aleph 1.2's to Ax100
GL and NP--I will take your suggestion when I get back from a business trip--adjust the absolute dc offset and then remeasure the ac gain on both channels. I will do a complete dc check at all nodes as well.
I am in India right now and then off for a thanksgiving holiday after that I will report back my issues. happy holidays-dave
GL and NP--I will take your suggestion when I get back from a business trip--adjust the absolute dc offset and then remeasure the ac gain on both channels. I will do a complete dc check at all nodes as well.
I am in India right now and then off for a thanksgiving holiday after that I will report back my issues. happy holidays-dave
Help with testing
GL-Grey-NP
I got home from my business trip a bit jet lagged and I may not be thinking straight yet (obviously I am building up to an excuse for not knowing what I am doing).
My Aleph 1.2 conversion to the xa 100 has been constructed and I have one nagging problem I can't solve but I have a lot of clues.
The amp is built to GL's schematic with the following exceptions:
It has 6 outputs per quad instead of 5--24 total.
I did not install the AC coupling cap on the input and the 100K resistor at the input to ground in front of the coupling cap. All else is the same.
I have been using a variac and a single ended signal generator and square wave generator.
Testing procedure:
I intend to run the amp only in balanced mode
To test I installed an rca jack and grounded the - signal to ground
in the balanced connector using the pin supplied by pass labs for my 350.x. I connected the rca positive jack to pin 2 of the balanced connector and the ground tab of the rca jack to Pin 1 of the balanced connector.
My problem is that at start up the absolute dc was +28volts and I adjusted it with U2 to +24 volts on both outputs until the 20 turn pot hit 0 and no further adjustment could be done.
So I just finished DC mapping the circuit board looking for clues:
With the input shorted to ground using the rca connector
relative dc offset -30mv
bias set to approx. 5.5 amps
Rail voltage approx +/- 30volts
4.40volts at the exit of the ccs for the diff pair to the Sources of the diff pair
4.38volts across the 392 ohm R23
4.32 volts across the 392 ohm R26
Looking at the negative signal output fets for the CCS Q1 etc
29.70 volts at the drain
25.40 volts at the source
.380mv to .510mv across the 1 ohm output source resistors
43.8mv at node of Q3 collector to base
Looking at the negative signal outputs Q2 etc
-26.32 volts at the drain
-30.29 volts at the source
.338 to .600mv across the source resistors
For the positive signal side
43mv at Q3 collector to base
29.55 volts at the CCS Drain Q10 etc
25.33 volts at the CCS Source Q10
the output CCS source resistors about the same values as the negative side .350 to .500mv
Negative Output Fets
-30.58volts at the source
-26.32 volts at the drain
At various times I measured the voltage at the connection node between the Macmillian resistor and the source of the input diff pair and was shocked to see over +25volts for both signal sides.
Well I know I am being long winded and I am at home so I couldn't scan in the values on a schematic.
I went back to the Wiki and re read the threads on dc offsets.
I did the following expeirments:
I took off the shorting wire between signal positive and signal ground and the absolute dc offset dropped immediately to less than 15 volts but of course the relative offset went to .5volts.
The bias jumped to .900mv per device on the negative ouputs and went to 0 on the positive side. I tried it again later after I calmed down and the positive side was working again.
I then tried to parallel the R26 332ohm resistor attached to U2 with a 750 ohm resistor to give me more adjust range. That worked except it raised the bias on the negative outputs.
Conclusions:
Looking at the dc mapping I noticed that the negative rail voltage does not load down the same as the positive rail.
Reading NP suggestion to ac couple the amp would help to avoid dc related issues. I can try this but I don't know why this would have any affect.
I could try reducing the bias adjustement resistor from the 100k value to a much lower value which would lower the bias and then adjust U2 again and see what happens but I don't know why this would have an affect.
I could change the value of the Macmillian resistor from 10k to something lower.
When running a number of signals through the amp they look clean, I haven't tackled the ac gain yet.
My reaction right now is that:
The negative ps rail is not loading down like the positive rail due to some kind of a signal drive issue.
If you have any other suggestions for what to look for or if you think that the problem lies at the input and try ac coupling please advise. I have some high voltage PPcaps that are real honkers but I can try to expierment with them.
This is an good learning test for understanding small signal analysis.
