Hi , i posted a comment and you recomanded me to build the first schematic at post no1
this one:
Mooly said : Q3 actually needs to be an NPN
kasey197: " two initial comments:
biasing for Q5 looks dodgy - missing a resistor i think.
Q3 needs to be fed from junction of Q1 and R5 - looks like a typo. "
so i need to change q3 to be npn and it works ?
Thanks
this one:
Mooly said : Q3 actually needs to be an NPN
kasey197: " two initial comments:
biasing for Q5 looks dodgy - missing a resistor i think.
Q3 needs to be fed from junction of Q1 and R5 - looks like a typo. "
so i need to change q3 to be npn and it works ?
Thanks
Ranchu LTSpice Analysis
Hi Folks,
I have put the Ranchu QUASI through LTSpice, and some of the findings are in the schematic attached.
A few issues:
1. Gain is modified by R5 68k and is 22.1, which is 26.9dB.
2. On the schemat I have deleted the input offset network for simplicity, which would normally be on the real circuit as shown on Ranchu's schemat. I have inserted the offset into the source heading.
3. I have tagged a few actual (simulated) values to give some idea of current and voltage in critical areas around the circuit. They have 7 sig figs, which is of course the ideal. In reality it won't be measured that well and there will be variations due to component imperfects and tolerances.
4. I have kept lag comp as C4 (33pF) but added the feedback shunt C11 (68pF) while dropping the bypass across R5 68k. I have added a Miller cap across base/collector on Q5, the phase inverter. All this flattens the gain structure (it was toppy, dangerous for stability and ringing) and ensures the net gain is below unit at the frequency where phase shift is 180 degrees (where the negative feedback turns nasty into positive feedback, creating a destructive oscillator).
5. These tiny pF caps used in compensation are very difficult to predict with math and simulators. The badly affect the sound quality too, so the best option is to try it on a real amp and have a listen. If you have done it a few times, you develop a sense of under comp, or over comp. Once you are ready, you try it with a few caps across an 8R resistor load. The most difficult combination if 100nF//8R.
6. Notwithstanding, I do not say this is the correct combination of compensation caps. It's a start, there are no definitive answers unless you actually DO it.
7. This amp has very good harmonic profile. H2 is high at 12.5W into 8R; it's at -70dB, and H4 is around -84dB. H5 is well below -100dB, which is very good - no machine tones, very warmish and engaging. Recommended.
Thimios, I hope this helps, and directs your efforts to polish this lovely little amplifier! Thank you for your hard work, I'm just the remote fanatic!
Cheers,
Hugh
Hi Folks,
I have put the Ranchu QUASI through LTSpice, and some of the findings are in the schematic attached.
A few issues:
1. Gain is modified by R5 68k and is 22.1, which is 26.9dB.
2. On the schemat I have deleted the input offset network for simplicity, which would normally be on the real circuit as shown on Ranchu's schemat. I have inserted the offset into the source heading.
3. I have tagged a few actual (simulated) values to give some idea of current and voltage in critical areas around the circuit. They have 7 sig figs, which is of course the ideal. In reality it won't be measured that well and there will be variations due to component imperfects and tolerances.
4. I have kept lag comp as C4 (33pF) but added the feedback shunt C11 (68pF) while dropping the bypass across R5 68k. I have added a Miller cap across base/collector on Q5, the phase inverter. All this flattens the gain structure (it was toppy, dangerous for stability and ringing) and ensures the net gain is below unit at the frequency where phase shift is 180 degrees (where the negative feedback turns nasty into positive feedback, creating a destructive oscillator).
5. These tiny pF caps used in compensation are very difficult to predict with math and simulators. The badly affect the sound quality too, so the best option is to try it on a real amp and have a listen. If you have done it a few times, you develop a sense of under comp, or over comp. Once you are ready, you try it with a few caps across an 8R resistor load. The most difficult combination if 100nF//8R.
6. Notwithstanding, I do not say this is the correct combination of compensation caps. It's a start, there are no definitive answers unless you actually DO it.
7. This amp has very good harmonic profile. H2 is high at 12.5W into 8R; it's at -70dB, and H4 is around -84dB. H5 is well below -100dB, which is very good - no machine tones, very warmish and engaging. Recommended.
Thimios, I hope this helps, and directs your efforts to polish this lovely little amplifier! Thank you for your hard work, I'm just the remote fanatic!
Cheers,
Hugh
Attachments
Hi Bruno,
You should glance over from the beginning of the thread, to understand some of the design goals of this amp.
reg
Prasi
Very interesting thread, I just find non-conformism amp fascinating !!
I hope a GB for the PCB shown on post 477 will soon be created, or has it been done already and I'm late to the party...lol
Thiagomogi did an amazing job with his pcb design.
BR,
Eric
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Hi Ranchu,
Post 477 shows 2 different PCB, have a look at the right one.
This design seems to be from you and Hugh (written on the PCB), do you authorise someone to go aheah and order PCBs ?
Thanks,
Eric
