Did anyone ever build the FetZuMo? I had intended to but somewhere along the way of selling of my extra boards I misplaced a set. I would love to know how it compares to the tube version. I love the sound of the TubSuMo but if the FetZuMo sounds as good you could avoid the hassle of startup offset issues.
I've been wanting to build the Fet version, but haven't found any fets from a reliable source yet. I can send you a pair of boards if you want to try it.
What jfet is called for?
I have never done an A/B comparisons. My over all impression is the tubesumo sounds as good as the f4 while running cooler and delivering more power to the speaker. I say build both. The pass amps are amazing in their sound quality and simplicity. The parts and boards for both amps are available.
I have never done an A/B comparisons. My over all impression is the tubesumo sounds as good as the f4 while running cooler and delivering more power to the speaker. I say build both. The pass amps are amazing in their sound quality and simplicity. The parts and boards for both amps are available.
Thanks
to cultivate sumo to how much this bias is consistent sir
Im runing -+ 70vdc
I have actually built the Jfet input version in the similar ckt like Kypton v2 and its actually sounding nice with good resolution but I actually wanted to try the 12AX7 tube for the input. I doubt if tube can actually give that fine details.
I am actually looking for more natural tone along with Jfet kind of detail.
If tube can do both the detail as jfet and tube tone then nothing like that. Its worth to wait and build something like that and the startup issues can be solved once the tube i warmed up I believe.
The 12AX7 is not a good substitute for the 12AU7 in this circuit. Unless the circuit is redesigned to specifically use the 12AX7, the 12AX7 will be biased into positive grid territory. It's not that the circuit won't work at all, but the tube will not be operating in its linear region.
Thats fine well we can still use 12AU7 but my big problem is that will I miss the detail from the Jfet if 12AU7 is used? Can this tube deliver the detail as much as the Jfet?
You will hear a lot of strongly held opinions if you start a conversation about whether tubes are as good as semiconductors or not, so it's not my intent to start that debate here. I design with both tubes and semiconductors and both technologies can provide "detail" if properly used. In fact, in small signal applications, tubes can actually be more linear than FETs or BJTs. There are tubes that are more linear than the 12AU7 but in this circuit you would not likely hear any difference as long as the tube is biased into its linear operating region.
I hope this helps.
ok but how do we have the startup sequence.
IPS > where the valve is connected
VAS>
OPS>
Can we turn on the OPS after 30 seconds of heating the filament? and then turn on the relay for the OPS? or are there multiple turnons?
IPS > where the valve is connected
VAS>
OPS>
Can we turn on the OPS after 30 seconds of heating the filament? and then turn on the relay for the OPS? or are there multiple turnons?
If you can run the tube heater for 10-20 seconds first then the offset will be low enough to fire up the rest all at once but you still need speaker protection for the initial startup. The "21st century" protection is perfect for this.
I have the 12au7 version running. Does not lack for detail as far as my ears go.
As Terry said. Tube heater for 20-30 seconds and then the rest of the amp. It still has some offset at start up so a speaker delay/protection setup is needed.
As Terry said. Tube heater for 20-30 seconds and then the rest of the amp. It still has some offset at start up so a speaker delay/protection setup is needed.
Ray, Terry, Evan - thank you for the good comments while I was not quick enough with the answers 😉
I have tested an option with BJTs at the input - I can reach lower measured distortion (due to higher loop gain), but the variant with the tube is still my favourite one in terms of the way it sounds - I believe, due to very good transients handling - lots of micro-nuances, particularly natural sound at mids-highs.
12AU7 is relatively low gain (good for the purpose here), fast and linear - showing rather precise operation in a small signal input stage.
Start-up - yes, 20-30 seconds in advance for the filament, then power-on the whole thing with 5 seconds inrush for the PSU, after 5 seconds at full rails - connect the speakers. "21-st century" control board does it nicely, providing all the safety features at the same time. It will not connect the speakers if something is wrong with the amp (DC offset of too much current through the output devices).
I have tested an option with BJTs at the input - I can reach lower measured distortion (due to higher loop gain), but the variant with the tube is still my favourite one in terms of the way it sounds - I believe, due to very good transients handling - lots of micro-nuances, particularly natural sound at mids-highs.
12AU7 is relatively low gain (good for the purpose here), fast and linear - showing rather precise operation in a small signal input stage.
Start-up - yes, 20-30 seconds in advance for the filament, then power-on the whole thing with 5 seconds inrush for the PSU, after 5 seconds at full rails - connect the speakers. "21-st century" control board does it nicely, providing all the safety features at the same time. It will not connect the speakers if something is wrong with the amp (DC offset of too much current through the output devices).
in general what would go wrong? Just curious about it? why cant we just use 30 sec delay to start the ops after the filament turn on?