Group Buy: Mauro Penasa MyRef Rev C kit

[linuxguru]

Just a few updates:

1) I have finished testing a new fully-discrete opamp module, the LF05, that replaces the LM318 in the MyRef. This is a Class-A, folded Kaneda-style topology with a gain-BW product of about 10 MHz and input-stage voltage-noise of 1 nV/sqrt(Hz). In my test setup, the output offset voltage is typically below 20 mV, and often as low as a few mV. Initial audible impressions are that it is dark, detailed, smooth and laid-back - sort of like the best monolithic BB opamps, but Class-A and completely stable in the MyRef.

I have a few prototypes in hand for evaluation, and will arrange for the assembly of some more within a few weeks. Those who have already purchased LF01 modules earlier from me are welcome to evaluate the LF05 at no charge, and keep whichever one (LF01 or LF05) they prefer and return the other. LF05s will also be available for general use within a few weeks - it can generally replace any DIP8 bipolar single opamp like the 741, LM318, NE5534, etc. in most line-level applications, with more transparent and darker audible sonics.

2) For C1, C2 in the MyRef, the Elna RE3 Silverblue electrolytics are a better choice than the Panasonic FC or Nippon Chemicon KY that I included in most of the earlier standard kits. Those who have not yet assembled the standard kits in Bangalore are welcome to exchange the FCs or KYs for the Elna RE3s. These are almost as good as the Nichicon Muse KZ in the premium kits.

3) MyRef V1.4 PCBs and standard kits will be available with me for a while. A few premium kits will also be available, subject to the availability of premium electrolytic and film/foil caps.

4) LF01 opamps are still available, for the benefit of anybody who prefers them over the new LF05 opamps.

For details, PM or email me at siva dot chander at gmail dot com.

 

[Audiodoc]

I am interested as my LF01 were not stable. I have been listening with my lm318s ( both variants ). Would love to give these a try.

 

[murali_n]

Hi siva,

How do they compare with LM 49990 opamps?

N.Murali

 

[linuxguru]

@Audiodoc: Great, will send you a pair of LF05s. If there's any change of address, please email me.

@Murali: The LME49990 are ultra-low distortion, high open-loop gain, Class-AB output opamps that will provide exceptionally good results in circuits that have been designed specifically for them. Care has to be taken with bypass, decoupling, layout, etc., to ensure stability and get good results. They will not work in a MyRef without major changes in the compensation schema.

OTOH, the LF05 is a relatively low open-loop gain Class-A folded Kaneda topology that is renowned for its audible sonics and stability. It does work well without any changes to a MyRef Rev C/E. It also has very low-noise transistors in the input stage (4401, which is praised by numerous experts including Bob Cordell, Scott Wurcer and Salas), which are lower-noise than any monolithic opamp except the LT1028.

In other words, I'm striving for very low noise (darkness), Class-A sonics (smoothness), stability (freedom from oscillations under transients or clipping) and I'm willing to accept moderate measured distortion which is mostly 2nd-harmonic (non-fatiguing). I believe these objectives have largely been met.

Note that it's not terribly fast at 10 MHz GBW, but neither is the highly-regarded OPA627. It's not tremendously low-distortion either, but comparable to numerous respectable monolithics like the OPA2134, NE5534, etc.

 

[suraj]

@linuxguru,email sent.please check and reply!

sorry to bother you by email,as i am a newbie and cant send PM's yet.

 

[Audiodoc]

My address is the same. Thanks!

 

[suraj]

Hello,
now that i can get started,maybe in a weeks time(or two or three),I thought of testing out my own MYREf.i have built it for others before,but i still want to experiment.
This is because,i have bits and bobs left over from previous projects and want to cheap out on them.
1.Now,i have quite a few Vishay-Dale resistors (1%) left over and thought of using them.I havent seen these in use in the myref,so how good are they?i know they are standard in a lot of headphone amps but all that are reccomended are Xicon,KOA etc.

2.I dont have any carbon resistors,like required in the premium BOM.Are these compulsory?How much of a hit will i get if i dont use them?

3.I plan to use SIP sockets/pins in some places.Dario at DIY-A says its OK to use them,but has anyone used these?how good/bad were they?Oh,and,to make it 'audiophile',i have gold plated sip pins so,yeah.

4.What input caps(C13) do you use?any recommended ones?i mean,budget-recommended,no Mundorf/Obbligatos/PIO/etc .Cheap caps,which are good enough and can be bought in India/online without having to spend too much.I saw some CTR(Indian make) at an online store and they look promising.

5.I dont have much money remaining to buy a transformer,so,to test it,i will be using my college lab's variac.Its a pretty big one,single phase,220v.Is it fine to start giving AC in at 0v and gradually building it up to rated?i have seen circuits blow up at low voltages,so will this damage the MYREF too?

