Group Buy: Mauro Penasa MyRef Rev C kit

[linuxguru]

I have the following wima's - 100nf mkp2, 220nf - mkp2, 1uf - mkp4... planning to use for c4, c5. where else can i use these and not waste them.

If they fit, you can use the 220nF at C4, 100 nF at C5 and 1uF at C13 (if there isn't any better alternative for C13).

I also have a few pieces of vishay monocaps 10pf, 22pf, 33pf, 47pf, 150pf, 220pf. There are second choice caps in bom for c10, 12 and 34, so I can use them there. Would it also work well for c32.

No idea about the Vishays, but C32 can be a C0G if an FKP2 is not available. Same with
C10, C12, C34, C30.

Is the wima mkp4 1uf a good choice for coupling cap. I also have bennic 2.2uf polypropylene (speaker cap) and a bunch of yellow indian polyester caps from sp road.

If the bennic is an axial MKP, you can go with it over the MKP4.

What about C7, saw 10nf, 100nf, 220nf etc being used. whats the best value and cap here.
I still have nothing for C21/22nf (some sp road small box caps i do have), C30/1nf too. whats good for these.
Are c0g/np0 good choices for these.

C7 should be preferably be film/foil, around 10 nF. The order of preference is: KS (polystyrene), FKP, FKS, FKC, MKI, C0G. They can be mounted either at C23 (5mm x 5mm square) or at C7 (5mm or 7.5mm box type) - they're connected in parallel, and only one is required.

C21 is optional - if C9 is good enough, you don't need C21 to bypass it.

C30 can be C0G, though film/foil types are slightly better.

How are locally made cf resistors from sp road. what should i use for R3. whats the absolute minimum required wattage here. I only see wirewounds on sp road or element14 for this kind of power.

Locally-made Watts, Philips, Thakor are pretty good. They're slightly magnetic, but that's OK. If available, use Panasonic ERO metal-films (they have a green epoxy coating).

For R3, you can use a plate-type ceramic resistor in 3 to 5W rating if available, otherwise use a 0.22/2W in series with 0.33/2W bent in a U-shape - it will fit comfortably.
2 x 0.22 or 2x 0.33 will also work with slight impact on stability.

 

[linuxguru]

220uf - panny fc 63v(8), elna re3 100v (4), elna re3 160v(2). which is the best option for c9. these are cheap and i dont mind getting some more from element14.

If they fit, all will work at C1, C4 and C9, though they're one level below Panasonic FM, and about 2 levels below Muse KZ, FG, Elna Silmic and Cerafine.

100uf - nichicon pj and vr, elna, ucc kze, ncc kme. which is the best option. can get panny fc or fm from e14.
22uf - got NCC KME.

Which Elna? RE2, RE3, RJH, RJJ, Silmic and Cerafine will do fine, otherwise Panasonic FM, FC.
KME is fine for 22uF - it's only for the protection relay circuit.

for psu caps, i got nichicon GU (green ones) 12k 35v. since i am using 230-22v trafo, it might be ok. do i need to go for higher voltage caps.

I'm not sure about the authenticity of the S.P.Road Nichicon GUs. for 22-0-22, it's OK, but if you plan to change trafos later to 24-0-24 or higher, you may want to look for 50V-rated electrolytics. At S.P.Road, you can look for Epcos (Siemens) and ROE (Roederstein) large cans (up to 35mm diameter, anything larger won't fit on board).

 

[tnvijay]

Has anybody built miniref 1875 designed by linuxguru?
I recently built its standard version and pleased with the performance.

 

[linuxguru]

Thanks, Vijay. Keith Correa has got a very similar kit from me, but I'm not sure if he has finished assembling it.

I hope you're able to locate a suitable cabinet for the Sony 6" drivers - I believe that they will play well when driven by the MiniRef. I have tried it with JBL LX2001 2-way bookshelves, with good results.

 

[tnvijay]

Hi sir,
I am yet to get a cabinet.upon preliminary testing,
I feel its more useful as a woofer in a 3 Way.As of now, the philips Hi Q and miniref are a match made in heaven!!

 

[xboxxtech]

Hello Siva,

Nice to see someone from chennai so active in DIY. Im Also shiva from chennai. Are the kits with the components or only pcb? I need one pair Bro.

Shiva

 

[linuxguru]

Nice to see someone from chennai so active in DIY. Im Also shiva from chennai. Are the kits with the components or only pcb? I need one pair Bro.

Hi Shiva - ping me or email me at siva dot chander at gmail dot com for further details. I have bare boards as well as kits for the MyRef (suitable for Rev C, E or FE compensation) and the MiniRef 1875. The MyRefs are monoblocks rated at 40W per channel, while the MiniRef is a 2-channel board rated at about 20W per channel.

The MiniRef can generally be used in more compact cabinets and upgrades, and its sonics are now as good or better than the MyRef Rev C.

I also offer some optional opamp upgrades for both the MyRef and the MiniRef, which can be done as needed at a later stage.

 

[mandyrhtdm]

Hi I would also want a kit of Mini Ref can you tell me the cost of the kits ?

 

[jls001]

The transformer is 24-0-24, 5A, i.e. 240 VA. This translates to DC rail voltages of approx. (1.4142 * 24V) - 2V ~= +/- 32 V, which is the recommended rail voltage for the MyRef. H

@Lunuxguru: I checked the outputs of the secondary windings of the transformer I had bought (many moons ago) for MyRef Rev C, and they're 26.3 and 26.4V, so regulated voltages will be 35.x V. Will this higher voltage work? The primary in my building is 240V and not 230V so secondary also increases by the same proportion.

