Myref Evo-2 Build

[avesbilal]

Hi Everyone

fitted the boards in a chassis, now amp is singing well and has the most detailed SQ I have ever heard.

I couldn't do better than this with my experience and in budget I allotted for chassis. For me it is the best I have done in all previous cab's.

Wiring is crude I will make it better with zip locks when i get them on hand.

I am thinking to upgrade the internal signal wire with shielded one. will also try to add a wood/acrylic Face plate

Few more upgrades I am thinking to add a remote volume control with ALPS RK27(10K) (Blue-Velvet) Currently I am using a 10K Stepped Potentiometer with SMD resistance inside, I am afraid if I will degrade the SQ by switching from Stepped to ALPS, Could someone shed some light on this.

I want to thank Linuxguru and all the FM's helped me

 

[Audiodoc]

I am also interested in this amplifier as the original myref rev C is incapable of driving my power hungry elac uni-fi speakers with an impedance of 4 ohm and have to use a 125+125W Modded Norge 1000 gold instead.

Have you tried this amp with 4 ohm loads without clipping or activation of spike protection. What is the rating of the toroidal transformer that you have used.

By the way I have the remote alps potentiometer and it works well. I am presently using the pass b1 group build the control the volume.
The Alps potentiometer has a motor and circuit board to rotate the pots central pin.

 

[keith_correa]

Tight twists please, for:
The power wires from switch to trafo.
Secondary wires from trafo to the terminal block.
And from terminal block to PCB.

Can you post a pic of the sides of the amp?

 

[jls001]

@avesbilal, I've had really good experience with Helusound AES DMX cable for internal signal wiring. It beats every other wire I've tried for internal signal level cabling.

Great project, BTW :thumbsup:

 

[sachu888]

@avesbilal, I've had really good experience with Helusound AES DMX cable for internal signal wiring. It beats every other wire I've tried for internal signal level cabling.

Great project, BTW :thumbsup:

Hi Joshua,
from where to get this wire. I will need good signal wire for my Hiraga build.

Regards
Sachin

 

[Audiodoc]

You can get a lot of stuff from diyaudio kart or import from eBay hong kong from good sellers like along1980

 

[jls001]

Hi Joshua,
from where to get this wire. I will need good signal wire for my Hiraga build.

Regards
Sachin

You can order from Promedia. Phone number +91 22 6702 1711

 

[avesbilal]

Sorry for the late reply, thank you Keith for the suggestion, i have twisted the wires.

I can confirm the instability i faced earlier of LM3886 chips heating up for one side is due to some mistake during assembly not due to actually Amp design.

Audiodoc: I haven't tried it with 4Ohm speakers, I have Boston 8" Full range 4 ohm drivers, will try and update you. My Transformer is 25-0-25 V -500A/10A per secondary. (I am getting 27-0-27 out from this transformer as my mains voltage is higher then standard, Myref X2 is running stably at this voltage, Linuxguru suggested to go for 24-0-24)

I identified the issue with the one board, when I fit the board at particular angle it becomes unstable, may be some loose shoulder joint but unfortunately i wasn't able to find the loose joint even after trying a lot. Now after fixing the board in the cabinet the board is stable and singing well.

I will also add a emi power filter in few days and see the difference.

I'm amazed at how beautifully it can sing even with my basic vintage speakers, instrument separation is awesome even in very complex music, amp does not even feel stressed at higher volumes (though my knowledge is very limited in Hi end audio), and the obvious one no hum/hiss from speakers at 100% volume with source DAC connected (music paused)

I again measured the DC voltage at speaker out it is ~2.3mv at one ~6.3 at other channel.

My chain is as below
Laptop-->SMSL M8 DAC-->Myref X2-->Cosmic covox 2500


I'm wondering what it can do on better speakers. ( I'm thinking of building a 3-way using Dayton Reference series drivers)

Jks001: could you please let me know the cost of shielded wire per metre.

Here are the side pics

Thanks Keith, Audiodoc, jls001 and all other FM's.

Any more upgrades and suggestions are welcome

Regards
Bilal

Sent from my Redmi Note 3 using Tapatalk

 

[jls001]

Bilal, it's about Rs 85-100 per metre. If you're going to use balanced cable for internal wiring do follow the methods I mentioned in my Kuartlotron buffer thread. It's important to wire it correctly.

 

[keith_correa]

Something that was suggested to me a long time ago for mounting toroidal transformers - I do not know how effective it is but no harm in trying it.
Get transformer away from base by at least a cm by cutting cardboard rounds and inserting between transformer and base.
Substitute steel bolt for nylon bolt and nut.
Substitute top and bottom round mounting plates on transformer for wooden roundels.

 

[avesbilal]

I'm using CD instead of cardboard to isolate the transformer from base, will try to get nylon nut bolt and washer to replace the metal one.

Have anyone compared the step potentiometer against ALPS RK27 (blue velvet), I'm using a DACT step potentiometer as shown in the below pic and URL, could someone advise if I replace this step potentiometer with blue will it be an upgrade or a downgrade?

