I need help to solve problem with Lamm LL2.1 preamp.
Not sure whether this is a DC offset problem, but the outputs used to produced a high DCmV fluctuation, exceeding +-300mV.
I replaced the output caps and coupling in both channel (Vishay MKP1841 2.2uF 400V & Electrocube 0.033uF 100V), resulting a good Left Channel measurement and steady at 0.7mV. However the Right Channel remain in problem, it still produces a fluctuative DCmV exceeding +-30mV and causing speakers woofer moving back and forth.
Appreciate your help and thought.
Not sure whether this is a DC offset problem, but the outputs used to produced a high DCmV fluctuation, exceeding +-300mV.
I replaced the output caps and coupling in both channel (Vishay MKP1841 2.2uF 400V & Electrocube 0.033uF 100V), resulting a good Left Channel measurement and steady at 0.7mV. However the Right Channel remain in problem, it still produces a fluctuative DCmV exceeding +-30mV and causing speakers woofer moving back and forth.
Appreciate your help and thought.
Wow a Lamm,
you must be a rich man.
If its not the output-caps maybe there is an issue with the pulldown-resistor after the caps.
Perhaps it will be usefull to see a schematic?
Hilmar
you must be a rich man.
If its not the output-caps maybe there is an issue with the pulldown-resistor after the caps.
Perhaps it will be usefull to see a schematic?
Hilmar
This looks like a very simple and straightforward design, meaning that as long as the output caps are ok, there is just no dc offset. Could it be the replacement caps are also defective?
Dear Hilmar,
Thanks for the advice. Absolutetly Iam not rich man 🙂. It is a sad story, I spend years doing saving for this Stereophile's highly recomended unit, yet I have to strugle with the problem since I bought this brand new unit a year ago.
I checked all resistors in both signal path, and measurements showed all in good condition. Perhaps I need to double check, particularly the pull-down resistors in both input and ouput caps.
Unfortunately, I dont have the schematic, have tried to get it from Lamm but no reply. Let me see whether I can decode it and share with you.
Thanks for the advice. Absolutetly Iam not rich man 🙂. It is a sad story, I spend years doing saving for this Stereophile's highly recomended unit, yet I have to strugle with the problem since I bought this brand new unit a year ago.
I checked all resistors in both signal path, and measurements showed all in good condition. Perhaps I need to double check, particularly the pull-down resistors in both input and ouput caps.
Unfortunately, I dont have the schematic, have tried to get it from Lamm but no reply. Let me see whether I can decode it and share with you.
Dear Analog_sa,
Thanks for your advice. I replaced the right channel output caps twice, so this is the second replacement, unlike the left channel.
however, I still have 2 spares, perhaps it is worth to retry.
Wandering DC can be caused by mains voltage fluctuations, poor LF stability (verge of motorboating) and some component being on the edge of breaking.
A common modern problem is coupling caps which are too large so the amp LF rolloff is below the HF rolloff of the PSU filtering. This leaves a band where voltage variations come straight through into the output.
A common modern problem is coupling caps which are too large so the amp LF rolloff is below the HF rolloff of the PSU filtering. This leaves a band where voltage variations come straight through into the output.
Hi,
A lot of wisdom in there.
If DC blocking caps break down repeatedly then something is likely to be wrong with the voltage at their input.
So check the DC voltage at the input and further upstream. It may be a faulty tube as well so check those too by swapping them L to R channel and so forth.
In the mean time I'd suggest you disconnect the amps/speakers as the DC current may end up toasting the speaker coils.
Ciao, 😉
A lot of wisdom in there.
If DC blocking caps break down repeatedly then something is likely to be wrong with the voltage at their input.
So check the DC voltage at the input and further upstream. It may be a faulty tube as well so check those too by swapping them L to R channel and so forth.
In the mean time I'd suggest you disconnect the amps/speakers as the DC current may end up toasting the speaker coils.
Ciao, 😉
Could also be a bad tube.. The Lamm gear has a reputation for being very well built with non gimmicky parts..
