USSA-5 Build with Review

[fab]

Over the top. simulation done. Thanks fab alot.

You are welcome ....but I am not sure what you mean exactly..
Fab

 

[tonza75]

It's only simulation nothing special about it the Sim really can't put all the measured values in in a few hours.


Well parts N&P 250W coming in a week about from profusion. 102€ for 3 pairs S suffix, cheap almost.

 

[e_fortier]

Received a padded envelope today

I’m a slow builder but at least I now have the essentials.

The N are both green and P are both orange

 

[Luke]

Are reneas parts as good as the profusion parts for this amplifier?

 

[gaborbela]

Are reneas parts as good as the profusion parts for this amplifier?

Renesans does not have the high power mosfet you need for this project.

 

[fab]

Renesas does not have double die Mosfet to my knowledge. You need double die Mosfet (2 Mosfet transistors in parallel in same package thus perfectly matched) otherwise the damping factor would be much too low, distortion would rise and the sound would be very different.
The pcb only fits one pair (N and P) of double die Mosfet.
Fab

 

[fab]

Received a padded envelope today

I’m a slow builder but at least I now have the essentials.

The N are both green and P are both orange

That should work fine
Fab

 

[Luke]

Renesas does not have double die Mosfet to my knowledge. You need double die Mosfet (2 Mosfet transistors in parallel in same package thus perfectly matched) otherwise the damping factor would be much too low, distortion would rise and the sound would be very different.
The pcb only fits one pair (N and P) of double die Mosfet.
Fab

Thanks for the concise explanation Fab and Garborbela.

 

[e_fortier]

Here is a useful link to compare

Exicon Lateral MOSFETS - Cross-reference Charts

 

[fab]

Thanks
This confirms that Renasas had no double die Mosfet.
From the remaining Semelab, Alfet and Exicon it seems only Exicon is still active for production.
Fab

 

[sthcoaster]

Is a scope absolutely necessary for adjustments to this amp. I read somewhere about using scopes and signal generators etc. while taking bias and other measurements.

Thanks

 

[ggetzoff]

No, it is not. You are simply biasing the amp per Fab’s instructions. If you build the amp properly:

1. Mounted all values properly
2. matched and authentic driver fets
3. Final VGS calculations and bias properly.
4. PSU caps that adhere too Fabs specs.

If you do all of that you will achieve good performance from the design, no scope required.

 

[sthcoaster]

No, it is not. You are simply biasing the amp per Fab’s instructions. If you build the amp properly:
If you do all of that you will achieve good performance from the design, no scope required.

Brilliant. That is what I was hoping and about what I thought.

I also note in these build pics for C5/6 a larger cap is used than the value in the BOM. Both are easily available from Mouser. Is this a case where more UF is better/worse/indifferent?

Thanks

 

[ggetzoff]

Use only the values Fab has specified, you may use higher service voltage, though.

 

[Project16]

We still find the Allfet (apparently genuine) but this company only sells in Romania, it refuses to sell abroad.

ALF16P16W
ALF16N16W

 

[fab]

Use only the values Fab has specified, you may use higher service voltage, though.

That is right but for C5/C6 I have also used 7500uf instead of 4700uf in one of my build. However, both caps are the same brand/type/diameter.

Also, input cap may be better in quality than specified in BOM. You can use other members build experience or yours to chose how much you want to pay ...
Fab

 

[pinnocchio]

For input cap I use Jantzen Supreme on USSA 3 and Alumen on USSA 5. I really like the result. The cap in the BoM is also doing a good job.

Do

 

[tonza75]

I read your subjective review about the nordic caps.

 

[pinnocchio]

Hi tonza75,

But please keep in mind that it is subjective review as you said. The other ones that I really like are the ClarityCAP MR/CMR. I'm sure there's much better alternatives but since it is a question of personal taste as well, some people might even like caps that add more coloration to the mix... I prefer as transparent as possible.

I've also tried the much cheaper Cornell Dubelier and found them excellent for the price after +/-50 hours of burn in. Their P/N : 940C6W4P7K-F

All the best!
Do

 

[tonza75]

Yes, I knew it was a subjective test, elektor did their test in maybe 90 with audio analyzer gear,
but we can choose what we like, let's face it high end audio design. Looks are one of the important factor I think.