Low gain
William - i got home and checked the resistor values - R16 & R30 are 100K, R18 & R28 are 10K, so i suppose the gain should be 10 times, but i'm only seeing 4 times.
The 0.5v p-p signal is coming into the AX via 4.7uf polypropylene capacitors ( i had them in my junk box). What values should be used normally?
William - i got home and checked the resistor values - R16 & R30 are 100K, R18 & R28 are 10K, so i suppose the gain should be 10 times, but i'm only seeing 4 times.
The 0.5v p-p signal is coming into the AX via 4.7uf polypropylene capacitors ( i had them in my junk box). What values should be used normally?
Diff pair very prone to drift...
I have a minor issue with the diff pair - each time i walk past the PCB the disturbance in the air temporarily causes small fluctuations in the Abs DC offset (about 100mv). Is it feasible to put a little bit of pipe insulation/lagging around the diff pair to prevent this external influence or is it better to just ignore it?
I have a minor issue with the diff pair - each time i walk past the PCB the disturbance in the air temporarily causes small fluctuations in the Abs DC offset (about 100mv). Is it feasible to put a little bit of pipe insulation/lagging around the diff pair to prevent this external influence or is it better to just ignore it?
Hi,
ignore the 100mV. Every change in mains voltage causes more fluctuation.
4.7muF should be OK.
Do you see the 2V square wave between both outputs or between one output and ground?
William
ignore the 100mV. Every change in mains voltage causes more fluctuation.
4.7muF should be OK.
Do you see the 2V square wave between both outputs or between one output and ground?
William
Just had a homer simpson moment...
Doh!
William - thanks very much for pointing out to me - yes the output was measured from one side of the load resistor, the otherside will of course be swinging in the other direction as this is a bridged amplifier - Doh! again.
Seems everything is working ok - thanks again for taking the time out to answer what has turned out to be a silly question.
I cannot measure both sides at once (my scope is single trace) - if i connect the scope ground to one side of the load resisror i am shorting one side out to ground and the load resistor starts heating up (so i guess i have an isolation issue with the scope).
Just four more channels to go now....
Doh!
William - thanks very much for pointing out to me - yes the output was measured from one side of the load resistor, the otherside will of course be swinging in the other direction as this is a bridged amplifier - Doh! again.
Seems everything is working ok - thanks again for taking the time out to answer what has turned out to be a silly question.
I cannot measure both sides at once (my scope is single trace) - if i connect the scope ground to one side of the load resisror i am shorting one side out to ground and the load resistor starts heating up (so i guess i have an isolation issue with the scope).
Just four more channels to go now....
Power supply options
I have an 18v transformer that i need to get back down to 15v DC - i have a few options open to me, some of which involve throwing away quite a lot of power as heat;
1. a CRCRC or CRCC filter arrangement
2. a choke input filter (just not sure where to get appropriate chokes in uk). I can wind my own, but what would an appropriate value be (i have some 2.2mh aircores i could use, but will need to make more as i don't have enough).
3. a regulated power supply - was thinking to use one or two LT1083's in a C-REG-CC arrangement so the last two reservoir caps "swamp" any audible effect the regulator might introduce. The regulator adj pin would be slugged with a small cap in order to bring the rails up over a few seconds.
Not seen any AX's with regulated supplies so i'm a little dubious about treading that path - Any coments appreciated
I have an 18v transformer that i need to get back down to 15v DC - i have a few options open to me, some of which involve throwing away quite a lot of power as heat;
1. a CRCRC or CRCC filter arrangement
2. a choke input filter (just not sure where to get appropriate chokes in uk). I can wind my own, but what would an appropriate value be (i have some 2.2mh aircores i could use, but will need to make more as i don't have enough).
3. a regulated power supply - was thinking to use one or two LT1083's in a C-REG-CC arrangement so the last two reservoir caps "swamp" any audible effect the regulator might introduce. The regulator adj pin would be slugged with a small cap in order to bring the rails up over a few seconds.
Not seen any AX's with regulated supplies so i'm a little dubious about treading that path - Any coments appreciated
Re: Power supply options
Maybe you could carefully unwind some of the transformer.
Jason Hubbard said:
Maybe you could carefully unwind some of the transformer.
Unwinding transformer
I too had thought to take a few windings off the secondary, but would prefer to avoid doing that.
I also have issues with varying mains voltage - i live in a rural area with a lightly loaded main transformer, so the nominal 230v rises to 250v+, hence my considering active regulation.
I too had thought to take a few windings off the secondary, but would prefer to avoid doing that.
I also have issues with varying mains voltage - i live in a rural area with a lightly loaded main transformer, so the nominal 230v rises to 250v+, hence my considering active regulation.
Jason,
Could you indicate why you want to reduce the psu voltages?
Is it heatsink/dissipation related? If you go with active regulation you will need to dissipate more heat. parralleling the output devices will also create more heat but then you will have more power and still be able to use the trannie you have.
regards,
Joris
Could you indicate why you want to reduce the psu voltages?
