The kit was purchased from Audiosector. You can see my build in the photos I attached to my first post.
I have two kits. I just swapped in a different amp board and I'm experiencing the same issue. Though clearly I could have built both incorrectly. Check if this link to my photos works.
https://plus.google.com/photos/1100...s/6007793734994963409?authkey=CJ2ku4_c6pTxoQE
Thanks, the link works. It's not clear, but the input wiring looks rough! You are using a pre-amp then? I would check the pre-amp with another amp if poss, and check the interconnects, but to be faulty on both channels is unusual. Check the + and - voltage from the psu
The input wiring is fine. What you see is just the cotton insulation fraying. My wiring is just temporary to test everything. I will be cleaning it all up. I own an AV company..I have many preamps speakers and interconnects..I've tested and none of these things are the culprit.
Measurements:
(Oddly) Led tabs are outputting 33 volts dc
Pg - v - 33 volts dc
Pg + v + 33 DC
Speaker Terminals .013 DC
Anyone else have any thoughts?
What source and speakers are you using?
Those amps have 30dB gain, so even without preamp they sound pretty loud.
Your build seems to look good, so the problems are most likely with the equipment connected to the amp. Confirm that the resistor values are as follow:
R1 220R
R2 22K
Rfb 22K
R3 680R
I would also recommend removing AC filter, the amp sound worse when using those.
Those amps have 30dB gain, so even without preamp they sound pretty loud.
Your build seems to look good, so the problems are most likely with the equipment connected to the amp. Confirm that the resistor values are as follow:
R1 220R
R2 22K
Rfb 22K
R3 680R
I would also recommend removing AC filter, the amp sound worse when using those.
Anemic sound? Snubberize? Capacitors?
Thanks Peter! As luck would have it I did mistakenly swap resistor values. Also I removed the power filter. Thank you for the suggestion.
A few additional questions for you and your loyal followers. I've got about 100 hours on the amplifier and to my ear it's sounding a bit anemic and sometimes shrill on top. I'm in the audio business and have access to a lot of gear. Mated with the amplifier I've listened to several Shindo preamplifiers (Shindo always being my preference). Digital sources have been Naim Audio & DCS. Vinyl Garrard 301. Speakers...DeVore Nines, Altec Valencias, Wilson Duettes, AE AE-1s.
Amp is running with your recommended Plitron transformer.
R1 as you recommend is simply jumped with a wire.
Thinking that trying the snubber may be my ticket. As of now I've had a pair of 10,000uf @ C2 and C1. Not sure if this is wrong to do without the rest of the snubber circuit in place? (10u Panasonic FC Capacitors were not included with my kits as advertised..I searched the forums to figure out if this was change to the design, frankly, I've had a hard time keeping track of the consensus on the most current design)
Also, I'm sure this has been hashed out a million times so please excuse me but I've spent about 5 hours scouring the forums and the web with little luck. When implementing the snubber...(which Peter I know you don't prefer) what caps for C2 & C1 are popular? Same question for C3 C4. Also I've seen or at least I think I've seen people say that when you snubberize that pins on the amp chip should be bridged by a resistor? I'm happy to pay for premium parts.
Again I hate to beat a dead horse but after many hours of searching I never quite stumbled upon the answers.
Thanks so much! Building and playing with this amp has been a blast!
Thanks Peter! As luck would have it I did mistakenly swap resistor values. Also I removed the power filter. Thank you for the suggestion.
A few additional questions for you and your loyal followers. I've got about 100 hours on the amplifier and to my ear it's sounding a bit anemic and sometimes shrill on top. I'm in the audio business and have access to a lot of gear. Mated with the amplifier I've listened to several Shindo preamplifiers (Shindo always being my preference). Digital sources have been Naim Audio & DCS. Vinyl Garrard 301. Speakers...DeVore Nines, Altec Valencias, Wilson Duettes, AE AE-1s.
Amp is running with your recommended Plitron transformer.
R1 as you recommend is simply jumped with a wire.
Thinking that trying the snubber may be my ticket. As of now I've had a pair of 10,000uf @ C2 and C1. Not sure if this is wrong to do without the rest of the snubber circuit in place? (10u Panasonic FC Capacitors were not included with my kits as advertised..I searched the forums to figure out if this was change to the design, frankly, I've had a hard time keeping track of the consensus on the most current design)
Also, I'm sure this has been hashed out a million times so please excuse me but I've spent about 5 hours scouring the forums and the web with little luck. When implementing the snubber...(which Peter I know you don't prefer) what caps for C2 & C1 are popular? Same question for C3 C4. Also I've seen or at least I think I've seen people say that when you snubberize that pins on the amp chip should be bridged by a resistor? I'm happy to pay for premium parts.
