MF A3 Amp Opamp Rolling

[Deleted]

Matt
Further to PM, as I thought your A3, the silver one, is altered a bit inside compared to my gold-trimmed one. Have a look in the archive section of MF site, there's a review PDF which loosely explains it.
juke

[matt7941]

Good evening Syd,

I must apologise as it seems you were totally correct. The review blurb would seem to suggest some changes in the power supply side of things. I was under the impression that the only difference was the trim pieces, how wrong can one be. I'm quite pleased now I know I've got the later model and it has been enhanced further.

Cheers

Matt

[matt7941]

Syd

The LME49740s arrived today, pretty quick delivery from Hong Kong! I'm just about to swap out the Motorola that's in there and I'll get back to you with initial impressions.

Alex, sorry I missed your post re the reply to the UF4004/7 question and never got round to swapping out the W04M. Maybe one for the future?

Matt

[Deleted]

Hi Matt
I'll have to open mine and take a few pics so I can work out if the same mods will be OK. No sign of my bits yet, they're from US and canjunkie mentioned they are slow. Must read up what MF did to produce the 3.2.
juke

[matt7941]

Alex, I had to go back in to bypass the power rails of the LME49740 with the 10uf foil/1uf film combo to ground on each rail. Had to drill through the board avoiding all the other traces but managed no problem. Took the opportunity to replace the small bridge rectifier with the UF4007s (my supplier was out of UF4004s). Between them they seem to have given the LME49740 a slighter smoother sound, the top end was quite lively without bypass.

Thanks

Matt

[matt7941]

Update; I'm not 100% sure whether I like the LME49740's sound. It is a genuinely noticeable difference compared to the MC33079P that was in previously. The treble is very lively, but once bypassed extremely expressive and quite delicate where necessary and the midrange is detailed and energetic. However, the bottom end response appears to be somewhat dulled and lacking in detail. Basslines don't seem to have the fluidity and richness of timbre compared to the Motorola chip, the naturalness has evaporated and leading edges are somewhat blurred. It cannot be argued that overall it is an exciting and energetic listen, which in a relaxed system may bring a touch of needed sparkle but in mine appears to be mismatched.

Overall I have to agree with XTR Prof when he talked about the qualities of the LM4562 in a previous thread, good for rock etc but maybe not so good for more subtle (or as he termed it "pretty") music.

I'm thinking of trying the National Semiconductor LM837N, same stable as the LME49740 but from reviews seems to have a slightly different character. Does anyone have experience of this opamp and its quality for use use in the A3? Again, I can source it inexpensively in the local area.

Hope someone can help.

Cheers

Matt.

[Deleted]

Overall I have to agree with XTR Prof when he talked about the qualities of the LM4562 in a previous thread, good for rock etc but maybe not so good for more subtle (or as he termed it "pretty") music.

Matt
That statement is incorrect, as many of the constructors of the Jaycar Headphone Amplifier with JLH can verify.
The LM4562 is a superb chip in ALL respects if properly implemented. However, the LM4562 is less forgiving of mediocre power supplies than devices like the OPA2134.
Alex

[matt7941]

Alex,

I stand corrected. I didn't mean to infer that the LME49740 was a bad opamp, merely that it is not suited to this application in its current state. The dual version (LM4562) seems to work quite well in the X-24K. As you know I have done very little to the actual power supply topography, apart from bypassing the power supply rails to the opamp, and thus the results are explained by your comments.

I hope as per your post that the opa4134 does suit the amp, more so than the LME49740, as the Burr Brown sound is quite musical and thoroughly enjoyable.

Would your comments re the LME49740 apply equally to the LM837N, and indeed opa404, or would these be more forgiving? I know the opa404 is a little more expensive but the opamp really does seem to change the character of the sound and could be worth investigating; I presume its character is most akin to a quad version of the opa604/2604 (which I could live with all day long)?

Matt

[Deleted]

Matt
I am only disagreeing with the statement by XTRPro that you quoted. I don't have hands on experience with the other I.C.s you mentioned. However,the power supply is probablythe most important part of any design, and even minor changes to a power supply can make audible changes to how virtually any opamp sounds. The power supply should have the lowest posible impedance, that is low right across the range to at least 100KHZ. All electrolytic filter capacitors have a broad resonance frequency, depending on their value of capacitance. This will influence the sound in that part of the spectrum. This is why a lot of people use the "Super regulators" etc. to keep the PSU impedance low, and flat over a much wider range than a conventional voltage regulator is capable of. There is of course, the added advantage of a much lower noise level when using these designs.
Alex

[matt7941]

Update:

Well we have a winner for anyone who has been watching this thread, and it may surprise.

