Sounds like excellent progress Dave. Thanks for the update.
Graeme
P.S. I look forward to seeing your son on Sunday at the Burning Amp event.
Graeme
P.S. I look forward to seeing your son on Sunday at the Burning Amp event.
Re: aleph 1.2's to Ax100 testing 1st day
I am happy to know that I am not the only one with ridiculously hot inductors. I have been converting my PS to LCLC and while burning in the inductors to get rid of the stench, I managed to burn off the enamel from the inner copper coils and shorted the inductor. This was while only dissipating slightly more power than they would be required to handle in the amplifier.
The solution, put two 4mH chokes in parallel on each rail. It cuts the power dissipation nearly in half for each inductor and greatly increases the surface area for cooling. The added feature is that now I can adjust the rail voltage by adjusting the coils' spacing or by connecting them anti-parallel. For reference, these are 14 gauge Erse air core inductors and the PS current is 7.0-7.5 amps. It appears that a single inductor will stand up to the current in the second L position.
Jeremy
daly41k said:
I am happy to know that I am not the only one with ridiculously hot inductors. I have been converting my PS to LCLC and while burning in the inductors to get rid of the stench, I managed to burn off the enamel from the inner copper coils and shorted the inductor. This was while only dissipating slightly more power than they would be required to handle in the amplifier.
The solution, put two 4mH chokes in parallel on each rail. It cuts the power dissipation nearly in half for each inductor and greatly increases the surface area for cooling. The added feature is that now I can adjust the rail voltage by adjusting the coils' spacing or by connecting them anti-parallel. For reference, these are 14 gauge Erse air core inductors and the PS current is 7.0-7.5 amps. It appears that a single inductor will stand up to the current in the second L position.
Jeremy
aleph 1.2 to XA100
GL and GR, after a few hours of trying to get the relative dc offset ok I made some changes. I could get it near 0 but the next time I turned on the amp it would start up way to high. I noticed that the schematic calls for a 332ohm resistor in series with U2 (200ohm pot). I paralled this with 33.2 ohms to see if I could get a wee bit more adjustment. But in the process I poped several output devices -source resistors blew up. The reason I think is that I had the board proped up on a piece of wood horizontally so I could check the vitals but the board I think pressed one of the ps leads against the ccs outputs and put too much voltage through the gate resistors turning on the fets full bore and after about 10 minutes the devices overheated. So I will replace them and continue the testing. I just wanted to make sure that the 332 ohm resistor value is correct. dave
GL and GR, after a few hours of trying to get the relative dc offset ok I made some changes. I could get it near 0 but the next time I turned on the amp it would start up way to high. I noticed that the schematic calls for a 332ohm resistor in series with U2 (200ohm pot). I paralled this with 33.2 ohms to see if I could get a wee bit more adjustment. But in the process I poped several output devices -source resistors blew up. The reason I think is that I had the board proped up on a piece of wood horizontally so I could check the vitals but the board I think pressed one of the ps leads against the ccs outputs and put too much voltage through the gate resistors turning on the fets full bore and after about 10 minutes the devices overheated. So I will replace them and continue the testing. I just wanted to make sure that the 332 ohm resistor value is correct. dave
aleph 1.2 to xa100
kropf--thanks for the suggestion, I may try it if I can find the room in the chasis. I am still expeirmenting with bias quantities and I have decided to reduce it a bit so I don't have to redesign the chasis by adding cooling fans. Instead of going for 16o watts/channel I am cutting it back to 120watts and will see what happens. thanks again. dave
kropf--thanks for the suggestion, I may try it if I can find the room in the chasis. I am still expeirmenting with bias quantities and I have decided to reduce it a bit so I don't have to redesign the chasis by adding cooling fans. Instead of going for 16o watts/channel I am cutting it back to 120watts and will see what happens. thanks again. dave
Hi Dave,
Do you really mean the relative offset? That should not get too far away from zero even at turn on. About 100mv or less. Relative offset is not adjustable directly. You get good performance there by matching everything well.
Maybe you mean absolute offset. It's normal for the absolute offset to start at large values like you're seeing, drop to a couple of volts after a few minutes, and slowly drop below 100mv after an hour or so. After a while when you get your amps running you won't even think about it anymore.
