My "audiophile" LM3886 approach

Latest modifications:

I found the amp had a slightly darkish quality or a very slight lack of air compared eg to my tube amp.
I suspected the input filter and sure enough when I took out the 220pf
cap the sound brightened up considerably.However there was a bit of a roughness in the upper mids especially with female sibilants becoming more noticeable.
I then substituted the 3.3k resistor with a 2w 1k carbon film and the sound smoothed out quite obviously.Detail seems to be increased and soundstaging width as well.Female sibilants are well handled although they may be a little more noticeable than on the original version.For sure they are there on the recording but who knows what is accurate?

These are what I would call more ´´voicing`` the amp and not changing its intrinsic qualities.Of course very dependable on your speakers etc but still quite noticeable changes even though in theory they should be inaudible (filter works at 220khz so go figure).
 
Hi protos :)
I found your findings interesting.
That's what I was talking about when I mentioned Riken-Ohm on signal path: voicing, not changing the intrinsic qualities of Mauro's amp. These Riken resistors have always been a good swap in my limted experience.

That said, I must admit that my own amp is waiting for final connections and test :( because something bigger (in terms of size) came in and took away all my strength. :cool:

Thanks for sharing
Mauricio
 
I'm also thinking of using some Riken Ohm resistors in my second Rev C, where they might be of benefit,and will fit. The My Reference amp is good enough to justify quality parts. Whether they will sound better in the REV C is another matter.

The system I have my Rev C in surprised me once again the last time I listened. It usually sounds good straight away, but improves after the first record in every parameter. Presence ,detail dynamics.bass, tone, are admirable. The only aspect to the reproduction that could be better is the soundstaging.
Well, this last time I came in for a big surprise! The first three record sides were enjoyable, but dynamics were a little restrained from the norm, and soundstaging was good but not great.
As soon I began to play the fourth record side the sound was transformed. The soundstage seemed to fill the end of the room in every dimension with seemingly expanding air. Every other aspect of the sound, dynamics bass etc was as good as you could wish for. I was amazed and thought that if the system could produce such a sound, then not one thing in the setup should be changed.
And I had not even had a drink - or anything!

My main system can sound to me sometimes as if it can't get any better. This was something different.
I am wondering if I will get the same sound the next time. For whatever reason, I find the quality of sound can change at different times.


The Rev C was part of the marvellous sound I was hearing, so any other changes I might make to my second amp are not likely to improve things much, if at all. Maybe i should heed the advise: "If it ain't broke, leave it alone".

Audie.
 
:bigeyes:
I guess you guys spend a lot of time swapping bits out here and there, but surely Rev C is a fine Amp as is? Why doesn't one of you guys publish a differant offering? It would be great to get us all frantically building, making comparisons and ting!!!!



*******In an earlier posting from myself, I find thet my comments about ESP were taken a derogatory by some, so please allow me to rectify ?????
Sir Elliot is a legend, to find such straight forward advice is a ruddy gift!!!
Nuff Said.;)
 
LOL

If it ain´t broke don´t fix it he says!

Thanks, I think you just helped me find my moniker.I think it will be:

Fix it even if it ain´t broke!

this is the zen of audiodiy.Our fingers are always itchy ,our spirit always in search of the next audio epiphany.

I am teasing but only a little....
 
Yes I find myself changing components from time to time, but just because it is in my nature. In the end I usually end up at square one or very close to it. :)

The one single best tweak (which has been mentioned before) is to omit the input cap (doesn't matter how good it is) if you can (must have no DC from source). It does make an appreciable difference.

Also running the rails too low will sound inferior to running them at the proper voltage. I am using two dual 25V secondaries these days on one pair and two 48VCT on the other pair. I tried for a while with 22V dual secondaires, but did not like that very much. It worked fine, just lacked headroom.

Cheers!
Russ
 
Hi,

Having a second Rev C is handy, as one can be used as a reference while the other can be used to experiment with components. This way you are better able to judge the effect of the changes - ideal for the tinkerer. I would not rate myself as a tinkerer though, as I can no longer afford the time for it.

