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eBay mono LM1875 kit
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Old 12th October 2019, 05:31 AM   #191
rabbitz is offline rabbitz  Australia
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Location: Newcastle, Australia
Interesting to see what you get with a genuine LM1875. Mine still has a small pop at turn off which I've never solved.
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Old 12th October 2019, 05:56 AM   #192
chermann is offline chermann  Austria
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Quote:
Originally Posted by FauxFrench View Post
Yes, I have some future plans for a mono version with some 6 LM1875. BTL coupling and three in parallel on each side. Buffer transistors is an alternative. A composite structure (error correction) should take the sound to audiophile levels.

Good night.
Good morning...FF
this sound like e monster LM1875

@rabbitz
will see this weekend...what a genuine chip can/do

chris
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Old 12th October 2019, 08:09 AM   #193
chermann is offline chermann  Austria
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Default other chips....fine sound

Hi

i desolder the fake chip and installed the chips i got from amazon - recycled.
i chip feels at it legs strange-loosy so i be carefully at soldering.maybe they pull it out with too hard mechanic stress. additionally i add at the supply some 100F caps i got with the kits. the caps which were inside had after lot of hour running an ESR of 0,3R at 100Hz (LCR meter). so with 2 caps in parallel i should achieve the datasheet requirement.


first test i go too fast forward-why? i dont check the DC voltage at the right channel!!! - i am an idiot.....luckly in my lab!


i see during the test with 100mvrms input that i got no signal at the speakers terminals -i checked the rail voltage and see that the -V gets down to 25V and the +V stays at 26,75V. then......i switched off and see that i had 6,37V DC at the output...chip was F*** hot and i burned my finger...dead...that chip was the loosy one...
so i changed and every thing stays at 3mV DC on both channels.



i did the shortcut test and both channels survived - so they are original chips --result 3/5 chips are now in my hand from the amazon kits



pop on/off at my lab speaker

no pop on sound - but yes a noticable pop off plop




sound is better and the power is much better. thanks to TI
bass controlled - still not really satisfied (my best is the TPA3255 "fake amp" with...and that new.. 440nF Zobel..at the speakers out....i will report).. separation adn voices come better...and the dynamic (less loud to sme peaks) is much better...but i miss more darkness.....its too foggy in the backround.
i listing now 50 minute and enjoy it...



the flamenco title at my listening level was 44 and i can play up to 50 without problems. sorry actually no measurement...today i will enjoy the weather and at the evening i do this task


pic is my playlist

chris
Attached Images
File Type: jpg playlist for testing.JPG (87.0 KB, 102 views)
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Old 12th October 2019, 07:16 PM   #194
chermann is offline chermann  Austria
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Default ...compared to post 184

Hi


the kit is running some hours and i just checked the "performance" with the "flamenco title" i push 6 time the same track

2 times for the different voltage rails. 3 times for output and once for the input probe.
with the volume level 50 (instead 44). the speakers are 6R (venere1.5)
i cannot explain why i sea at the fake chip at the same title more voltage (38Vpp)at less volume level 44(not 50) now its "just" 35,4Vpp max.--> 26Watt at 6R

the voltage sag down to 25,1V at the heaviest rolls.


no clipping and sound level feels stressed but not at the end...

pic 1 output Rchannel
pic 2 input


chris
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Old 12th October 2019, 07:35 PM   #195
chermann is offline chermann  Austria
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Default noise at the power supply

Hi


please can you give me ideas to get a better = lower ripple at my power supply. my idea is the get a better sound because of less ripple voltage at the rails
i read about some small caps at the bridge rectifier
and what about bleeder resistors at the cap bank or some foil caps?

amp on, complete connected but no signal
pic 1 ripple at the +V and -V after the rectifier
pic 2 ripple at the L channel +V and 0 at the cap bank
pic 3 ripple at the L channel -V and 0 at the cap bank

pic 4 L channel off pop

thanks in advance
chris
Attached Images
File Type: png noise after rectifier +V and -V.png (59.1 KB, 96 views)
File Type: png nosie L channel cap bank +V.png (61.6 KB, 95 views)
File Type: png nosie L channel cap bank -V.png (61.8 KB, 12 views)
File Type: png pop.png (38.2 KB, 14 views)
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Old 13th October 2019, 05:41 PM   #196
chermann is offline chermann  Austria
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Quote:
Originally Posted by chermann View Post
.........
sound is better and the power is much better. thanks to TI
bass controlled - still not really satisfied (my best is the TPA3255 "fake amp" with...and that new.. 440nF Zobel..at the speakers out....i will report).. separation adn voices come better...and the dynamic (less loud to sme peaks) is much better...but i miss more darkness.....its too foggy in the backround.
i listing now 50 minute and enjoy it.....
chris
i did my reporting- fyi
What is wrong with TPA3255?