Thanks for the help, right now I am using my A-75 on my ribbon tweeters and my Pass 350.5 on the mids and bass of my line arrays. Eventually I will repalce the A75 with the XA100 conversion-------I hope-------------dave
GL-Grey-NP
I got home from my business trip a bit jet lagged and I may not be thinking straight yet (obviously I am building up to an excuse for not knowing what I am doing).
My Aleph 1.2 conversion to the xa 100 has been constructed and I have one nagging problem I can't solve but I have a lot of clues.
The amp is built to GL's schematic with the following exceptions:
It has 6 outputs per quad instead of 5--24 total.
I did not install the AC coupling cap on the input and the 100K resistor at the input to ground in front of the coupling cap. All else is the same.
I have been using a variac and a single ended signal generator and square wave generator.
Testing procedure:
I intend to run the amp only in balanced mode
To test I installed an rca jack and grounded the - signal to ground
in the balanced connector using the pin supplied by pass labs for my 350.x. I connected the rca positive jack to pin 2 of the balanced connector and the ground tab of the rca jack to Pin 1 of the balanced connector.
My problem is that at start up the absolute dc was +28volts and I adjusted it with U2 to +24 volts on both outputs until the 20 turn pot hit 0 and no further adjustment could be done.
So I just finished DC mapping the circuit board looking for clues:
With the input shorted to ground using the rca connector
relative dc offset -30mv
bias set to approx. 5.5 amps
Rail voltage approx +/- 30volts
4.40volts at the exit of the ccs for the diff pair to the Sources of the diff pair
4.38volts across the 392 ohm R23
4.32 volts across the 392 ohm R26
Looking at the negative signal output fets for the CCS Q1 etc
29.70 volts at the drain
25.40 volts at the source
.380mv to .510mv across the 1 ohm output source resistors
43.8mv at node of Q3 collector to base
Looking at the negative signal outputs Q2 etc
-26.32 volts at the drain
-30.29 volts at the source
.338 to .600mv across the source resistors
For the positive signal side
43mv at Q3 collector to base
29.55 volts at the CCS Drain Q10 etc
25.33 volts at the CCS Source Q10
the output CCS source resistors about the same values as the negative side .350 to .500mv
Negative Output Fets
-30.58volts at the source
-26.32 volts at the drain
At various times I measured the voltage at the connection node between the Macmillian resistor and the source of the input diff pair and was shocked to see over +25volts for both signal sides.
Well I know I am being long winded and I am at home so I couldn't scan in the values on a schematic.
I went back to the Wiki and re read the threads on dc offsets.
I did the following expeirments:
I took off the shorting wire between signal positive and signal ground and the absolute dc offset dropped immediately to less than 15 volts but of course the relative offset went to .5volts.
The bias jumped to .900mv per device on the negative ouputs and went to 0 on the positive side. I tried it again later after I calmed down and the positive side was working again.
I then tried to parallel the R26 332ohm resistor attached to U2 with a 750 ohm resistor to give me more adjust range. That worked except it raised the bias on the negative outputs.
Conclusions:
Looking at the dc mapping I noticed that the negative rail voltage does not load down the same as the positive rail.
Reading NP suggestion to ac couple the amp would help to avoid dc related issues. I can try this but I don't know why this would have any affect.
I could try reducing the bias adjustement resistor from the 100k value to a much lower value which would lower the bias and then adjust U2 again and see what happens but I don't know why this would have an affect.
I could change the value of the Macmillian resistor from 10k to something lower.
When running a number of signals through the amp they look clean, I haven't tackled the ac gain yet.
My reaction right now is that:
The negative ps rail is not loading down like the positive rail due to some kind of a signal drive issue.
If you have any other suggestions for what to look for or if you think that the problem lies at the input and try ac coupling please advise. I have some high voltage PPcaps that are real honkers but I can try to expierment with them.
This is an good learning test for understanding small signal analysis.
Thanks for the help, right now I am using my A-75 on my ribbon tweeters and my Pass 350.5 on the mids and bass of my line arrays. Eventually I will repalce the A75 with the XA100 conversion-------I hope-------------dave
Hi,
I think the sollution is quite simple. You need to change the setting range for the current through the input diff pair.
With the bias through the input you set the voltage acros the drain resistors (392R). This needs to be spot on to get the absolute dc offset to zero.
So you need to change the resistors that control the current source for the diff pair.
