Kenwood Basic M1 Power Amplifier Restoraton/Upgrade
- Thread starter Leestereo
- Start date
Leestereo
Super Member
There is no problem per se using Elna Silmic II capacitors in the M1. Note however that they are often quite physically large compared to other types for the same capacitance/voltage and such there may not be sufficient board space to accommodate them. Also, IMO, they are not ideal for power supply duty; better to use low ESR types, e.g., Nichicon PW, UCC KY, Panasonic FR...etc...
i think you will need to swap out better matching Q1/Q3 and Q2/Q4 for the diff pairs. I don't see any way to adjust the offset. I don't have my M1 notes in front of me and I don't recall it being bad enough to replace the diff pairs.
You could also contact https://drmaudio.com/ to see if he provides better matching transistors for M1 amps.
You could also contact https://drmaudio.com/ to see if he provides better matching transistors for M1 amps.
Hi Ben, was wondering if OK to dust this off and ask a question. What is the physics-reasoning for the reduction in capacitance at C1, C2? Seems like it might be interesting why we are taking the capacitance 'down' here. -Matt
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Spencer, I used 4.7uF WIMAs for C1,C2. I had these in my spare parts box. I think 3.3 would work too.
I'm sure you recall from your EE days about filter theory. A simple hi-pass frequency cutoff fc = 1/(2*pi*RC). R=100,000, C=1x10-6, fc=1.59Hz.
it has been a long time since I've been in an EE class so this could be wrong. Sorry no physics involved. all math.
I'm sure you recall from your EE days about filter theory. A simple hi-pass frequency cutoff fc = 1/(2*pi*RC). R=100,000, C=1x10-6, fc=1.59Hz.
it has been a long time since I've been in an EE class so this could be wrong. Sorry no physics involved. all math.
Leestereo
Super Member
In signal coupling/high pass filter applications, to pass the full frequency range (i.e., 20Hz - 20kHz) the capacitor should have a F3 of ≤5Hz for a flat response down to 20Hz. In the M1, since the input impedance is 47kHz, a 0.68µF film capacitor would be sufficient to a 4.9Hz cut-off. A 1µF stacked film capacitor was installed as this was a more readily available size (compared to 0.68µF) at the time of the M1 restoration.
For those of you putting together your parts list, don't skip the step where you go through your specific Kenwood Basic M1 and verify what you have in your actual machine against what you were thinking you needed. In other words, don't just go by the schematic and service manual parts list. Look on the underside of the PCB, which of course you've already done. None of us in our excitement rush past our mandatory, early on, all over close inspection. You may have a couple aluminum electrolytic capacitors on the underside of the PCB.
I think it's time for an update, I had the work done by Leestereo in 2015, and I've had some opportunity to try it with and against a few different components now. It's in use with my computer as my digital-sourced "daily driver" system, which means it gets used the most, and for videos and games too-not just music. I've used a Schiit Modi DAC, and the newer/fancier Modius, both were/are great. After the DAC is an Emotiva Control Freak passive pre-amp/volume knob on my desk, then -12 dB Harrison Labs attenuators, and then the amp. I'm using Klipsch KSB 1.1 speakers with the computer, and as B speakers in another room I have some KLF-10's with titanium tweeter diaphragms (these will be moved to be used with the main TV someday, and the computer drives it as a 3rd monitor for movies and games).
When I got the KLF-10's things got interesting, because until then I had only used this amp on a regular basis with the little KSB's. They're good little speakers, but they're little, and set up at my desk for near-field listening. I bought an Acurus A250, thinking that would be what I need to rock the house with the KLF-10's. That was sort of an impulse buy, which is unlike me, but I thought I was due to treat myself I guess. And if you've seen pictures of the A250, especially inside, well it's a serious amplifier, I had to know first-hand what it would be like. The A250 was great, BUT I found the treble to be fatiguing after listening to music loudly for 15+ minutes. So I went back to the M1, and to my surprise it rocks just as hard and still has all the detail, just no fatigue! I know many might not like that comment, and would probably claim the A250 is a better amp. I'm not making any claims as to what is better, but with my system the brighter sounding Acurus didn't have the right synergy-I think different speakers or analog sources would do the trick, but I'm not changing those. My relatively efficient speakers didn't need all of the power that it has on reserve either. In other cases, I'm sure the Acurus could outperform the M1, it all depends on the synergy of your system, what other components are in play, in my opinion. I actually don't want to let go of the Acurus, it has so much going for it, but I'm happy with my system and ready to leave things alone (unless I find a good deal on some KLF-20s, to try the 3 way version of my current speakers). I'm not the most serious audiophile out there, but I have decent ears and like decent sound, I think the fact that this amp held up against something like the Acurus, in my system, is amazing! Right now, and especially on the bigger speakers, I can say my system sounds just right to me with any source at any volume level. Tight and powerful bass, detailed yet non-fatiguing treble, decent imaging, decent dynamics, good loud or quiet, etc. I don't feel pressured to upgrade, and it wouldn't be cheap either to get a noticeably better sounding system.
