"Yuanjing" Gainclone 3886 - eBay amazing value ? - Page 13 - diyAudio
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Old 22nd March 2010, 05:02 AM   #121
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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!!
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Old 22nd March 2010, 05:18 AM   #122
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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!
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Old 22nd March 2010, 05:51 AM   #123
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Quote:
Originally Posted by skodaboy View Post
it is nearly twice the price for not much more!!
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.
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Old 22nd March 2010, 02:45 PM   #124
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Quote:
Originally Posted by linuxguru View Post
OK - I guess you removed the DC blocking cap and bridged the resistor to the adjacent resistor as well? .
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!!!
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Old 22nd March 2010, 04:44 PM   #125
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Quote:
Originally Posted by bcarpman View Post
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?
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.
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Old 22nd March 2010, 05:41 PM   #126
AndrewT is offline AndrewT  Scotland
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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.
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Old 22nd March 2010, 06:03 PM   #127
a.wayne is offline a.wayne  United States
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Quote:
Originally Posted by linuxguru View Post
It looks like the Goldmund/Symasym clone kit is back on EBay:

COMPLETE STEREO AUDIO POWER AMPLIFIER KIT! - eBay (item 380144028687 end time Mar-26-10 08:20:45 PDT)

The price has gone up to $69.99 + $20 s&h, but it now includes the NJW0281 and NJW0302 power BJTs. I think the earlier offer at $42.99 + $6.99 s&h without the power BJTs was the better deal.


Has anyone tried this kit yet ?
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Old 22nd March 2010, 07:00 PM   #129
srinath is offline srinath  United States
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Default Back ordered.

Its actually back ordered. Scroll down in the ebay listing and it says so in red.
Cool.
Srinath.
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Old 22nd March 2010, 07:47 PM   #130
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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.
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