Ive done all the mods ,changed input caps,resistors pre and chip sides and lifted ground pre and chip sides and it sounds great.
only noise on mine if volume turned right up and ear next to tweeter!!
only noise on mine if volume turned right up and ear next to tweeter!!
Hey linux just checked out that board.it is nearly twice the price for not much more!!
i doubt it will sound twice as good as the modded cheapo!
i doubt it will sound twice as good as the modded cheapo!
I agree about the relative value, though the blue board has better grounding and components. If it is offered as a bare PCB at less than $10 each, I'd probably snap up a few.
Incidentally, an EBay auction for a pair of Twisted Pear Audio Mauro Penasa MyRef Rev C boards (fully assembled, without heatsink) ended today without any bids - they were a steal at $49.95 for both, but shipping costs out of the US were steep.
Have you seen these Chinese aluminium enclosures on EBay?
Aluminum Box Enclosure Case Electronic DIY-square-1176 - eBay (item 330409178172 end time Mar-29-10 11:50:36 PDT)
Probably a bit small for a stock gainclone + transformer, but perfect for headphone amps. preamps, etc.
Ughh! Am I being dense? Again, I know I'm not an expert on this stuff, but is there any way you can be more specific? When you refer to the "DC blocking cap" are you refering to the WIMA on the input or the cap to ground in the feedback loop? And when you say "bridged the resistor to the adjacent resistor" which resistors are you refering to? Any way you can reference them on the below diagram?
Sorry if this stuff is obvious to you. I'm usually not one that has problems figuring this stuff out on my own, but I think I've done what is recommended and still have a very noisy amp.
Thanks much!!!
Attachments
I apologize - I should have been more specific.
DC blocking cap: Ci (cap to ground in the feedback loop) - remove it.
bridged resistor: disconnect R2 from ground, and connect it to the junction of R3 and Ci on the schematic. This node is the newly-created lifted ground on the chipamp side.
Jumper the lifted ground: connect the junction of R3 and Ci to the lifted-ground on the op-amp side, with a piece of hook-up wire. The op-amp lifted ground is isolated from the ground plane by the ground-loop breaker, i.e. the 10 ohm resistor from the first mod.
the problem we are having comes from the universal use of the same symbol for Ground in all these schematic drawing software packages.
We really must think of each Ground with it's true purpose in the circuit.
The signal ground is really the signal return.
The speaker ground is the speaker return.
The PSU ground is really the Power zero volts reference.
The mains ground is really the Safety Earth, otherwise known as the Protective Earth wire (third wire) in the mains cable.
We really must think of each Ground with it's true purpose in the circuit.
The signal ground is really the signal return.
The speaker ground is the speaker return.
The PSU ground is really the Power zero volts reference.
The mains ground is really the Safety Earth, otherwise known as the Protective Earth wire (third wire) in the mains cable.
Back ordered.
Its actually back ordered. Scroll down in the ebay listing and it says so in red.
Cool.
Srinath.
Its actually back ordered. Scroll down in the ebay listing and it says so in red.
Cool.
Srinath.
Now I'm really starting to feel like an idiot. You've now outlined what I should do so thoroughly that I can't imagine how I could mess it up, but somehow I did. My drawing below is what I "think" you have told me to do, but somehow I think I'm missing something.
Yes , i see, what about this one ?
COMPLETE STEREO AUDIO POWER AMPLIFIER KIT! - eBay (item 380144028687 end time Mar-26-10 08:20:45 PDT)
Any good to play with .......
Hey bcarpman ,go back down the thread there are photos for all this!!I have done the mods with no schematics just description and photos.
Thanks, although I've gone through every post about 10 times now. Got any of the relavent one printed out and I'm either missing something or perhaps already screwed something up.
Everything is correct, except the value of R3 in your drawing. It stays the same as before - 680 ohms in your drawing (1k on the Yuanjing board), not 10 ohms as you have shown (which would make the gain of the LM3886 too high).
With 10 ohms at R3, the closed-loop gain of the LM3886 would be ~2200, which would drive it into clipping with signal levels as low as 10s of mVs. 680 ohms to 2.2k is a reasonable range of values for R3.
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I bought one of the 150 watt 3x Lm3886 boards 150W 3 x LM3886 Mono Channel Audio Amplifier Board - eBay (item 230453000602 end time Mar-25-10 19:00:18 PDT) and i expect to replace the caps but for the price if it works for a sub amp its good deal. schematic looks simple enough so...what the heck, I will give it a try.
Zc
Zc
Hi Linux,
why are you recommending a DC block on the input and no DC block on the NFB.
I call this mixed AC & DC coupling and often advise against it.
Please explain.
why are you recommending a DC block on the input and no DC block on the NFB.
I call this mixed AC & DC coupling and often advise against it.
Please explain.
Good review about this seller
im looking to this amp
LM3886*3 Amp + Power supper kit/DIY - eBay (item 320464946907 end time Apr-19-10 00:03:59 PDT)
im looking to this amp
LM3886*3 Amp + Power supper kit/DIY - eBay (item 320464946907 end time Apr-19-10 00:03:59 PDT)
It may not be the optimal circuit for the LM3886, but it's the simplest way to mod this board without cutting traces, isolating pads, etc. The main objective is to somehow quieten the input and feedback signal ground for the LM3886, by isolating it from the speaker return currents in the ground plane, which can generate 10s to 100s of mVs of ground bounce, depending on the resistance of the ground plane and the width of the plane (which is not uniform).
The downside to it is higher output offset voltage, but it is bounded by the closed-loop gain x input offset, and turns out to be ~100 mV on my board.
In the op-amp section, the mixed coupling doesn't matter because the output of the op-amp is at any rate AC coupled to the LM3886. That DC blocking capacitor (between the NE5532 and LM3886) is probably needed, because otherwise the output offset of the opamp is also going to be amplified by the LM3886 (actually, I need to measure and check if this is going to be an issue - if it's small enough, I'll dispense with the DC blocking cap between the op-amp and LM3886).
Edit: With the LT1213 as the pre/buffer, the output offset of the op-amp measures to be 26 mV, referenced to the input shield ground, for both channels. That's a bit too high to pass on to the LM3886 (26 mV x 28 (gain) = 0.728 V).
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No idea
I have no idea, I am yet to even receive it, but I bought a 3886 with tube buffer ~1 week ago. That is my first foray into building something. Lets hope it works and I dont burn the house down.
I'll figure out and go from there. In the mean time, I better learn to be patient and work on my speakers ... now that I got the realistic electrostats refoamed and in the listening loop ...
Cool.
Srinath.
I have no idea, I am yet to even receive it, but I bought a 3886 with tube buffer ~1 week ago. That is my first foray into building something. Lets hope it works and I dont burn the house down.
I'll figure out and go from there. In the mean time, I better learn to be patient and work on my speakers ... now that I got the realistic electrostats refoamed and in the listening loop ...
Cool.
Srinath.
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