Also I did use this amp for a bit with a C2 preamp and a turntable, that was wonderful but I decided to do secondary vinyl-focused system more for the hobby side of things and music only.
When I got the KLF-10's things got interesting, because until then I had only used this amp on a regular basis with the little KSB's. They're good little speakers, but they're little, and set up at my desk for near-field listening. I bought an Acurus A250, thinking that would be what I need to rock the house with the KLF-10's. That was sort of an impulse buy, which is unlike me, but I thought I was due to treat myself I guess. And if you've seen pictures of the A250, especially inside, well it's a serious amplifier, I had to know first-hand what it would be like. The A250 was great, BUT I found the treble to be fatiguing after listening to music loudly for 15+ minutes. So I went back to the M1, and to my surprise it rocks just as hard and still has all the detail, just no fatigue! I know many might not like that comment, and would probably claim the A250 is a better amp. I'm not making any claims as to what is better, but with my system the brighter sounding Acurus didn't have the right synergy-I think different speakers or analog sources would do the trick, but I'm not changing those. My relatively efficient speakers didn't need all of the power that it has on reserve either. In other cases, I'm sure the Acurus could outperform the M1, it all depends on the synergy of your system, what other components are in play, in my opinion. I actually don't want to let go of the Acurus, it has so much going for it, but I'm happy with my system and ready to leave things alone (unless I find a good deal on some KLF-20s, to try the 3 way version of my current speakers). I'm not the most serious audiophile out there, but I have decent ears and like decent sound, I think the fact that this amp held up against something like the Acurus, in my system, is amazing! Right now, and especially on the bigger speakers, I can say my system sounds just right to me with any source at any volume level. Tight and powerful bass, detailed yet non-fatiguing treble, decent imaging, decent dynamics, good loud or quiet, etc. I don't feel pressured to upgrade, and it wouldn't be cheap either to get a noticeably better sounding system.
Also I did use this amp for a bit with a C2 preamp and a turntable, that was wonderful but I decided to do secondary vinyl-focused system more for the hobby side of things and music only.
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During recently completed restoration upgrade of my M1 -- thank you again Ben Lee what a fantastic plan you put forth here -- it was interesting to witness incremental improvement in performance when powering up after replacement every half dozen or so components.
Generic CD/DVD player into restored/upgraded C1 pre (also plan by Ben); into the M1; into a pair of upgraded crossover / tweeter Klipsch KG-4.5 floor standing speakers.
Music selection: Orchestral Introduction and Welcome to the World of the Plastic Beach with Gorillaz and Snoop Dogg. Yeah baby. Haha. Good stuff. Quite a lot of fun this musical piece, and to be able to hear more and more detaill and nuance each step. What a treat.
I haven't yet had a chance to really put the C1/M1 pair through their paces. For now I've got a restored Denon TU-660 AM/FM stereo tuner into the C1/M1 into a pair of Mission 770s, in a medium sized room. For now my impression is that the C1 and M1 together offer a nice even representation of whatever you put into them, across the full frequency range of human hearing. No holes that I can hear. No unequal emphasis. For comparison had a restored upgraded NAD 1155 pre into an Adcom GFA 5300 power with same tuner and speakers. There is a lot of 'excitement' in the GFA 5300. I like it very much. In other words, my thinking is that this possibly is because there is emphasis = distortion in areas that are pleasing to me personally on the low end and the upper mid and up high. This plays into what Dane795 is saying about listener fatigue. I think that what we have here in the C1 / M1 is a more neutral representation. So the presentation breathes. Pleasurable, more easy, listening. More physically relaxing on your anatomical systems. Strong and open. I could be wrong but thinking not euphonic; more so, accurate. I like it very much. Looking forward to eventually checking out with vinyl and enabling the Sigma Drive. Thanks again Ben. You da man.
Generic CD/DVD player into restored/upgraded C1 pre (also plan by Ben); into the M1; into a pair of upgraded crossover / tweeter Klipsch KG-4.5 floor standing speakers.
Music selection: Orchestral Introduction and Welcome to the World of the Plastic Beach with Gorillaz and Snoop Dogg. Yeah baby. Haha. Good stuff. Quite a lot of fun this musical piece, and to be able to hear more and more detaill and nuance each step. What a treat.
