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PostPosted: Sun Jul 02, 2017 8:15 pm 
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Location: Layton, UT, US
Brooster wrote:
There is only one choke.(my bad) The value is around 1H @ 200ma. The choke is pretty important for the power supply and its too small. For a couple of reasons, one is size and the other is cost.
I think there would be more benefit in upping the inductance value of the choke rather than changing out the rectifier. Though if there was more room it would be nice to do both.

The whole power supply is a little problematic. The circuit is not not running anywhere near true class A as the cost and size of the associated parts simply wont work. This is a cathode biased, ultralinear, amp running in A/B. One of the main reasons these things run so hot is that the power supply is being pushed to the max. In absolute terms it is woefully underpowered. We have talked about this before but its a problem you cant really get around.

After finding out a little more about the circuit and what is actually involved in trying to improve the power supply I dont think I am going to do anything more to my 301. Ive sent a transformer of to Cinemag to find out if it can be improved, but thats all. The next step for me( just my novice opinion) would be to totally gut the power supply and start basically from scratch in a different enclosure. The basic circuit must be pretty darned good to sound the way it does running on a shoestring .

Thats my analysis for what its worth. I think the choke is more important than the rectifier at this stage, but really the whole power supply needs some help. The problem with the choke is that higher inductance units running at that current rating start to get much larger than what is available for space in the chassis.


If this truly is a class A/B amp that might explain why I get such a performance increase and less distortion by implementing a power factor correcting device such as my Furman PF-PRO conditioner, just a thought. Might be why Garry offers the MP-T1 in malaysia that also has power factor correction built in.


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PostPosted: Sun Jul 02, 2017 9:10 pm 
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Location: Chino Hills, CA, US
Stevedlu wrote:
I am officially calling it quits on modding this amp. I believe I have maximized the most performance possible within reason. Here is a list of my changes in order of impact.
8< ... snip... >8
I want to thank Lethargy for starting this thread and Peter for providing the initial mods and being our guiding Wizard.
The 301 was already a fantastic sounding amp and I can not describe how amazing it sounds now. Learned a lot and it certainly has been fun.


Thanks Stevedlu, I thought I'm done as well but then you added those C8 and crossover caps mods. So I'm gonna have to try those :mrgreen:

I have acquired a used Vincent SV226Mk2 hybrid amp (monstrously big!) to relieve my MP301MK3 for daily background music duties. So I'm focused right now in rolling 12AX7 tubes. This amp has outstanding power supply and drives my speakers with ease; however, it still cannot touch the imaging, clarity and detail my MP301 delivers :lol:. It looks like will probably replacing the stock wima caps with Mdorf equivalents.

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PostPosted: Sun Jul 02, 2017 9:35 pm 
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Location: Calgary, AB, CA
[If this truly is a class A/B amp that might explain why I get such a performance increase and less distortion by implementing a power factor correcting device such as my Furman PF-PRO conditioner, just a thought. Might be why Garry offers the MP-T1 in malaysia that also has power factor correction built in.]

The Furman probably is helping the 301 but not necessarily because it is A/B. Its more likely due to the quality of the power supply rather than the type of circuit.


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PostPosted: Sun Jul 02, 2017 10:22 pm 
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Quote:
Thanks Stevedlu, I thought I'm done as well but then you added those C8 and crossover caps mods. So I'm gonna have to try those


3USD for 2 caps on EBAY right now

http://www.ebay.com/itm/2PCs-Panasonic-CAPACITOR-150UF-150MF-250V-RADIAL-REPLACING-FOR-200V-160V-100V-/151625672818?epid=1101592986&hash=item234d982872:g:zVMAAOSw7aBVDKWI

You can't beat that, and the best part is that the sound change is immediate. No burning in like coupling capacitors. Make sure to get these EE series caps. I tried several other brands with no change what so ever. The high frequency ripple current is what sets these apart from the others.