6.How much does a E-I core transformer for the MYREF cost?

7.what input pot to use?the only one i have,as of now is a ALPS RK097 10Kohm.

8.Also,say,i want to use a iPOD or as PSP as a source.then,how do i give input?
I thought
iPOD->Buffered CMOY->MYREF.good enough?
or do i use the super-simple pre-amp?i can build it,as i have all the parts,except for the caps.

 

[linuxguru]

1.Now,i have quite a few Vishay-Dale resistors (1%) left over and thought of using them.I havent seen these in use in the myref,so how good are they?i know they are standard in a lot of headphone amps but all that are reccomended are Xicon,KOA etc.

2.I dont have any carbon resistors,like required in the premium BOM.Are these compulsory?How much of a hit will i get if i dont use them?

Dale MFRs are just fine - actually much better than some seriously expensive boutique resistors like Kiwame, Shinkoh, etc. I'd avoid the Dale wirewounds though, because they tend to be inductive.

Good CFRs are readily available in India - Watts brand has non-magnetic leads, but weakly-magnetic bodies. They should be fine at the few shunt locations where CFR is recommended, but MFRs will work fine at all locations.

4.What input caps(C13) do you use?any recommended ones?i mean,budget-recommended,no Mundorf/Obbligatos/PIO/etc .Cheap caps,which are good enough and can be bought in India/online without having to spend too much.I saw some CTR(Indian make) at an online store and they look promising.

Skip the desi polyesters and go with Panasonic ECQ-E4 or similar, if you're OK with polyesters. If you're adamant about polypropylene, go with Epcos/Siemens.

5.I dont have much money remaining to buy a transformer,so,to test it,i will be using my college lab's variac.Its a pretty big one,single phase,220v.Is it fine to start giving AC in at 0v and gradually building it up to rated?i have seen circuits blow up at low voltages,so will this damage the MYREF too?

6.How much does a E-I core transformer for the MYREF cost?

Variac: not sure - I'd skip it and use a light-bulb attenuator on the primary side instead.
EI-core trafo: Depends on the rating, but it runs about Rs.500-1k.

7.what input pot to use?the only one i have,as of now is a ALPS RK097 10Kohm.

8.Also,say,i want to use a iPOD or as PSP as a source.then,how do i give input?
I thought
iPOD->Buffered CMOY->MYREF.good enough?
or do i use the super-simple pre-amp?i can build it,as i have all the parts,except for the caps.

Alps 10k should be fine as the input pot. A pre- or CMoy is not really necessary, but it depends on your source signal level. The ipods are typically at 0.3Vrms out, which is a bit low for max volumes on the MyRef. You can listen and decide if you want a pre- later. Any opamp-based preamp before a MyRef will cause the sonics to become veiled/closed, though that probably doesn't matter anyway when you use a portable source with compressed/lossy digital tracks.

 

[suraj]

Ok.Now,i dont have nat semi lm318,and since ive spent some time messing with opamps,would like to know which all work.
Confirmed working ones are(?)-
1.BB OPA627AU-costs a bomb!
2.the Siva LF01
3.the Siva LF05
4.TI TL071-Jellybean TL071 or bought from etailers?

You said the LT1028 is unstable,did you try it out in your boards though?I tried it out with my twisted pear board and it starts giving out rhythmic ticks.like a little metronome.oscillating very badly,and gets really hot in seconds.

also,What about these opamps?I bought them to make a pimeta/PPA,which never materialized,so are lying free.
1.AD8610
2.LT1363-bipolar
3.AD8065
4.AD4627-1-allegedly AD reply to the 627.how would it pan out?
5.OPA827-similar to the OPA627 isnt it(or is it?).I have just one single opa827 and am very curious to know how it would work out,but sadly have no adapters to mount it on,neither the MKP1837 bypassing caps needed for it.
6.OPA1641-seems to be a pet of those on head-fi.I have the opa1642,and was curious about it.

noob question.
havent seen the lm318 datasheet,but its fet input right?so,shouldnt any decent fet input amp work there?

I do know the lm318 is maxed out in the MYREF (maybe except for the class A biasing that the LF01 provides) and opamp rolling MAY give a 5-0% gain over the stock lm318,just curious what will happen

 

[linuxguru]

(deleted duplicated post)

 

[linuxguru]

...opamps,would like to know which all work.
Confirmed working ones are(?)-
1.BB OPA627AU-costs a bomb!
2.the Siva LF01
3.the Siva LF05
4.TI TL071-Jellybean TL071 or bought from etailers?

