K501 vs K12M

[jmillerdoc]

For a while I thought these 2 amps were the same amp! As I got down to ordering one of them I was looking at some mods at www.diyaudioprojects.com and realized they indeed were different. Now I am in a delimma....which to choose! There appears to be more well documented mods on the K12 at that website but I am still uncertain. Can anybody point me in the right direction here? They appear to be very similar but I can tell at this point. Both are at the same pricepoint. I am leaning towards the K12 at this point though. Also, can anybody tell me what the minimun voltage rating can be used for the coupling caps, I have some (10) Wima's but I think they are rated at 160v, not sure if they will work here. To date I have not been able to find a schematic for either of these amps, help here would be great too, that way when I get down to ordering I can purchase the upgrades I want to make at the same time.
Thanks to all!
Jeff M.
Lawton, USA

[jmillerdoc]

Also, almost forgot, are the coupling caps for both of these the same? 0.22uF? And while I'm back asking questions, has anybody tried to replace all of the carbon comps with metal film. My understanding from building chipamps (far more familiar with these, tubes are relatively new for me) is metal film resistors are less "noisy". I would think that would hold true for the tube amps as well, but you never know what can change between the two.
I also had thoughts of "choking the power supply" any thoughts there?
Thanks again,
Jeff M.
Lawton, OK

[ambience exists]

I built a version of the k12, probably pretty similar to the one you are thinking of. I believe that the caps you have are too low in voltage rating. Choking the power supply is probably a good idea, although I never got around to doing it. Make sure that your speakers are at least 90 something db/1 watt/1 meter as this amp has some headroom issues. I would lean towards above 94. It will play with a heavier load but the amp will quickly lose its muscle in the bass department and just not sound too good.

I feel as though I jumped the gun a little on 'improvements' and jumped into modding the amp too quickly. If I could do it all over again I would let the amp just BE for a while and break in- just play music on the thing and don't worry about whether it is 'audiophillic grade' or whatnot. Run your source right into the PCB mounted RCA jacks using the included volume pot. Then, once the flavor of the amp is absorbed and you feel like you want to modify (and by all means: MODIFY!) then go to hell on it! So that means not making the parts completely unable to be removed from the board- especially coupling caps. I made that mistake and messed up some of the PCB plating taking them off.

I think that the amp is a nice rewarding project especially for a first time tube effort, and you may be very happily surprised with the result!

Good Luck!

[discomonkey]

Originally posted by ambience exists

I feel as though I jumped the gun a little on 'improvements' and jumped into modding the amp too quickly. If I could do it all over again I would let the amp just BE for a while and break in- just play music on the thing and don't worry about whether it is 'audiophillic grade' or whatnot. Run your source right into the PCB mounted RCA jacks using the included volume pot. Then, once the flavor of the amp is absorbed and you feel like you want to modify (and by all means: MODIFY!) then go to hell on it! So that means not making the parts completely unable to be removed from the board- especially coupling caps. I made that mistake and messed up some of the PCB plating taking them off.

I think that the amp is a nice rewarding project especially for a first time tube effort, and you may be very happily surprised with the result!

Good Luck!

I agree... I built the 12G a while back and built it up with all the mods and "improvements" that I could find. Voltsecond mods, attenuator, multiple inputs, etc. If I had to do it all over again... I would have just built it up stock - maybe with the upgraded coupling caps (p.s. I used 400V auricaps) but not much more. It is what it is... a basic, beginner amp and not much more.

you will most likely move up to a more "high-end" amp (tubelabse, etc.) and the money you save on trying to get a 12G up to audiophile grade will come in handy there.

that being said, it's a pretty good office amp right now... with some high efficiency bookshelf speakers, it does quite a good job.

[Soonerorlater]

Hi all,
I built the K502 version. (The K501 I believe is a mono block version of the K502 ) It was built entirely of stock parts except I had to use a mains step-up transformer to cope with our UK 240V power supply. From the start it was quiet with no audible hisses or hums coming from it unless you put your ear up close to the speakers.( monitor audio bronze ).Volume levels were acceptable.Compared to my Thompson SS though it didn't quite make the grade, anyway I was happy it worked. After a week or so of constant listening it did improve (a lot!) I guess it had burnt itself in. Now that I had a working amp I went ahead and did all the usual mods on it ( apart from using a ccs ) and I now prefer it to my ss amp.

Getting back to the thread, I still have the schematic for the K502 and also the K12G or K12M ( I'm not sure which) There may be copyright reasons for posting them here so please feel free to Email me at

williammassey@soonerorlater.fsnet.co.uk