My "audiophile" LM3886 approach

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#2,621
My_Ref C lessons

Hello.
I am thinking of purchasing one of the My_RefC kits, but had a couple questions...

Does it explain - somewhere in this thread - what the different parts of the circuit do? It looks like it might provide speaker protection... There are a lot more parts in the MyRefC than in other Chipamp designs, and I am hoping to learn while I build. I did check http://www.twistedpearaudio.com/ but it doesnt have much more than the parts list.

Thanks for any help/suggestions!
 
#2,623
billabong said:
Panelhead,

Mauro prefers the Base version.

This what he recommended, lower distortion. With high efficiency speakers insane levels are still around one watt output.

Dynamics

I'm not so sure high dynamice are such a good thing. It may be impressive, but it can be unsettling to be continually startled (especially with the many audiophile vinyl records I have), and really makes it difficult to relax and enjoy the music. My wife is continually screaming to "turn it down", which I do, then I can barely hear the quiet passages.
I've been tinkering with a diy ss MC Head amp and my aim is to get a balanced sound. If that means high dynamics, so be it. If not, that is ok. and my wife will thank me.

Audie.
Click to expand...


Dynamics is one thing this amp does very well. To me, after low noise, high resolution, and flat midband, dynamics is what seperates the wheat from the chaff.
The dynamic range of most classical is a problem. But to be enjoyed, it is very important.
Without knowing your system, the MC pre amplifier is one of the last places to build in compression. This has to be first rate, the levels are so low.
A transformer may do a better job of softening the swings. Sowter iron seemed to compress the slam a little, at least compared to AN UK stepups.
Wish I only had to deal with my wife right now. My in-laws are staying in the room next to my system. It is not even powered up anymore. I would guess played 30 minutes in ther last six weeks.

George
 
#2,624
Panelhead wrote:

I would guess played 30 minutes in the last six weeks
Click to expand...

I sympathise with you. The upside is that you have more time for diy projects.

I have three good phono preamps, two valve and one ss. Later today I will use the ss preamp with the My_Ref c, for the first time.
It is a Classe DR6, which I consider the best of my preamps.

The diy MC Head Amp I have been tinkering with is the Marshall Leach jnr common base design. It sounds very good using black gate caps. I've been trying some different resistor values to get the best sound with my Benz Micro MC3 cartridge, but have not yet found the "perfect match". Once I have sorted it out, I will rebild it using BG super E-caps ( using NX HiQs).
One of my valve phono preamps is MM only, so I could use the Head amp with it. It is just something interesting to do, though not really necessary, as I have an AT 650 MC stepup with adjustable impedances, which I normally use.

Cheers, Audie.
 
#2,628
Well, I've ordered a RevC kit from Russ and Brian today.

Guys, are there instructions with the kit, or how do you know which component goes where? Of course, the boards are marked, but I assume not with the different values.

Russ, is it still the LM3886TF that you provide in the kit? I'd prefer this, but I see you're contemplating the T version. I just prefer the lack of hassle with insulation, albeit minor.

Cheers

Stuey
 
#2,631
Hi folks,

I'm wondering what the best way is to hook up via a single transformer. With both rectifiers on their respective boards and the transformers end and start of windings twisted to make a CT transformer then the winding is effectively being rectified twice. This leads to excessive hum and is a problem I had trying to rectify a transformer hooked up to a valve pre at one stage which was sorted via removing some diodes and linking the DC across to the other board. THis doesn't seem to work with My_Ref.

I have one of Brian Bell's gainclone rectifiers here and wonder if its possible to remove the onboard rectifiers and use this instead?

Cheers & thanks!
 
#2,632
lazyfly said:
Hi folks,

I'm wondering what the best way is to hook up via a single transformer. With both rectifiers on their respective boards and the transformers end and start of windings twisted to make a CT transformer then the winding is effectively being rectified twice. This leads to excessive hum and is a problem I had trying to rectify a transformer hooked up to a valve pre at one stage which was sorted via removing some diodes and linking the DC across to the other board. THis doesn't seem to work with My_Ref.

I have one of Brian Bell's gainclone rectifiers here and wonder if its possible to remove the onboard rectifiers and use this instead?

Cheers & thanks!
Click to expand...


OK a couple issues....

First, I and many other use RevC amps with just a single transformer with out any hum issues. Using two rectifiers on a single transformer should not cause hum in and of itself... if it does it means there there is something else wrong.

Second, if you look closely there are two rectifiers on each PCB, one for the protection circuit, and one for the amp.

If for some reason you just wanted to use one set of rectifiers you would have to take the DC from BOTH. I would strongly suggest against it.

Cheers!
Russ
 
#2,634
Hum

The hum is more likely grounding related. Or leads dressing as Nordic posted.
One trick used by Mauro is to reverse the leads for the AC in one channel. This way the surges in your transformer are reduced. The original stereo boards were wired this way.
To clarify: The three wires used to connect ac for the +/- rails. The groiund or centertapped stays the same, just the wire connecting to the + side of the diode is connected to the - on the other channel. The the - from channel one goes to the + on the other.
Give it a try, I never tried the other way, the board was wired to do this. I did wire the two power transformers for my mono Rev C this way. Figured in could not hurt.


George
 
#2,635
Thanks for all the advice and suggestions gents. I'll have another go at it this afternoon - it certainly could be wiring and if I went into the line of thinking that led me to the tranny and two rectifiers you'd get lost in the trip and so would I :/

I'm now thinking that the tranny is just to close (damn making cases to suit shelves!) and needs some orientation to perhaps help out. Bear in mind that the hum isn't dramatic, just a shade more than I remember when I was running 2 trannies.

I'll report back later.

Cheers!
 
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