Hi,
Some of those parts I do not particularly like. Good on paper but soundwise not very convincing if you'd ask me.
Ciao, 😉
Some of those parts I do not particularly like. Good on paper but soundwise not very convincing if you'd ask me.
Ciao, 😉
Dear All,
Many thanks for your advices, really appreciated.
I've tried new tube replacements (at least 3 new combination) and lots of swapps, so this is not the tubes.
Ciao, the left channel took only one replacement and the problem permanently fixed. You might be right regarding the parts, it was surprising when I measured the old output and coupling caps, they showed a good condition. it is different with the right channel, two times replacement of the output and coupling caps didn't fixed the problem at all. I did also replace the input stage caps, but problem remains.
DF96, I agree with you, this caused by main voltage fluctuation. I did simultaneous measurement to the unit and main outlet, a small rapid change in main outlet (as small as 0.3V) can caused rapid change in DC exceeding +-60mV. The problem is, how to find the breaking components? or some that might be in the breaking edge?. Further, I need your advice regarding poor LF stability, PSU Filtering, and how to handle this. Is it about the design itself? or would the problem be solved by replacing some component in the path? I started being nervoeus that this is about the desgn.
Many thanks for your advices, really appreciated.
I've tried new tube replacements (at least 3 new combination) and lots of swapps, so this is not the tubes.
Ciao, the left channel took only one replacement and the problem permanently fixed. You might be right regarding the parts, it was surprising when I measured the old output and coupling caps, they showed a good condition. it is different with the right channel, two times replacement of the output and coupling caps didn't fixed the problem at all. I did also replace the input stage caps, but problem remains.
DF96, I agree with you, this caused by main voltage fluctuation. I did simultaneous measurement to the unit and main outlet, a small rapid change in main outlet (as small as 0.3V) can caused rapid change in DC exceeding +-60mV. The problem is, how to find the breaking components? or some that might be in the breaking edge?. Further, I need your advice regarding poor LF stability, PSU Filtering, and how to handle this. Is it about the design itself? or would the problem be solved by replacing some component in the path? I started being nervoeus that this is about the desgn.
Unfortunately my crystal ball is away for repair and upgrading at present. When it comes back I will be able to diagnose design problems in circuits I have never seen and fault-trace with no symptom description.
Until then I need a circuit diagram to work from.
Until then I need a circuit diagram to work from.
Hi DF96,
Sadly I don't have the schematic right now. I will try to decode it and share with you.
However, if somebody out there have the scheme or ever do a draw/sketch, it would be highly appreciated if you could share with us.
Sadly I don't have the schematic right now. I will try to decode it and share with you.
However, if somebody out there have the scheme or ever do a draw/sketch, it would be highly appreciated if you could share with us.
Hi!
This might be a naive question, but:
Why are you not sending this to the dealer or manufacturer for repair? Should be under warranty.
Without a circuit diagram and proper understanding of the unit any attempt to repair will be guesswork and poking in the dark.
Best regards
Thomas
This might be a naive question, but:
Why are you not sending this to the dealer or manufacturer for repair? Should be under warranty.
Without a circuit diagram and proper understanding of the unit any attempt to repair will be guesswork and poking in the dark.
Best regards
Thomas
Hi Thomas,
Good advice and question as well.
Yes, it was a brand new and should be under warranty. The problem actually was occured just about three week after the unit landed in my listening room, it was even not reaching 40 running hours. Since then, I've been strugling with the dealer and manufacturer, and it make me frustrated. I don't think relying to them will help me to solve the problem.
To make the long story short, here are their general attitudes in responding to the problem:
The dealer: It is hopeless. They just keep pushing back and blame the problem is not caused and in the Lamm, but my other system, my Power Amp. They are too ignorance and even reject to replace the caps that suggested by the manufacturer, which then I did it by myself and get a good result but only in the left channel. I finnaly knew from some friends and other dealer that this is some kind of their typically attitude.