I haven't yet had a chance to really put the C1/M1 pair through their paces. For now I've got a restored Denon TU-660 AM/FM stereo tuner into the C1/M1 into a pair of Mission 770s, in a medium sized room. For now my impression is that the C1 and M1 together offer a nice even representation of whatever you put into them, across the full frequency range of human hearing. No holes that I can hear. No unequal emphasis. For comparison had a restored upgraded NAD 1155 pre into an Adcom GFA 5300 power with same tuner and speakers. There is a lot of 'excitement' in the GFA 5300. I like it very much. In other words, my thinking is that this possibly is because there is emphasis = distortion in areas that are pleasing to me personally on the low end and the upper mid and up high. This plays into what Dane795 is saying about listener fatigue. I think that what we have here in the C1 / M1 is a more neutral representation. So the presentation breathes. Pleasurable, more easy, listening. More physically relaxing on your anatomical systems. Strong and open. I could be wrong but thinking not euphonic; more so, accurate. I like it very much. Looking forward to eventually checking out with vinyl and enabling the Sigma Drive. Thanks again Ben. You da man.
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Hello,
I have a M1 in similar condition - or even worth - to the Ugly Betty presented in this thread. The upgrade detailed seems impressive and I want to do it as well.
Issue is I'm a newbie in electronic components specification. After reading the thread and taking notes, I have hard time sourcing the right components, either from radiospares or mouser. Some are not available at all and some have not exactly the same spec.
Example: I did not found all the C0G ceramic capacitors. Essentially Kemet ones are available at mouser.
For electrolytic caps, 105°C and low ESR seem not available for the large 8200µF.
Could anyone having completed this upgrade share his BOM? That would really helpful!
Cheers,
I have a M1 in similar condition - or even worth - to the Ugly Betty presented in this thread. The upgrade detailed seems impressive and I want to do it as well.
Issue is I'm a newbie in electronic components specification. After reading the thread and taking notes, I have hard time sourcing the right components, either from radiospares or mouser. Some are not available at all and some have not exactly the same spec.
Example: I did not found all the C0G ceramic capacitors. Essentially Kemet ones are available at mouser.
For electrolytic caps, 105°C and low ESR seem not available for the large 8200µF.
Could anyone having completed this upgrade share his BOM? That would really helpful!
Cheers,
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You are on your way to building your own BOM sounds like. IMHO best way to go.
Might want to consider starting your own thread. Attract broader attention. Get more help.
For my project I might have used a cornell dubilier lx series snap in for the larger filter capacitors (8200uF/80V), like maybe 380LX822M080A052 however this might not have been the best choice. (Am now in the middle of moving.) For one thing my memory is that the lead spacing was not right and so the installation required adaptation. Temperature rating is a subject of debate. For one thing power supply filter capacitors are not known to get hot, it's said. So not a concern here. Others might disagree.
Might want to consider starting your own thread. Attract broader attention. Get more help.
For my project I might have used a cornell dubilier lx series snap in for the larger filter capacitors (8200uF/80V), like maybe 380LX822M080A052 however this might not have been the best choice. (Am now in the middle of moving.) For one thing my memory is that the lead spacing was not right and so the installation required adaptation. Temperature rating is a subject of debate. For one thing power supply filter capacitors are not known to get hot, it's said. So not a concern here. Others might disagree.
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ajfink
Member
Hi all,
I took at a turn with my recently-acquired M1.
I've only replaced the low-voltage filter capacitors so far since I CANNOT find something that will physically fit the high voltage rail side. Typically I buy from Mouser. Any tips?
Here's the full board:
I applied the current source mod:
The casualties:
I don't think Dan Mattis has output connector kits for the M1 like he does for the M2 and M2A. I might try to create replacements of my own to replace the stock, substandard speaker cable connectors. I need proper banana or spade connectors.
I took at a turn with my recently-acquired M1.
I've only replaced the low-voltage filter capacitors so far since I CANNOT find something that will physically fit the high voltage rail side. Typically I buy from Mouser. Any tips?
Here's the full board:
I applied the current source mod:
The casualties:
I don't think Dan Mattis has output connector kits for the M1 like he does for the M2 and M2A. I might try to create replacements of my own to replace the stock, substandard speaker cable connectors. I need proper banana or spade connectors.
I just checked his website and it looks like that is in progress! Also he's working on a beefier power supply board. Cool stuff.
ajfink
Member
Hopefully I'll have both in-hand over the next few weeks. Stay tuned!