"Yuanjing" Gainclone 3886 - eBay amazing value ?

[Cruzs]

Hi all..

I'm a newbie and just wondering if anybody have information how to
contacts the owner of this web: www.hifizone.net

I'm really interested on their 3 good looking PCBs:
1. ALEPH3886 : http://www.hifizone.net/shop_view.asp?id=964
2. X-PP : http://www.hifizone.net/forum_view.a...4&view_id=1619
3. X-PT : http://www.hifizone.net/forum_view.a...4&view_id=1620

I mailed them many times but it seems they ignore me.. hiksz..

If anybody can't help me getting those stuff, I'd really appreciate.



Blessings,

- Cruzs -

[Zen Mod]

Originally Posted by Cruzs

Hi all..

I'm a newbie and just wondering if anybody have information how to
contacts the owner of this web: www.hifizone.net

.......

- Cruzs -

1. IP issues - steal

2. same ?

3. seeing 30K as anode load for ECC83 make me laugh

[linuxguru]

The kit may be dodgy, but the bare PCB is available and easy to assemble. I got one, and it's OK for the price. However, there are some issues with the design.

1) No star grounding. It uses two ground planes instead for the NE5532 and LM3886 sections, and the planes are connected at a single point. However, this is not good enough, since the main PSU filter capacitors are located and grounded on the NE5532 side, and the 7812/7912 regulators for the opamp supply are located and grounded on the LM3886 side. Significant ground-bounce issues are a certainty, and there's no easy fix for this.

2) No lifted ground for the input near the NE5532 - this is what contributes to the hum. However, this easily fixable with minor mods:

i) Remove the 10uF, 25V DC blocking cap for the feedback network for the input gain stage. Replace it with a 10 ohm, 1W metal-oxide resistor, mounted vertically as shown in the attached pictures. The upper lead of this resistor will be the lifted signal ground. The shield ground from the input connector is soldered to this lead (instead of being connected to the input terminal block), while the input goes to the terminal block as before.

ii) The input resistance from the non-inv terminal of the NE5532 gain stage is grounded at the lifted ground, not the PCB ground. This is done as shown in the attached picture - the resistor is (physically) diagonally bridged over another intervening resistor.

3) Lower frequency cutoff is too high. This is fixed by changing the values of the input resistance and feedback resistance to 47k instead of 22k. This changes the gain from 3.2 to 5.7, and improves the bass response for a given input capacitor.

4) The NE5532 opamp is not an optimal choice - it can easily be upgraded to a better opamp using 8-pin DIP sockets to permit rolling. I used an LT1208 lying around, but better choices are available - probably LM4562, LT1213 or OPA2134 will sound better.

5) Upgrade the DC blocking capacitors. I've used both Siemens MKL 2.2uF/630V and Pilkor MKP 1uF/275 VAC X2 with good results.

6) The bypass caps for the LM3886 are not close enough to the input pins. I soldered 100 nF MLCCs between +Vs and GND, -Vs and GND close to the pins on the bottom of the PCB.

With these mods, it sounds acceptably good for the price, but nowhere close to a decent audiophile-class gainclone like a Pavel Dudek or a Mauro Penasa Rev C.

[linuxguru]

One other mod (optional): solder a 47p to 470p Styroflex or Silver Mica cap between the non-inv and inv inputs of the LM3886 on the solder side. This helps suppress some RF interference, as well as helps the LM3886 recover better from some kinds of clipping, as per the NatSemi Application Note. I used 68 pF, but the use of this cap is entirely up to the taste of the builder. You can omit it if the LM3886 is never going to be driven to clipping.

[CharlieLaub]

I have purchased from Ebay and used several China sourced LM3886 chip amps. They have all worked perfectly. I didn't check for star grounding or anything like that - it was just plug and play.

They look like this (below) and can be sourced from several vendors. Just search LM3886 in the Electronics>Home Audio>Amplifiers category. I would avoid the "all in one" boards that have on board PS.



-Charlie

[linuxguru]

That little unbuffered one is probably ok, within the constraints of its topology. Could you post its schematic, if you have one? I'd like to see if a lifted signal ground is implemented.

[CharlieLaub]

Originally Posted by linuxguru

That little unbuffered one is probably ok, within the constraints of its topology. Could you post its schematic, if you have one? I'd like to see if a lifted signal ground is implemented.

If you are referring to my post, the schematic is pretty much straight from the LM3886 datasheet. There is no muting switch, it is permanently connected to be "on" (no muting). There is a 1 ohm series resistor on the output, which I plan to replace with a link or the parallel resistor/inductor.

-Charlie

[barry.childs]

I bought one of these Yuanjing boards, and i'm quite pleased with the results. I think I will try linuxguru's mods though. I would like someone to explain the pre-amp. Is it a buffer and pre? Should the pot go where the jumpers are or are they just for bypassing the pre. I changed the op-amps for 4562's and it is much better. In fact it sounds very good, although bass is lacking. I considered getting a Pass B1 buffer and not using the op-amp, would this be an improvement? Any help would be appreciated. Cheers Barry

[linuxguru]

Originally Posted by barry.childs

... I would like someone to explain the pre-amp. Is it a buffer and pre? Should the pot go where the jumpers are or are they just for bypassing the pre. I changed the op-amps for 4562's and it is much better. In fact it sounds very good, although bass is lacking. I considered getting a Pass B1 buffer and not using the op-amp, would this be an improvement? Any help would be appreciated. Cheers Barry

The pre-amp is a 2-stage amp, consisting of a gain of 3.2 stage, followed by the jumper block, followed by a unity-gain buffer. I used the jumper block for a dual-ganged pot, but you can just jumper it (actually, you need to jumper it or use a pot to get any sound at all). The jumper just connects the output of the gain stage to the input of the unity-gain buffer.

To improve the bass, increase the input and feedback resistances to 47k (from the 22k shown). That will change the gain to 5.7, which doesn't hurt. Also consider larger-valued input caps (say 3.3 uF or 4.7 uF) if you can fit them.

To remove the 50/60 Hz hum, use the lifted-ground mod that I showed earlier - it will get rid of about 95% of the hum, and the remaining hum is not noticeable.

[barry.childs]

Thank you Linuxguru for you extremely quick reply. I will do these mods tomorrow as I have to go to the pub now! Do you think it is beneficial to put the pots where the jumpers are or is it just personal preference? I'll get back tomorrow after the mods are done. Thank you very much for your help. Barry