Also could someone advise suitable speakers for this amp, wharfedale 220/225 good match or should I go with DIY by using Dayton Reference drivers. (I'm inclined to go for DIY route)

http://m.ebay.com/itm/DACT-Type-21-...3D201239685917&_trksid=p2056116.c100408.m2460

Regards
Bilal

Sent from my Redmi Note 3 using Tapatalk

 

[linuxguru]

(Sorry, didn't check the forum for a while, so I missed a lot of posts.)

I haven't tried either the DACT stepped attenuator or the ALPS RK27, but either of them should be fine. I'm guessing that the DACT may have a slight edge in resolution. In principle, it should be possible to modify the DACT using better SMD resistors, including Susumu RG and/or Beyschlag MMU0102 micro-MELFs, but it probably involves a lot of painstaking work to unsolder and solder the SMDs. It may also be difficult to find replacement SMDs of the same values.

 

[linuxguru]

I am also interested in the Evo 2. The my references rev c are singing well for the past few years but with the LM chip instead of the modded opamps LF01 which were showing sone instability.

I did some minor mods to the LF02 (basically, a dual LF01) earlier this year, with some improvement in audible sonics, but it is still a bit iffy on stability with faster opamps. I've been meaning to transplant those changes to the LF01 and check if there's any improvement to audible sonics and/or stability in the MyRef Rev C, but haven't had the time (due to unrelated reasons) - will give an update once it's done.

The Evo-2/MyRef-X2 respin is also on hold. Actually, I got started last year on a version with LM4780 instead of 2x LM3886, but then TI discontinued the LM4780, and there's no point in designing with (soon to be) unobtainium parts. For the moment, there seems to be no credible alternative to 2x LM3886 for driving 6-ohm or lower impedance loads. The old ST TDA7250 with discrete BJT outputs would have been a workable alternative, but that has also been discontinued for many years now (though there's a trickle of NOS parts that's still available on EBay and other online sources).

 

[avesbilal]

I am also interested in this amplifier as the original myref rev C is incapable of driving my power hungry elac uni-fi speakers with an impedance of 4 ohm and have to use a 125+125W Modded Norge 1000 gold instead.

Have you tried this amp with 4 ohm loads without clipping or activation of spike protection. What is the rating of the toroidal transformer that you have used.

By the way I have the remote alps potentiometer and it works well. I am presently using the pass b1 group build the control the volume.
The Alps potentiometer has a motor and circuit board to rotate the pots central pin.

Hi Audiodoc,
I have tried this amp with 6 and 4ohm speakers and it is able to drive them without any issues or clipping.

Regards
Bilal

 

[hifiramr]

Hi step potentiometer will bet better than ALPS RK27 but stepped need to be with good quality switch .The above mentioned one is very good what I have got good feedback from many users.Also somebody told me it produces a click sound sometimes not sure about it.

If you looking for Alps there is one old model which is excellent that is ALPS black beauty they stopped production will be costly to find out but worth

 

[jls001]

+1 to hifiramr.

I used to use ALPS Blue Velvet RK27 on Kuart buffer. Changing it to the 23-step stepped attenuator definitely improved sonics. Recommended!

 

[kpsthakur]

Hi Linuxguru, I think I sent you a PM earlier than finding this blog, any chance this design has stabilised and I can get my hands on these boards??

 

[venki7744]

Hi Aves - Good to hear that one board is stable with the heatsink installed. On the other board, R12 is OK - the coating tends to flake off with age, etc. You can measure and check if it's within spec (4.5k). Regarding R11, you can check if the signal ground to PGND resistance measures the same as R11 (1.5 ohms) - you have to use the lowest multimeter resistance range to measure this. The exact value is not important, as long as it is around 1 to 1.5 ohms.

Also clean the solder side with IPA to check if there are any small solder bridges or shorts to the ground planes.

Edit: I have no clear explanation for how it stabilized after running for a while, but new electrolytics do take a while to run in (the oxide barrier has to form on the aluminium foils). However, it should not have a bearing on stability, since all the electrolytics are bypass caps or related to the speaker protection. The only exception is C9, the Elna Cerafine, which is in the feedback path. The other possibility is that one of the resistors drifted a bit and stabilized - R11 is one such candidate, since it's a carbon composition.

My wild guess should be something to do with solder. May be a dry solder (unwanted connection) or a thin bridge which got disconnected with heat.

 

[Gebrey]

PM sent. The Evo-2 is derived from the MyRef Rev C, but with dual current pumps in parallel at the output stage to double the current drive capability, thus allowing it to drive 4 ohm loads with twice the power rating (80W into 4 ohms) as the original MyRef (40W into 8 ohms).

The FE/Fremen Edition uses a different schematic and compensation values, but the FE compensation alone can be transplanted either to the MyRef Rev C or the Evo-2 if required.

The Evo-2 is still at the experimental/evaluation stage - only a total of 6 PCBs were fabricated, of which 4 are committed to prototypes, and the remaining 2 went to the OP of this thread who was willing to take the chance of building an amp which was still experimental.

If there's interest, I'll eventually run a respin of the Evo-2 including fixes (if any) that are found in the experimental phase. Meanwhile, I have kits and PCBs for the MyRef Rev C monoblock, and MiniRef v1.04 stereo board - both of which are lower power, but proven and validated designs.

Hallo linuxguru, Im intrested too in these PCBs..
Ive discovered recently My Ref world and Im looking for a parallel pump that Dario PCB cant offer me yet.
Can you?