[proid]

Hi everyone
I have done all necessary mod to the Indeed G2 that was mention in Rockgrotto but i still want find some way to improve it. In this schematic, what is the task of 2n3906? Can i change it to BC556 to get better sound?

 

[Avro_Arrow]

The 2N3906 is part of the current source. Changing to BC556 is not likely to be audible.

 

[duncan1]

AVRO is correct but if you want to improve it then make it a dual bjt current source-increased PSR and lower noise/high gain by using-BC560C- the C- makes a big difference. If your equiv.BJT book only shows the basic type then realise that more dedicated professional books show variations of each type 
Look up circuit diagrams of high quality power amps.by major audio design engineers.and you  will see what I mean.On single-ended circuits and those that dont use split-rail PS you need a series capacitor of large value like you have in this circuit.
So being a signal carrier this capacitor MUST be of VERY high quality[the dearest you can buy] Check the type to see if it comes up to scratch.bypass by Poly-prop-Film -NOT metallic. NOT mains ripple types.X2 etc.
 

 

[wakibaki]

What's the 30R1 doing between C2 and the output jack? If you take a look at the Millett design that this is modelled on, it doesn't have this resistor, which AFAICS just increases the output impedance and wastes power. Unless somebody can point out a good reason for having it there, I'd take that out and put a jumper in. It keeps the rolloff down, but at the cost of reducing the damping factor and distorting the frequency response with phones that don't have a constant impedance with frequency. Which most don't.. Output impedance should be a fraction of headphone impedance, probably less than 2R with 16 ohm phones. 
 
w

 

[proid]

Quote:

AVRO is correct but if you want to improve it then make it a dual bjt current source-increased PSR and lower noise/high gain by using-BC560C- the C- makes a big difference. If your equiv.BJT book only shows the basic type then realise that more dedicated professional books show variations of each type 
Look up circuit diagrams of high quality power amps.by major audio design engineers.and you  will see what I mean.On single-ended circuits and those that dont use split-rail PS you need a series capacitor of large value like you have in this circuit.
So being a signal carrier this capacitor MUST be of VERY high quality[the dearest you can buy] Check the type to see if it comes up to scratch.bypass by Poly-prop-Film -NOT metallic. NOT mains ripple types.X2 etc.
 

 
Thanks for your suggestion, i search mouser and there are a many type of BC560 like BC560CTA, BC560CG ... are they just BC560C?
Quote:

What's the 30R1 doing between C2 and the output jack? If you take a look at the Millett design that this is modelled on, it doesn't have this resistor, which AFAICS just increases the output impedance and wastes power. Unless somebody can point out a good reason for having it there, I'd take that out and put a jumper in. It keeps the rolloff down, but at the cost of reducing the damping factor and distorting the frequency response with phones that don't have a constant impedance with frequency. Which most don't.. Output impedance should be a fraction of headphone impedance, probably less than 2R with 16 ohm phones. 
 
w

That is the output resistor like in the cmoy as i know. 

 

[wakibaki]

Quote:

That is the output resistor like in the cmoy as i know. 

 
What does it do?

 

[duncan1]

Proid.Yes they are variations on the basic BC560C made by different companies just buy the standard BC560C-gain 420-HFE at 2MA  Audio/low noise.
This is for the input any noise here will be amplified at output
That output resistor although Wakibaki is correct in what he says is used as a current limiter found in many DC outputs of Audio chips to   limit the current drawn by the device to stop it burning out BUT in your case the IRL510 has an output current of 5.5 AMPS! just imagine if it developed a FAULT and the full current was applied to your head-phones-Toasted! 
You pay your money and take your choice!
 

 

[proid]

This amp use a swiching power supply for the heater, if i change it to a linear regulator like LM317, will it improve sound quality? If i use a LM317, do i need to apply some diodes and capacitor to filter the current?

 

[duncan1]

It depends on whether the switching current provided for the heater contains some RF products [radio frequency]  either as a fundamental or as a harmonic .Tubes work okay with 6.3V AC but that is an analogue  voltage not digitally produced  and therefore has 50/60 HZ [c/s]  as a fundamental at that frequency the higher harmonics are very low level. But if by action of the switching current 
 HF [high frequency] harmonics are produced at a HIGHER level  than the analogue version then yes it could have a small but detrimental effect.
    But I must admit I am not a fan of switching power supplies. They were a "Godsend" to the industry to get rid of transformers and SAVE money.
     IMO yes I would change the switcher to a LM 317 they have a low noise output in comparison  to fixed regulators and yes again capacitor filtering  at the output of it is recommended by the manufacturer . From what I remember up to   40V DC cant be applied to it. and adjusted to suite.

 

[proid]

Today i change the heater using LM317. When the vout is not connected to the heater, i measured 6.3V but when it connected to the heater, it was only 1v and the tube didn't light up?

 

[duncan1]

Dropping under load . One cause is not enough input current to the 317  it is okay for up to 1.5 Amps output  A switch mode power supply has one  advantage of a high output current  what is the spec. of the chip? and check if both pins of the heater are "floating" whether they are connected to earth or not  and therefore affecting the reference of the  317 or using a MM check the resistance of the heaters. Small tubes usually have a current of  300 MA so that is well within the spec. of a 317. Switch the MM to the current range set at 1  amp and connect the MM leads in Series with one heater connection and measure the current drain.