However, the relative offset should be small. If it isn't, then re-check your construction. The CCS under the input MOSFET's works fine as is and I'm concerned that you feel you have to make such large value changes. As far as I know the resistor values used in the original Aleph-X have worked fine for all of the different iterations of the circuit shown on this site.
Graeme
Do you really mean the relative offset? That should not get too far away from zero even at turn on. About 100mv or less. Relative offset is not adjustable directly. You get good performance there by matching everything well.
Maybe you mean absolute offset. It's normal for the absolute offset to start at large values like you're seeing, drop to a couple of volts after a few minutes, and slowly drop below 100mv after an hour or so. After a while when you get your amps running you won't even think about it anymore.
However, the relative offset should be small. If it isn't, then re-check your construction. The CCS under the input MOSFET's works fine as is and I'm concerned that you feel you have to make such large value changes. As far as I know the resistor values used in the original Aleph-X have worked fine for all of the different iterations of the circuit shown on this site.
Graeme
With the two parallel (or anti-parallel) 4mH inductors I can achieve a nearly continuous range of inductances between 1mH and 3mH. The DC resistance is 0.25 ohms - equivalent to a 1.2mH inductor in the same product line (14 gauge Erse).
Jeremy
Jeremy
aleph 1.2's to Ax100
GR-thanks, I have a wiring problem that I am sleuthing. At one pt I had just about 0 relative dc output and 8volts absolute output with the ccs resistor at 169k, I measured every output device as follows:
Left channel positive Left Channel negative
outputs ccs outputs outputs ccs outputs
.510mv .593mv .391mv .563mv
.507mv .569mv .438mv .563mv
.735mv .600mv .497mv .568mv
.665mv .663mv .481mv .452mv
.473mv .601mv .501mv .442mv
.474mv .557mv .487mv .469mv
total 3.4 volts/1.2 ohms=2.75amps 3.04/1.2=2.53amps
This was across the 1.2 ohm source resistors. They are close indicating about 2.75 amps per rail.
the diff pair read 4.05 volts across one 392ohm resistor and 4.01 across the other resistor. I did not trim anything.
Howerver I felt like I was leaning over a blast furnance so I want to reduce the mv across the output souce resistors closer to 5amps and will install your 100k resistor value and re start. It could be I will need to better match the input diff pair. my 1kva trannie was squaking as well at these levels.
I am assuming that I can adjust the dc offset to ground and balance the rails using U2? If not I may have to replace some outputs with closer matching. dave
GR-thanks, I have a wiring problem that I am sleuthing. At one pt I had just about 0 relative dc output and 8volts absolute output with the ccs resistor at 169k, I measured every output device as follows:
Left channel positive Left Channel negative
outputs ccs outputs outputs ccs outputs
.510mv .593mv .391mv .563mv
.507mv .569mv .438mv .563mv
.735mv .600mv .497mv .568mv
.665mv .663mv .481mv .452mv
.473mv .601mv .501mv .442mv
.474mv .557mv .487mv .469mv
total 3.4 volts/1.2 ohms=2.75amps 3.04/1.2=2.53amps
This was across the 1.2 ohm source resistors. They are close indicating about 2.75 amps per rail.
the diff pair read 4.05 volts across one 392ohm resistor and 4.01 across the other resistor. I did not trim anything.
Howerver I felt like I was leaning over a blast furnance so I want to reduce the mv across the output souce resistors closer to 5amps and will install your 100k resistor value and re start. It could be I will need to better match the input diff pair. my 1kva trannie was squaking as well at these levels.
I am assuming that I can adjust the dc offset to ground and balance the rails using U2? If not I may have to replace some outputs with closer matching. dave
aleph 1.2's to Ax100
GR, I don't know why my table of values go scrunched together but what I was explaing was the measurements I took accross the source resistors with my vom meter.
Spaced out it should read:
Left Positive rail
outputs CCS outputs
Left negative rail
outputs CCS outputs
dave
GR, I don't know why my table of values go scrunched together but what I was explaing was the measurements I took accross the source resistors with my vom meter.