Not using the input caps (on + and - IN) does lead to trouble as has been proved quite often on this forum. Remember that the connection between -IN and ground needs to be made with a cap equal to the one used for the +IN
The bias change when changing absolute offset is normal! First set the absolute offset to zero, then adjust the bias.
William
I think the sollution is quite simple. You need to change the setting range for the current through the input diff pair.
With the bias through the input you set the voltage acros the drain resistors (392R). This needs to be spot on to get the absolute dc offset to zero.
So you need to change the resistors that control the current source for the diff pair.
Not using the input caps (on + and - IN) does lead to trouble as has been proved quite often on this forum. Remember that the connection between -IN and ground needs to be made with a cap equal to the one used for the +IN
The bias change when changing absolute offset is normal! First set the absolute offset to zero, then adjust the bias.
William
aleph 1.2's to Ax100
to all, i went back and read the aleph x builders thread and the Alelp x wiki and it seems that others have had the same start up experiences that i have. I have gotten some fix ideas to try. It is like never reading the instructions first while trying to put up the kids swing set. More to come next week. dave
to all, i went back and read the aleph x builders thread and the Alelp x wiki and it seems that others have had the same start up experiences that i have. I have gotten some fix ideas to try. It is like never reading the instructions first while trying to put up the kids swing set. More to come next week. dave
Hi Dave,
You are right. Reading and following the instructions is very important and all of the instructions are in the WIKI or on the Aleph-X main thread. Complete and thorough start up instructions are not in this thread here.
William is right. Adjust the bias in the output section first. Then adjust the absolute offset. Do both of these initially with the variac turned half way up so that you have half the operating voltage across the amp. This will keep heat generation low in case anything is seriously mis-adjusted. It's important to have at least 10V across the CCS so that the zener is doing it's thing and the CCS is generating it's 20ma.
Remember that the absolute offset adjustment is very twitchy. A small adjustment will make for a large swing at the output terminals. Be persistent. It will drift by what seems like a huge amount for the first hour or two after turn-on. Just keep bringing it back to zero.
All of the part values for the input diff pair CCS in the original Aleph-X schematic should work fine. You shouldn't need to change any of those to make your amp work.
Keep at it I think you're almost there.
Graeme
You are right. Reading and following the instructions is very important and all of the instructions are in the WIKI or on the Aleph-X main thread. Complete and thorough start up instructions are not in this thread here.
William is right. Adjust the bias in the output section first. Then adjust the absolute offset. Do both of these initially with the variac turned half way up so that you have half the operating voltage across the amp. This will keep heat generation low in case anything is seriously mis-adjusted. It's important to have at least 10V across the CCS so that the zener is doing it's thing and the CCS is generating it's 20ma.
Remember that the absolute offset adjustment is very twitchy. A small adjustment will make for a large swing at the output terminals. Be persistent. It will drift by what seems like a huge amount for the first hour or two after turn-on. Just keep bringing it back to zero.
All of the part values for the input diff pair CCS in the original Aleph-X schematic should work fine. You shouldn't need to change any of those to make your amp work.
Keep at it I think you're almost there.
Graeme
happy thanksgiving
GL, have a good thanksgiving and thanks for your help. I am sure all the turkey I eat today will replenish my brain power. I can't wait to hear what NP did with the xa.5 series. Although I plan to just listen for awhile. I may add your input caps since eventually I will be using this amp for my line array tweeters and this would offer some protection. I don't think it would affect the sound very much especially if I use High quality input caps. dave
GL, have a good thanksgiving and thanks for your help. I am sure all the turkey I eat today will replenish my brain power. I can't wait to hear what NP did with the xa.5 series. Although I plan to just listen for awhile. I may add your input caps since eventually I will be using this amp for my line array tweeters and this would offer some protection. I don't think it would affect the sound very much especially if I use High quality input caps. dave
success
GL-NP-Grey,
I finally got my Aleph 1.2 to XA100 conversion successfully tested.
My problem was that U2 did not have enough adjustment range to get my absolute dc offset down to zero from 26 volts. I paralled the 332 ohm resistor with a 402 ohm resistor and started adjusting with my variac set at 60 volts and then raised the voltage slowly while adjusting. After about a bottle of wine and a few beers I got it to +20mv and called it a day. The amp starts up with a 2.5 -3.0volts and settles down after 4 hours to the 20mv figure.
