Group Buy: Mauro Penasa MyRef Rev C kit

[Audiodoc]

Tried the NE5534s, OPA 627 and TL071. My ref is the most stable with TL071. Bass and treble are good however mids are a little veiled.

DC offset is around 150mV with the OPA627 and I could hear some distortion. With the TL071 it is around 1mV and you need a stethoscope against the woofer diaphragm to hear any hiss with no signal at the input.

 

[linuxguru]

With the TL071 it is around 1mV and you need a stethoscope against the woofer diaphragm to hear any hiss with no signal at the input.

Impressive - it suggests that the way forward for future opamp upgrades for the MyRef is a JFET-input high-end opamp, probably with modified compensation values. The OPA1641 comes to mind as a possibility.

Another possibility is an LF01 with a SOIC8 TL071 in place of the LM318 - I'll give this a shot this week.

 

[exljp]

Hi
I searched all over SP Road (Chethan, Advance Micro, Arihant, Amar Radio shop and so many others) for LM3886TF and Panasonic 10,000uF/50v capacitors. I just cant get it anywhere. One shop offered the IC, but no guarantee, I avoided it since he specifically told this without me even asking for guarantee. Can anyone help me with any other source?

Instead of Panasonic cap , any other brand good enough? Few shops had some other brands.

 

[Audiodoc]

Yes you may try other brands too. You can purchase it online too. I bought 7 LM3886 from Hongkong for 1200 bucks and I am sure they are genuine. They even came packed in the original national semiconductor transparent strip with lot No etc. If you want to play in safer waters order from element 14 for around 400 bucks each. Capacitors are also available on ebay from nippon chemicon cheapos to nichicons, elna gold tune, BC, nover. Indian capacitors can also be used like pusumi, alcon.

 

[sachu888]

Hi
I searched all over SP Road (Chethan, Advance Micro, Arihant, Amar Radio shop and so many others) for LM3886TF and Panasonic 10,000uF/50v capacitors. I just cant get it anywhere. One shop offered the IC, but no guarantee, I avoided it since he specifically told this without me even asking for guarantee. Can anyone help me with any other source?

Instead of Panasonic cap , any other brand good enough? Few shops had some other brands.

Hi,
look here :
LM3886TF Formerly Farnell | Electronic Components Distributor | element14 India

Panasonic 10,000uF/50v PANASONIC|ECOS1HA103EA|CAPACITOR, 10000UF, 50V | element14 India

Please confirm with Linuxguru before buying.

Regards,
Sachin

 

[linuxguru]

At S.P.Road, Chetan has authentic LM3886TF from time to time, but not necessarily in quantity. I bought a few from him this month.

Regarding caps, most high values in Japanese brands are in short supply as distributors hold back stock in anticipation of a weaker Re leading to higher prices.

You can use anything from 6800uF to 15,000uF rated at 42V or higher, and any diameter up to 35mm. You should be able to get Samwha, at the very least. The best I've used are Yamaha-branded blue/silver Nippon-Chemicons in 12,000uF/71V and 10,000uF/71V, but stocks have dwindled and prices have climbed quite a bit. Elna LP5/LA5 10,000uF and 12,000/63V used to be available earlier, but the flooding in Thailand has disrupted the supply chain. Rotel-branded (possibly Nichicon OEM) 10,000uF/63V 30mm is a recent arrival, if you can find it. I've also seen samples (but not quantity) of Vishay-Roederstein EYN large electrolytics - please post here if you locate anybody with decent stocks.

If you can't find any of these, I still have a few Panasonic 6800uF/50V and Elna 4700uF/50V, both of which are fine if you're using the MyRef to drive HT satellites, bookshelves or even small monitors.

 

[exljp]

I ordered lm3886tf from ebay

Amar radio had Rubycon 10000uF/63V. Is this good enough?

 

[navin advani]

I will be offering a kit (including the PCB and everything on the PCB) for Rs.1500 each. These are monoblock kits, and you will need two to assemble a stereo amplifier. The kits will be supplied unassembled. In addition, you will need cabinet and chassis components, transformers, connectors, cabling, standoffs, heatsinks, bezels, switches, etc. of your own choice.

Nice idea. I was looking to build a 3886 mono for my 1875 stereo amp (2.1 way active ipod speaker).

What is the cost of a mono kit?

 

[linuxguru]

Nice idea. I was looking to build a 3886 mono for my 1875 stereo amp (2.1 way active ipod speaker).

What is the cost of a mono kit?

If you want a sub-woofer amp, the MyRef is not the optimal choice - it is rated at 40W out, and is only rated to drive 8-ohm loads.

If that is sufficient, I have standard monoblock kits for Rs.2k and premium monoblock kits for Rs.4k. PM me or email me at siva dot chander at gmail dot com for details.