Spaced out it should read:
Left Positive rail
outputs CCS outputs
Left negative rail
outputs CCS outputs
dave
aleph 1.2's to Ax100 testing 1st day
Grey and GR--in my last response I said I was getting 2.75 amps bias on the 6 output fets, do I add the CCS fets current to this number? I have 4 quads of 6 fets. 12 fets for the positive signal rail and 12 fets for the negative signal rail. If I add just the output fets I get 5.5amps but if I add in the current source fets I get 11 amps of total bias. Which is correct? dave
Grey and GR--in my last response I said I was getting 2.75 amps bias on the 6 output fets, do I add the CCS fets current to this number? I have 4 quads of 6 fets. 12 fets for the positive signal rail and 12 fets for the negative signal rail. If I add just the output fets I get 5.5amps but if I add in the current source fets I get 11 amps of total bias. Which is correct? dave
adjusting the bias
GL--I found my problem as one of the small signal transistors in the CCS gave up the ghost. I have one unit under test and I am using your values except I have a voltage rail of +/- 31 volts and due to my heatsinks I am aiming for <400ma per device across a 1.2 ohm resistor (two 1.5's in parallel). I am using 6 outputs per quad as previously discussed. MY Aleph 1.2 circuit had about 350ma across each device x 24 devices and the amp ran at 55C measured in the middle of the heat sink.
Yesterday I ran a series of signal sweeps and things looked good and I did not detect any hum on the scope on the outputs using a 250watt 5 ohm resistor.
The vitals are for Now:
relative dc offset measured at the outputs settles down to -40mv after about a 1/2 hr warmup.
Absolute offsett I have not tried to adjust, I am assuming you have to use U2 the 200ohm pot for this. I am still getting a relatively high reading of over 20 volts at start up. I will let it run all afternoon and then measure it again.
How do you adjust absoulte offset? Wait for several hours and then use U2?
Or do you remeasure the CCS gain and readjust for 50%? I will reread the earlier comments in your threads but the only meaningful thing that I saw was to go back and match output devices better. If long term testing goes ok I will hook it up to a cd player drive it into the resistor and watch the scope over a day or so to see what happens. dave
dave
GL--I found my problem as one of the small signal transistors in the CCS gave up the ghost. I have one unit under test and I am using your values except I have a voltage rail of +/- 31 volts and due to my heatsinks I am aiming for <400ma per device across a 1.2 ohm resistor (two 1.5's in parallel). I am using 6 outputs per quad as previously discussed. MY Aleph 1.2 circuit had about 350ma across each device x 24 devices and the amp ran at 55C measured in the middle of the heat sink.
Yesterday I ran a series of signal sweeps and things looked good and I did not detect any hum on the scope on the outputs using a 250watt 5 ohm resistor.
The vitals are for Now:
relative dc offset measured at the outputs settles down to -40mv after about a 1/2 hr warmup.
Absolute offsett I have not tried to adjust, I am assuming you have to use U2 the 200ohm pot for this. I am still getting a relatively high reading of over 20 volts at start up. I will let it run all afternoon and then measure it again.
How do you adjust absoulte offset? Wait for several hours and then use U2?
Or do you remeasure the CCS gain and readjust for 50%? I will reread the earlier comments in your threads but the only meaningful thing that I saw was to go back and match output devices better. If long term testing goes ok I will hook it up to a cd player drive it into the resistor and watch the scope over a day or so to see what happens. dave
dave
further testing results
Gl--further testing reveals that I have a different gain evident beteen the + and - outputs. My signal generator is single ended so I have the - input shorted to the signal ground. This should not make a difference as the diff pair is just amplyfying the difference.
Using 100 hz and 1k as test signals with my scope set to 1 volt and a 5ohm resistor across the outputs I will get 5volts P to P on the positive and 10volts P to P on the negative side. Of course the phase is opposite. The only thing that I can come up with is the input gain of the differential pairs is off. Even though the dc gain is matched to 40mv. I have plenty of spare devices so I will rematch another pair. If you have any other ideas let me know.
Erno Borbely in his diff line amp design put a pot between the cathode resistors to balance the ccs source that he used but I don't think this is an issue. He also trimmed the plate resistors with a pot between them to balance voltage gain.