I want to complete this build -better late than never

 

[doors666]

@Lunuxguru: I checked the outputs of the secondary windings of the transformer I had bought (many moons ago) for MyRef Rev C, and they're 26.3 and 26.4V, so regulated voltages will be 35.x V. Will this higher voltage work? The primary in my building is 240V and not 230V so secondary also increases by the same proportion.

I want to complete this build -better late than never

35v will be fine.Absolute max voltage it can handle is +-42v. I havent seen many people using it with more than 35v though. And this will be strictly 8 ohms only..

 

[jls001]

35v will be fine.Absolute max voltage it can handle is +-42v. I havent seen many people using it with more than 35v though. And this will be strictly 8 ohms only..

I got similar advice from Linuxguru.

I will go ahead and use the transformer. I spent most of yesterday doing up the cabinet. Now it's ready to receive the boards, heat sink, transformer and cabling.

Is there some elegant way to bring down the rectified secondaries to about 28V from circa 35V so that I won't have to worry about 4 ohms speaker load? I'm OK to lose some power due to the reduced Vcc, but would like the ability to handle lower Z.

 

[Audiodoc]

There is no simple way. The best way is to get a regulated power supply circuit lm 317 lm337 based with 3055 transistors to get the adequate current but that would be as costly as getting a new toroid.

I also have only 4 ohm and 6 ohm nominal speakers from elac, Qacoustics and wharfedale and all have problems with the myref when playing bass heavy tracks

For 4 ohm speakers 18 0 18 to 20 0 20 secondaries are essential so the dc voltage is below 28 0 28. This may not be great for 8 ohms speakers but is essential for 4 ohms if you want to play loud.

 

[jls001]

For 4 ohm speakers 18 0 18 to 20 0 20 secondaries are essential so the dc voltage is below 28 0 28. This may not be great for 8 ohms speakers but is essential for 4 ohms if you want to play loud.

Thanks for the replies, Audiodoc.

Does this mean we can tailor this amp only for one type of load, namely, 4 ohms or 8 ohms, but not for both?

My current speakers are nominally 8 ohms, but I just wanted to be able to drive a lower load should the need arise.

Probably an easier option would be to have the secondaries reduced by the guy who wound this toroid for <=28V regulated output. I have not asked him if it would be feasible, but I think it can be done.

 

[quad]

Is there some elegant way to bring down the rectified secondaries to about 28V from circa 35V so that I won't have to worry about 4 ohms speaker load? I'm OK to lose some power due to the reduced Vcc, but would like the ability to handle lower Z.

Joshua, you can try a "bucking transformer" -

Bucking Transformer DIY (Drop 240V to 220V) | DMS Audio (Sound Kontrol)

Bucking Xfmrs

 

[jls001]

Joshua, you can try a "bucking transformer" -

Bucking Transformer DIY (Drop 240V to 220V) | DMS Audio (Sound Kontrol)

Bucking Xfmrs

Thanks for the pointer, quad.

One line catches my attention from the first link: "Live is taken off the remaining secondary and neutral is just connected through."

Since we need +V/0/-V, one lead of the secondary cannot be sacrificed in our case. It would have been perfect for a single voltage application.

 

[omishra]

In each rail I will simply add 10 x 10A diodes in series before filter capacitors. 0.7V x 10 = 7V.

I tried 4 diodes in my t amp to bring rails down to 33V from 36V.

 

[quad]

Thanks for the pointer, quad.

One line catches my attention from the first link: "Live is taken off the remaining secondary and neutral is just connected through."

Since we need +V/0/-V, one lead of the secondary cannot be sacrificed in our case. It would have been perfect for a single voltage application.

You are referring to using an unused secondary tap to buck the voltage.

What I meant is to use another transformer to provide a suitably bucked line voltage -

Vintage Voltage Adapter

 

[jls001]

OK, I read the Rod Elliott article too and that's what it suggested (another transformer). My cabinet is rather tight as it was custom made for the MyRef Rev C so I'll have to see if I can fit a smaller transformer. I do have unused transformer.

But I'll probably try wherever voltage I get with the default windings, and may be experiment later with bucking. In any case, I don't have a speaker of 4 ohms nominal rating.

In each rail I will simply add 10 x 10A diodes in series before filter capacitors. 0.7V x 10 = 7V.

I tried 4 diodes in my t amp to bring rails down to 33V from 36V.

Om, is the series diodes put after the rectifier diode bridge? And before the filter caps?

Any recommended diodes please?

 

[jls001]

OK, I powered up the amp and I'm greeted by low level hum, audible from about two feet away from both the speakers. I'll troubleshoot my cabling as it sounds like induced AC hum. It has constant SPL at all volume levels.

On connecting speakers, the volume is very feeble even at full volume. It sounds like I've barely turned the volume up from zero. I need troubleshooting help from folks who've built this amp.

Some observations:
1. Distortion audible when volume is pumped up to near full.
2. Left channel volume is lower than right.
3. DC offset with inputs shorted is 21.x mV and 26.x mV. When open, one channel is 7.x mV and the other channel varies continuously from about -15 mV to about +77 mV. The varying offset doesn't feel normal.
4. Secondaries from the toroid are 26.x V.
5. Speakers are nominally 8 ohms.
6. Audio chain --- music PC running Bughead player at full volume Kuartlotron buffer with volume control MyRef C speakers.
7. LM3886 chip is cool even after one hour as heat sink is substantial. But biasing resistors get hot. I think I'll need to beef it up.

 

[omishra]

Yes those series diodes to be placed between rectifier bridge and filter caps.