I wonder if any of Hafler users ever upgraded XL600 with the PA4 or PA2 boards from musical concepts . I have just finished installing a couple of NOS PA2 boards and i am in a few troubles ....
1) In the original condition of the Hafler XL 600 as delivered in our lab there was miller caps connected in the main block as following
--on the right channel 2 capacitors mica type marked 910 and an additional one of 10 between drain and gate ( only at positive rail side )
--on the left ch. only one capacitor marked 910 ( only at positive rail side )
Question : In the schematic given ( for PA 4 boards though ) the capacitors are 2 one for the P mosfets ( 22 or 27pf ) and one for the N mosfet ( 47pf ) but in the hand drawing they seem to be connected between source and gate .
Now which one of two is correct ?
2) i am having trouble to bias the amplifier right channel while the trimmer is turned foully CCW the bias is about 190ma and no matter how carefully you try to increase bias the bias increases way too high and makes impossible to adjust in the expected level of 330 ma . That is either wrong bias calculation ( regarding the trimmer and parts ) or there is some oscillation probably related to wrong installation of miller caps ( in between scope presents a perfect sine wave from 1K to 100 K without signs of oscillation )
3) For the second channel it is impossible to achieve any bias at all and trimmer makes absolutely no change from CCW to full CW .It may as well be a faulty trimmer but before checking that please advice .
4) It could be very helpful to have a schematic , of PA2 boards if anyone has
Kind regards
Sakis
1) In the original condition of the Hafler XL 600 as delivered in our lab there was miller caps connected in the main block as following
--on the right channel 2 capacitors mica type marked 910 and an additional one of 10 between drain and gate ( only at positive rail side )
--on the left ch. only one capacitor marked 910 ( only at positive rail side )
Question : In the schematic given ( for PA 4 boards though ) the capacitors are 2 one for the P mosfets ( 22 or 27pf ) and one for the N mosfet ( 47pf ) but in the hand drawing they seem to be connected between source and gate .
Now which one of two is correct ?
2) i am having trouble to bias the amplifier right channel while the trimmer is turned foully CCW the bias is about 190ma and no matter how carefully you try to increase bias the bias increases way too high and makes impossible to adjust in the expected level of 330 ma . That is either wrong bias calculation ( regarding the trimmer and parts ) or there is some oscillation probably related to wrong installation of miller caps ( in between scope presents a perfect sine wave from 1K to 100 K without signs of oscillation )
3) For the second channel it is impossible to achieve any bias at all and trimmer makes absolutely no change from CCW to full CW .It may as well be a faulty trimmer but before checking that please advice .
4) It could be very helpful to have a schematic , of PA2 boards if anyone has
Kind regards
Sakis
According to the Hafler XL600 schematic and parts list there should be two 910 pf mica caps on N channel devices from gate to source and that is it as far as attachments to the gate. No attachments are made to the P channel device gates.
In addition to this, before the gate stopper resistors there should be a .10 mfd polyester connected between the P and N channels.
Also, the drain on both P and N channels should have a .10 mfd polyester cap connected to chassis ground.
The XL600 schematic I attached on my PC40 upgrade posting that you replied to shows these connections.
Have you contacted Musical Concepts to see if they can be of any assistance to you?
In addition to this, before the gate stopper resistors there should be a .10 mfd polyester connected between the P and N channels.
Also, the drain on both P and N channels should have a .10 mfd polyester cap connected to chassis ground.
The XL600 schematic I attached on my PC40 upgrade posting that you replied to shows these connections.
Have you contacted Musical Concepts to see if they can be of any assistance to you?
I actually did ... response was slow i was told that PA 2 boards are veeeery old and they have to look for a schematic 24h later still no response .
i Agree with what you say all was according to the schematic before ( in the original boards ) still though i am installing PA2 boards with PA3 installation manual so things are not clear enough ....
as said the gate capacitors was installed between the gate and the output of the mosfet while in the installation manual it seems that are connected between the rails and the gate
To make this more confusing random schematics similar with mosfets in the output have capacitors in the gates while half of them return the capacitors in the power supply from the gates and the other half returns the capacitor from the gate to the output...
puzzled about this ....
Kind regards
Sakis
i Agree with what you say all was according to the schematic before ( in the original boards ) still though i am installing PA2 boards with PA3 installation manual so things are not clear enough ....
as said the gate capacitors was installed between the gate and the output of the mosfet while in the installation manual it seems that are connected between the rails and the gate
To make this more confusing random schematics similar with mosfets in the output have capacitors in the gates while half of them return the capacitors in the power supply from the gates and the other half returns the capacitor from the gate to the output...
puzzled about this ....