1.AD8610
2.LT1363-bipolar
3.AD8065
4.AD4627-1-
5.OPA827
6.OPA1641

noob question.
havent seen the lm318 datasheet,but its fet input right?so,shouldnt any decent fet input amp work there?

The LM318 is actually a BJT darlington input opamp, and the compensation of the MyRef is specifically designed for it. There aren't any monolithic opamps that have better sonics in a MyRef than the LM318, though the discrete LF01 and LF05 are probably smoother because of their Class-A output stage.

The monolithic opamps that work without changes in the MyRef are only the TL071 and LM318. Edit: NE5534 also probably works, at least when mounted in an LF01.

OPA627 is marginally stable - it will trigger SPike protection at higher volumes. LT1028 is unstable, as you found out.

I haven't tried the other opamps, but most of them will need compensation changes to work stably in a Rev C. Some opamps, e.g. LME49710, will work with mods in a Rev A, the first of Mauro's designs, but that's not recommended for new builds.

For rolling and experimenting with dual opamps, the MiniRef is a much better platform, because it was designed to allow a very wide range of opamps to work without compensation changes.

 

[suraj]

okay..So its best left at stock.
I guess we have discussed it before,but couldnt resist.

 

[Deleted member 25636]

Hai siva,

I send you a PM., Please consider.,

 

[doors666]

Is there a published bom that i can use for this. unfortunately our forum rules dont allow me to search for bom. I just need the part values. i saw the revc 1.3 bom but that doesnt seem to apply.

 

[linuxguru]

... I just need the part values. i saw the revc 1.3 bom but that doesnt seem to apply.

The V1.3 BOM is the same as V1.4 for almost every component. Some legacy rail-to-ground bypass caps which were there in V1.2 and V1.3 have been omitted in V1.4 after they were found to be unnecessary. The only additional components in V1.4 are optional bypass caps which are in parallel with existing caps from V1.3, and are only rarely populated as alternates. These are:

C22: 10nF..100nF/100V film/foil - not used if C4 (100nF MKP10 or similar) is installed.
C23: 10nF polystyrene film/foil in 4-pin square 5mm x 5mm package - not used if C7 is populated with a 10nF Wima FKP2 or ERO KP1830 or similar.

AFAIK, everything else is exactly the same as the V1.3/V1.2 BOMs - e-mail me if you have any specific doubts about the V1.4 BoM. Note that there are alternate compensation schemes (Rev E, Rev FE) in addition to the stock Rev C, which can be built on the V1.4 board by simple component substitution. However, if this is your first MyRef build, it's probably best to stay with the proven Rev C compensation values as shown in the V1.3 BoM.

 

[doors666]

yeah, its my first myref.... will stick to revC, I have a 22-0-22 trafo and 4 and 8 ohm speakers that i will be driving... any changes needed for that?
I also have some 'which cap goes where' kind of questions, will post once i have all the info.

 

[linuxguru]

I have a 22-0-22 trafo and 4 and 8 ohm speakers that i will be driving... any changes needed for that?

Stay with 8 ohms loads if possible. With 4 ohm loads, NatSemi/TI only specifies the LM3886TF for +/- 28V rails (which corresponds to a little more than 20-0-20 for the trafo). 22-0-22 will work, but may trigger SPiKe protection at high volumes, or on a hot day, or if the mains voltage is a bit higher than normal (rare in India, but it occasionally happens), or combinations of the above.

 

[doors666]

Stay with 8 ohms loads if possible. With 4 ohm loads, NatSemi/TI only specifies the LM3886TF for +/- 28V rails (which corresponds to a little more than 20-0-20 for the trafo). 22-0-22 will work, but may trigger SPiKe protection at high volumes, or on a hot day, or if the mains voltage is a bit higher than normal (rare in India, but it occasionally happens), or combinations of the above.

cant do that. i want to replace the topping with this one for my desktop use. i have two speakers on my desk. one is 8 ohm and other is 4 ohms (drops down to 3.6 ohms)... but thats alpair 7, its PE is 20 watts, at lower frequencies, it can only handle some 7-8w. I am real careful with these speakers, so wont be blasting, so I guess I am going to be fine.

 

[doors666]

There are tons of wima that are being recommended in the published boms. what are some of the good places to use them. I cant buy so many of them. Planning to order from element14, but they have minimum order quantity of 5 or 10. I can probably get one or two values more.

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.

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.

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. Can get whatever from sp road or element14. whats the best option for this.

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.

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.

will post another message for electros.

 

[doors666]

for electros, i got the following options:

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.

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.

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.

electros are pretty cheap and i am anyway placing an order on e14 as well as going to sp road for heatsinks tomorrow. please suggest whats the best option from what i have and what i can get thats better.