 

[gobble]

If you want a sub-woofer amp, the MyRef is not the optimal choice - it is rated at 40W out, and is only rated to drive 8-ohm loads.

Hi Linuxguru
You mean it wont drive a 4ohm speaker ?

--G0bble

 

[sunilj]

Hi,

Running the 3886 with 4ohm SUB, you might run out of grunt very quickly. Try these links which explain the output of National chips a little more.

http://www.national.com/assets/en/other/Using_Overture_Design_Guide.pdf

http://www.google.com/url?sa=t&rct=...sg=AFQjCNFIUeCVqtgSBNYltDZfyTi72X1MNw&cad=rja

 

[linuxguru]

You mean it wont drive a 4ohm speaker ?

If you keep the supply rails at +/- 28V or lower, it will drive 4 ohm loads also. However, it will have higher distortion and run less efficiently than with 8 ohm loads, which is what it's designed for.

If the rails are higher than 28V while driving 4 ohm loads, SPike protection will kick in pretty quickly, and continued operation may lead to permanent damage.

 

[omishra]

If you keep the supply rails at +/- 28V or lower, it will drive 4 ohm loads also. However, it will have higher distortion and run less efficiently than with 8 ohm loads, which is what it's designed for.

If the rails are higher than 28V while driving 4 ohm loads, SPike protection will kick in pretty quickly, and continued operation may lead to permanent damage.

You mean to say, what I got from you will not work for 4 ohms load, but what for 6 ohm?

 

[sunilj]

Hi,

If your speakers are 4ohms nominal, meaning, they run at 4ohms over most of the bandwidth they're playing, the likelihood of the impedance dipping to ~ 2 ohms is very real. Typically 8ohm speakers can dip to 5ohms.

At 28v the 3886 is rated for 38W@8ohms and 68W@4ohms and cannot give you the output required to continue playing "and pretend" all is well.

As somebody explained, the in-built 'Spike' protection will kick in quickly and/or distortion will be audible. This is a link to the National spec sheet. Explains quite a bit what this chip and cannot do.

This is another good no-nonsense read of a 3886 implementation.

If you're going active this little bugger will shine over a limited midrange bandwidth.

 

[linuxguru]

This is another good no-nonsense read of a 3886 implementation.

The ESP project actually uses an LM3876 (with an option for the LM3886), but the principles are the same. By virtue of its smaller output transistors (with smaller base and collector capacitances), the LM3876 actually sounds better in a basic gainclone than an LM3886.

However, please note that the LM3876 does not work correctly in a MyRef Rev C/E, despite having a pinout compatible with the LM3886 - it usually latches up high on power-up, triggering the protection circuit. However, the LM3876 may work in a MyRef Rev A (now largely obsolete), though I haven't tried it.

 

[navin advani]

Hi Joshua & Sachin, i am in the process of completing the LM3886 project soon, here is my cabinet design[/IMG]

Beautiful. What does this cabinet cost?

Running the 3886 with 4ohm SUB, you might run out of grunt very quickly.

If you want a sub-woofer amp, the MyRef is not the optimal choice - it is rated at 40W out, and is only rated to drive 8-ohm loads.

At 28v the 3886 is rated for 38W@8ohms and 68W@4ohms and cannot give you the output required to continue playing "and pretend" all is well.

I am looking to drive a small 7" sub with this. I think 40W will suffice for this. It is part of a 2.1 system for an home made ipod dock.

 

[sunilj]

Hi Navin,

I have the 3875, 3886 & 4780, with variable gain and was happy with none. They were driving the woofer in a 3-way, actively crossed above 100hz. At low volumes they sounded really good, I would say the amp had great control over the woofer (subjective, I know).

With the volume turned up the sound was not good, just plain lousy. I can only guess it ran out of power.

Your mileage may vary w.r.t the SUB design.

regards.

 

[navin advani]

Hi Navin,

I have the 3875, 3886 & 4780, with variable gain and was happy with none.
Your mileage may vary w.r.t the SUB design.

regards.

Thanks for the warning I'll look at other options.

 

[Audiodoc]

Received new LM318s for my built and using the new chips didn't help with my high latching up problem. However on replacing the 22pF C34 to 100pF everything settled down well with a DC offset of 5mV and 6mV on the two channels. So the problem was not in the ICs but the capacitor.

 

[linuxguru]

However on replacing the 22pF C34 to 100pF everything settled down well with a DC offset of 5mV and 6mV on the two channels. So the problem was not in the ICs but the capacitor.

Great - that issue didn't show up in simulation or even in the prototype build with C34=22pF or 47pF. I'll fix it at 100pF for future builds if there's no significant regression in audible sonics.