Myref Rev C in Hyderabad

[avesbilal]

Hi FM'S,

I'm thinking to build a Myref Rev C Amplifier from Linuxguru, so want to audition it before starting, so that I know what I should be expecting out of it.

I always built an amplifier based on LM3886 sourced the assembled board from China and I am pretty satisfied with the performance of this amp, I will showcase my built once it is 100% complete, but now curious to know what differences it has then compared to Myref Rev C as I heard a lot about Myref.

Is there anyone from hyderabad who built Myref Rev C Amplifier sourced from linuxguru and willing let me audition it at their convenience?

Any help is greatly appreciated.

Thanks for taking time.

Regards
Aves Bilal

 

[avesbilal]

Hi FM'S,

I'm thinking to build a Myref Rev C Amplifier from Linuxguru, so want to audition it before starting, so that I know what I should be expecting out of it.

I already built an amplifier based on LM3886 sourced the assembled board from China and I am pretty satisfied with the performance of this amp, I will showcase my built once it is 100% complete, but now curious to know what differences it has then compared to Myref Rev C as I heard a lot about Myref.

Is there anyone from hyderabad who built Myref Rev C Amplifier sourced from linuxguru and willing let me audition it at their convenience?

Any help is greatly appreciated.

Thanks for taking time.

Regards
Aves Bilal

No one from Hyderabad has built Myref Rev C Amplifier. ...?

If audition is not possible, at least people who has heard a normal LM3886 which is similar to below pic vs Myref Rev C, please highlight differences. ...

 

[avesbilal]

No one from Hyderabad has built Myref Rev C Amplifier. ...?

If audition is not possible, at least people who has heard a normal LM3886 which is similar to below pic vs Myref Rev C, please highlight differences. ...

 

[linuxguru]

There are a few MyRef Rev C builds in Hyderabad, but not all are my boards/kits - some are Twisted Pear kits from the diyAudio GBs.

BTW, I haven't seen that Chinese board before, but it seems to have quality components on it, including an opamp-based tone-control section, good pots, good film caps for coupling, etc. Is that a Jim's Audio board or something else?

 

[avesbilal]

Thanks for replying Linuxguru,

I bought it from aliexpress, I just bought this board on risk and before i came across Myref Rev C, all I know is this is designed by some person "JR" not sure what JR means.

Now I want to compare my amp with Myref and if Myref wins, I will build one. No one from Hyderabad has responded yet:sad:

I am attaching the schema, I am pretty impressed with the performance of this board, didn't expected it to be so good. (I am not a audiophile and this is only my opinion)

 

[avesbilal]

Hi Everyone,

No one yet, I was expecting at least some expert inputs how different Myref Rev C is when compared to the Chinese amp I posted in my earlier post.

I believe that there might me a lot of people had this curiosity of comparing SQ.

I wanted your all help for the same reason that everyone has that I should build a excellent amp with the money I can afford. I am expecting to complete my amp in the budget of 20K with the best SQ I can achieve.

One more question I want to ask is that what is the amp in the market with which I can compare My Rev C, I mean to say how much I have to spend if I want to buy similar SQ ready made amp from market.

Any recommendations, opinions are welcomed and greatly appreciated.

Thanks again for all the help and for taking time reply.

Regards

 

[linuxguru]

I bought it from aliexpress, I just bought this board on risk and before i came across Myref Rev C, all I know is this is designed by some person "JR" not sure what JR means.

I must say that the schematic of that JR gainclone is somewhat unique and clever - it has a current-feedback loop nested within a conventional voltage-series feedback loop, which I have not seen in common use with chipamps. I'll try to run a simulation of this idea later with an LM1875 - I have no idea if there's any advantage. However, it is still possible to nest the whole chipamp block within an outer opamp feedback loop, similar to the MiniRef 1875.

Edit: What's the value of R15? It's obscured on the posted schematic on the right.
R13-C9 RC product is too low as a low-pass filter to suppress RF, but it's probably not a big issue since there's already an opamp tone-control section before it. Also C10 looks either unneccessary or too large, but need to check in simulation - it's probably a stability/compensation element.

