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Kenwood Basic M1 Power Amplifier Restoraton/Upgrade

HPMguy said:
I have a KM-106, and the schematic looks very very close
Click to expand...

I have a KM209 and know the 208 looks very similar electrically. I thought about adding a current source/sink like @Leestereo did to the M1 on page 1 but so far I only replaced the input caps to films.

my guess the KM-205-9 are very similar electrically with only minor meter/faceplate changes. The KM-10x are probably similar.

I think ajfink was planning (or did) an update to the KM-10x series. Maybe he is enjoying his m2 too much.
 
I will eventually re-cap them, they are old enough to be having problems with small value caps. Film as coupling caps for sure, in both amp and pre-amp.
 
i found this. we can take our conversations on the KM-xxx over there and not cr*p on this thread.
 
Hello everybody. Today I decided to change all the resistors in the signal path with some with metal film at C1 and M1. If anyone has done that please some opinion. Regards
 
IME, upgrading the resistors in the feedback loops had the most impact on the sound performance. And although worth doing, it was a relatively subtle improvement.
 
Hello Basic M1 owners,

I’ve got my M1 modded as per this thread, it worked great. I recently bought a eversolo dac/streamer with a 2V max line output. I think you get it, it seems like I’ve pushed it too much and fried something on the M1…
what I hear: after few minutes playing at mid volume and even lower, the mid/high frequencies saturates. I hear it on the speakers L+R speaker tweeter.
I do not have that issue with another amplifier connected to the speakers even pushing it, with the same source. Tweeter failure is ruled out according to me.
I also looked at the back of circuit to detect bad solder, rectified few, despite none failed as whenever I did the overhaul 2 years back. No improvement, even worst result.

Any idea where to start troubleshooting ?

Reducing the eversolo ouput line voltage will be done anyway. That’s another stuff.

Thanks
 
Colin111 said:
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,
Click to expand...
Hello Colin111

Same problem, haven't tried to source parts yet.
Only reason I tackled my C1 upgrade was due to AntiSkates BOM list.
Which I did exactly as he instructed and copied and pasted the appropriate list into Mousers order form and it automatically populated the list. Then contacted them they filled the list with only one back ordered component, which I was able to then find at DigiKey, simple.

Going through the build was also easier for this rank amateur because of the component bags from Mouser and using AntiSkates BOM list and Mousers supplied order list, simple like "Paint By Numbers" so to speak.


Did you ever get a BOM list or where sent one?

With the added confusion regarding Dan Mattis DRM Audio Kit.
Is that implemented with Lee Stereo (Ben) pictures and components in this thread and I'm not understanding it?

Long winded and maybe confusing, bottom line .

Want to do this upgrade on the M1, just feel comfortable starting project with the very useful BOM list.


thank you
 
chazplt said:
Hello Colin111

Same problem, haven't tried to source parts yet.
Only reason I tackled my C1 upgrade was due to AntiSkates BOM list.
Which I did exactly as he instructed and copied and pasted the appropriate list into Mousers order form and it automatically populated the list. Then contacted them they filled the list with only one back ordered component, which I was able to then find at DigiKey, simple.

Going through the build was also easier for this rank amateur because of the component bags from Mouser and using AntiSkates BOM list and Mousers supplied order list, simple like "Paint By Numbers" so to speak.


Did you ever get a BOM list or where sent one?

With the added confusion regarding Dan Mattis DRM Audio Kit.
Is that implemented with Lee Stereo (Ben) pictures and components in this thread and I'm not understanding it?

Long winded and maybe confusing, bottom line .

Want to do this upgrade on the M1, just feel comfortable starting project with the very useful BOM list.


thank you
Click to expand...
Anyone?
 
Hello everyone, I have a problem with a channel that cuts out every day on my Kenwood M1 amplifier. Any ideas, thanks
 
Could be any number of reasons....bad relay, weak solder joints, bad transistor....

Does it happen after a certain time, is the amp hot when it happens, are you playing it loud?

Probably best to start your own thread in the Kenwood sub forum vs tacking onto this restoration thread..
 
Hello everyone, I can replace all polarized capacitors under 1 micro with non-polarized capacitors of the same value in a Kenwood GE1100 equalizer.
THANK YOU
 
Not sure if this is a statement or a question, as I believe English may not be your first language. It’s really better to start your own thread, especially since this thread is about the Basic M1 amplifier, not a graphic equalizer. However, in general, you can replace polarized capacitors with non-polarized, but not the other way around UNLESS you can confirm that there definitely is no chance of a reverse voltage would a polarized capacitors be used. Film caps are NP by design and are a good choice to replace small value electrolytics.
 
I typically replace all electrolytic caps 4.7uF or less with film caps (Wima MKS or Kemet 8R2 series). In that equalizer it's likely there are a lot of them in the signal path, and film is better than electrolytic caps there.

Do not replace ceramic caps unless you suspect they have actually failed.
 
Hi everyone,

I'm currently restoring a Kenwood Basic M1 and would like to confirm a crucial detail regarding the bias adjustment.

I replaced both VR3 and VR4 with the same recommended trimmers (Piher PT10LV 500Ω, like Leestereo suggested).
However, I noticed there is no continuity between VR3 and R113, nor between VR4 and R114.
I also measured between the outer legs of R113 and VR3, and between R114 and VR4: still no continuity.

Following an accidental short, the left output stage was damaged. I had to replace the full bank of left-side transistors. AS well, I've changed R113 and R114, which I replaced with new 0.22Ω 5W wirewound resistors.

Despite all this, I still cannot measure anything across these resistors when powering on the amp, so I cannot set the bias correctly.

Before going any further, could someone confirm:
Is it safe and correct to manually bridge VR3 to R113 and VR4 to R114 using a small wire?
This seems necessary to complete the bias adjustment path, but I want to be 100% sure before doing it.


Thanks a lot in advance for your help and insights!

Best regards from France
 
I suspect you will blow something up doing that. Any connection between the bias control trimmers and the outputs is going through a dozen or so transistors, you won't see continuity.

The bias trimmers adjust the voltage/current between the NPN and PNP "sides" of the amplifier channel to give a small current flow through the output pairs. this keeps the transistors "on" at a very low level to prevent a "notch" in the signal due to switching time for transistors.

No voltage at the output emitter resistors would indicate to me you have either a power supply problem or an open circuit somewhere. Note you must measure across the dual resistor. (from the NPN emitter to the PNP emitter). Those emitter resistors are dual, with three legs. Center leg is output to speakers.

With the unit on a dim bulb tester, check the voltages marked on the schematic and verify you have an intact circuit before doing any other changes. On the dim bulb the rails will have low voltage, but the transistors should otherwise have the correct values. Insulate your probe except for the very tip to avoid shorts.
 
Oh, almost forgot -- check all the current limiter transistors. A shorted output usually takes them out too, and if they are shorted they will ground the input. Took me a while to find this issue on another similar amp.
 
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