Kind regards
Sakis
I just realized that the later generation 9300/9500 schematics showed that the output mosfets were wired in the manner you stated the PA-4 instructions outlined. The values of the caps are even the same.
"In the schematic given ( for PA 4 boards though ) the capacitors are 2 one for the P mosfets ( 22 or 27pf ) and one for the N mosfet ( 47pf ) but in the hand drawing they seem to be connected between source and gate."
I would wire the output stage capacitors up in the manner that the PA-4 directions state. I do not think that the way the output stage mosfets and the manner in which the film caps are tied to their gates would have changed from PA-2 to PA-3 or PA-4. In addition to this I found a thread where one DIY'er stated that Erno Borbely instructed him to wire his dh-200 with the caps from Gate to Drain and not from Gate to Source as the amplifier originally came. Erno supposedly stated it was a mistake made early on. If so that mistake continued through the XL series and did not get corrected until Jim Strickland redesigned them into the 9300/9500's.
I welcome any experts thoughts on this subject!
"In the schematic given ( for PA 4 boards though ) the capacitors are 2 one for the P mosfets ( 22 or 27pf ) and one for the N mosfet ( 47pf ) but in the hand drawing they seem to be connected between source and gate."
I would wire the output stage capacitors up in the manner that the PA-4 directions state. I do not think that the way the output stage mosfets and the manner in which the film caps are tied to their gates would have changed from PA-2 to PA-3 or PA-4. In addition to this I found a thread where one DIY'er stated that Erno Borbely instructed him to wire his dh-200 with the caps from Gate to Drain and not from Gate to Source as the amplifier originally came. Erno supposedly stated it was a mistake made early on. If so that mistake continued through the XL series and did not get corrected until Jim Strickland redesigned them into the 9300/9500's.
I welcome any experts thoughts on this subject!
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a) '' i would " is not my type of expression i dlike to know for sure , or even better know exactly what and why i am doing it . Its not like me to play with this type of equipment . I will not power it up before i learn . 😉
b) I welcome any experts thoughts on this subject! me too !!!😀
I find your remarks useful , and thank you for that😱 ...lets us expect people with more knowledge to help us out here .
Thanks !!
Sakis
b) I welcome any experts thoughts on this subject! me too !!!😀
I find your remarks useful , and thank you for that😱 ...lets us expect people with more knowledge to help us out here .
Thanks !!
Sakis
Its good for future customers of Musical Concepts to know that they offer slow or possibly NO support on their past products.
Just a few days later JPG of the installation manual arrived ...
The manual is pretty much or even more confusing since inside there is more information about various amplifiers that these boards could fit in .
Obviously for such a product which is supposed to be a gourmet thing to get a dedicated manual should be in order rather than information that are not precise ...
The documentation is available to any one asking and the boards next to the schematic is just a huge misunderstanding....
for starts capacitors related in the bias and feedback area by the schematic was 2200 ufd 6.3 volts but on the boards are actually 1000
safety resistors R15-16 in the schematic 68.1R while on the boards 100
Boards are in original condition equipped with DALE precision resistors and specifically R20 and 21 suppose to be 22R ( type:9421J/RN60D/22R1F ) While one of them measures 22.5 other 25 another 28 and another 34 ...that cant be right !!!
If boards after all are mend to be for XL 600 amplifiers then the bias scheme must be wrong cause if you have a trimmer that is scaled in a range from 1 to 100 only the first 15% is usable area to adjust bias ...When we all know that trimmers ( especially cheap piher ones when you are close to the end of either side adjustment is not secure )
As about the miller caps in the forget all written above for the PA 3 boards and it seems that PA 2 boards keep the original 910 pf caps from gate to output and add an 22 and 47 pf to both N and P but from gate to rail .....
Finally in the schematic the well known diode string that protects gates from overdrive exists but not on the boards ....
things are getting pretty rough and it seems that one way or another i will be able to make it work but i don't think that i can secure the safety of the amp
The manual is pretty much or even more confusing since inside there is more information about various amplifiers that these boards could fit in .
Obviously for such a product which is supposed to be a gourmet thing to get a dedicated manual should be in order rather than information that are not precise ...
