When I built my moskido I ran the heater ac through a common mode choke. About 40 turns on a ferrite core. Maybe the choke could provide some of the voltage drop you meed for your heaters.
Evan
Evan
Yes, it will work with 4 ohm load - just don't go to full amplitude - 2 pairs of output fets will simply not handle such power.
It warmed up pretty fast an the dummy load so I couldn't run it long there. I had it playing on junk speakers for an hour. So far, so good. I need to adjust a protection board for it now and try it on some good speakers.
BTW, what quiescent current did you set per pair? I run my prototype at around 85-90mA now.
Hope you will like the sound 🙂
It's around 85mA. My heat sinks are pretty light so I'm trying to keep it low. I want to hear it before I build a chassis for it so I know the heat sink will work.
Vas current seems to have dropped as this amp burned in. I can only get around 55mA bias now and the driver heat sink is running cold. I did an A B comparison with the TubSoMo and the CFA-CFP on a small pair of Mission speakers. The TubSoMo had fuller base but the CFA-CFP was noticeably more detailed. TubSoMo also hardly warmed up so it will likely improve considerably once I get the VAS current corrected. Both did a remarkable job driving these speakers. The owner of the speakers and I both were surprised. They have never sounded that good before. I'm going to try them out on my Klipsch in the morning.
Yes, at 55mA you simply get THD increase, especially at mids-highs, so needs to be raised up to 90mA.
Fully agree - TubSuMo gives an excellent, pleasant bass - I call it "Velvet bass" 🙂
Fully agree - TubSuMo gives an excellent, pleasant bass - I call it "Velvet bass" 🙂
I've been listening to TubSoMo on my Klipschs for a couple hours. It sounds noticeably better when it's warmed up. It keeps cooling down on me though. Once I get the bias current up where it's supposed to be this likely won't be an issue. It sounds great. Excellent bass. We need to figure out how to give this amp the high frequency detail that the CFA-CFP has. That's still the winner on these speakers.
I've got a little 60Hz noise that I can't seem to cure so I'm going to need to get it in a proper chassis to evaluate it better.
I've got a little 60Hz noise that I can't seem to cure so I'm going to need to get it in a proper chassis to evaluate it better.
This is actually a sort of... dilemma 🙂
CFA is faster by design, higher slew rate, also, having CFPx2 output arrangement, it controls the speaker very tightly, even at high frequencies. High-current (low impedance) NFB also adding to this, making the sound even more natural. The bass feels a little bit "harder" though.
VFA behaves differently - NFB is much higher impedance and this is one of the reasons why the speaker is controlled differently (purely voltage feedback). Also, lateral FET OPS is slower than that CFAx2. The whole thing gives somewhat slightly "softer" sound. The detail is there, but not as accented, as "sharp", as with CFA one. Rather comfortable for long listening though. And very good bass.
I'm now experimenting with simple designs (both CFA and VFA) to better understand the nature of those nuances. Extremely interesting field 😉
Try no global feedback one with the same speakers - also an interesting experience. That one will sound much more "tubish" - a little bit of 2-nd harmonic is there, at the level, where you start hearing it.
CFA is faster by design, higher slew rate, also, having CFPx2 output arrangement, it controls the speaker very tightly, even at high frequencies. High-current (low impedance) NFB also adding to this, making the sound even more natural. The bass feels a little bit "harder" though.
VFA behaves differently - NFB is much higher impedance and this is one of the reasons why the speaker is controlled differently (purely voltage feedback). Also, lateral FET OPS is slower than that CFAx2. The whole thing gives somewhat slightly "softer" sound. The detail is there, but not as accented, as "sharp", as with CFA one. Rather comfortable for long listening though. And very good bass.
I'm now experimenting with simple designs (both CFA and VFA) to better understand the nature of those nuances. Extremely interesting field 😉
Try no global feedback one with the same speakers - also an interesting experience. That one will sound much more "tubish" - a little bit of 2-nd harmonic is there, at the level, where you start hearing it.
Or FB from the pre-drivers only (leave the final OP's out of the FB loop).
I thought I was crazy .... but the same basic conclusions about CFA/VFA
feedback vs. SQ. Good summary .
Lazy cat says there is a "trick" to get a CFA to excel in bass. 🙄
OS
Member
Joined 2009
Paid Member
Yes very good summary. I have 5 pair cfa slew master and tubesumo runnining on similar power supplies . This is exactly the difference I hear. Right now the slew monsters run woofers and the tubesumo does mid bass up.
Pure heaven.
Pure heaven.
I did change the bias pot to 100 ohm on the tubesumo to get a bit more current. The amp still runs cool.
Is it better to change the pot or change R29 to raise current? My drivers are running cold too.
My mistake. I didn't realize you were thinking of vas current. I played with r29 when trying the tubesumo ips with the slew master ops. I ended up back where the schematic called for. Vas current looked good in isolation...I never rechecked hooked to the output stage.