Other specs:
With the input shorted to ground
PS rails are +/-31 volts under load
relative dc offset -20vdc
output fets bias between 440ma to 510ma for 6 fets per quad
AC sinewaves good from 20 to 20k--ac gain looks balanced at +/- outputs across a 5ohm 250watt resistor.
I have not done full power testing yet nor have I checked the 50% CCS gain. I used the 845 ohm resistor like GL and my CCS resistor is 100k.
I have to reattach the heatsinks to the frame in which the top and bottom plates are used as part of the heat sink and redress and shorten the signal wires. Once this is done I will test the heat sink temperatures under load. I expect to have a few adjustment problems after reassembly but I know the cirucuit works. I am using the 2mh choke in the power supply so I have to test for 120hz hum but I didn't see any on the scope.
I feel intellectually better today, hopefully I can get a listen in during the christmas season. I still have to be on the road for two more weeks yet this year overseas and this cuts into my hobby time plus the Prime Minister has work for me around the house. thanks --dave
GL-NP-Grey,
I finally got my Aleph 1.2 to XA100 conversion successfully tested.
My problem was that U2 did not have enough adjustment range to get my absolute dc offset down to zero from 26 volts. I paralled the 332 ohm resistor with a 402 ohm resistor and started adjusting with my variac set at 60 volts and then raised the voltage slowly while adjusting. After about a bottle of wine and a few beers I got it to +20mv and called it a day. The amp starts up with a 2.5 -3.0volts and settles down after 4 hours to the 20mv figure.
Other specs:
With the input shorted to ground
PS rails are +/-31 volts under load
relative dc offset -20vdc
output fets bias between 440ma to 510ma for 6 fets per quad
AC sinewaves good from 20 to 20k--ac gain looks balanced at +/- outputs across a 5ohm 250watt resistor.
I have not done full power testing yet nor have I checked the 50% CCS gain. I used the 845 ohm resistor like GL and my CCS resistor is 100k.
I have to reattach the heatsinks to the frame in which the top and bottom plates are used as part of the heat sink and redress and shorten the signal wires. Once this is done I will test the heat sink temperatures under load. I expect to have a few adjustment problems after reassembly but I know the cirucuit works. I am using the 2mh choke in the power supply so I have to test for 120hz hum but I didn't see any on the scope.
I feel intellectually better today, hopefully I can get a listen in during the christmas season. I still have to be on the road for two more weeks yet this year overseas and this cuts into my hobby time plus the Prime Minister has work for me around the house. thanks --dave
Hi Dave,
Thank you for the update. Congratulations on getting your amps to this stage.
A couple of points:
1) Your absolute offset performance sounds great.
2) I think that your -20vdc for relative offset is a typo. ?????
3) I hope that the 440ma to 510ma of variation is not within a supposedly matched group of transistors.
4) I'm still wondering what is going on in your circuit that caused you to have to lower the 332 ohm resistor value.
Regards,
Graeme
Thank you for the update. Congratulations on getting your amps to this stage.
A couple of points:
1) Your absolute offset performance sounds great.
2) I think that your -20vdc for relative offset is a typo. ?????
3) I hope that the 440ma to 510ma of variation is not within a supposedly matched group of transistors.
4) I'm still wondering what is going on in your circuit that caused you to have to lower the 332 ohm resistor value.
Regards,
Graeme
aleph 1.2's to Ax100
GL, yes that is a typo it is -20mv relative offset. I would have to adjust for a week to get it to zero. I am retesting this coming weekend and I will let it sit running some sine waves for a while to see how hot the heat sinks get.
The final adjusted value from U2 to the source pin of the CCS for the diff pair is 204 ohms measured in circuit vs the 332 plus U2 on the schematic.
I noticed a response in the Wiki or the Aleph X thread that others had to deviate from this setting to get their dc offset to zero so that is where I got the idea.
I don't know what is causing this but I am getting about 4.6 volts across the 392 ohm drain resistors of the differential pair. My only humble explanation is that my rail voltage is higher at a +/- 31 volts loaded down.
Do I need to get the absolute dc voltage to zero-I don't think it should have any affect?
I smoked a couple of out put fets when I had the 2ohm source resistors which overheated and I don't have the measurement data from 2000 when I originally built these amps so I could have more than a .01 deviation. My input diff pair is definetly at .01 at room temperature.