The documentation is available to any one asking and the boards next to the schematic is just a huge misunderstanding....
for starts capacitors related in the bias and feedback area by the schematic was 2200 ufd 6.3 volts but on the boards are actually 1000
safety resistors R15-16 in the schematic 68.1R while on the boards 100
Boards are in original condition equipped with DALE precision resistors and specifically R20 and 21 suppose to be 22R ( type:9421J/RN60D/22R1F ) While one of them measures 22.5 other 25 another 28 and another 34 ...that cant be right !!!
If boards after all are mend to be for XL 600 amplifiers then the bias scheme must be wrong cause if you have a trimmer that is scaled in a range from 1 to 100 only the first 15% is usable area to adjust bias ...When we all know that trimmers ( especially cheap piher ones when you are close to the end of either side adjustment is not secure )
As about the miller caps in the forget all written above for the PA 3 boards and it seems that PA 2 boards keep the original 910 pf caps from gate to output and add an 22 and 47 pf to both N and P but from gate to rail .....
Finally in the schematic the well known diode string that protects gates from overdrive exists but not on the boards ....
things are getting pretty rough and it seems that one way or another i will be able to make it work but i don't think that i can secure the safety of the amp
small update :
Replacing all 22R resistors did some soldering made the amp work and also bias properly though only using a 15% of the all usable are of the trimmer .
Main concern before closing is what to do with the diode protection string which i would like to have installed before the amp goes away from my hands ...
in the previous boards installed inside the Hafler the protection is made out of a simple 1N4148 and a zener 52 volt ( per rail )
Problem is that in the schematic of the PA2 boards the protection is made with a 1X1N4148 and one 1N4742 which is a 12 volt zener ...
Huge difference
Replacing all 22R resistors did some soldering made the amp work and also bias properly though only using a 15% of the all usable are of the trimmer .
Main concern before closing is what to do with the diode protection string which i would like to have installed before the amp goes away from my hands ...
in the previous boards installed inside the Hafler the protection is made out of a simple 1N4148 and a zener 52 volt ( per rail )
Problem is that in the schematic of the PA2 boards the protection is made with a 1X1N4148 and one 1N4742 which is a 12 volt zener ...
Huge difference
The Hafler XL-600 parts listing shows the zener diodes in the protection string as 15V (1N5245).
It sounds like you just about have the issues worked out, nice job.
One question for you on the original boards you removed. Does the resistor R37 on the output zobel shows signs of heating? Mine were actually black but they still measured 5 ohms and had not opened up yet. I assume this is due to oscillation. I plan to make the change to the output miller caps that Erno Borbely suggests. Here is a link to that info in posts 198, 199, & 200.
Good luck and let us know how this turns out.
It sounds like you just about have the issues worked out, nice job.
One question for you on the original boards you removed. Does the resistor R37 on the output zobel shows signs of heating? Mine were actually black but they still measured 5 ohms and had not opened up yet. I assume this is due to oscillation. I plan to make the change to the output miller caps that Erno Borbely suggests. Here is a link to that info in posts 198, 199, & 200.
Good luck and let us know how this turns out.
Well Nice guy John from Musical Concepts is working with me to solve all the problems one by one ...very service minded from our American friends if one thinks that the boards are stamped 1994 as a date of design if not production
I will look more closely about the diodes may be i am wrong i repair too many amplifiers and my eyes don't seem to agree with that any more ...
As about the colored resistors or fried if you like better ,well ...not really ...one RCA plug with a missing ground producing a high pitch noise may fry the resistors in less than a second
Excessive use of treble in the preamplifier can do that also ... it may also as well be oscillation but after all only scope will tell
John also said that in some cases ( probably depending on the mosfet choice )they had issues with miller cap scheme ...yet again only scope will tell .
YEs ...it seems that all the problems seem to work out one by one
Kind regards
Sakis
I will look more closely about the diodes may be i am wrong i repair too many amplifiers and my eyes don't seem to agree with that any more ...
As about the colored resistors or fried if you like better ,well ...not really ...one RCA plug with a missing ground producing a high pitch noise may fry the resistors in less than a second
Excessive use of treble in the preamplifier can do that also ... it may also as well be oscillation but after all only scope will tell
John also said that in some cases ( probably depending on the mosfet choice )they had issues with miller cap scheme ...yet again only scope will tell .
YEs ...it seems that all the problems seem to work out one by one
Kind regards
Sakis
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