I don't think so 🙂The logs show that all your posts have been approved within minutes of you posting. You would have to revisit or refresh the page to see them though.
For some reasons my reply took that long to be posted. This message is sent at 10:51pm of June 26 pacific time in Canada. Let's see when it will posted.
Thanks Mooly, the message posted at 11:17pm June 26, 2020 Pacific Time. 26 min after I sent it. Perhaps i forgot to refresh the page and thought it took more than 24 hours.
MERK123
Can anyone out there send me the Bias and DC Ofset procedure on an ML23.5 Thanks, Stephen
Can anyone out there send me the Bias and DC Ofset procedure on an ML23.5 Thanks, Stephen
There is no offset procedure for the LS output.
Bias current should be ca 275 mA and can be measured on one of the two big 0.1R resistors as 27.5mV on the corners of the base board.
Try to measure it and if outside the range I can tell you how to adjust.
Hans
Bias current should be ca 275 mA and can be measured on one of the two big 0.1R resistors as 27.5mV on the corners of the base board.
Try to measure it and if outside the range I can tell you how to adjust.
Hans
Just an educated guess.
The 27 output topology is the same as the 23, but with 8 drivers instead of 12.
So I would go for 8/12 x 275mA = 180mA bias current.
Hans
P.s. adjustment is done with a multiturn pot on the PCB
The 27 output topology is the same as the 23, but with 8 drivers instead of 12.
So I would go for 8/12 x 275mA = 180mA bias current.
Hans
P.s. adjustment is done with a multiturn pot on the PCB
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Thank you, Hans. Would you be referring to the .022R emitter resistors at the output transistors?
The 27 is a bit different from the 27.5/23.5 as you know, and it has two trimmers - one blue near the emitter resistors, and one yellow earlier in the circuit.
I've attached both schemos.
Thanks again, Hans,
Greg
The 27 is a bit different from the 27.5/23.5 as you know, and it has two trimmers - one blue near the emitter resistors, and one yellow earlier in the circuit.
I've attached both schemos.
Thanks again, Hans,
Greg
You have to measure one of the four 0.22R resistors that are connected to the LS output.
Since they are in parallel two by two, you will have to measure 20mV for 180mA Bias current.
In fact you should have 3 pots, two for adjusting the regulated voltage and one for the Bias current.
Try one and you should see an immediate effect on the Bias current.
If not, put it back in the original position and try the next pot.
Hans
Since they are in parallel two by two, you will have to measure 20mV for 180mA Bias current.
In fact you should have 3 pots, two for adjusting the regulated voltage and one for the Bias current.
Try one and you should see an immediate effect on the Bias current.
If not, put it back in the original position and try the next pot.
Hans
You are of correct, of course, Hans! It's been awhile since I did the work on my 27, so I had to review my photos to remind myself of the locations of the trimmers. I'll be opening it up soon to make adjustments, so I appreciate your information.
Greg
Greg
Hello Greg,
You have a great technical document for your amp. I wish I had one for my No.23 too. The layout picture could have saved at least one week of my work😉
You have a great technical document for your amp. I wish I had one for my No.23 too. The layout picture could have saved at least one week of my work😉
Handel, I didn't know you had no documentation!
I can pm what I have on the 23.5 to you if you'd like.
I can pm what I have on the 23.5 to you if you'd like.
I'm thinking of designing and producing a new high grade PCB for the ML23 / ML23.5 because of the age and the meagre quality of the ML PCB that does not allow very well for repairs without damage.
The idea is to stay relatively close to the 23.5 design, but equip the board as much as possible with modern (SMD) components, making it possible to fit everything with ease on one single board.
To guarantee that this new board will fit perfectly over the existing transistors on the heatsinks, I need the lower AC-7 board for it's sizes.
This board may be burnt, damaged, depopulated or whatever, as long as the connection points are still perfectly intact for taking the exact size.
So my question is, does anybody have a written off AC-7 board available or alternatively one on a loan base.
Hans
The idea is to stay relatively close to the 23.5 design, but equip the board as much as possible with modern (SMD) components, making it possible to fit everything with ease on one single board.
To guarantee that this new board will fit perfectly over the existing transistors on the heatsinks, I need the lower AC-7 board for it's sizes.
This board may be burnt, damaged, depopulated or whatever, as long as the connection points are still perfectly intact for taking the exact size.
So my question is, does anybody have a written off AC-7 board available or alternatively one on a loan base.
Hans
I was so impressed with the boards you made for your own unit. I've got a 27; have you considered making boards for the 27/27.5?
Cheers,
Greg
Cheers,
Greg
Everything depends on the amount of people interested in such a board swop, and to be honest I really have no idea.
But I have already repaired quite a number of 23.5 amps with all sorts of difficult to find problems that would have saved a lot of time with a board exchange with fresh new components on a stable PCB.
Hans
P.S. Thinking of it, It could even be an option to design a socketed non soldered PCB with all the amp components, that can be used on both the 27.5 the 23.5, where the large lower board is hardly populated but just serves to bring the signals from the heatsinks components to this upper board.
In that case the lower boards are specially for the 27.5 or 23.5 but the upper board is the same for both..
But I have already repaired quite a number of 23.5 amps with all sorts of difficult to find problems that would have saved a lot of time with a board exchange with fresh new components on a stable PCB.
Hans
P.S. Thinking of it, It could even be an option to design a socketed non soldered PCB with all the amp components, that can be used on both the 27.5 the 23.5, where the large lower board is hardly populated but just serves to bring the signals from the heatsinks components to this upper board.
In that case the lower boards are specially for the 27.5 or 23.5 but the upper board is the same for both..
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Hmm. Interesting, Hans.
At least two things interest me here. Improving the performance of the amp, and avoiding the high charges to update the amp if sent to an ML repair station. I was quoted $2,500 to re-cap and update the boards, which of course means $3,000 before it's said and done. The amp just isn't worth that much money. However, improving the performance substantially adds value. I've never found the amp to be as detailed as some of my much less expensive amps, though it was greatly improved in dynamic range and bass response when I replaced all of the electrolytic caps.
At least two things interest me here. Improving the performance of the amp, and avoiding the high charges to update the amp if sent to an ML repair station. I was quoted $2,500 to re-cap and update the boards, which of course means $3,000 before it's said and done. The amp just isn't worth that much money. However, improving the performance substantially adds value. I've never found the amp to be as detailed as some of my much less expensive amps, though it was greatly improved in dynamic range and bass response when I replaced all of the electrolytic caps.
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I Think that is absolutely great idea Hans. I have been dreaming if I could make my own new PCBs for my 23 but only for me it would be maybe too much.
I have multiple destroyed AC-2 boards from the 23 but not AC-7. Is that the same board but used in 23.5?
It would be even better if I could get the update to 23.5 too! 😀
Handel
I have multiple destroyed AC-2 boards from the 23 but not AC-7. Is that the same board but used in 23.5?
It would be even better if I could get the update to 23.5 too! 😀
Handel