Re: 5W fet power amplifier with "tube" sound
Posted: 23 Aug 2010, 09:26
Another one test with different knob settings
tracing pedals since 2007
https://www.freestompboxes.org/
Can you tell me anything about the underlined part?I don't know... to me at least the MicroPA output looks pretty much like one coming from a generic tube amp: somewhat rounding up on the clipping onset and it even features the same type of crossover/blocking distortion mechanism due to shifting bias point. But, I think those scoped waveforms are either from running to a resistive load or the amplifier's response stays fairly linear regardless of load impedance. So the mechanism where amp's gain interacts with a reactive load is not showing up in there. Otherwise, it pretty much nails the "PP tube power amp thing".
It`s really true, but modelling speaker complex load is not simple problem.Well, this project looks cool. I've been checkin' your website (KMG) and these Fet/micro poweramps may be what i've been searchin' for.
I posted these projects (micro PA + fet PA) at the SSGuitar Forum, and I had this answer about your PA:
Can you tell me anything about the underlined part?I don't know... to me at least the MicroPA output looks pretty much like one coming from a generic tube amp: somewhat rounding up on the clipping onset and it even features the same type of crossover/blocking distortion mechanism due to shifting bias point. But, I think those scoped waveforms are either from running to a resistive load or the amplifier's response stays fairly linear regardless of load impedance. So the mechanism where amp's gain interacts with a reactive load is not showing up in there. Otherwise, it pretty much nails the "PP tube power amp thing".
Any speaker simulation sounds like a "rubber woman" - similar, but not those feelings.Silly questions: what are the -sonic- differences between this amp and the microfet pa?
Micro PA has "split load phase inverter", 5W PA has "Long tail phase inverter" like in most tube PA (marshall for example).I saw Micro's schematic and the structure looks slightly different than this one. Also, the values on the Micro are pure Marshall ("Phase inverter", bias splitter, etc).
Can I built this 5w with Marshall values?
They works like in tube poweramps.How effective are the presence and depth controls?
Cut is an optional control. It allows to suppress "sand" in soundhow the "cut" works? is it effective?
Yes, simmetry is a trimmer potentiometer for matching aplitude at phase inverter outputs.is the simmetry knob something i can mess around? or is it like a "set and don't move" kinda knob?
Have you tried it? Can you give us some samples?RnFR wrote:sounds great!
Well, I think I'll go with the 5w or maybe the 15w. I some minor differences between those 2:KMG wrote: Micro PA has "split load phase inverter", 5W PA has "Long tail phase inverter" like in most tube PA (marshall for example).
I tried to use long tail phase inverter in micro PA, but it gives much more gain.
With it sensistivity of micro PA was about 5mV. So i returned to split load phase inverter for micro PA.
The gain of PI stage depends on R4&8 value, because 5w requires less current of output stage it requires less PI gain in order to have same sensitivity.Well, I think I'll go with the 5w or maybe the 15w. I some minor differences between those 2:
R4&8; C15; D1, 3&4
If you`ll increase R5&6 you`ll need to increase R3 to 36k, R7 to 47k RV1 to 30k.Now, is it ok if I change the values of the long tail resistors to Marshall specs.? Will I have more gain, noise, Marshallesque sound?
R4&8 to 470 ohm; R5 to 10k; R6 to 4k7? (and maybe C4 to 47p?)
I'm asking b'cos I'm some kind of OCD person and I prefer typical values.
One of my friends on GTLab made interesting version of this PA.Also, if I build the 15w and apply less voltage (say 24v) and change the bias, will it be the same as the 5w version?
Same things goes for the 40w version, right? 3 times the value.KMG wrote:If you`ll increase R5&6 you`ll need to increase R3 to 36k, R7 to 47k RV1 to 30k.Now, is it ok if I change the values of the long tail resistors to Marshall specs.? Will I have more gain, noise, Marshallesque sound?
R4&8 to 470 ohm; R5 to 10k; R6 to 4k7? (and maybe C4 to 47p?)
I'm asking b'cos I'm some kind of OCD person and I prefer typical values.
Ok. Now i want this. How can I do it? where do I have to put a switch? R10?KMG wrote:One of my friends on GTLab made interesting version of this PA.Also, if I build the 15w and apply less voltage (say 24v) and change the bias, will it be the same as the 5w version?
As a base he took 40W version.
He powered PI stage from separate supply (separate winding of power transformer), but output stage from switchable winding (variable supply voltages).
So he have PA wtih 5W/15W/40W of output power in one device.
Why not just build a 100watt tube power amp?file1 wrote:Dear All,
I want to build 90W PA version for my brother , but I have a huge problem with output transformer. Plase could somebody provide me some more information about it? Link on internet where it could be bought also can be usefull. Does it someone tried to build it with EI core and could provide parameters for 90W version? Which type of tpk-190, exactly could be used for rewinding ? Thank you in advance, Igor