All comments are always appreciated in order to improve my new design. Please.
P=200W @ 8ohm
P=300W @ 4ohm
P=200W @ 8ohm
P=300W @ 4ohm
If you liked the early Krells (which many do) then you'll
enjoy this, I imagine.
😎
I forgot to mention the obvious: an RC network to ground at the
output.
enjoy this, I imagine.
😎
I forgot to mention the obvious: an RC network to ground at the
output.
Nelson Pass said:
Yes, after all the time I've spent looking at Krell schematics over the past month or so, it certainly looks famiiar!
Do you like Dan's designs, or are you just being diplomatic? 😉
Hi bvp,
What can I say. It's a bit Barry Manilow.
Is that 2 electros directly in the signal path?
Have you considered bypassing that offset adj pot to gnd (on both sides)?
have you tried a cascode on the input stage to raise collector impedance? The high degen you have helps and with reducing Ccomp. This should be stable without those 22pF - (take off the feedback lead C and disable the input 100p and view a 10KHz sq wave) You can improve the PSRR and HF distortion both.
Your feedback lead C seems to be the dominant HF rolloff - would be better at the input RC which is 5 times higher.
The tail current sources could be better 2 tr unless you need the lights.
Just at first glance. Looks VERY stable (with zobel of course)
What can I say. It's a bit Barry Manilow.
Is that 2 electros directly in the signal path?
Have you considered bypassing that offset adj pot to gnd (on both sides)?
have you tried a cascode on the input stage to raise collector impedance? The high degen you have helps and with reducing Ccomp. This should be stable without those 22pF - (take off the feedback lead C and disable the input 100p and view a 10KHz sq wave) You can improve the PSRR and HF distortion both.
Your feedback lead C seems to be the dominant HF rolloff - would be better at the input RC which is 5 times higher.
The tail current sources could be better 2 tr unless you need the lights.
Just at first glance. Looks VERY stable (with zobel of course)
pinkmouse said:
Dan and I are very old friends, dating back to '76 or so. At that
time, as the Dayton-Wright rep, he did me the great service of
hauling an 800A around with which to demo the XG8 speakers -
no trivial effort.
😎
/pass/: has a book full of Dan stories and Mike Wright stories
as told by Dan.
I've been putting a filter capacitor of 100uF across my CCS LEDs.
The 10 ohm base resistors on the output transistors are larger than my normal values of 3.3 ohms, down to 1 ohm for low voltage outputs with high hfe. I think the latest Leach uses 3.3 ohms.
I have been putting my DC offset bias on the feedback input of the differential, not at the input. My current amp uses a servo that nudges the two front-end constant current sources to get a DC null. Do you need the input resistors bias with the large 100uF capacitor on the feedback circuit?
The 10 ohm base resistors on the output transistors are larger than my normal values of 3.3 ohms, down to 1 ohm for low voltage outputs with high hfe. I think the latest Leach uses 3.3 ohms.
I have been putting my DC offset bias on the feedback input of the differential, not at the input. My current amp uses a servo that nudges the two front-end constant current sources to get a DC null. Do you need the input resistors bias with the large 100uF capacitor on the feedback circuit?
bvp,
If you've simmed this, try resistors similar to your output Re's to superimpose the output stage commutation currents on the rails and see how it affects THD, FFT. You don't want it hypersensitive to power supply hash or you'll be doubling up supply caps and transformer size chasing minute ( maybe 6dB) improvement when
a few low cost refinements can make maybe 20-30 db better isolation.
If you've simmed this, try resistors similar to your output Re's to superimpose the output stage commutation currents on the rails and see how it affects THD, FFT. You don't want it hypersensitive to power supply hash or you'll be doubling up supply caps and transformer size chasing minute ( maybe 6dB) improvement when
a few low cost refinements can make maybe 20-30 db better isolation.
Thank You
Thank you all for your valuable inputs. I'm very grateful for that. With all of your feedback at once, I would like to say (if I missed any question, please forgive me and I'll get back to that)
1. I got the idea of the circuit from the Motorola Application Notes where I found from the Internet. I don't know why it is not available at Onsemi anymore. I haven't have a chance to see any Krell Amp yet. However, I would love to if I have a chance.
2. About the Zobel Network, yes, I included it in the second part - speaker protection ultilizing uPC1237HA.
3. Couple of electrolytic caps across the Leds recommendation sounds good to me. I'll add them in rightaway. I guess they just hold the voltage across leds (1.82V), don't they?
4. And I probalby don't need the 100uF in series with 1k-resistor in the feedback circuit. I'll find out in the lab soon.