Maybe I an obsessing about nothing. I know one thing that my cheap solution to use 2 watt carbon film resistors across my exisiting 1.5 ohm wirewound source resistors is a mistake as one started to smoke so I am going to spent some money and buy 5watt wirewound or cement boat source resistors for reliability at one ohm. more to come as I see some late nights coming up with this project. dave
Gl--further testing reveals that I have a different gain evident beteen the + and - outputs. My signal generator is single ended so I have the - input shorted to the signal ground. This should not make a difference as the diff pair is just amplyfying the difference.
Using 100 hz and 1k as test signals with my scope set to 1 volt and a 5ohm resistor across the outputs I will get 5volts P to P on the positive and 10volts P to P on the negative side. Of course the phase is opposite. The only thing that I can come up with is the input gain of the differential pairs is off. Even though the dc gain is matched to 40mv. I have plenty of spare devices so I will rematch another pair. If you have any other ideas let me know.
Erno Borbely in his diff line amp design put a pot between the cathode resistors to balance the ccs source that he used but I don't think this is an issue. He also trimmed the plate resistors with a pot between them to balance voltage gain.
Maybe I an obsessing about nothing. I know one thing that my cheap solution to use 2 watt carbon film resistors across my exisiting 1.5 ohm wirewound source resistors is a mistake as one started to smoke so I am going to spent some money and buy 5watt wirewound or cement boat source resistors for reliability at one ohm. more to come as I see some late nights coming up with this project. dave
aleph 1.2's to Ax100 testing 1st day
Gl, I think the gain imbalance on my amp may lie in the feedback network so I am checking that out as soon as I get home tonight.
I am awaiting my 1%-5watt-1 ohm wirewound resistors from Digikey to replace my paralleled 1.5ohm resistors since the carbon film 2 watts are not sturdy enough. I will then restart and go from there. dave
Gl, I think the gain imbalance on my amp may lie in the feedback network so I am checking that out as soon as I get home tonight.
I am awaiting my 1%-5watt-1 ohm wirewound resistors from Digikey to replace my paralleled 1.5ohm resistors since the carbon film 2 watts are not sturdy enough. I will then restart and go from there. dave
aleph 1.2's to Ax100
GL-I found my gain issue, I was testing with my dual trace scope and "dah" and a lot of other words, I didn't have my VAR's set the same-double uncool. This then gave me different gain readings.
Up too late I guess, as soon as my new resistors show up I can retest and listen. At least I was able to test every output fet and I have one still hogging the current so I can change that out while I am at it. Stay tuned. dave
GL-I found my gain issue, I was testing with my dual trace scope and "dah" and a lot of other words, I didn't have my VAR's set the same-double uncool. This then gave me different gain readings.
Up too late I guess, as soon as my new resistors show up I can retest and listen. At least I was able to test every output fet and I have one still hogging the current so I can change that out while I am at it. Stay tuned. dave
GL and Grey-suggestions?
I have finished bench testing my aleph 1.2 conversion to XA100.
I followed GL's schematic with the following exceptions:
I have 6 outputs per quad instead of 5
I have +/- 31 volts per rail instead of 27
My specs are:
8-14mv relative dc offset with input shorted
24.5 volts of absolute dc after one hour-it only drops a few volts
I measure 4.45 volts across the 392 ohm resistor giving approx 11ma bias to the input differential pair.
Heatsinks get hot but not hotter than my Aleph
total current bias on the outputs is 5.40 amps
Now the problem--AC gain
With a 5 ohm resistor across the outputs
Using my sine wave signal generator at 100hz I set the gain
on the postive signal rail to 50mv ac by adjusting the signal generator output but I only measured
34mv ac signal on the negative signal gain?
I verified the measurements on my scope and digital vom meter.
I don't know how to account for the difference in signal gain unless it has to do with the setting of R12 and R34. I have some 2k pots that I can put in these locations and try to adjust them to get equal gain from both sections. Or maybe one of the current gain MSP18 transistors are not functioning as they should.
