6L6, here's a link to the discussion of the Legato. It's not DC offset that's 6-9V.
http://www.diyaudio.com/forums/twisted-pear/183663-legato-3-look-ma-no-caps.html
According to that first post, when running single ended the output has zero offset relative to chassis ground. In balanced configuration the DC offset of the balanced signal is also zero, but the balanced outputs are at 6-9V relative to chassis ground.
So if I'm understanding it correctly, it's almost like a "Class A" amp. The commond mode DC of the balanced output signals null each other out. They still have 0V offset relative to each other so there shouldn't be any DC as far as the signal going through the amplifier.
I found another post that stated that Pass Labs said this would work on an XA150, but I'm not familiar with that topology (nor am I an electrical engineer) so I can't figure out if the F5T would work as well.
Brian
http://www.diyaudio.com/forums/twisted-pear/183663-legato-3-look-ma-no-caps.html
According to that first post, when running single ended the output has zero offset relative to chassis ground. In balanced configuration the DC offset of the balanced signal is also zero, but the balanced outputs are at 6-9V relative to chassis ground.
So if I'm understanding it correctly, it's almost like a "Class A" amp. The commond mode DC of the balanced output signals null each other out. They still have 0V offset relative to each other so there shouldn't be any DC as far as the signal going through the amplifier.
I found another post that stated that Pass Labs said this would work on an XA150, but I'm not familiar with that topology (nor am I an electrical engineer) so I can't figure out if the F5T would work as well.
Brian
6-9V of absolute ( even if differential is non-existent) DC offset will cut in one side of voltage swing
that's not much if you're having amplifier with 100V rails , but if you're using amp with 25-ish V rails ...... shooting him with 9V on inputs is equally reckless as shooting him with 9V on just one input
look Ma , ignore that bare mains wire I wrapped around your leg ......... just walk in very small steps ....
that's not much if you're having amplifier with 100V rails , but if you're using amp with 25-ish V rails ...... shooting him with 9V on inputs is equally reckless as shooting him with 9V on just one input
look Ma , ignore that bare mains wire I wrapped around your leg ......... just walk in very small steps ....
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Thank you for the answers. I'll stick with the buffered single ended outputs (which don't have the common mode DC) for now . I can always experiment with going to AC coupled differential later.
Out of curiousity, what makes the X150 capable of handling the common mode DC? Is it the 'supersymmetry' approach, AC coupling on the input or just higher rails?
Brian
Out of curiousity, what makes the X150 capable of handling the common mode DC? Is it the 'supersymmetry' approach, AC coupling on the input or just higher rails?
Brian
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any decent amp with differential input is able to cope with common mode DC offset ;
AC coupled ( cap on input ) are just ignoring it as non-existent
DC coupled are not going to fry speaker (common mode voltage, be it signal or DC level, resulting in nill gain) but both lsp outputs are going to jump (or fall) in some amount
which amount , depends of amp construction ...... resulting in anything from cutting output voltage envelope , to gray smoke
X150 , having caps on input , is immune on that sort of mishaps
AC coupled ( cap on input ) are just ignoring it as non-existent
DC coupled are not going to fry speaker (common mode voltage, be it signal or DC level, resulting in nill gain) but both lsp outputs are going to jump (or fall) in some amount
which amount , depends of amp construction ...... resulting in anything from cutting output voltage envelope , to gray smoke
X150 , having caps on input , is immune on that sort of mishaps
One more newbie question...
How do I know whether my F5t is 'oscillating' or not? Do I need scope and feed let's say a square wave? Or is another method necessary? Thanks!
How do I know whether my F5t is 'oscillating' or not? Do I need scope and feed let's say a square wave? Or is another method necessary? Thanks!
Have you checked which way the pots are working, I mean checked not guessed.
Can you measure across R5 R6 and see the value change as the pots are turned with no power on?
Are Q7 Q8 the correct way round?
Can you measure across R5 R6 and see the value change as the pots are turned with no power on?
Are Q7 Q8 the correct way round?
Pots orientation make no difference in this PCB and I can measure Across the pot because it is parrallel to R 5 and R 6. There is a picture on the PCb how to place Q 7 and Q 8
Thank you for answering
Power OFF all capacitors discharged:
Can you set the resistor array to measure 0r0 when you turn the pot to end stop?
and for the other pot?
Can you set the resistor array to measure 0r0 when you turn the pot to end stop?
and for the other pot?
Yes Andrew I can. I use multiturn pots. Two of the legs is shorted at the pcb. I guess it is the idss of the Jfets wich is the problem.
Did you get a chance to measure the Vdrop across those resistors with power on. That would give you a general idea of the current flowing through the Jfets with the 10ohms of degeneration.
I did at the negative it is aprox zero and at the positive max 32 mv. From 4 to 32 mv. All mosfet should be selected from Jims audio.
Thats with max 20 vdc
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To be clear, I am talking about the source resistors(10ohms) of the Jfets on the FE. if that's what you measures, the numbers you got sound low.
When you say that it is changing when turning the pots, are you talking about the bias setting pots, or P3?
When you get the new fets, post a schematic that you are using to create a reference to the Jim's Audio boards. That will help keep things clear as you work through it.
When you say that it is changing when turning the pots, are you talking about the bias setting pots, or P3?
When you get the new fets, post a schematic that you are using to create a reference to the Jim's Audio boards. That will help keep things clear as you work through it.
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What are the minimum resistances when the pots are on the end stops?
Now set the pots to the other end stops. What are the two resistances now?
On my F6 build I zeroed the pots before installation, Turned anti clockwise and checked at zero.
Installed as per the diagram on the pcb showing the correct installation.
They were at full power at switch on, reversed operation!
Take nothing for granted.
Installed as per the diagram on the pcb showing the correct installation.
They were at full power at switch on, reversed operation!
Take nothing for granted.
0,2 ohm and 1260 ohm A little bias at positive side and nothing at negative. I ordered 3,9 kohm resistors as R 5 and R 6. Must wait to they arrive
F5 Turbo V2 power supply.
Hello everyone.
I do not know if this is the right place for this question. 😕
I have two toroidal transformers with 25-0-25 v 300 VA each, you can use them to build an F5 Turbo V2 instead of 24-0-24v. They were from another project, did not need to buy new.
If I'm in the wrong place my apologies. I began to purchase components for assembly.
Thanks.
P. Dias
Hello everyone.
I do not know if this is the right place for this question. 😕
I have two toroidal transformers with 25-0-25 v 300 VA each, you can use them to build an F5 Turbo V2 instead of 24-0-24v. They were from another project, did not need to buy new.
If I'm in the wrong place my apologies. I began to purchase components for assembly.
Thanks.
P. Dias