chris
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Old 13th October 2019, 07:58 PM   #197
FauxFrench is offline FauxFrench  France
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Location: The mountains, calm and quiet.
Quote:
Originally Posted by chermann View Post
Hi
please can you give me ideas to get a better = lower ripple at my power supply. my idea is the get a better sound because of less ripple voltage at the rails
i read about some small caps at the bridge rectifier
and what about bleeder resistors at the cap bank or some foil caps?
amp on, complete connected but no signal
pic 1 ripple at the +V and -V after the rectifier
pic 2 ripple at the L channel +V and 0 at the cap bank
pic 3 ripple at the L channel -V and 0 at the cap bank

pic 4 L channel off pop

thanks in advance
chris

Hi Chris,

A typical ripple-form for a non-regulated power supply. If you double the decoupling capacitance, you will have close to half the ripple but you can't just increase the capacitance without getting space problems and too much invested in capacitors.
It is a 100Hz ripple of a moderate amplitude. In-between recharge of the capacitors every 10ms, the capacitors provide the current and are discharged as you see. The curve is a bit blurred but with a sampling scope and high gain, my experience is that a blurred picture can be expected.
Rectifier capacitors and foil capacitors will only have a small effect on higher frequency ripple. Bleeder resistors serve to give a slight minimum-loading (which you already have from quiescent current) and more importantly quickly remove charge from the decoupling capacitors when you switch the amplifier off.

What to do then? Use regulators on the two rails. Then, you have considerably less ripple but only audiophiles like you can evaluate the improvement of the sound. Several volts of ripple can be an important issue, not your modest level.

Last edited by FauxFrench; 13th October 2019 at 08:06 PM.
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Old 13th October 2019, 08:38 PM   #198
chermann is offline chermann  Austria
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Good Evening FF

greetings from the foggy Vienna .
Thanks for your feedback. yes every 10ms the caps get juice. with my 2x2200+2x1000 (6400) per rail for both amp boards i am not in the correct window.
10000F are required per rail and amp. correct?.....and yes the space is not really big in my housing / or mock up
i will try to get some extra caps in my mock up.....
i have no bleeder resistor maybe this is the reason why i have a off pop.

so far i am still happy with the sound of the original LM1875. the power is just fine. sound wise the background is still foggy - means its a lack of dynamic especially from the background + the bass is still bloated


chris
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Old 13th October 2019, 08:42 PM   #199
chermann is offline chermann  Austria
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Hi


i did a small modification in the morning on my bridged rectifier- a solder a 22nF ceramic caps at all pin (diodes) + i add a 220nF /250 X2 caps after the rectifier at +V and -V.


the results is not better...soundwise the same....should i pull that out?
amp on, complete connected but no signal
pic 1 ripple at the +V and -V after the rectifier
pic 2 ripple at the L channel +V and 0 at the cap bank
pic 3 ripple at the L channel -V and 0 at the cap bank



chris
Attached Images
File Type: png ripple after rectifier +V and -V_2.png (53.6 KB, 5 views)
File Type: png ripple L channel cap bank +V_2.png (60.8 KB, 2 views)
File Type: png ripple L channel cap bank -V_2.png (60.6 KB, 1 views)
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Old 13th October 2019, 09:24 PM   #200
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


i did a small modification in the morning on my bridged rectifier- a solder a 22nF ceramic caps at all pin (diodes) + i add a 220nF /250 X2 caps after the rectifier at +V and -V.

the results is not better...soundwise the same....should i pull that out?
amp on, complete connected but no signal
pic 1 ripple at the +V and -V after the rectifier
pic 2 ripple at the L channel +V and 0 at the cap bank
pic 3 ripple at the L channel -V and 0 at the cap bank

chris
Hi Chris,

The small capacitors on the rectifier diodes may help the diodes switching off but they hardly change the sound. I never used such capacitors myself so I will let more competent people advise on "stay, or go".

10000uF is not a magical value. Theoretically - the more, the better. With the moderate prices for 10000uF, my advice is not to use too little or even some of more ordinary quality.

The off pop comes from when the amplifier gets starved for voltage during switch-off and looses regulation control. The bleeder resistors may not help on that. In the old days, a safety relay disconnected the speakers before the amplifier lost control.
NB: Always switch off the power amplifier before the pre-amplifier and source. Else, the pop comes via the input.

Sun and 27 degrees today. But, Atlantic air is approaching.

Last edited by FauxFrench; 13th October 2019 at 09:26 PM.
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