Again I hate to beat a dead horse but after many hours of searching I never quite stumbled upon the answers.
Thanks so much! Building and playing with this amp has been a blast!
I don't include 10uF with a kit now, they are not really needed.
The components for the snubberized PS have been specified here: http://www.audiosector.com/lm4780 psu.pdf
You may also check this thread for a different GC approach: DIYHiFi.org • View topic - carlosfm's schematics
The components for the snubberized PS have been specified here: http://www.audiosector.com/lm4780 psu.pdf
You may also check this thread for a different GC approach: DIYHiFi.org • View topic - carlosfm's schematics
Or use half of the LM4780 chip, simplified circuit schematic posted here: http://www.audiosector.com/lm4780 amp.pdf
When using this primarily as a headphone amp are there different components needed to be added to the mix to enhance SQ on cans ?
I had hoped to use this kit for planar magnetic headphones @ 50/60 ohm respectively which can handle 3 watts and about 8 watts of headroom...and add self-build Ted Jordan full range cones later...
Can this amp be run off a battery kit vs mains, it seems much simpler and takes the mains noise variable out the equation (?)
Do you Peter, or anyone else have a lead on a good battery kit and any special cables needed to bridge them together ?
Is it very complex to make this amp run in current mode vs voltage mode like a Bakoon HPA-21 amp ?
I had hoped to use this kit for planar magnetic headphones @ 50/60 ohm respectively which can handle 3 watts and about 8 watts of headroom...and add self-build Ted Jordan full range cones later...
Can this amp be run off a battery kit vs mains, it seems much simpler and takes the mains noise variable out the equation (?)
Do you Peter, or anyone else have a lead on a good battery kit and any special cables needed to bridge them together ?
Is it very complex to make this amp run in current mode vs voltage mode like a Bakoon HPA-21 amp ?
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The amp can work with headphones without any modifications:
http://www.diyaudio.com/forums/headphone-systems/62828-lm3875-headphone-amp-another-try.html
http://www.diyaudio.com/forums/audi...kit-building-instructions-68.html#post2432391
http://www.diyaudio.com/forums/headphone-systems/62828-lm3875-headphone-amp-another-try.html
http://www.diyaudio.com/forums/audi...kit-building-instructions-68.html#post2432391
Thanks Peter and as to battery power, is it an easy alternate route ? Is there anything off-the-shelf that works...scooter batteries etc ?!
I'm already going the Anker V2 12 volt isolation battery route for my DAC but I note this amp is 22 volts ?
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Right, so I may also be able to track down a single 48 volt scooter battery etc as 4x Ankers would be too expensive.
Final Q Peter, did you ever compare this amp's SQ under voltage and current drive like an F1J ?
Another question about power star ground with audiosector LM3875 kit and external PSU
Hello everybody, I'm new to this forum and I hope you can help me. I'm planning my version of the audiosector LM3876 kit and during this I've read a lot in this and other threads during the last week. But I've got still one question about grounding with an external PSU.
I've read that I can use a 4-wire umbilical like its used in the Patek amp. So i can build up power star ground with V+, PG+, V-,PG- like its shown in post #73 by Peter Daniel or seen in the picture of Patek amp.
But I don't understand in which way I have to connect the mains ground to the star and in which way i have to connect the chassis of PSU and amp to mains ground.
Is it necessary to use shielded cable for the umbilical?
I hope somebody can clarify this for me!
thanks
Hello everybody, I'm new to this forum and I hope you can help me. I'm planning my version of the audiosector LM3876 kit and during this I've read a lot in this and other threads during the last week. But I've got still one question about grounding with an external PSU.
I've read that I can use a 4-wire umbilical like its used in the Patek amp. So i can build up power star ground with V+, PG+, V-,PG- like its shown in post #73 by Peter Daniel or seen in the picture of Patek amp.
But I don't understand in which way I have to connect the mains ground to the star and in which way i have to connect the chassis of PSU and amp to mains ground.
Is it necessary to use shielded cable for the umbilical?
I hope somebody can clarify this for me!
thanks