Hi All
I need a little help !
I am building a pair of briged A75 Monoblocks
I am going to use 50v O/P Rails and am using IRFD220/9220, IRF620/9620 and IRFP240/9240 (10 Pairs per 1/2 Monoblock) and will bias enhanced AB rather than 300W Class A For obvious reasons
The MOSFET choice is for the 50V + Rails and availibility
I have heard Bob Ellis and others talking about replacing the IRFD9110 and 110's with IRF9610 and 610s does this affect the sound quality or operation at all ?
Also is the regulator for the input stage OK or is there a better alternative ?
Thanks
Dam
I need a little help !
I am building a pair of briged A75 Monoblocks
I am going to use 50v O/P Rails and am using IRFD220/9220, IRF620/9620 and IRFP240/9240 (10 Pairs per 1/2 Monoblock) and will bias enhanced AB rather than 300W Class A For obvious reasons
The MOSFET choice is for the 50V + Rails and availibility
I have heard Bob Ellis and others talking about replacing the IRFD9110 and 110's with IRF9610 and 610s does this affect the sound quality or operation at all ?
Also is the regulator for the input stage OK or is there a better alternative ?
Thanks
Dam
Broadly speaking, the choice of MOSFET for the front end will boil down to two factors: Capacitance and possibly case style if you're going to do something that increases heat dissipation. Or some people may just want to use up some MOSFETs they've already got on hand.
There are things that you've left out of your description, so it's difficult to guess where you're trying to go with your amps. You say you're going to bridge the amps...are you going to redo the front end to include two sets of outputs or are you going to build four completely separate A-75s and operate them as pairs?
There's nothing wrong with the regulator. You can simplify it, but not by too much. You can make it more complicated. You can increase the current capability. You can do most anything you want. Again, the question is what do you want to change about it and why?
Grey
There are things that you've left out of your description, so it's difficult to guess where you're trying to go with your amps. You say you're going to bridge the amps...are you going to redo the front end to include two sets of outputs or are you going to build four completely separate A-75s and operate them as pairs?
There's nothing wrong with the regulator. You can simplify it, but not by too much. You can make it more complicated. You can increase the current capability. You can do most anything you want. Again, the question is what do you want to change about it and why?
Grey
Hi Grey
Thanks for that
The reason they were changing the 110/9110 is overheating when used at higher rail voltages as I am doing. I wondered wether this changes the sound quality
I dont really see how you can have one front end running 2 OP stages
Not easily anyway I think this would ruin the elegance of the circuit if tried so I am building 2 Mono A75's in the same case per channel
As for the regulator I remember reading someone said there was an inprovement to be had but could not find it by searching the forum
Dam
Thanks for that
The reason they were changing the 110/9110 is overheating when used at higher rail voltages as I am doing. I wondered wether this changes the sound quality
I dont really see how you can have one front end running 2 OP stages
Not easily anyway I think this would ruin the elegance of the circuit if tried so I am building 2 Mono A75's in the same case per channel
As for the regulator I remember reading someone said there was an inprovement to be had but could not find it by searching the forum
Dam
If it's overheating that you're concerned about, then something in a TO-220 case will definitely give you more latitude for heat dissipation. I generally run TO-220 cases up to about 1/2W naked; I use a heatsink above that.
As for how to configure the front end, have a look at the Aleph-X, the GR-25, or Nelson's patent for X feedback. There's also a thread called UGS adventures that covers pretty much the same ground. I'm sure there are others that I'm just not remembering at the moment.
There are lots of potential ways to "improve" the regulator circuit, depending on your point of view. The question then becomes whether someone else's idea of an improvement matches your philosophy--not always a given.
As an example, I used a similar circuit to regulate the main output rail in the GR-25...except that I used a current mirror as a load, put a cap alongside the Zener so its charging time served as a slowstart feature, ran a separate sense wire from the regulator...and so on and so forth. Do these qualify as "improvements" to the basic regulator? Maybe. Maybe not. It's just what I felt like doing at the time. If I were to build the regulator today, I'd probably do it differently. Next week might yield yet another variation. Who knows?
Bear in mind that there are folks who feel that the best regulator is no regulator. To them, the ideal thing is to junk the regulator entirely. There are all sorts of options.
If you are intent on both bridging the thing and increasing the rails, just how much wattage were you aiming for, anyway?
Grey
As for how to configure the front end, have a look at the Aleph-X, the GR-25, or Nelson's patent for X feedback. There's also a thread called UGS adventures that covers pretty much the same ground. I'm sure there are others that I'm just not remembering at the moment.
There are lots of potential ways to "improve" the regulator circuit, depending on your point of view. The question then becomes whether someone else's idea of an improvement matches your philosophy--not always a given.
As an example, I used a similar circuit to regulate the main output rail in the GR-25...except that I used a current mirror as a load, put a cap alongside the Zener so its charging time served as a slowstart feature, ran a separate sense wire from the regulator...and so on and so forth. Do these qualify as "improvements" to the basic regulator? Maybe. Maybe not. It's just what I felt like doing at the time. If I were to build the regulator today, I'd probably do it differently. Next week might yield yet another variation. Who knows?
Bear in mind that there are folks who feel that the best regulator is no regulator. To them, the ideal thing is to junk the regulator entirely. There are all sorts of options.
If you are intent on both bridging the thing and increasing the rails, just how much wattage were you aiming for, anyway?
Grey
Hi Gray
Thanks for your input I've been mulling things over and reading about the XA 's and your GR-25
In answer to your questions about how much power I was looking for the answer would be around 300WRms / 8 Ohm.
I would like to build a supersymetric driver to drive O/P mosfets IRFP240/IRFP9240 at -+40V Rails @ about 50W class A and the rest AB but having trawled the DIYaudio forums have not been able to find any schematics yet
I will probably build bridged A75s and then maybe experiment on a supersymetric driver later
Dam
Thanks for your input I've been mulling things over and reading about the XA 's and your GR-25
In answer to your questions about how much power I was looking for the answer would be around 300WRms / 8 Ohm.
I would like to build a supersymetric driver to drive O/P mosfets IRFP240/IRFP9240 at -+40V Rails @ about 50W class A and the rest AB but having trawled the DIYaudio forums have not been able to find any schematics yet
I will probably build bridged A75s and then maybe experiment on a supersymetric driver later
Dam
It might have been me you remember whining about the regulator. The stock regulator used a voltage doubler which I think is a ripple tripler. Even with beefed up caps all around in the regulated PS, I could still see ripple on the 'scope in the PS output.
I can't see any ripple in the output of my simple BZLS regulated
(but grossly beefed up) PS.
PS--I highly recommend using the folded cascode connection in the A75 -- it changes the whole sound and it is really amazing.
JJ
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