The Manufacturer: They simply said that the unit is reliable and never experienced such problem before, they said this is a mystery. Same with the dealer, they then blame my other equipment. They finally suggested to replace the output caps, but when it's only work to the left channel, again I have to face difficut situation to communicate and get some advices from them.
It has been desperately difficult to communicate with them. They are very bussy of being defensive rather then trying to find and solve the problem. They tend to underestimate our knowledge, even in doing basic measurement, the are too much pride of themselves. Now I am trying to do a trial and error, but strugling to order some replacement parts from them. No email reply from manufacturer, while the dealer keep pushing me to directly order from the manufacturer. what a great manufacturer-dealer combo.
Good advice and question as well.
Yes, it was a brand new and should be under warranty. The problem actually was occured just about three week after the unit landed in my listening room, it was even not reaching 40 running hours. Since then, I've been strugling with the dealer and manufacturer, and it make me frustrated. I don't think relying to them will help me to solve the problem.
To make the long story short, here are their general attitudes in responding to the problem:
The dealer: It is hopeless. They just keep pushing back and blame the problem is not caused and in the Lamm, but my other system, my Power Amp. They are too ignorance and even reject to replace the caps that suggested by the manufacturer, which then I did it by myself and get a good result but only in the left channel. I finnaly knew from some friends and other dealer that this is some kind of their typically attitude.
The Manufacturer: They simply said that the unit is reliable and never experienced such problem before, they said this is a mystery. Same with the dealer, they then blame my other equipment. They finally suggested to replace the output caps, but when it's only work to the left channel, again I have to face difficut situation to communicate and get some advices from them.
It has been desperately difficult to communicate with them. They are very bussy of being defensive rather then trying to find and solve the problem. They tend to underestimate our knowledge, even in doing basic measurement, the are too much pride of themselves. Now I am trying to do a trial and error, but strugling to order some replacement parts from them. No email reply from manufacturer, while the dealer keep pushing me to directly order from the manufacturer. what a great manufacturer-dealer combo.
Hi!
That is strange that a manufacturer is risking his reputation by such behaviour. I would make it clear to the manufacturer that you are discussing this issue in a public forum since they are not taking care of the problem. Maybe that will change their mind.
Any equipment no matter how well made can experience a technical fault. Just saying that this never occurred before is not acceptable and no excuse to refuse to repair a defective unit.
If they still don't move maybe you can find a shop in your area which is capable to service tube gear and which has proper measurement equipment. Of course I would present the bill and service report to both the dealer and manufacturer afterwards
Best regards
Thomas
That is strange that a manufacturer is risking his reputation by such behaviour. I would make it clear to the manufacturer that you are discussing this issue in a public forum since they are not taking care of the problem. Maybe that will change their mind.
Any equipment no matter how well made can experience a technical fault. Just saying that this never occurred before is not acceptable and no excuse to refuse to repair a defective unit.
If they still don't move maybe you can find a shop in your area which is capable to service tube gear and which has proper measurement equipment. Of course I would present the bill and service report to both the dealer and manufacturer afterwards
Best regards
Thomas
Perhaps not so unusual, I had a very similar experience with a dealer here. Some dealers are very conscientious about after sales service and others just tend to ignore it.
What caps did you replace the originals with? The same exact parts may exhibit the same exact problem.
What caps did you replace the originals with? The same exact parts may exhibit the same exact problem.
A further comment is that tube circuits with unregulated supplies will quite faithfully pass low frequency mains variations right to their outputs - the only defense against this is large time constants in the supplies and choosing coupling caps with appreciably smaller time constants so that the LF garbage is heavily attenuated.
A tube power amp is not going to care much generally, but a solid state amp undoubtedly will. (Some older big VTL tube amps care too from experience)
An output coupling cap value into the following R that gives you -1dB around 20Hz will help significantly.
There is probably nothing wrong with the pre-amplifier or the power amplifier, they just were not designed off the shelf to be universally compatible with everything out there.