I have more testing to do and I will report my findings. thanks, dave
GL, yes that is a typo it is -20mv relative offset. I would have to adjust for a week to get it to zero. I am retesting this coming weekend and I will let it sit running some sine waves for a while to see how hot the heat sinks get.
The final adjusted value from U2 to the source pin of the CCS for the diff pair is 204 ohms measured in circuit vs the 332 plus U2 on the schematic.
I noticed a response in the Wiki or the Aleph X thread that others had to deviate from this setting to get their dc offset to zero so that is where I got the idea.
I don't know what is causing this but I am getting about 4.6 volts across the 392 ohm drain resistors of the differential pair. My only humble explanation is that my rail voltage is higher at a +/- 31 volts loaded down.
Do I need to get the absolute dc voltage to zero-I don't think it should have any affect?
I smoked a couple of out put fets when I had the 2ohm source resistors which overheated and I don't have the measurement data from 2000 when I originally built these amps so I could have more than a .01 deviation. My input diff pair is definetly at .01 at room temperature.
I have more testing to do and I will report my findings. thanks, dave
Pass DIY Addict
Joined 2000
Paid Member
Hi William,
I have a clarification question for you about the AC coupling cap. Since I'm still learning here, I want to make sure I have this right.
When using unbalanced RCA inputs, it sounds like I need to do the following for each channel:
1) Connect the +in to one leg of a 100k resistor and the other leg of this resistor goes to ground.
2) Connect one leg of the 4.7uF PP cap to the +in after the 100k resistor and the other leg to ground.
3) Connect the +in (after the resistor and cap) to R18 on the schematic.
4) Do the same for the -in.
Is this correct ?
Thanks!
Eric
I have a clarification question for you about the AC coupling cap. Since I'm still learning here, I want to make sure I have this right.
When using unbalanced RCA inputs, it sounds like I need to do the following for each channel:
1) Connect the +in to one leg of a 100k resistor and the other leg of this resistor goes to ground.
2) Connect one leg of the 4.7uF PP cap to the +in after the 100k resistor and the other leg to ground.
3) Connect the +in (after the resistor and cap) to R18 on the schematic.
4) Do the same for the -in.
Is this correct ?
Thanks!
Eric
Hi,
it would be easier to make a drawing but I´ll try to describe it.
You just build the amp as per Hifizen without any input caps.
Wenn you connect the XLR input you put a cap between the +IN and XLR Pin 2 and a cap between the -IN and XLR Pin 3
If you use it unbalanced you connect your cinch + to pin2 of the xlr and ground to pin 1 of the XLR
Then you connect Pins 1 and 3 of the XLR (-IN to ground)
It is important that:
a: The caps have the same value
b: -IN at the amp is not connected directly to ground
William
it would be easier to make a drawing but I´ll try to describe it.
You just build the amp as per Hifizen without any input caps.
Wenn you connect the XLR input you put a cap between the +IN and XLR Pin 2 and a cap between the -IN and XLR Pin 3
If you use it unbalanced you connect your cinch + to pin2 of the xlr and ground to pin 1 of the XLR
Then you connect Pins 1 and 3 of the XLR (-IN to ground)
It is important that:
a: The caps have the same value
b: -IN at the amp is not connected directly to ground
William
Pass DIY Addict
Joined 2000
Paid Member
testing results-help from GL and Grey and NP
Well I got back from my business trip and started my AX100 conversion project. When doing the absolute dc offset adjustment I got it down to the .25mv level after several hours.
The amp starts up at about 3.5 volts absolute dc and slowly gets down to .25 volts.
AC sine waves are excellent, I don't have a THD analyzer but when I combine (add) the waves on the scope set at 20mv per division the line is squiglly within 80mv.
Now my problem. The relative dc offset is .25mv and I know that is too high. I just need some advise.
I measured the source to gate voltage of both members of the diff pair in circuit with the input shorted. I do not have ac input coupling caps installed.
I took the measurement from the drain to of the diff pair ccs to the 221 gate resistor of each half of the diff pair and the results are:
3.805 volts
3.799 volts
diff is .006mv--seems good right?
I then measured across each drain resistor of the diff pair and the results are:
4.86 volts
4.77 volts
diff is .090 mv
when measuring each output half (at the speaker jacks) to realtive ground I get the following results:
positive output +.50mv
negative output -.200mv
it stays rock steady no matter how I adjust the absolute offset.
My solution, change the diff pair I have one set that measures at room temp exactly the same at 3.766 volts at 10ma.
