Studio Reference Amplifier

[Arif Budiyanto]

HD series have FETs at the input and no dc servo, just pot for adjust offset but it's DC amplifiers (DC-300kHz, THD 0,002%, 200V/us...)
Regards

Uh...my plan to build next Sr200 seems to be cancelled .... I ordered pcbs already
I am standing in line waiting for that project...

 

[usman899]

A soon as the bias regulaste. (ma)

Could i please have the schematic & PCB .pdf file.

 

[thimios]

studio reference

..... here it's the files you wish to have.....
Regards ,
Alex

Use pcb by Alex mm, follow post.
And this schematic will be ok.

 

[Walkalone]

In schematic, V reference of Vas's cascoded by ~ 1.2V (1N4148 x 2).
Q5 (Q6) have 0.6V Vce for 5mA Iq (per side)? It's ok?!
How to choose voltage cascode reference? I usually see about 4 ~ 5V in many schematic.

 

[Vostro]

It can be lower since its not terminated to the negative rail but to the emitter of the transistor instead (Hawksford 'Enhanced' cascode), some argue that this is a 'better' way to cascode the VAS/TIS.

Regards

 

[AndrewT]

In schematic, V reference of Vas's cascoded by ~ 1.2V (1N4148 x 2).
Q5 (Q6) have 0.6V Vce for 5mA Iq (per side)? It's ok?!
How to choose voltage cascode reference? I usually see about 4 ~ 5V in many schematic.

If you have technical evidence that the transistors works well with Vce=0.6V then go ahead.
Personally I would go for 2Vce to 10Vce as a guess at what might allow the transistor to perform well.

 

[Walkalone]

If Iq of Q5 (Q6) is very high, 0.6V Vce is ok. They're near the saturation.
Datasheet don't show Vce/Ic characteristics.
I agree with AndrewT, 2 ~ 10V Vce for work well. Personally i choose 5V by 2 LED in series.

 

[Vostro]

http://www.essex.ac.uk/csee/research/audio_lab/malcolmspubdocs/J10%20Enhanced%20cascode.pdf

In figure 9. Hawksford seems to use a single Green LED for Bias Voltage.

Regards

 

[Walkalone]

Thanks Vostro!
Green LED have 2 ~ 4V drop, this is like my opinions and AndrewT.

 

[Walkalone]

In this case, Wilson and cascode current mirror.
What's better?! And why?!

 

[keantoken]

The kind of current mirror used in Dado's GainWire has the lowest THD. It is important to have cascode AND base current recirculation like a Baxandall mirror. Not unlike what Edmund Stuart uses in his SuperTIS.

 

[apexaudio]

In schematic, V reference of Vas's cascoded by ~ 1.2V (1N4148 x 2).
Q5 (Q6) have 0.6V Vce for 5mA Iq (per side)? It's ok?!
How to choose voltage cascode reference? I usually see about 4 ~ 5V in many schematic.

Amplifiers with separate PSU for VAS with about 10V higher rail voltage than output stage can use 4~5V cascode reference voltage but with common PSU clip level will be lower.

 

[Vostro]

Using amp with 60Vpk(out) at full load, with IPS, VAS and OPS on same rail voltages.

With values of 5-10V for cascoding, if I'm correct that can mean amplifier can clip 30-65W lower than without cascode.

I personally won't think of doing this beyond 3V.

Regards

 

[Walkalone]

Thanks to your opinions!!!
What's about current mirror? Cascoded current mirror will loss more a few volt at output. I'm used Wilson improved current mirror and i have seen this problem.

 

[joeyt]

can i use 63v with these capacitors, 470pf,220nf,100pf and 22nf?

 

[usman899]

i cant seem to find MAC224 what else can i use? please, help me.

 

[JOHN BALI]

can i use 63v with these capacitors, 470pf,220nf,100pf and 22nf?

Hi Joeyt, no you can't
470pF & 220nF will fine but 100pF & 22nF at least 160v. I use 100pF/500v & 22nF/250v

i cant seem to find MAC224 what else can i use? please, help me.

Hi Usman,
try to find BT139 ar any TRIAC rated 16A or more

 

[joeyt]

thank you john. i am planning to build sr2oo, maybe this is my second amp project. my first was ax11

 

[AndrewT]

........but 100pF & 22nF at least 160v.........

could you explain why?

 

[JOHN BALI]

could you explain why?

because I measure voltage across it...
if the rail is +/-75VDC (max as Apex suggestion) then on this cap will be almost 150VDC
also the parallel 10k resistor will be hot, use at least 2w.

Hi AndrewT, where have you been
I'm not so much understand how it's circuit work/operate
but I've build it... (3 x SR200 monoblock)
May you explain better?