Firstly, after finding out that the power supply just wasn't good enough for the LME49740 to shine (at least in this amp or to my ears), the opa4134 arrived from Juke (thanks again) along with the Browndog. It was duly soldered up and installed. The result was suprising as I was expecting a similar sound to that when the NE5532s in my X-24K were swapped for opa2134s. Not a bit of it, the sound was instantly dynamic and deep. After listening for a while though the initial impressive nature of the sound became a little fatiguing. The top end was "splashy" and the bottom end deep but not particularly well defined. However, the soundstage was impressively wide but somehow less 3D. The separation afforded by the MC33079P had also somehow been lost and music sounded less natural and quite artificial. This was something I'd heard talk of on other forums but hoped for a different outcome. I presume in this instance the power supply would have been ok and not been the problem as the opa2134 (and therefore presumably opa4134) is generally accepted to be forgiving in this department. The opamp was bypassed as per the data sheet so hopefully wasn't an issue.

Disappointingly, the opa4134 was removed.

However, I'd taken the opportunity to pick up an LM837N from my local supplier. What a difference! This is how I want my hifi to sound, deep, controlled, dynamic, sweet, detailed, expansive soundstage, far more natural timbre to instruments, excellent separation, wonderful pinpoint imaging within the soundstage etc etc. I could go on with the plaudits but I think I have made my point.

I presume that following on from what Alex mentioned, the LM837N has some of the same "house" sound as the LME49740 but not probably not quite to the same level, but is obviously more forgiving of supply. It is certainly an excellent sound that I'm more than happy to settle for.

From nowhere this little opamp has completely revamped the sound of my amp and to my ears at least elevated to the next level (comparatively speaking). I am aware that it hasn't lifted it to Krell pre/power status or anywhere near but it has been a substantial improvement and has gone a long way to giving me the musical sound of the Sugden A21 and the dynamics and impact of the Arcam A85 as stated at the start of this thread.

Thanks to all who have contributed and offered help and advice, especially Alex and Juke, as I think the improvement has been relatively substantial and certainly rewarding.

Mmmm.........but then there's the opa404 that's on its way to try yet.

Cheers

Matt.

[Deleted]

matt
I am not surprised at the results. Don't forget too, that the extra sections in a quad I.C. give even greater potential for coupling between sections with a lesser power supply.
Alex

[Spirit]

Oct 25, 2008 20:11:04 GMT @sandyk said:

matt
I am not surprised at the results. Don't forget too, that the extra sections in a quad I.C. give even greater potential for coupling between sections with a lesser power supply.
Alex

Is there anywhere I can read more about this?

[Deleted]

spirit
Many people use 2 singles on an adaptor PCB to replace a dual, and some people replace a quad with 2 duals on an adaptor.One of the reasons cited is thermal coupling between sections. PCB layout is also a factor . Try and locate some of the manufacturers Application Notes.

SandyK

[Deleted]

spirit
Why not ask Graham Slee why he chose to use 2 single opamps on an adaptor PCB with Solo SRG ? It could of course been that the type of opamp he wished to use was not available as a dual.
(See the photo Graham posted in Novo thread)
SandyK

[Deleted]

While we are on this subject, are there any "drop-in" replacements for the Inca Tech Claymore?

The current line level units are TL072CP x2, Phono section is OP27GP x4. (I have non-official sketched diagrams if of help).

The amp itself is quite punchy and detailed but not big on sound stage or openness (maybe too much headphone listening recently).

The phono stage is renowned as a good one, certainly between this and my TT the CD is seriously lagging behind.

So is there an alternate that would open things up without loosing the positive points.

THEN, poss of inserting JLH?

[Deleted]

cjarchez
You could try a couple of OPA2134 in the TL072 location. They are a little better in most respects.

SandyK

[Deleted]

That's handy! 1 spare from Jaycar, 1 more to find.

Thanks.

[matt7941]

Good evening folks.

I hope someone can help and that this is an easy question, although going slightly off topic.