This issue can be fixed if you are willing to look at things closely and not just blindly replace parts.
A tube power amp is not going to care much generally, but a solid state amp undoubtedly will. (Some older big VTL tube amps care too from experience)
An output coupling cap value into the following R that gives you -1dB around 20Hz will help significantly.
There is probably nothing wrong with the pre-amplifier or the power amplifier, they just were not designed off the shelf to be universally compatible with everything out there.
This issue can be fixed if you are willing to look at things closely and not just blindly replace parts.
The unit is probably following a mains play cycle as noted before. There is no active regulation to be spotted other than a sinked TO-5 with own rectification diodes and filter capacitor near by (LM317K for heaters?). There is a row of blue electrolytic caps forming some large capacitance bank and a Hammond choke to the left. It looks like a Russian 6X4 rectifier & choke input passive cell. Vishay 1843 PP output caps can be spotted as 2.2uF on some pictures on the web. I have read that its using a 12AU7 with its sections paralleled as input stage right after the volume pots and a 6DJ8 in SRPP mode as output stage. Not sure how they came to such a general description in some older Greek review, no other info.
I would exchange the 6X4 too, and if no cigar, I would see what happens with a Stavol* on the mains as a last resort of what can be done installation wise.
*Naming a range of AC stabilizer big box products well known in some Pacific countries. The power companies mains supply is lacking vs. demand and monitoring is reputably not best in many regions there, creating much uncertainty with stable mains assuming gear.
I would exchange the 6X4 too, and if no cigar, I would see what happens with a Stavol* on the mains as a last resort of what can be done installation wise.
*Naming a range of AC stabilizer big box products well known in some Pacific countries. The power companies mains supply is lacking vs. demand and monitoring is reputably not best in many regions there, creating much uncertainty with stable mains assuming gear.
Dear All,
Many thanks for your advices and thoughts.
Dear Thomas: I don’t think they would be bother with their reputation. It has been a year, and the one that I bought is their least expensive gear, why bother then? I believe this also caused by the prejudice that might be occurred and driven by dealer-manufacturer communications. So, after some quite struggles, I have and better to move then get some help from elsewhere, there when I finally try to find and solve the problem with my technician friend. The problem is when we need the schematic and some replacement parts, yet I still have to contact them. I agree with you and did send them service report and result. I've spent lots, but definitely we can't expect bill & reimbursement from them. I once asked them to send the suggested replacement resistors and asked whether those are still under warranty, they stop responding my email then, even when I finally placed an order to buy.
Dear Kevinkr: The output and coupling caps are MKP1841 2.2uF 400V and Electrocube 950B1G333J, 0.033uF 1000V, those are all original replacement caps. One time replacement to the left channel fixed the problem, but two times replacement to the right channel did not. I did also move to replace the input stage caps (MKP1840 6.8uF 250V the same Electrocube 950B1G333J, 0.033uF 1000V), still no good result. Those replacements are made based on manufacturer suggestion (after some struggle off course, sorry for being skeptical). They finally suspect some resistors, but I loss contact when I asking them for the (under warranty) replacement parts.
Yes it is unregulated supply, this drove me to suspect the design that may not be universally compatible to every circumstance, but why only the right channel? Why the left channel works well? The manufacturer never confirms when I asked this design matter. I did some measurements in two different circumstances:
1. When it was unconnected to any other equipment, I did measurement only to the unit alone. Right channel showing a rapid fluctuation while left channel is steady at 0.7mV.
2. When it was connected to the power amplifiers (Off). It was clear that measurement to the preamp’s left channel output jack showed a steady 0.7mV while right channel rapidly fluctuated.
I agree to start investigate resistors as you and Hilmar suggested, but I need to secure some spare parts before do some replacement, Dale Resistor FP000222K6F9521 (22.6K, 2W, 1%) is difficult to find. Meanwhile, my visual investigation shows me they are in good conditions as the measurements did, but who knows?
