08:44 PM   #258
FauxFrench is offline FauxFrench  France
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Join Date: Dec 2017
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Quote:
Originally Posted by chermann View Post

......dont ask me why the 100hz ripple signal is scattered

chris

OK, we don't ask..........
"Scattered", do you mean the sine-wave signal modulated on top of the saw-tooth signal? If so, isn't it the consumption of the amplifier that causes the sine-wave?
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Old 23rd October 2019, 09:13 PM   #259
chermann is offline chermann  Austria
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Quote:
Originally Posted by FauxFrench View Post
Am I right, there is little difference with the other board?

yep...you are the expert...explain me
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Old 23rd October 2019, 09:21 PM   #260
chermann is offline chermann  Austria
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Default do not use a too small heat sink at 4R...thermal protection kicks in

Hi


i try my phas shift test at 4R with the200VRMS 1khz tone . but during measruring at the rail a feel/smell the heat of the poor guy = Lm1875


output signal = 200Vrms in - out 13Vpp at 4R its about 5,2 WATT
rail ripple - 2 pics
thermal protection - every 4 sec lm1875 try again.. 82 C
so please do not do that with a heatsink of 2,3k/W !! if you look at the datasheet - figure 9 - if you request 5 W the LM1875 has to dissipate with a rail of 25V abut 22WATT heat !!




the test was 2 hours ago...so now its playing fine...LM1875 is a robust chip


chris
Attached Images
File Type: png output signal_4R or 8R_v4_v41_v5.png (49.1 KB, 7 views)
File Type: png after rectifier_4R_v4.png (43.7 KB, 5 views)
File Type: png after R_psu board out_4R_v4.png (47.3 KB, 3 views)
File Type: png current limiter at 4R_v4.png (67.0 KB, 6 views)
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