I think ZM's first Lazy Singing Bush is this one, which is a common drain mu follower:
Single Ended Tokin SIT THF-51S Common Drain Mu Follower Amplifier , 45W?
Then there is the common source choke load that mbrennwa point out.
I don't recall seeing a common drain choke loaded Singing Bush.
Single Ended Tokin SIT THF-51S Common Drain Mu Follower Amplifier , 45W?
Then there is the common source choke load that mbrennwa point out.
I don't recall seeing a common drain choke loaded Singing Bush.
Ah, Lazy Bush... why lazy?
Am I right to assume that the "upper" PCB could run with a choke instead of the "lower" PCB (mu stage / CCS)? And the choke version could run at a much lower voltage (since there is no active current source that needs the extra voltage to work)?
Also, what's the reason for running four input JFETs in parallel? Wouldn't one be enough? Also, the PCB would be awkward without a 2SK77B, which I don't have... I guess I could just be lazy and build the input buffer in dead-bug style of a piece of strip board. Or use a beefy front end to start with...
Hi Ben,
Now that you have had more time with the Mu follower, how does it compare to the Choke loaded? I'm thinking about this for my summer amp as the 150W/Ch of dissipation is more than my room likes in the summer. What differences do you hear? How does the output impedance compare?
Thanks,
Now that you have had more time with the Mu follower, how does it compare to the Choke loaded? I'm thinking about this for my summer amp as the 150W/Ch of dissipation is more than my room likes in the summer. What differences do you hear? How does the output impedance compare?
Thanks,
If I'm running 2.3 amps bias do I just cut the voltage in half to ~33V or do I need a bit more to maintain the same operating point?
Hi Botte,
Are you asking about choke load for summer?
I enjoy both my Mu follower common drain THF-51S and choke loaded 2SK180 follower equally. I don't know if I hear any big difference in sound between the two. When I have one or the other in the system, I do not miss the one that is not in the system. Because my speakers are very sensitive, the difference in power output between the two is also not an issue.
I am not sure exactly what your question is about 2.3A, but I would keep Vds to about 33V to 35V. That seems to be a good value. Interestingly, I did some LTSpice runs because of your questions and the simulations show that for the Mu follower THf-51S with 66VDC power supply and Vds=33V, there is really not much difference in power or distortion between 2.3A and 3.0A. I should have done a bit more investigation initially. However that is based on LTSpice simulation and not on actual testing of the amplifier.
I also did some LTSpice simulations to determine output impedance. The Mu follower THF-51S was 0.35 Ohm and the 2SK180 choke load follower was 0.60 Ohm.
Are you asking about choke load for summer?
I enjoy both my Mu follower common drain THF-51S and choke loaded 2SK180 follower equally. I don't know if I hear any big difference in sound between the two. When I have one or the other in the system, I do not miss the one that is not in the system. Because my speakers are very sensitive, the difference in power output between the two is also not an issue.
I am not sure exactly what your question is about 2.3A, but I would keep Vds to about 33V to 35V. That seems to be a good value. Interestingly, I did some LTSpice runs because of your questions and the simulations show that for the Mu follower THf-51S with 66VDC power supply and Vds=33V, there is really not much difference in power or distortion between 2.3A and 3.0A. I should have done a bit more investigation initially. However that is based on LTSpice simulation and not on actual testing of the amplifier.
I also did some LTSpice simulations to determine output impedance. The Mu follower THF-51S was 0.35 Ohm and the 2SK180 choke load follower was 0.60 Ohm.
Hi Ben,
Yes, the choke loaded version of the thf-51s
Sounds like you think the supply should be just a bit more than half. So my MU is at 64v and Vds is 33. So with 2.3A bias across the 1 ohm choke 2.3v drop. So I need about a 36v supply.
As for the output impedance, see attached actual impedance sweep. The sim is very close. What about the THF-51 choke loaded?
thanks
Attachments
So I did LTSpice for a Hammond 193V loaded THF-51S follower, 36VDC PS, Iq 2.3A, Vds 33.7V.
The simulation gave 0.45 Ohm output impedance.
The output power was much less than the Mu follower version as the Mu follower provided quite the boost. The choke loaded version maxed out at somewhere between 20W and 25W, depending on how much distortion and clipping is tolerated. This is more or less the same as my 2SK180 choked loaded follower amp's power.
The THF-51S has a higher power rating than the 2SK180 so I increase Iq to 2.8A, Vds 33.2V. That added about 7 or 8W of power output. However the distortion profile changed to less H2 such that H2 was less than H3. But that was LTSpice and reality may be different. 🙂
The simulation gave 0.45 Ohm output impedance.
The output power was much less than the Mu follower version as the Mu follower provided quite the boost. The choke loaded version maxed out at somewhere between 20W and 25W, depending on how much distortion and clipping is tolerated. This is more or less the same as my 2SK180 choked loaded follower amp's power.
The THF-51S has a higher power rating than the 2SK180 so I increase Iq to 2.8A, Vds 33.2V. That added about 7 or 8W of power output. However the distortion profile changed to less H2 such that H2 was less than H3. But that was LTSpice and reality may be different. 🙂
H2 vs H3 is very dependent on all the variables - AC and DC Volts, Current and Load, as well as the parameters specific to the part. These are the blessings and curses that come with Triode-like character, and you pretty much have to measure and adjust against all these things to get a particular performance, and maybe not even then.
That said, it's worth the effort.
That said, it's worth the effort.
This is what I have been using. I can't remember where I found it.
.SUBCKT thf51 D G S ; Drain Gate Source
+ PARAMS: MU=43.571 X=1.494 K=1.339 N=0.902 VCT=0.831 RG=5MEG
*--------------------------------------------------
B1 D S I=K*PWR(URAMP((V(G,S)+VCT)+(N*LN(V(D,S))+(V(D,S)/MU))),X)
FOR MULTISIM COMMENT OUT ABOVE LINE () AND UNCOMMENT NEXT LINE
*B1 D S I=K*PWR(MAX((V(G,S)+VCT)+(N*LN(V(D,S))+(V(D,S)/MU)),0),X)
R1 G S {RG}
CGS G S 5000P
CGD G D 5000P
CDS G S 0P
.ENDS thf51-1x0063
.SUBCKT thf51 D G S ; Drain Gate Source
+ PARAMS: MU=43.571 X=1.494 K=1.339 N=0.902 VCT=0.831 RG=5MEG
*--------------------------------------------------
B1 D S I=K*PWR(URAMP((V(G,S)+VCT)+(N*LN(V(D,S))+(V(D,S)/MU))),X)
FOR MULTISIM COMMENT OUT ABOVE LINE () AND UNCOMMENT NEXT LINE
*B1 D S I=K*PWR(MAX((V(G,S)+VCT)+(N*LN(V(D,S))+(V(D,S)/MU)),0),X)
R1 G S {RG}
CGS G S 5000P
CGD G D 5000P
CDS G S 0P
.ENDS thf51-1x0063
Looking for a diy electronics challenge, I downloaded KiCad the other day and gave it a try. I've always used perf board for building amplifiers that I concocted but with the availability of low priced pcb manufacturers, I thought why not give it a try.
So after a few days, this is what I have. Being a complete newby, I hope there aren't any errors, fatal or otherwise.
So after a few days, this is what I have. Being a complete newby, I hope there aren't any errors, fatal or otherwise.
Attachments
Wow! Now you've got me considering trying it. Just 'considering' at this point. Heck, Mark Johnson got me to order my own PCBs (using MZM's Gerbers). I've played around with LTSpice, so why not KiCad? Well, lots of reasons, none of them valid...
Well done Ben!
Well done Ben!
