300b Circuit Mod.

[ttray321]

Hi:

I am building the SV-300B SE power-amp, it's circuit comes from Sun Audio (/jc morrison?). I want to listen rich/warm mid-range vocal song with comparatively enough detail. Now, I want to ask some questions:

1. Is there any parts value I should change to suit my need?

2. Use electrolytic capacitors or mkp cap for the cathode bypass, what is the sound different between them?

3. If I don't care about the power and tube life, but the sound quality. 320V, 340V, 360V plate voltage for the 300b is better?

4. Is there any improvement if I put one small choke for the 300b filament voltage regulation?

Many Many Thanks!

Tray

 

[garbage]

hi tray

in a singapore diy forum, a member built the sun audio 300b with ac filaments.

i've had a listen to it before. it is real quiet. the speakers used are coral beta 8s.

you might want to contact the owner via the forum.

here's the link to the posting of that amp.

 

[kmtang]

Increasing the plate voltage, B+ changes the style of the sound. Higher the voltage, clearer and faster the sound it will get.

However, I am wondering how you could do it?

For better result, it would be nice if you could change the electrolytic capacitor in the power supply to oil or properlene type. You would be amazed how the sound changes.

Have fun.

Johnny

 

[kmtang]

When you increase the B+, you should keep the filament constant to 5V. The tube life will be shorten dramatically if the filament voltage exceeds by few percent.

It would be nice if you could have stablized DC supply for the filament by using Low-Drop-Out 5V regulator IC such as LT1085.


Johnny

 

[ttray321]

Garbage and Johnny, really thanks for your reply.

Garbage:

The message has been posted a year ago, I think it is hard to contact the owner, anyway. Thanks!

Johnny:

My power transformer has some taps such as 290V, 330V ac that I can select.

I would consider to use oil or MKP cap for PS (but it is big and expensive !!!) How about if I parallel a 15uF MKP with a 150uF electrolytic capacitor?

What is a sound quality different between using a choke and regulated IC for the 300b filament supply. Anyone knows?


Tray

 

[kmtang]

I believe you could try parallel a MKP cap to the original power cap for trial.

If you use a regulator IC for the filament, there's no need to use a choke at all. Just forget about it.

 

[Sherman]

The 5U4G has a max limit of 40uF for the first cap (between the tube and the choke). I'd stick with that limit.

 

[garbage]

The message has been posted a year ago, I think it is hard to contact the owner, anyway. Thanks!

on the contrary, he's still using that amp and i heard it about 3 months ago.

 

[ttray321]

So I should follow the original design 47uF + 47uF for the power supply, or change their value and type?

 

[Bas Horneman]

I would use the original 47uF + 47uF...else you MIGHT introduce unknown factors...like ringing. I've learned that building a psu is not just simply adding capacitance. Make the PSU as simple as possible ...but not simpler than is necessary.

 

[ttray321]

ok, i will use the original design, i.e. 47uF+47uF for the power supply filtering. But, which type of capacitor is better to the sound. Oil or motor run is the best?

 

[Bas Horneman]

Many motor run's are in oil...

Many paper in oils are good. (Some are not so good)

Polyprop in oil (modern production) are good. a good example is the ASC one..

http://www.angela.com/catalog/capacitors/Ang_Poly_Oil.html