My question is would using a single ended input cause this (I don't think so since the diff amp is just applifying the difference between signal on one gate and 0 ground signal on the other.
The output signal is clean as compared to the input signal. I am not sure what the absolute dc means since people report all different kind of numbers. thanks for any ideas in advance. dave
I have finished bench testing my aleph 1.2 conversion to XA100.
I followed GL's schematic with the following exceptions:
I have 6 outputs per quad instead of 5
I have +/- 31 volts per rail instead of 27
My specs are:
8-14mv relative dc offset with input shorted
24.5 volts of absolute dc after one hour-it only drops a few volts
I measure 4.45 volts across the 392 ohm resistor giving approx 11ma bias to the input differential pair.
Heatsinks get hot but not hotter than my Aleph
total current bias on the outputs is 5.40 amps
Now the problem--AC gain
With a 5 ohm resistor across the outputs
Using my sine wave signal generator at 100hz I set the gain
on the postive signal rail to 50mv ac by adjusting the signal generator output but I only measured
34mv ac signal on the negative signal gain?
I verified the measurements on my scope and digital vom meter.
I don't know how to account for the difference in signal gain unless it has to do with the setting of R12 and R34. I have some 2k pots that I can put in these locations and try to adjust them to get equal gain from both sections. Or maybe one of the current gain MSP18 transistors are not functioning as they should.
My question is would using a single ended input cause this (I don't think so since the diff amp is just applifying the difference between signal on one gate and 0 ground signal on the other.
The output signal is clean as compared to the input signal. I am not sure what the absolute dc means since people report all different kind of numbers. thanks for any ideas in advance. dave
testing ax100
One other quick thing, I double checked the 10k resistors on the input network and they are hooked up ok. I did not install the 5uf pp input cap or the 100k resistor to ground. I have a business trip and I must leave the project for the week but I am much encouraged, once I get this ac thing behind me we are good to go. the gain at least resistor wise 220k/10k seems ok. dave
One other quick thing, I double checked the 10k resistors on the input network and they are hooked up ok. I did not install the 5uf pp input cap or the 100k resistor to ground. I have a business trip and I must leave the project for the week but I am much encouraged, once I get this ac thing behind me we are good to go. the gain at least resistor wise 220k/10k seems ok. dave
Hi Dave,
Sorry I haven't been posting. I've been on vacation for a couple of weeks. However I see that you have been solving problems really well on your own and making great progress.
Yes, the 200 ohm pot is used to adjust the absolute DC offset. When the amp is brought up for the first time you need to adjust this control every couple of minutes to bring the both outputs back to zero volts. You need to be able to access this pot easily. After an hour to an hour and a half you can make a final adjustment and call it done.
I recall NP saying that the factory units are initially adjusted to zero volts of absolute offset over a couple of hours and left on for a couple of days then given a final adjustment.
I have given a description earlier in the thread of absolute offset values I've measured on my amps over the first hour after a typical power on cycle in my system. I believe wuffwaff gave the same info for his amps too.
I measured the AC gain using the unbalanced input. AC gain on the two halves of the amp are unrelated to whether the test signal inputs are balanced or unbalanced.
Regards,
Graeme
Sorry I haven't been posting. I've been on vacation for a couple of weeks. However I see that you have been solving problems really well on your own and making great progress.
Yes, the 200 ohm pot is used to adjust the absolute DC offset. When the amp is brought up for the first time you need to adjust this control every couple of minutes to bring the both outputs back to zero volts. You need to be able to access this pot easily. After an hour to an hour and a half you can make a final adjustment and call it done.
I recall NP saying that the factory units are initially adjusted to zero volts of absolute offset over a couple of hours and left on for a couple of days then given a final adjustment.
I have given a description earlier in the thread of absolute offset values I've measured on my amps over the first hour after a typical power on cycle in my system. I believe wuffwaff gave the same info for his amps too.
I measured the AC gain using the unbalanced input. AC gain on the two halves of the amp are unrelated to whether the test signal inputs are balanced or unbalanced.
Regards,
Graeme
Re: GL and Grey-suggestions?
If this figure is correct, then this is your problem.
😎
daly41k said:
If this figure is correct, then this is your problem.
😎
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