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PostPosted: Mon Jul 03, 2017 11:48 pm 
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Location: Chino Hills, CA, US
Thanks Steve, I got a pair from another seller already shipped. I'm afraid I'll have to fight with the board out again due to those Mdorf supremes on the side :P


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PostPosted: Tue Jul 04, 2017 11:52 am 
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Hahaha. Such a pain. I removed one of the wire clips for AC going to the Power switch. Makes removing the board sooo much easier.


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PostPosted: Thu Jul 06, 2017 3:50 pm 
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Location: Dawsonville, GA, US
I replaced the 4 caps, switched out the top ones and put one i took out and replaced the one under. It was a tight fit because the leads were not the same width as the holes.
Did the cap and resister in parallel. Blows the fuse.
Removed the cap/resister and replaced the wire. Blows the fuse. Took it back apart and i cant find any solder bridges, any issues.
I marked every wire, took pictures too. So sick to my stomach i can hardly think.
Gives a little buzz and blows the fuses.

Fuses are 2 amp, 250 volt.


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PostPosted: Thu Jul 06, 2017 3:58 pm 
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Have a look and make sure the polarization of the capacitors is correct. If put in backwards it'll act like a short to the power supply. Other than that the single one on the component side could short if the case of the capacitor touched the traces.

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PostPosted: Thu Jul 06, 2017 4:19 pm 
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petersch wrote:
Have a look and make sure the polarization of the capacitors is correct. If put in backwards it'll act like a short to the power supply. Other than that the single one on the component side could short if the case of the capacitor touched the traces.



Well poo...
the 2 big ones up top i have in backwards. I took pictures of the bottom open, but failed to notice the polarity of the ones up top.

The cap on the component side is slightly off the board because the cap i replace it with from up top has leads which are slightly smaller than the holes in the board. so i had to kind of bend them outward a bit.

But i dont see a a polarity marking for the Mundorf Supreme S/O

I have one fuse left...


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PostPosted: Thu Jul 06, 2017 4:32 pm 
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the Mundorf's are not polarized, you can put them in either way without worrying. you might not have had to replace cap on the bottom. I believe the current MK3 releases have 180uf green Nichicon caps that are the same value as the top two that you removed.


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PostPosted: Thu Jul 06, 2017 5:24 pm 
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Stevedlu wrote:
the Mundorf's are not polarized, you can put them in either way without worrying. you might not have had to replace cap on the bottom. I believe the current MK3 releases have 180uf green Nichicon caps that are the same value as the top two that you removed.


Its literally been since 2000 i have done component level work. I even got to use my solder sucker and desoldering braid!
Blew those fuses and i was totally dumbfounded. Ate dinner quick, left and went back to it. Family neglected. :oops: lol
Totally forgot about polarity on caps. As soon as i read that suggestion......"oh Sh--t!. I totally forgot!"
Thank you!!!!


I bought my amp on Chinese New Years of 2015. Board says 2013. It has the blue 450V 150uf. Swapped it.


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PostPosted: Thu Jul 06, 2017 9:52 pm 
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Were you successful?

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PostPosted: Fri Jul 07, 2017 6:05 am 
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petersch wrote:
Were you successful?


Yes, late last night i got everything back together and was able to spin a record.
No lie, there is a big difference. Especially in the upper ranges which my ears used to hear as blended together and bright. Way more detail, depth and separation.
Midrange is still nice and the bass is crisper, not as muddy. I havnt played a CD or FLAC yet but i will later today.
Thanks again for the help too!
I did not add the filter back to the ground. I will later.


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PostPosted: Fri Jul 07, 2017 7:48 am 
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petersch wrote:
Were you successful?


Put the filter on the ground. Its so quiet i was wondering if something had went wrong!
So far so good, sounds good! Instruments are really forward and separate. Singing seems to be a bit more in the background. I do have to turn up the volume alot more to get to the volume i used to set it at.
I will play it on repeat with a CD and let the caps settle in than start rolling tubes.

What does that single cap on the component side of the board do? My original was 450V 150uf


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PostPosted: Sat Jul 08, 2017 8:42 am 
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I believe it is the input cap going to the choke, I could be wrong. Good to hear you are enjoying your modded 301. Which size Mdorf's did you end up going with?


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