Is it heatsink/dissipation related? If you go with active regulation you will need to dissipate more heat. parralleling the output devices will also create more heat but then you will have more power and still be able to use the trannie you have.
regards,
Joris
Need to reduce voltage because
Hi Joris,
I am using an 18v transformer - by the time that is rectified and smoothed i reckon on about 23 volts or so after dual bridge losses are considered - i have decided that running off standard 15 volt rails and maybe increasing the bias to 5amps will give me more than enough power, so i can stick with 4 FET's per channel instead of 8.
If i use a regulator i will mount it on a seperate heatsink and will dissipate about 40 watts - within the capability of an LT1083. i will swamp the regulator output with *lots* of capacitance - that should remove any audible effect the regulator may have on sound quality.
At the moment i have an AX up & running (using a junkbox 12-0-12 transformer via a variac) using LT1083's. All works OK but i'm not dropping a lot of power in the regulator and i don't currently have a speaker attached either.
I wondered if any body else has built an AX with active regulation? What are the pro's and con's?
Hi Joris,
I am using an 18v transformer - by the time that is rectified and smoothed i reckon on about 23 volts or so after dual bridge losses are considered - i have decided that running off standard 15 volt rails and maybe increasing the bias to 5amps will give me more than enough power, so i can stick with 4 FET's per channel instead of 8.
If i use a regulator i will mount it on a seperate heatsink and will dissipate about 40 watts - within the capability of an LT1083. i will swamp the regulator output with *lots* of capacitance - that should remove any audible effect the regulator may have on sound quality.
At the moment i have an AX up & running (using a junkbox 12-0-12 transformer via a variac) using LT1083's. All works OK but i'm not dropping a lot of power in the regulator and i don't currently have a speaker attached either.
I wondered if any body else has built an AX with active regulation? What are the pro's and con's?
Hello Jason,
Ok thanks, that explains. Not much experience there so can't help you there.
Why don't you just try if you can hear a difference with the configuration you have now? You can easily compare c-regulator-c with a c-r-c configuration.
regards,
Joris
Ok thanks, that explains. Not much experience there so can't help you there.
Why don't you just try if you can hear a difference with the configuration you have now? You can easily compare c-regulator-c with a c-r-c configuration.
regards,
Joris
Regulated supplies for my Aleph-X
Jason,
I'm currently building an Aleph-X with a partially regulated power supply i.e. the front-end of the amp receives a regulated voltage while the output stages are connected to an unregulated voltage.
The unregulated voltage comes from the main power supply which is passively filtered by means of a CRCRC configuration. The amp draws a 4A bias current from this supply, which results in a ripple of 10 mVpeak. This makes for a pretty quiet supply to start with. Not entirely satisfied though, I decided to use this allready clean voltage as an input for a voltage regulator stage for the low power front end (the diff amp). Again this voltage is passively filtered, followed by a regulator which in turn is followed by yet another passive filter. I've just finished building it but I've built similar supplies for my preamp and we're looking at a 90-110 dB suppression with this circuit.
I haven't tested it thoroughly and the amp hasn't played yet so I can't tell you anything about the sonic advantages in this particular amp. I can tell you however that I've built and designed numerous pre- and power amps and each and every one of them have increased their sonic capabilities with improved power supplies. I can't tell you when it's finished so if you want to know send me a message somewhere in the near future.
Regards,
Xcel
😎
Jason,
I'm currently building an Aleph-X with a partially regulated power supply i.e. the front-end of the amp receives a regulated voltage while the output stages are connected to an unregulated voltage.
The unregulated voltage comes from the main power supply which is passively filtered by means of a CRCRC configuration. The amp draws a 4A bias current from this supply, which results in a ripple of 10 mVpeak. This makes for a pretty quiet supply to start with. Not entirely satisfied though, I decided to use this allready clean voltage as an input for a voltage regulator stage for the low power front end (the diff amp). Again this voltage is passively filtered, followed by a regulator which in turn is followed by yet another passive filter. I've just finished building it but I've built similar supplies for my preamp and we're looking at a 90-110 dB suppression with this circuit.
I haven't tested it thoroughly and the amp hasn't played yet so I can't tell you anything about the sonic advantages in this particular amp. I can tell you however that I've built and designed numerous pre- and power amps and each and every one of them have increased their sonic capabilities with improved power supplies. I can't tell you when it's finished so if you want to know send me a message somewhere in the near future.
Regards,
Xcel
😎
The Aleph X schematics that I have seen all have the differential
pair directly driving the Gates of the negative half of the output
stages. If this is the case, the Drains of the input FETs will want
to connect to the same supply (through the resistors) that the
negative half of the output stage sees, otherwise the difference
between a regulated (-) supply for the front end and the output
stage (-) supply will be amplified. a lot.