I've finished tinkering with the A3 and it sounds lovely to me. However, it's recently developed a bit of an issue regarding channel imbalance. I know no amp is perfect with regard channel balance but the A3 has suddenly taken a turn for the worse. Lead vocals are no longer centre stage but somewhere to the left and the whole sound has shifted this way. I have swapped the speaker cables round and know it is not them. When I connect the left speaker to the right amp output and vice versa the soundstage shifts to the other side. I have checked using all my sources and it is the same on all of them. Thus it is definitely a problem with the amp and not speakers, source or cables. The left channel on the amp is noticeably louder than the right at all levels but especially (it appears) lower down the volume scale.

A couple of years ago I did get some "scratching" noise when turning the volume up or down but this seemed to cure itself and I've had no further problems until now. The amp is about 7-8 years old (I think, I'm getting old and it's hard to remember such details!!!) and I suppose it's time things like this started to happen.

Am I right in presuming it is most likely to be the volume pot. It is an ALPS dual log 50k (motorised) although it doesn't appear to be one of the "Blue Velvet" types. If it is not likely to be the volume pot does anyone know what else it is likely to be or has encountered the same issue with an A3?

If someone could assist it would be most appreciated.

Cheers

Matt

[Deleted]

matt7941
Do you have a Test CD with various tone levels, or some other stereo source that you can feed into the amplifier at low level ? You could set your volume control to maximum and feed in a suitable level tone to see if the image is centred. If it isn't, you will need to use a DMM or multimeter, to read the resistances of both sections of the volume control. The centre of the potentiometer to the earth side of the potentiometer ,should read very close to that from either side of the potentiometer. If it is , next step is to read the input resistances of both channels where the leads from the potentiometer terminate. (I am assuming it isn't PCB mounted)
Before you go any further, I would suggest that you check that you haven't disturbed any wiring while you were modifying the unit.
Let us know how you get on, and we will attempt to talk you through further fault finding.
A schematic would of course be very handy.
Alex

[XTRProf]

Check thru all the soldering of your modification and see whether they are still sound.

Btw, "scratch" the pot with some Philips contact cleaner or better still the Craig Cramolin and the "scratch' will be gone for good or, at least, a long time.

[matt7941]

Thanks to Alex and Prof.

The volume pot is PCB mounted as can be seen in pictures I posted earlier in the thread. I just measured the resistance on the pot and the two channels are slightly out. One channel is measuring 43.3k at the extremes (both from centre to input and centre to ground read the same at their respective ends of the full turn of the pot) and the other is reading 45.3k at the same points. At approximately half turn the readings from centre to input are 35.2k and 37.1k respectively with both showing centre to ground of 8.6k. Is this enough to be giving such an imbalance or would this be within decent and accepted tolerances?

I have also found a dry joint on one of the non polar caps immediately adjacent to the opamp in the pictures I posted earlier in the thread. I have resoldered the joint and it now appears to be fine. I have checked all other joints and they seem to be ok. There is no loose wiring or connections and no bulging caps. This may well be the cause but I thought I'd check with you regarding the pot resistance before I put everything back together.

Cheers

Matt

[Deleted]

Matt
Those readings are O.K. The dry joint on the non polar cap would certainly be a likely cause for such a drastic position shift.
Alex

[matt7941]

Thanks all for your help.

Once again the members of the forum ride to the rescue. It appears to have been my lack of quality control that let me down from my final round of tinkering. Once the dry joint on the non-polar cap was re-soldered and everything put back together things are fine again.

Truly thanks everyone.

Cheers

Matt

[matt7941]

Good morning all.

After opening up the A3 to replace the last of the ceramic caps, the 47pfs and 10pfs, with polystyrenes I noticed that 2 of the CapXon 10uf 63v non-polars appear to have started to bulge. These have only been in a few months. I thought, from my limited experience, this was generally a polarised electrolytic issue? Anyway, I digress.

Can anyone point me towards a source for some quality replacements. I have tried the usual UK suppliers (RS, Rapid, CPC, Farnell, DIYHi-Fi, HiFi Collective etc) looking for Nichicon Muse ES, Elna, Blackgates etc. and had no luck. I have also tried the dreaded eBay and had no luck here either. (One or two options did come up but from China and I am unwilling to go down this route as I don't want to end up with cheap clones rather than the genuine articles. I'd rather stick with the devil I know.) I may also be being a bit dim in searching via Google etc but I am finding little of help. I rather like the sound that the Muses in my DAC produce and would like to get similar from the amp.

If anyone can suggest somewhere reputable, whereabouts is largely irrelevant as long as they will ship to the UK, I would be most obliged.

Cheers

Matt.

[Deleted]

Matrt
Whereabouts in the circuit are these capacitors ?
Do you actually need nonpolars anyway ?
Alex