While I was dummy load burning in my Rev C, I noted that my 400VA Toroid output was +/_ 26VAC (RMS) giving DC rails of +/-35VDC with the Variac set to supply 238VAC (RMS).

The 240v mains supply here can vary by about 10V, so I monitor the voltage and adjust the Variac to the correct voltage.

I have found that 35V rails provides good performance.
 
Audie:
I am wondering if I will get the same sound the next time. For whatever reason, I find the quality of sound can change at different times.
I am glad that you are fully satisfied with your amp :)
Mine was completed yesterday but I will not have the time to test and listen to it until saturday! :bawling:

If sound changes maybe (or surelly) mains AC is dirthy ;)
I discovered I can't live without AC filter. I am building/modding my own, to my taste, by ear...slowly.

Have to be careful running amps thru variacs or any kind of autoformers eg 110-220v.They usually sound much worse in my view probably due to the increased impedance they have I think over normal txfmrs or isolation txfmrs.

I agree, but powering my cheap, modded Sony DVDP (SMPS) with autoformer actually improved sound maybe because of the same reason you gave.

Cheers
M
 
Have to be careful running amps thru variacs or any kind of auto transformers eg 110-220v. They usually sound much worse in my view probably due to the increased impedance they have I think over normal txfmrs or isolation txfmrs.

Possibly so. That was the reason I decided to use a larger 2000Watt variac, and it does not appear to have a negative effect on the sound, as far as I can tell.
Variacs are commonly used in high end Valve based systems.

If sound changes, maybe (or surely) mains AC is dirty.

To minimise the effect of dirty mains I have a dedicated 240V 30A circuit for my hi fi ,and outboard mains filters. My house has a 3 phase supply, which also is beneficial. Still, I usually find that my system sounds best late at night or on Sundays when generating system loading is lower.

Components can also effect the sound. Some need a significient burn in while others need a good warming up period. Some manufacturers require their components to be continually energised to achieve best sound. I owned a (fabulous) state of the art valve preamp, the Vacuum State RTP (Real Time Preamp), that I found needed to be on for about 12 hours prior to use to achieve the best sound.
The better the resolution of the system, the more moticeable will these changes be.

Then there is the receptiveness of the listener to the sounds he is hearing. This can be affected by stress, tiredness, being unwell, unattentiveness, biorhythms? etc. etc.

Audie.
 
Hi guys,

I have almost completed my 5-way MyRefC amp. All channels are working, the enclosure is complete and preliminary tests look promising.

However, I have a slight hum on 3 of the channels. I posted some pictures here (sorry for the crappy quality, I used my phone...). The humming channels are the ones on the left in pic #5. They are powered by the big trafo while the other 2 channels are powered by the small one.

On the pictures, the heatsinks are not attached and I didn't use them for the tests. I only powered the amp for a few seconds to test each channel. I don't think the spike protection had enough time to kick in, the chips weren't very hot.

Any advice on the most probable causes for that hum ?

Thanks in advance and many thanks to everybody who made it possible !

J.
 
Russ White said:
Wow! Still looking over you picture for signes of any source for the humm, but just have to say thats a very cool project! I am a little puzzled about your heatsink attachment. But its very ambitious!
Here's an explanation of how they are attached :

First, I removed some metal at both ends of each heatsink about 2mm x 2cm so that it looks a bit like this on the side : (not very pretty in ascii)
Code:
Before
  _  /\ /\ /\ /\ /\ /\ /\ /\  _
| | || || || || || || || || | |
| | || || || || || || || || | |
| |_||_||_||_||_||_||_||_||_| |
|                             |
|_____________________________|
After
 _  /\ /\ /\ /\ /\ /\ /\ /\  _
| | || || || || || || || || | |
| | || || || || || || || || | |
| |_||_||_||_||_||_||_||_||_| |
|___                       ___|
    |_____________________|

Then I cut a rectangular hole in each side of my case and inserted the heatsinks. That way, most of the surface of the heatsink is inside the case, the rest can be used to fix it securely to the side.

About my hum problem, I verified with a multimeter that the RCA connectors are isolated from the chassis, it looks ok. And if input+ is indeed the pin that is connected to the long 1.0µf WIMA cap, I think the RCA wiring is ok too.

J.