Hi All,
Just wanted to post a quick update and my impressions about this little amp I originally built around 2 years ago.
Initially, I thought it sounded so damn good. The mids and highs were crisp and clear. Vocals very lifelike. Bass, well I was also impressed with that too.
Over the lasts 2 years I have made a number of system upgrades and decided to have another listen today and hooked it up with my primary system. Which is as follows:
For the LM3875 listening, I replaced the Audiolab 8000P - keeping the rest of the system as is.
I played Norah Jones "Cold Cold Heart" as the first track on the system. The vocals reminded me of why i loved this amp 2 years ago. VERY LIFE like. The crispiness and tone is very real. (sorry I am not an audio reviewer, so I am not sure about the right words that would convey my impressions).
After some critical listening I started to notice something missing and rather fatiguing. The soundstage is rather FLAT and un-involving compared to the Audiolab. The authority and grip Audiolab has over the low end is also lacking with this. Its almost someone has sucked the soundstage depth out of this system and replaced the 3D sound with a bad flattened replica. Something like someone replaced the marinara sauce with ketchup.
Not sure if the above makes any sense.
How do I go about improving the 3D soundstage and give this amp some balls?
Here are some pics of the build:
Just wanted to post a quick update and my impressions about this little amp I originally built around 2 years ago.
Initially, I thought it sounded so damn good. The mids and highs were crisp and clear. Vocals very lifelike. Bass, well I was also impressed with that too.
Over the lasts 2 years I have made a number of system upgrades and decided to have another listen today and hooked it up with my primary system. Which is as follows:
- Speakers: ProAc Studio 140MK2 (pic)
- Pre: Audiolab 8000S (pic)
- Power: Audiolab 8000P (pic)
- Dac: Musical Fidelity M1-DAC (Async 192) (pic)
- Source: Raspberry PI using Logitech Squeeze Player
For the LM3875 listening, I replaced the Audiolab 8000P - keeping the rest of the system as is.
I played Norah Jones "Cold Cold Heart" as the first track on the system. The vocals reminded me of why i loved this amp 2 years ago. VERY LIFE like. The crispiness and tone is very real. (sorry I am not an audio reviewer, so I am not sure about the right words that would convey my impressions).
After some critical listening I started to notice something missing and rather fatiguing. The soundstage is rather FLAT and un-involving compared to the Audiolab. The authority and grip Audiolab has over the low end is also lacking with this. Its almost someone has sucked the soundstage depth out of this system and replaced the 3D sound with a bad flattened replica. Something like someone replaced the marinara sauce with ketchup.
Not sure if the above makes any sense.
How do I go about improving the 3D soundstage and give this amp some balls?
Here are some pics of the build:
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
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Hi Phil,
Its the Premium Kit from audiosector. I had added 2x 10000uf caps to the PSU as suggested here. Other than that, its all stock kit. The transformer is 250VA 18VAC as pictured here..
Its the Premium Kit from audiosector. I had added 2x 10000uf caps to the PSU as suggested here. Other than that, its all stock kit. The transformer is 250VA 18VAC as pictured here..
Hi,
I built LM3875 from Chipamp.com (same as Audiosector), and it's works well, good bass and nice soundstage..
I use snuberrized PSU (1 Ohm and 0,1 uF), a few values have been changed at amp pcb.
You can see this amp :
http://www.diyaudio.com/forums/chip-amps/271984-lm3875-chipamp.html
schematics and values post one..
Cf and Rf2 are for stability, I try without and with, it's better with, mid are a little more detailled, so a better soundstage.
I also added a safety loop breaker, no hum no bizz no noise, and better sounding.
Phil.
I built LM3875 from Chipamp.com (same as Audiosector), and it's works well, good bass and nice soundstage..
I use snuberrized PSU (1 Ohm and 0,1 uF), a few values have been changed at amp pcb.
You can see this amp :
http://www.diyaudio.com/forums/chip-amps/271984-lm3875-chipamp.html
schematics and values post one..
