Jason,
Are you suggesting a dual voltage supply with an elevated V on the input section to drive the mosfet amp to it ultimate limit? I'm thinking in this way you could keep your low noise input section and still drive the output section for full gain. I don't need a 500 watt amp but perhaps somebody does and could do it with the five pairs of mosfets?
Are you suggesting a dual voltage supply with an elevated V on the input section to drive the mosfet amp to it ultimate limit? I'm thinking in this way you could keep your low noise input section and still drive the output section for full gain. I don't need a 500 watt amp but perhaps somebody does and could do it with the five pairs of mosfets?
Just out of curiosity, has anyone heard anything at all from our OP? I know it has only been about a month since he last posted and he did say 'a month or two' he'd be off the radar for. I'd love ostripper to check in.
Yes, I'm suggesting a 'Quad Rail' PSU to get the most out of the MOSFET variant. The OPS boards were designed with this as an option, that's why there's a set of jumpers before power is delivered to the driver / pre-driver section. Of course the boosted rails can be lower in current capacity so the PSU providing them need not be large.
Main disadvantage with DMOSFETs without error correction is poor basic linearity compared with BJT .
No, error correction according Hawksford, also in B.Cordell book
http://www.cordellaudio.com/papers/MOSFET_Power_Amp.pdf , fig 12
http://www.cordellaudio.com/papers/MOSFET_Power_Amp.pdf , fig 12
There is one more consideration - in favor of MOSFET. OPS, consisting of 3 stages (like EF3) always introduces additional pole at around 1-5MHz. In many cases it influences stability and has to be addressed.
With MOSFETs we can easily use 2 stages topology without compromising low influence on VAS, and additional unwanted pole is not there. More stability.
Also, though - BV is right - MOSFET OPS is less linear, THD difference is less than one order with strong dominance of the 2-nd harmonic (I can see it with live measurements). 3-rd harmonic and all the above ones are comparable. Assuming, all the designs we are talking about here, utilize rather deep global NFB (at least 60db loop gain), lower linearity is no problem in fact. Attached picture shows the live measurement of MOSFET option at 4.5KHz (at 1 KHz there's nothing interesting as all components are below 100db).
Cheers,
Valery
With MOSFETs we can easily use 2 stages topology without compromising low influence on VAS, and additional unwanted pole is not there. More stability.
Also, though - BV is right - MOSFET OPS is less linear, THD difference is less than one order with strong dominance of the 2-nd harmonic (I can see it with live measurements). 3-rd harmonic and all the above ones are comparable. Assuming, all the designs we are talking about here, utilize rather deep global NFB (at least 60db loop gain), lower linearity is no problem in fact. Attached picture shows the live measurement of MOSFET option at 4.5KHz (at 1 KHz there's nothing interesting as all components are below 100db).
Cheers,
Valery
Attachments
This is exactly what I want. I would like to diy an amp to replace the crown ce2000 (400w/8ohm 660w/4ohm) that runs my OB woofers. Two per channel...4 ohm load.
I don't have the technical ability of most here but am a decent mechanic with some test equipment. I appreciate all the work that is going into this and am ready to start ordering parts.
Evan
So on a mosfet based Slewmaster design do we simply remove one stage of drivers or predriver by jumping or leaving components off the board or do we need a new circuit board to optimize that circuit?
I don't think there is much to gain by going to the trouble of making a dedicated layout for the purpose of using MOSFETs. It was just an experiment that happened to work out decently well. Besides the current layout is flexible enough to accomodate. Only some values to change, components to omit / replace with jumpers and a few diodes to tack onto the underside. No traces to cut and no holes to drill if you choose not to.
For those watching, I want to re-iterate that the SlewMaster OPS design remains a BJT based EF3. The MOSFET experiment was not intended to replace the basic design, but rather compliment it with additional options for builders looking to try out things for themselves. Some may even prefer it, and that is fine. The nice part is having choice.
For those watching, I want to re-iterate that the SlewMaster OPS design remains a BJT based EF3. The MOSFET experiment was not intended to replace the basic design, but rather compliment it with additional options for builders looking to try out things for themselves. Some may even prefer it, and that is fine. The nice part is having choice.
If I were you I would give me a couple weeks to do some comparison tests between the two. I have a Le Monstre on my bench right now that I am struggling to get playing properly. Once I have that sorted out I will hook up a SlewMOS and Slewmaster side by side with identical IPS and do my best to make a some honest comparisons. The SlewMOS can actually be built more cheaply that the standard Slewmaster. Fewer parts and the IRFP's are cheaper that the MJL's. The test to me will be whether there is any noticeable differences in sound. Pick an IPS, I have Spooky, Wolverine, CFA-XH, CFA BV mod1, CFA BV mod2, Symasui, Valery Low TIM hybrid.
Blessings, Terry
Thanks Terry, I will wait for your results. From my conversation with others not now on this thread there can be a preference in sound quality of the Mos-fet based amps. That is what I am going to wait to hear about. If it does have a nicer sound why not use the design? It seems that Lazy Cat and some others have chosen that type device to base their amps around.
Build one each for yourself and decide what you like. You can ask 10 people and get 10 opinions, but in the end yours is the only one opinion that will matter to you.
I'll try to get to it soon. I have several MOSFET amps. Perreaux B9000, Hafler 220, Soundcraftsmen 800 & 860, ESP P101, Peeceebee, VSSA X 4, SKA GB150. The GB150 is the only one that uses these vertical DMOSFETs. It is my least favorite of those listed. The others all use laterals.
I'm actually kind of surprised that you haven't built any of these to at least get your feet wet. I would suggest that at least you build one of Jason's VSSAs. It is a simple as your going to get and it sounds stellar. He is still selling the boards and is the best for supporting what he sells. Highly recommended.
Blessings, Terry
I'm actually kind of surprised that you haven't built any of these to at least get your feet wet. I would suggest that at least you build one of Jason's VSSAs. It is a simple as your going to get and it sounds stellar. He is still selling the boards and is the best for supporting what he sells. Highly recommended.
Blessings, Terry
perhaps a separate thread or a blog about this aspect? this is interesting. really...
just a sugestion, i wonder why Ostripper did not think about mosfet outputs looking at his works...