Or if the problem is a bad match on the outputs then I will have to measure again across each source resitor the bias current and then "switch devices between halves to bring in better balance.
Am on on the right course?
Well I got back from my business trip and started my AX100 conversion project. When doing the absolute dc offset adjustment I got it down to the .25mv level after several hours.
The amp starts up at about 3.5 volts absolute dc and slowly gets down to .25 volts.
AC sine waves are excellent, I don't have a THD analyzer but when I combine (add) the waves on the scope set at 20mv per division the line is squiglly within 80mv.
Now my problem. The relative dc offset is .25mv and I know that is too high. I just need some advise.
I measured the source to gate voltage of both members of the diff pair in circuit with the input shorted. I do not have ac input coupling caps installed.
I took the measurement from the drain to of the diff pair ccs to the 221 gate resistor of each half of the diff pair and the results are:
3.805 volts
3.799 volts
diff is .006mv--seems good right?
I then measured across each drain resistor of the diff pair and the results are:
4.86 volts
4.77 volts
diff is .090 mv
when measuring each output half (at the speaker jacks) to realtive ground I get the following results:
positive output +.50mv
negative output -.200mv
it stays rock steady no matter how I adjust the absolute offset.
My solution, change the diff pair I have one set that measures at room temp exactly the same at 3.766 volts at 10ma.
Or if the problem is a bad match on the outputs then I will have to measure again across each source resitor the bias current and then "switch devices between halves to bring in better balance.
Am on on the right course?
aleph 1.2's to Ax100
Wuffwaff-thanks, I did change the input pair and measuring dc offset at the 392 resistors I get 0volts so I am good to go in this regard.
GL - changing the input pair to spot on matching I now get about 100 to 150mv of dc offset that keeps slowly moving from a low of 85 mv to a high of 165mv after the amp is on about several hours.
My absolute dc is no higher than .250mv.
So just being picky I am going back to my tube days when to get the correct bias I had to move tubes back and forth from rail to rail to get the best balance in my OTL amp and then adjust the dc offset to zero.
So I will measure all 24 source resistors on the outputs and move them from rail to rail until I get as close to zero dc relative offset as possible.
I do not have an explanation why the dc offset moves over 50mv every few minutes. This is a very twitchy circuit. I tried the easy way out initially by adjusting the bias pots for the output CCS but to get better relative off set I had to really crank one side which I didn't like doing. 100k vs 120k. Oh well what else is there todo?
dave
Wuffwaff-thanks, I did change the input pair and measuring dc offset at the 392 resistors I get 0volts so I am good to go in this regard.
GL - changing the input pair to spot on matching I now get about 100 to 150mv of dc offset that keeps slowly moving from a low of 85 mv to a high of 165mv after the amp is on about several hours.
My absolute dc is no higher than .250mv.
So just being picky I am going back to my tube days when to get the correct bias I had to move tubes back and forth from rail to rail to get the best balance in my OTL amp and then adjust the dc offset to zero.
So I will measure all 24 source resistors on the outputs and move them from rail to rail until I get as close to zero dc relative offset as possible.
I do not have an explanation why the dc offset moves over 50mv every few minutes. This is a very twitchy circuit. I tried the easy way out initially by adjusting the bias pots for the output CCS but to get better relative off set I had to really crank one side which I didn't like doing. 100k vs 120k. Oh well what else is there todo?
dave
Hi Dave,
Yes, this is a twitchy circuit. You can simply blow on the heatsinks or the circuit board and watch the voltages move around. You need to learn to ignore this. It's one of those Dr. Strangelove things.
Relative offset is determined by the quality of component matching.
You talk about "offset" above without specifying relative or absolute. When talking about the Aleph-X the word "offset" must aways be qualified otherwise people don't know what you're talking about.
Graeme
Yes, this is a twitchy circuit. You can simply blow on the heatsinks or the circuit board and watch the voltages move around. You need to learn to ignore this. It's one of those Dr. Strangelove things.
Relative offset is determined by the quality of component matching.
You talk about "offset" above without specifying relative or absolute. When talking about the Aleph-X the word "offset" must aways be qualified otherwise people don't know what you're talking about.
Graeme
aleph 1.2's to Ax100 testing
GL- I have had some success, the amp has been running all day.