😎
pair directly driving the Gates of the negative half of the output
stages. If this is the case, the Drains of the input FETs will want
to connect to the same supply (through the resistors) that the
negative half of the output stage sees, otherwise the difference
between a regulated (-) supply for the front end and the output
stage (-) supply will be amplified. a lot.
😎
Nelson,
Thanks for the usefull comment.
Suppose I trim the regulated voltage at the same value of the unregulated voltage (just for the sake of presenting a regulated voltage to the diff amp), this problem wouldn't occur, right ?
In your white paper on power supplies you presented this approach to achieve a significant amount of the advantages the goals of fully active regulation, at reduced complexity and costs.
Correct me if I'm wrong, but from detailed photos of the insides of various XA.5's I made out that you're currently using this approach.
What do you consider as the particular sonic benefits of this approach ?
Greetz,
Xcel
😎
Thanks for the usefull comment.
Suppose I trim the regulated voltage at the same value of the unregulated voltage (just for the sake of presenting a regulated voltage to the diff amp), this problem wouldn't occur, right ?
In your white paper on power supplies you presented this approach to achieve a significant amount of the advantages the goals of fully active regulation, at reduced complexity and costs.
Correct me if I'm wrong, but from detailed photos of the insides of various XA.5's I made out that you're currently using this approach.
What do you consider as the particular sonic benefits of this approach ?
Greetz,
Xcel
😎
Hi,
just look at the unregulated voltage of your amp. It is changing all the time just as the mains voltage is. Therefore it will be very difficult to set a voltage.
It will also be difficult to get a regulated voltage with the same value as the unregulated one without using a seperate power supply 😉
William
just look at the unregulated voltage of your amp. It is changing all the time just as the mains voltage is. Therefore it will be very difficult to set a voltage.
It will also be difficult to get a regulated voltage with the same value as the unregulated one without using a seperate power supply 😉
William
xcel said:
difference in ripple between smoothed one and non-smoothed supply will transpose directly at output mosfet's gates as signal .
conclusion - try to better entire PSU ....... symmetrically , off course .
if you want - search any possible benefit for input stage - in bettering his CCS ......... but will that be audible ....... that's the question
Any New PCB for sale
Hi
Does anybody have a spare set of the latest version PCB for sale?
Please e-mail me.
Thanks
Jozua
South Africa
Hi
Does anybody have a spare set of the latest version PCB for sale?
Please e-mail me.
Thanks
Jozua
South Africa
Re: Any New PCB for sale
I have an extra pair of version one boards if you are interested.
Jozua said:
I have an extra pair of version one boards if you are interested.
labjr
Thanks for replying.
I have a set of the green the version 1 boards already but I want to rebuild the amp with the latest board.
Regards
Jozua
Thanks for replying.
I have a set of the green the version 1 boards already but I want to rebuild the amp with the latest board.
Regards
Jozua
shorted MOSFETs
I never finished my A-X....its been I hate to say how many years ago that I started!
I am going to get it working in the next few months. Heck its amost done. I think I made a mistake by using arctic silver thermal compond with mica insulators under the MOSFETs, I think the devices were under sufficient pressure that the grease become conductive.
Anyway I have measured the resistance between MOSFET terminals.
My A-X uses 4 banks of MOSFETs, each bank has 3 MOSFETs; these are connected to Grey's green Aleph-X boards.
One bank of 3 MOSFETs measures short-circuit between the pins. I know that the MOSFETs are supposed to be matched but I forget what you are supposed to match to what?
Question 1: How many transistors do I need to buy and match? and what is supposed to match what? Should I start over with a complete new set of 12 matched transistors for the channel or can I get 3 matched to each other? Putting in 12 matched devices is going to be pain! Maybe 24, have not looked at the other channel yet.
Question 2: I recovered some sil-pads from a 1998 receiver. Have these worn out or can I use them? I didn't think that it was possible for these to wear out but I could be wrong.
I never finished my A-X....its been I hate to say how many years ago that I started!
I am going to get it working in the next few months. Heck its amost done. I think I made a mistake by using arctic silver thermal compond with mica insulators under the MOSFETs, I think the devices were under sufficient pressure that the grease become conductive.
Anyway I have measured the resistance between MOSFET terminals.
My A-X uses 4 banks of MOSFETs, each bank has 3 MOSFETs; these are connected to Grey's green Aleph-X boards.
One bank of 3 MOSFETs measures short-circuit between the pins. I know that the MOSFETs are supposed to be matched but I forget what you are supposed to match to what?
Question 1: How many transistors do I need to buy and match? and what is supposed to match what? Should I start over with a complete new set of 12 matched transistors for the channel or can I get 3 matched to each other? Putting in 12 matched devices is going to be pain! Maybe 24, have not looked at the other channel yet.
Question 2: I recovered some sil-pads from a 1998 receiver. Have these worn out or can I use them? I didn't think that it was possible for these to wear out but I could be wrong.