Dear Salas: You have a good view to your attached picture. You right, no active regulator except for the heaters. I did try some replacement to the 6x4 rectifier tube (it is Jan Philips), I have three spares, yet no good result. Yes, Stavol or so might be the last resort. It does lowering the fluctuation, but considering the different result after left and right channel caps replacement, we need to find out the root of the problem, not only covering the symptom.
Many thanks for your advices and thoughts.
Dear Thomas: I don’t think they would be bother with their reputation. It has been a year, and the one that I bought is their least expensive gear, why bother then? I believe this also caused by the prejudice that might be occurred and driven by dealer-manufacturer communications. So, after some quite struggles, I have and better to move then get some help from elsewhere, there when I finally try to find and solve the problem with my technician friend. The problem is when we need the schematic and some replacement parts, yet I still have to contact them. I agree with you and did send them service report and result. I've spent lots, but definitely we can't expect bill & reimbursement from them. I once asked them to send the suggested replacement resistors and asked whether those are still under warranty, they stop responding my email then, even when I finally placed an order to buy.
Dear Kevinkr: The output and coupling caps are MKP1841 2.2uF 400V and Electrocube 950B1G333J, 0.033uF 1000V, those are all original replacement caps. One time replacement to the left channel fixed the problem, but two times replacement to the right channel did not. I did also move to replace the input stage caps (MKP1840 6.8uF 250V the same Electrocube 950B1G333J, 0.033uF 1000V), still no good result. Those replacements are made based on manufacturer suggestion (after some struggle off course, sorry for being skeptical). They finally suspect some resistors, but I loss contact when I asking them for the (under warranty) replacement parts.
Yes it is unregulated supply, this drove me to suspect the design that may not be universally compatible to every circumstance, but why only the right channel? Why the left channel works well? The manufacturer never confirms when I asked this design matter. I did some measurements in two different circumstances:
1. When it was unconnected to any other equipment, I did measurement only to the unit alone. Right channel showing a rapid fluctuation while left channel is steady at 0.7mV.
2. When it was connected to the power amplifiers (Off). It was clear that measurement to the preamp’s left channel output jack showed a steady 0.7mV while right channel rapidly fluctuated.
I agree to start investigate resistors as you and Hilmar suggested, but I need to secure some spare parts before do some replacement, Dale Resistor FP000222K6F9521 (22.6K, 2W, 1%) is difficult to find. Meanwhile, my visual investigation shows me they are in good conditions as the measurements did, but who knows?
Dear Salas: You have a good view to your attached picture. You right, no active regulator except for the heaters. I did try some replacement to the 6x4 rectifier tube (it is Jan Philips), I have three spares, yet no good result. Yes, Stavol or so might be the last resort. It does lowering the fluctuation, but considering the different result after left and right channel caps replacement, we need to find out the root of the problem, not only covering the symptom.
Hi!
I am surprised that a manufacturer gets away with such behaviour. Anyways I can understand that you are fed up with them and want to move on.
While it is true that preamps with unregulated supplies have their outputs move with line voltage, it should never be that bad that your woofers move along unless the line voltage fluctuates really badly.
Instead of randomly replacing parts I suggest to look at the circuit with a scope to understand what is going on. Also all op points should be checked. Measure the line voltage too and see if its fluctuations correlate with the output fluctuations. It is unlikely that output caps fail in both channels. If so, something else caused the failure.
Best regards
Thomas
I am surprised that a manufacturer gets away with such behaviour. Anyways I can understand that you are fed up with them and want to move on.
While it is true that preamps with unregulated supplies have their outputs move with line voltage, it should never be that bad that your woofers move along unless the line voltage fluctuates really badly.
Instead of randomly replacing parts I suggest to look at the circuit with a scope to understand what is going on. Also all op points should be checked. Measure the line voltage too and see if its fluctuations correlate with the output fluctuations. It is unlikely that output caps fail in both channels. If so, something else caused the failure.
Best regards
Thomas
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