Cf and Rf2 are for stability, I try without and with, it's better with, mid are a little more detailled, so a better soundstage.
I also added a safety loop breaker, no hum no bizz no noise, and better sounding.
Phil.
An externally hosted image should be here but it was not working when we last tested it.
The problem is it's an incomplete "gain clown" type circuit, that type of minimalist build will never deliver the best possible performance those chips are capable of delivering. I strongly recommend you read Tom Christiansen's excellent write up here: Taming the LM3886 Chip Amplifier
The Lm3886 is very similar to the LM3875, so the same principles apply. Pay particular attention to the Stability, Supply decoupling, and Grounding sections; those are the main areas where these chip amp kits fall short.
Mike
The Lm3886 is very similar to the LM3875, so the same principles apply. Pay particular attention to the Stability, Supply decoupling, and Grounding sections; those are the main areas where these chip amp kits fall short.
Mike
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This makes and breaks any audio circuit. I solder 0.1 uF ceramic caps directly to the power supply pins, right on the bottom of the board; whether they are "chip amp" chips, op amps, or buffer. Then each chip has its own local electrolytic capacitor reservoirs right next to them. Finally, any board that has more than one chip has an electrolytic capacitor reservoir right where the power leads connect.
Tom recommends using "os-con" capacitors for local electrolytic reservoirs. I have not tried this, but after looking at the data sheet for these capacitors I think it is good advice. I will order some next time I need parts. (They are more expensive and there's only a couple of through hole values available.)
As far as grounding, read about and understand Tom's "modified star ground" procedure. This is what works best for audio circuits.
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Flat soundstage I reckon is down to the supply rails having too much noise on them. Chipamps lack in the PSRR department - one way you could improve the depth is use an output step down transformer and compensate for the voltage loss by running the rails a little hotter. Or better still, go to bridged operation - running bridged means you no longer need to have a symmetrical supply so that's one fewer supplies to optimize.
Where did you find this caps in 25 or 35 volts ?
I looked at Panasonic, nothing in this voltage..
Phil.
You have to parallel them with bigger electrolytic capacitors.
10-22 uF is more than adequate for op amp and low current buffer local bypass. And for board or power supply bypass (where the capacitor is far from the chip), the higher resonance and lower impedance of the os-con capacitors doesn't offer any benefit, anyway.
Actually...If implemented correctly, os-cons do provide some benefit. Measurement data here: LM3886 chip amp supply decoupling.
Mike
Parallel bridging is the answer.
Having played with every configuration possible with these amps, parallel bridging will give you way better driver control, not to mention bass authority and slam. That means you need to buy two other kits and some .1 or .2 ohm 3 watts or more, 1% or better resistors to tie the outputs together (see data sheet). no need for 10 000 MF caps as in my experience it just makes the sound thick and sucks a bit of life out of the music. Happy tinkering.
Having played with every configuration possible with these amps, parallel bridging will give you way better driver control, not to mention bass authority and slam. That means you need to buy two other kits and some .1 or .2 ohm 3 watts or more, 1% or better resistors to tie the outputs together (see data sheet). no need for 10 000 MF caps as in my experience it just makes the sound thick and sucks a bit of life out of the music. Happy tinkering.
Hi,
I had already read that article, but without understanding its advantage..
I will try this for my next amp, and see what's happen at listening.
If I go with 1000 uF electrolytic, I add 22 uF oscon and 4,7 uF ceramic
with 1500 uF, I will add 33 uF oscon and 6,8 uF ceramic
Right ?
Phil.
Thank's,
I had already read that article, but without understanding its advantage..
I will try this for my next amp, and see what's happen at listening.
If I go with 1000 uF electrolytic, I add 22 uF oscon and 4,7 uF ceramic
with 1500 uF, I will add 33 uF oscon and 6,8 uF ceramic
Right ?
Phil.
NO, I don't recommend doing that, you could end up inadvertently creating resonances that would be detrimental to circuit performance. Just go with one large electrolytic, one os-con, and one ceramic. Doing that will give the optimal result if implemented properly.
Mike
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