Copying a £4500 amp from scratch...need input for improvement

[quadklipsh]

Hi all diyers ....
My tech and i have successfully worked on 2 smaller projects in the last few weeks and built amps after getting impressed with a bang olufsen 1800 and an older 2N 3055 transistor based design .

I got really happy with the sound from this product . And decided to replicate the amp section of the beocenter 1800.

http://beocentral.com/beocenter1800

.....
Now the next project is to copy a musical fidelity M3 .
I am sharing its schematics for all the diyers .

 

[quadklipsh]

My tech tells me its a hybrid design with pre amp tubes and power section has 200 watts of ss power .
He was happy for the improvement he found with this amp over his reference amplifier , the supreme 600 .

 

[quadklipsh]

The sound quality difference between the NU vista and all his amps ( including the kenwood supreme 600) has forced him to make this nu vista from scratch.
He found that the original nu vista amp has pretty ordinary capacitors too. And they had higher inherent ESR values . And they could be further improved with simple recapping with better quality caps in the audio path.
The nu vista uses tubes which are hard to come by ... But i will try to find em here !

 

[quadklipsh]

Hi all diyers ....
My tech and i have successfully worked on 2 smaller projects in the last few weeks and built amps after getting impressed with a bang olufsen 1800 and an older 2N 3055 transistor based design .

I got really happy with the sound from this product . And decided to replicate the amp section of the beocenter 1800.

http://beocentral.com/beocenter1800

.....
Now the next project is to copy a musical fidelity M3 .
I am sharing its schematics for all the diyers .
View attachment 1250643

View attachment 1250644

 

[quadklipsh]

After listening in detail he found that his kenwood supreme 600 and the other amplifiers sound quite inferior in detail ,imaging , clarity and overall beauty of sound to the nu vista M3 and hence the project.
He told me that the nu vista M3 is a hybrid amp. Tubes used inside are rare here and he found pretty ordinary capacitors with poor ESR values in there leaving room for improvement.
He was also concerned on the following issues which i narrate :
the beauty of sound from nu vista lies in the pre amp section (the power amp section sounded similar to our home made bang olufsen 1800 copy.)
1) numerous small transistors are used in the pre amp section with the 6cw4 ....
can we use some other tubes like 12 AU7 instead of using 6cw4 and its extensive use of transistors ...
2) what design of 12AU7 based pre amp would you suggest .
3) why nuvista m3 incorporated low quality caps in a pricey product..
Thanks

 

[quadklipsh]

Since the beauty of sound from nu vista comes from the pre amp section .
My tech has question :
1) can we use a 12Au7 based tube pre amp design here , instead of the numerous transistors used with the 6cw4 tubes .
2) why would a pricey amp be using lower quality caps with high ESR values in the signal path .
Thanks

 

[quadklipsh]

We are looking forward to seeing some suggestions here from diy gurus .
And for now a hybrid design is our best bet for that glorious sound

 

[elnaldo]

I've seen some expensive units with unknown name capacitors, it seems the manufacturer has tested they can do the job and are realiable at least the for the estimated life of the unit. I use good caps when doing a repair, but i don't call them "bad quality" since they work for several years without problems.

If getting a rare Tube is a problem for you, I'd copy a preamp with a regular tube. Building the amp will be a hard work. I'd simplify every other thing as finding parts.

My DAC uses a GE JAN 5670W tube and sounds great , but I don't know how easy is to find tubes or circuits around this. The 12au7 will be easier, it's used in hundreds of designs.

If your goal is to clone that exact unit, use the same tube and the same circuit.

 

[quadklipsh]

Thanks elnaldo,
To us the idea is to surpass the quality of sound of the said amplifier, the M3 .
Not just to make a pre amp with tubes like a million other made around the world but to clearly win over the sonic supremacy of the M3 .
Hope you are with me on our motto

 

[quadklipsh]

No one else seems to be with comments

 

[rothwellaudio]

The diagram for "stage 1" shows a fairly straight forward design. It's a differential input, two stage amplifier using a pair of valves for the differential input (aka "long tail pair") and a transistor for the second stage. At its most basic it would be a pair of valves and one transistor.
The circuit has been refined by using a current source instead of a resistor for the "long tail", a current source as an active load for the second stage transistor, and a current mirror for the differential input valves. R40, R41 etc. are used for feedback.
The circuit could be adapted to use different valves, no problem. In fact, there's probably not a lot to change - maybe the value for R39.

 

[quadklipsh]

And the 2nd stage ?

 

[rothwellaudio]

The second stage is very similar to the first. It uses transistors where the first stage used valves and there's an emitter follower (transistors T28 and T29 in push-pull configuration) but I thought you were only asking about the possibility of using different valves, so I didn't comment on the second stage - I assumed you would be copying the second stage without any changes.

 

[quadklipsh]

Thanks alot rothwellaudio,
What i asked is about building the pre amp section of this beautiful sounding amplifier.
The power amp section is 200 watts which my tech didnot suggest to follow . We have a few amps that may be used as power amps .
Now i donot know the following:
Can a tubed pre amp be used to run BJT transistors based power amps .
My idea is to run my luxman L550 X ,as a power amp to the tubed pre amp.
As this luxman uses BJTs i wonder if their bandwidth is sufficiently wide enough for aa tub pre.

 

[Hyperion]

Thanks alot rothwellaudio,
What i asked is about building the pre amp section of this beautiful sounding amplifier.
The power amp section is 200 watts which my tech didnot suggest to follow . We have a few amps that may be used as power amps .
Now i donot know the following:

Can a tubed pre amp be used to run BJT transistors based power amps.

Yes, it is reasonably common to do this.

My idea is to run my luxman L550 X ,as a power amp to the tubed pre amp.

Should be fine, but make sure you select 'AC coupled' input to the power amplifier, just in case there is any DC on the output of the pre-amp.

As this luxman uses BJTs i wonder if their bandwidth is sufficiently wide enough for aa tub pre.

Easily wide enough.

 

[quadklipsh]

The project is pending till i find the right transformers .
In a tubed setting the output trafo plays a major role in quality audio delivery ....
Isnt that So ????