I found a problem, one of my outputs on the negative rail in the driver quad section had a broken drain pin. This happened when I reconnected my heatsinks to the chasis. I had the heatsinks facing upwards when I was doing the mods so I could install new source resistors and test the circuit, when I twisted them back in place I must have broken the pin. This caused my adjustment problem.
Right now after 5 hours of operation and tweaking I am at 50 mv of relative dc offset at the speaker outputs and it does move around between 20mv and 80mv.
The absolute offset I am still working with but it is around -114mv on the negative rail and -164mv on the positive rail so I am still adjusting but maybe this is good enough. I haven't run square waves yet. I am not picking up any hum on my scope or digital meter on the outputs. I did measure the mv across all the source resistors and I have several candidates to swap if this adjustment phase doesn't work out but it looks good right now.
I have one odd measurement in that the ripple on the ps rail before the 2mh choke looks classical on the positive side by the negative side has a slight peak. after the chokes I don't see it.
Probably noise coming from my diodes (hexfreds).
I went back to my air coiled chokes becasue the iron core ones I had rattled and became magnetized and were trying to attach themselves to the capcitors clamps.
I got another problem, the meter on my Pass 350.x quit working as it won't move off zero where as before it was at 10'oclock, the amp seems to be working fine. I will have to call Pass on Monday so they can help me trouble shoot it--I am not sending it back as it weighs over 100lbs. It is good to be home after a week in Egypt. dave
GL- I have had some success, the amp has been running all day.
I found a problem, one of my outputs on the negative rail in the driver quad section had a broken drain pin. This happened when I reconnected my heatsinks to the chasis. I had the heatsinks facing upwards when I was doing the mods so I could install new source resistors and test the circuit, when I twisted them back in place I must have broken the pin. This caused my adjustment problem.
Right now after 5 hours of operation and tweaking I am at 50 mv of relative dc offset at the speaker outputs and it does move around between 20mv and 80mv.
The absolute offset I am still working with but it is around -114mv on the negative rail and -164mv on the positive rail so I am still adjusting but maybe this is good enough. I haven't run square waves yet. I am not picking up any hum on my scope or digital meter on the outputs. I did measure the mv across all the source resistors and I have several candidates to swap if this adjustment phase doesn't work out but it looks good right now.
I have one odd measurement in that the ripple on the ps rail before the 2mh choke looks classical on the positive side by the negative side has a slight peak. after the chokes I don't see it.
Probably noise coming from my diodes (hexfreds).
I went back to my air coiled chokes becasue the iron core ones I had rattled and became magnetized and were trying to attach themselves to the capcitors clamps.
I got another problem, the meter on my Pass 350.x quit working as it won't move off zero where as before it was at 10'oclock, the amp seems to be working fine. I will have to call Pass on Monday so they can help me trouble shoot it--I am not sending it back as it weighs over 100lbs. It is good to be home after a week in Egypt. dave
Hi Dave,
It sounds like you've arrived! Congratulations on working out your last few issues. Your measured voltages are fine. The various offset levels are in the same ranges as mine and the difting you see is normal.
Now I want to know how the amps sound!!!
I'm sorry to hear about X350. I know the Pass Labs folks will take care of you.
Hopefully you'll have time off over Christmas and New Years to do some serious listening.
Graeme
It sounds like you've arrived! Congratulations on working out your last few issues. Your measured voltages are fine. The various offset levels are in the same ranges as mine and the difting you see is normal.
Now I want to know how the amps sound!!!
I'm sorry to hear about X350. I know the Pass Labs folks will take care of you.
Hopefully you'll have time off over Christmas and New Years to do some serious listening.
Graeme
aleph 1.2's to Ax100 testing
GL, thanks, I am done adjusting, but in my eurphoria I forgot to check the 50% gain for the CCS. I used your resistor values.
I have this amp bolted up and ready for battle.
I have to do the checkout on the second amp tonight--just adjusting the values and I could check the ccs gain on this amp.
One question that I think you answered is that the 100% gain is checked with the 845 ohm resistor slot left "open" and not shorted. dave
GL, thanks, I am done adjusting, but in my eurphoria I forgot to check the 50% gain for the CCS. I used your resistor values.
I have this amp bolted up and ready for battle.
I have to do the checkout on the second amp tonight--just adjusting the values and I could check the ccs gain on this amp.
One question that I think you answered is that the 100% gain is checked with the 845 ohm resistor slot left "open" and not shorted. dave
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