 

[avesbilal]

I must say that the schematic of that JR gainclone is somewhat unique and clever - it has a current-feedback loop nested within a conventional voltage-series feedback loop, which I have not seen in common use with chipamps. I'll try to run a simulation of this idea later with an LM1875 - I have no idea if there's any advantage. However, it is still possible to nest the whole chipamp block within an outer opamp feedback loop, similar to the MiniRef 1875.

Edit: What's the value of R15? It's obscured on the posted schematic on the right.
R13-C9 RC product is too low as a low-pass filter to suppress RF, but it's probably not a big issue since there's already an opamp tone-control section before it. Also C10 looks either unneccessary or too large, but need to check in simulation - it's probably a stability/compensation element.

@linuxguru: R15 is 22K, I am uploading few better quality PIC's of schema

 

[rbalu72]

Just thought of throwing this idea..

earlier linuxguru ran a group buy for Myref C kits and there were many takers from Hyderabad (am a recent joinee to this forum so i didnt participated in that GB which happend in 2010)..

Search this forum for that thread and see if you can PM any folks who built that kit and still using

long shot but I keep hearing many good things about Myref version so nothing wrong in trying..

 

[venki7744]

I must say that the schematic of that JR gainclone is somewhat unique and clever - it has a current-feedback loop nested within a conventional voltage-series feedback loop, which I have not seen in common use with chipamps. I'll try to run a simulation of this idea later with an LM1875 - I have no idea if there's any advantage. However, it is still possible to nest the whole chipamp block within an outer opamp feedback loop, similar to the MiniRef 1875.

I am making a logical guess on the current feedback, this might be to iron out the non-linearity due to change in o/p impedance across the frequency spectrum (speaker being non-linear especially around the Fs). However I dont have any idea on how we can come up with those values (7.5K).

Cheers,
Venki

 

[linuxguru]

I am making a logical guess on the current feedback, this might be to iron out the non-linearity due to change in o/p impedance across the frequency spectrum (speaker being non-linear especially around the Fs). However I dont have any idea on how we can come up with those values (7.5K).

Yup, I checked it in simulation and it makes little or no difference to distortion when a resistive speaker load is used. With an L + R linear load, the current feedback appears to improve phase margin a bit. A big improvement will likely be seen only with real (non-linear) speaker loads with all effects including cabinet resonances, cone compliance, back EMF, etc. modeled accurately.

Nevertheless, it's worth checking it out experimentally and subjectively with an LM1875 or similar Pentawatt chipamp - it looks like an inexpensive way to improve audible sonics without the complexity of nested feedback as used in the MyRef, MiniRef and other composite amp topologies.

 

[tnvijay]

Just had a hunch that JR more might point to Joe Rasmussen? designer of jLTI ( just listen to it) amp?

 

[linuxguru]

Just had a hunch that JR more might point to Joe Rasmussen? designer of jLTI ( just listen to it) amp?

That gainclone from AliExpress is Chinese, but maybe they cloned an amp from elsewhere (could be any design).

On a related note, it's possible to employ the same current feedback idea in the MyRef, MiniRef and so on - the key idea is to return the current feedback to the *outer* GNFB loop that controls the small-signal opamps (e.g. LM318 in the MyRef). Maybe I'll try it out in a future re-spin which I've dragging my feet on for more than a year - it will complicate the trace routing, but it can be done in principle.

On an existing MyRef board, it can be implemented with several messy trace cuts, hand-drilled lead holes, jumper wires and resistors soldered on the bottom of the board - probably not worth the effort, except for experimental verification.

 

[avesbilal]

One question here about Lm3886

What should be the ideal temperature for LM3886? (When music is playing@ 40 of total volume)

 

[avesbilal]

The reason behind my above question is.

The Chinese LM3886 Amp board I'm using have different temperature at both IC's

When i mesured both the IC's when the Amplifier is operational (music playing at 35%/40% volume)

Left IC was at 52/53 degree and right IC at 49.. is this normal?

Regards
AB

 

[linuxguru]

A few degrees difference is OK - most heatsinks aren't thermally symmetrical, and the chipamps aren't mounted perfectly symmetrically on the heatsink either. Regarding temperature, the LM3886 can run at fairly high temperatures, but then you have to derate for Safe Operating Area.

As a rough rule of the thumb, up to 60c is fine. It can go much higher, subject to derating as per the datasheet.