Group Buy: Mauro Penasa MyRef Rev C kit

[Audiodoc]

Check the DC offset at the speaker.
Use some heatsink for testing too as the chip will get really hot which in itself will lead to distortion by bringing the inbuilt chip protection into play.
One more thing to note is that if you are using low impedance speakers the transformer should be 20-0-20 even then the volumes levels cannot be raised to very high levels. It is better to connect to an 8 ohm load.

I have a perfectly fine amplifier but since my speakers are 6 ohms (on checking with mm it is 4 ohms) I can hear the screeching if I turn up the volume beyond a certain level (it could either be due to clipping or the chip circuitry coming into play).

When you connect an 8 ohm load and do proper grounding the amplifier is dead silent. I hear on a very faint hiss when I place my ear against the tweeter even at normal listening levels.

Do use some volume control as the amplifier will definitely clip at a high input signal (all amplifiers do).

 

[exljp]

Thanks badrisuper and Audiodoc. I'll attach the heat sink and volume control and try again. As Audiodoc mentioned, may be a 4 ohm speaker combined with an absence of a volume control could be the reason for screeching sound. Let me connect these and try again. Also I'll measure the DC offset at speaker out.

 

[badrisuper]

Today I completed my MyRef. I assembled it in a old pioneer case. Sound is coming. But I made mistake I think I reversed the volume pot. I have to decrease instead of increase. Bass is really good. Please suggest me how to connect to volume pot and how to identify like which one is right and left. I am identifying it by RCA connectors.

I will post the pictures little later.

Thanks
Badri

 

[Audiodoc]

Just swap the connections to the outer two pins of the pot. That's all.

 

[badrisuper]

I completed MyRef. It sounds good. But at high volume it started clipping. Anyone knows the reason. I gone through the thread, I believe there is no dry joint.

Thanks
Badri

 

[Audiodoc]

Mine is also clipping at high volume levels. The main reason being the discrepancy between the power supply and speaker impedance.

For 8 ohms speaker impedance the input transformer should be 22-0-22 to 24-0-24V.

For 4 ohm speakers the transformer should be 18-0-18 to 20-0-20V.

I have used a 22-0-22V input transformer which after rectification and smoothing produced 32-0-32V DC which I use with my 6 ohms speakers. Which clip beyond 12o'clock position.

Try yours with 8 ohms speakers. Also check whether the LM3886 chips are getting very hot or just warm.

Eventually every amplifier clips.

And most IMPORTANT POST THE PICTURES!

 

[omishra]

Tried searching this thread, but in vain. Can anyone tell me heat sink requirement for this kit. I recently purchased bare bone cab of Pass B1 thread from Magma. It has thick side walls of some excursion. Can I attach chips to that walls and use as a heat sink?

 

[gopib]

I have used a "small" 2" x 1" sink with vertical fins for each of the LM. At about 9 o'clock position and with a 28-0-28 rail it gets warm after about an hour. These sinks I picked up as scrap in the local aluminium market.

The side walls may be ok. But then you have to consider the aesthetics as well
as the ventilation. Unfortunately Magma's cabs do not have ventilation, unless you change the top plate.

I am also trying to box my MyRef in the additional cab I picked up from magma. Looking at various alternatives...

Gopi

 

[Audiodoc]

The chips don't get very hot on 8 ohm loads so they can be mounted on the cabinet walls however the protruding bolts may ruin the aesthetics. My cab has dimensions of 30 x 17 x 5.4 cm with ventilation slits in the top and bottom.

I know recently came into contact with a dealer in china who sells all sorts of enclosures. They are good quality ones from 1 kg to 15 kg. If DIY geeks are willing we may get together for a group buy and save on shipping etc.

The site in in Chinese however one can easily understand by checking pictures and internal dimensions.

 

[omishra]

Okay, so will go ahead with magma's cab and sidewall mounting. I will take care to maintain aesthetic of the cab. I have some idea and tool to do it. I will post some pics later on. Now need some time.

Now need to find some time, it seems I will be working in office this week end.

@Audiodoc: Can you PM that site to me. I would like to see the designs. I am missing that Thailand guy who provided me power amp cabs very reasonably.

 

[Audiodoc]

Here is the link, let all see and benefit mishraji

?? ?? ??_????

 

[Audiodoc]

This guy is genuine and active on diyaudio. He is a dealer from Hongkong by the name bigpandahk. Here are his posts:

diyAudio - Search Results

In case you like them I will also be interested in a group buy.

 

[kroyin]

I bought his 4xwm8741 dac...currently on it's way from HK...very nice gentleman

 

[Audiodoc]

I have a 4xWM8740 DAC courtesy a forum member who donated it to me as its power supply had short circuited. With a few replacements (toroid, rectifiers and voltage regulators) it is up an running. The 8741 is a better and costlier chip than the 8740 so will sound even better. Do click some pics of the innards and post the link.

 

[kroyin]

Pics in the sell thread

Wolfson 4.0 DAC upgraded to WM8741 - diyAudio

 

[Audiodoc]

@kroyin. I have the same one with older WM8740 chips, sounds great. Cheers!

@ badrisuper. Did you try the MyRef with 8 ohm speakers and check for clipping as well as chip temperatures?

 

[vijaycool]

I am closely watching this thread and I may build one. While searching over the net I have found this
Why do some chip amps / gainclones sound so bad? (updated 2012-03-30) - diyAudio

Is this the reason why some of the members getting clipping and screetching sound?

 

[mbhangui]

Just came across this thread. I think I am too late to have arrived on the scene :sad:

Any possibility of late comers like me to get this kit? Where do I obtain parts like the transfomer, case, heatsink, etc. I have DIY skills like soldering, etc. But not in building a good looking case and external finish. Where can one get a nice case for this?

Audiodoc, where did you get the good looking cabinet for your amp, or did you make the case yourself?

 

[josephjohnt]

Just came across this thread. I think I am too late to have arrived on the scene :sad:

Any possibility of late comers like me to get this kit? Where do I obtain parts like the transfomer, case, heatsink, etc. I have DIY skills like soldering, etc. But not in building a good looking case and external finish. Where can one get a nice case for this?

Audiodoc, where did you get the good looking cabinet for your amp, or did you make the case yourself?

For R-core transformers, this is a good option
electro magnetic devices <http://emagdevices.com>
B-1, Electronics Complex
ECIL-X-Roads, Kushaiguda
Hyderabad, AP 500062, India
ph (91) 40 27121513

The cabinet you see in Audiodoc's post is from 8 Audio, HK 8Audio - DIY Audio, Hi-end Audio Supplier

 

[captrajesh]

Just came across this thread. I think I am too late to have arrived on the scene :sad:

Any possibility of late comers like me to get this kit? Where do I obtain parts like the transfomer, case, heatsink, etc. I have DIY skills like soldering, etc. But not in building a good looking case and external finish. Where can one get a nice case for this?

Audiodoc, where did you get the good looking cabinet for your amp, or did you make the case yourself?

I had made this amp many moons ago and also sold it off. It is a very decent amp. You may PM our FM Linuxguru for the kit. I understand that he now has premium kits which have superior quality components.