• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Kenwood Basic M1 Power Amplifier Restoraton/Upgrade

Hello. I have problem with my Basic M1. I have a buzzling sound in right channel. I'v done restoration point to point of this thread. It helps for 2-3 days. Then i replace ralay with new one. Nothing change. What i can do now ? Sorry for my poor english.
 
Buzzing in right channel or could it be described more as a hum?

Does it increase in volume when you increase the volume knob of whatever preamp you're using?

Is the buzzing present with no signal at the inputs, in other words, with only the amp powered on and nothing else?

Have you checked the solder joints and ground wire connections?

Especially look at the power supply... capacitors, rectifier diodes, zener diodes, etc. you may need to take voltage measurements comparing the good Left channel to the buzzing Right channel and see where the two diverge.

It might be better to start your own thread about this issue instead of adding on to this one though.
 
I'm using Pioneer VSX D1011 as a preamp. I put also my smartphone and same situation. It is loud poping when I power on amplifier. When music is playing sound is disorted and I'm hearing static noise. I was thinking this is right thread. In left channel I have 35mV on right something about 40-50 mV DC offset. This weekend I'm gonna do other measurments.
 
I replaced differential pair transistors and DC offset in both chanells is 35mV. The distortion was caused by a missing 100k resistors at input.
 
The embedded Photobucket pictures can be viewed with a Chrome Extension or a Firefox Add-on.

I have noticed that at different times one or the other workaround will stop working; currently, at the time of writing, both workarounds allow the pictures to be viewed.
 
Hi Leestereo.

I always enjoy reading all your great contributions.
Thank you very much for sharing your knowledge.

I am in the process of upgrade my basic M-1 after having done my Basic C-1 according to your instructions with great results.

I noticed in your post #13 you recommend to change C75-78 to 100uf but I can not find any Nichicon PW in 8-10 mm.
After viewing all caps options and choosing a Panasonic FC (10 mm.) I see in the first photo of the post # 3 a cap of 47 uf at the C75 position. Is this value correct and text is wrong?
 
Hi acmmty,

You are correct, the stock C75-C78 capacitors were replaced with 47µF/100V low ESR types as seen the picture in post #13 (the text is incorrect).

Also note that in subsequent M1 restorations that have been done since this original post, the following additional components were also replaced/upgraded: the C99-C102 ceramic capacitors were replaced with same value (100pF) C0G types; R61-R64 on which C99-C102 are installed were replaced with 332 ohm metal film types; C15/C16 and C19/C20 were upgraded to C0G types, and R21/R22, R25/R26 and R43/R44 were upgraded to equivalent metal film types.
 
Leestereo, Thank you very much for the information.

My amp has 27k in R43 and R44 but the service manual says RN (Metal film) 5.6k
I know that some manuals have errors or version changes. In these cases the correct values are those currently installed.
But, In addition they are not like yours or those of jheu02 "Ugly Betty" thread. Yours look like films capacitors coincidentally marking 273 wile in my amp are like 1% 1/8wts resistors.

Are those orange parts resistors or capacitors?
Is 27kΩ the correct value?

I just bought this Basic M-1 and don't know about its history but the amp looks all original, it seems nobody has been inside and everything works fine. I am amazed to see that all the original caps are in good shape (Cs, ESR, Ɵ, Q and D, 1Khz) some better than the new ones.

Thank you

PD Sorry for my English
 
Last edited:
Thank you pictures work fine. What is value of resistors R21/22 and R25/26 ? There are missing at parts list in service manual. C15/16 can be 2,2pF ?
 
Last edited:
Hi mateoJazz,

Another error or change in the diagram!
R21 R22: The schematic diagram that I have says 200Ω but my amp have 1kΩ installed and photos from here confirm this.
See what is installed on your equipment and install the same value.

R25 R26: 56KΩ

I found a manual with better resolution here:
http://kenwood.pytalhost.eu/BasicM1s/

Greetings from Mexico...
 
Hi acmmty
Thanks for better manual. At the moment I'm just gathering as much information as I can so later I can make one order with all the needed parts.
 
acmmty said:
...My amp has 27k in R43 and R44 but the service manual says RN 5.6k (I don't know what RN means. Military?)
I know that some manuals have errors or version changes. In these cases the correct values are those currently installed.
But, In addition they are not like yours or those of jheu02 "Ugly Betty" thread. Yours look like films capacitors coincidentally marking 273 wile in my amp are like 1% 1/8wts resistors.
Are those orange parts resistors or capacitors?
Is 27kΩ the correct value?
I just bought this Basic M-1 and don't know about its history but the amp looks all original, it seems nobody has been inside and everything works fine. I am amazed to see that all the original caps are in good shape (Cs, ESR, Ɵ, Q and D, 1Khz) some better than the new ones....
Click to expand...

There may have been production line changes during the manufacturing of the M1 that could explain the different components installed for R43/R44. If your M1 has 27kohm 1% metal film resistors installed from the factory, there is no need to replace. In the M1 that is the subject of this thread, 0.047µF fiim capacitors are installed in R43/R44; generally, replace with what is installed in the unit you are working on.
 
I have a Basic M1 and the right channel is breaking up severely on both A and B. I have cleaned all of the speaker output contacts and the line in contacts with Deoxit. What should I look for next?
 
Found it!
Wiggling Q15 brings makes the speaker cut in and out (its actually the left channel not the right as I said above).

Hopefully just a cold solder joint....
 
The speaker protect relay is a weak point and an exact replacement is no longer available to my knowledge. There is a workaround to it to replace it, but you may first try to clean the contacts. You may also have cracked solder joints that need reflowed. Get nice bright light and look closely (under magnification) at the trace-side of the board, especially focusing on the output transistors, drivers and large resistors. Probably best to start your own thread so this one doesn't get cluttered up.

The image below is courtesy of patfont (hope you don't mind) in his Basic C2 restoration thread.

IMG_3701-L.jpg
 
Last edited:
Yep! Got back panel off and 2 pins had bad solder joints. I just re-flowed them and we are in business!
 
after a little messing around I found Q17 also has bad solder joints. Guess I better start looking at ALL solder joints.

Wow, I found 3 more Q26, Q28, Q62
 
Last edited:
You must log in or register to reply here.
Back
Top Bottom