5. Please introduce me with Dan's Design as you mentioned.
6. I wanted to load the pcb I made in pdf format, but its size is 450kB which is not allowable. Sorry for that.
Thanks again
Thank you all for your valuable inputs. I'm very grateful for that. With all of your feedback at once, I would like to say (if I missed any question, please forgive me and I'll get back to that)
1. I got the idea of the circuit from the Motorola Application Notes where I found from the Internet. I don't know why it is not available at Onsemi anymore. I haven't have a chance to see any Krell Amp yet. However, I would love to if I have a chance.
2. About the Zobel Network, yes, I included it in the second part - speaker protection ultilizing uPC1237HA.
3. Couple of electrolytic caps across the Leds recommendation sounds good to me. I'll add them in rightaway. I guess they just hold the voltage across leds (1.82V), don't they?
4. And I probalby don't need the 100uF in series with 1k-resistor in the feedback circuit. I'll find out in the lab soon.
5. Please introduce me with Dan's Design as you mentioned.
6. I wanted to load the pcb I made in pdf format, but its size is 450kB which is not allowable. Sorry for that.
Thanks again
i would definitely look for better vas and pre-driver transistors, if they're just what you have it should work but generally i would think the triple darlington should have decreasing ft from the fast pre to medium driver to slow output device, you have relatively fast output devices so the pre-driver in particular may benefit from being smaller and faster (@ 300 V, 20 W the mje340 has to be pretty slow, my data sheet doesn’t think ft is worth mentioning) - check out some of the vas Q suggestions in several other threads - low Vce, higher hfe, smaller die (= smaller Ccb,ib) pre-driver should present smaller, more linear load to vas
also i would consider raising driver current, with 12A peak output needing 100 mA base current with typ hfe ( 300mA if you use min hfe! ) and 4x power device base C to charge/discharge 30 mA driver bias may be light for low distortion with so little loop gain – not that high loop gain can fix a poorly commutating class B output
also i would consider raising driver current, with 12A peak output needing 100 mA base current with typ hfe ( 300mA if you use min hfe! ) and 4x power device base C to charge/discharge 30 mA driver bias may be light for low distortion with so little loop gain – not that high loop gain can fix a poorly commutating class B output
Yes FAST-SLOW -SLOWEST (OUTPUT).
I have found that a CFP for the pre/driver works well to reduce stage distortion in this type of amplifier, and reduces the driver's influence on bias.
I have found that a CFP for the pre/driver works well to reduce stage distortion in this type of amplifier, and reduces the driver's influence on bias.
WELL
should I say something different when everybody says
that design actually works?
hey one thing
R30=220 and R29=560, I guess this should be R29=R30=560
hienrich
should I say something different when everybody says
that design actually works?
hey one thing
R30=220 and R29=560, I guess this should be R29=R30=560hienrich
You're right, hienrich. They are indeed equal to 560. My schematic error.
Thank you. Nice catch.
By the way, the circuit works well as I expected to see in the simulation profiles. Its PCB is 8''x3'' double-sided.
BvP
Thank you. Nice catch.
By the way, the circuit works well as I expected to see in the simulation profiles. Its PCB is 8''x3'' double-sided.
BvP
Hi there,
Here is the pcb layout artwork. I've already made 2 PAs - Hi-Fi Grade.
They worked well.
BvP
Here is the pcb layout artwork. I've already made 2 PAs - Hi-Fi Grade.
They worked well.
BvP
Sorry,
Forget about the zip file due to the server limitation.
Give me your e-mail address, I'll send you the files if you're interested.
Forget about the zip file due to the server limitation.
Give me your e-mail address, I'll send you the files if you're interested.
Nice to see someone else trying a triple darlington output like me 🙂
I'm looking for something better than MJE340/350 for vas and predrivers - with models as i'm still at the simulation stage. BD139/140 works well but I don't think these have a high enough Vceo for 50V rails. I tried MJE243/253 but these seemed to be very unstable in the design (although perhaps the OnSemi spice model is wrong - it wouldn't be the first one!)
http://www.darkmatter.myby.co.uk/EFvas.png is my current attempt, not too dissimilar from your schematic. I'm probably exceeding the Vceo of the 546/556's there but I plan to add a cascode in there to 24v for each of the LTP's. Yes - the currents through the top and bottom half are different, this is to remove the 40mV output offset that seems to occur otherwise.
I'm looking for something better than MJE340/350 for vas and predrivers - with models as i'm still at the simulation stage. BD139/140 works well but I don't think these have a high enough Vceo for 50V rails. I tried MJE243/253 but these seemed to be very unstable in the design (although perhaps the OnSemi spice model is wrong - it wouldn't be the first one!)
http://www.darkmatter.myby.co.uk/EFvas.png is my current attempt, not too dissimilar from your schematic. I'm probably exceeding the Vceo of the 546/556's there but I plan to add a cascode in there to 24v for each of the LTP's. Yes - the currents through the top and bottom half are different, this is to remove the 40mV output offset that seems to occur otherwise.
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