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PostPosted: Mon Jan 02, 2017 2:41 pm 
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Location: london, ON, CA
I have seen references on this site and elsewhere to mods to reduce hum in the Musical Paradise MP-301, but no specific instructions.

There is a definite hum with mine that gets louder as the volume knob is turned up. A Canadian user on Audiokarma named hypertone (Is that anyone here?) said a shielded cable from the input jacks was helpful. He also said he got worthwhile improvement to noise levels and sound quality by removing the cathode bypass caps in the preamp. I would be interested in any further input anybody can provide on these mods, or any others.

Also is there anything to be gained through capacitor upgrades?

Thanks in advance. And obviously, I absolve everyone in advance for any damage I might do to my amp or myself as a result of any mods suggested in this thread, as should anyone else reading it. :D


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PostPosted: Mon Jan 02, 2017 3:16 pm 
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Sorry not much help, but the 501 may have the same issue.
https://www.canuckaudiomart.com/forum/viewtopic.php?f=9&t=36946&start=0

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Ohms

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PostPosted: Mon Jan 02, 2017 3:34 pm 
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Which version is your MP-301 ?


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PostPosted: Mon Jan 02, 2017 3:39 pm 
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I had the Mk3 and it was dead quiet, even with 94db speakers.


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PostPosted: Mon Jan 02, 2017 3:48 pm 
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Lethargy, are you on headphones or speakers?

Can't recall what your pre-amp tubes are but RCA 5693 red metal are nice and quiet vs. many others. I tried a bunch and the 5693 were the ticket for me.

If you are listening through headphones, low impedance ones will produce a noticeable hum. Garry offers a 75ohm impedance adapter cable that should solve the hum.


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PostPosted: Mon Jan 02, 2017 3:52 pm 
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akanrg wrote:
Which version is your MP-301 ?


Sorry, I should have specified up front. It's the Mk3

akanrg wrote:
Lethargy, are you on headphones or speakers?


Both. I have a range of headphones. The hum is worst on the the Grados and very hard to notice on the 600 ohm AKGs. The hum isn't horrible in any circumstance (except with the Ken-Rad 6HS7 tubes that came with the amp, which I think must be bad) but it is loud enough to be irritating.


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PostPosted: Mon Jan 02, 2017 4:27 pm 
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I have the 501 and its dead quiet.
Maybe a ground issue or power source problem...?


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PostPosted: Tue Jan 03, 2017 5:54 pm 
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I've done a bit of tweaking to the MP301 all 3 versions. To my ears and from experience the worst version seems to be the MK3 for noise and poor performance.

I've done some simple things that have improved the performance and had a major impact on the hum issues. First off, on the original 6V6 version the filter capacitors were 390uF @ 450V, the later versions cheaped out here and went to 180uF @ 450V. It's a no brainer to restore the filtering back to 390uF. Digi-Key has them under part number 1189-2631-ND, order 2. Once you replace the filters take one of the old 180uF you removed and upgrade the other large black capacitor (120uF @450v) on the inside (circled in red). This had a major impact on hum, slam and power reserve. Next up "Lethargy" touched on it, the driver tube Cathode bypass capacitors cause the drivers to clip and also provide too much gain for the next stage, get a pair of good snips and remove C6 both circled in red as well. This will tame the response curve a bit and lessen the drive enough to eliminate the horrible overdriving of the output tubes. Next up, the IEC grounding to the chassis is less than spectacular, remove the wire and clean the crud, paint and otherwise and re-install with a star washer, this should solve the AC noise. In my case I had a ground loop and found that the 301 MK3 was extremely sensitive to them. I removed the ground wire and installed a 10 Ohm,2 watt resistor in line with the ground wire and paralleled the resistor with a 0.1uF Orange drop capacitor, noise is 100% gone.

**** For safety's sake before you work on any tube amp, please make sure that the large black filter capacitors have been discharged completely or else you will have an extremely nasty burn coming courtesy of 400+ DC volts. TUBE AMPS ARE NOT TOYS!! Please respect the high voltage coming from within.

As a side note, I found after the mods that the Chinese V1 & V2 aren't too bad after all! I coupled them up with JJ EL34's and the 301 sounds simply excellent, better than the RCA 6SJ7 Metals I had installed before. One of these days I'll be upgrading the internal wiring and getting rid of the crappy rubber feet that couple all the hum from the transformers to the table and otherwise.

Have fun!


Attachments:
File comment: Leftover capacitors when you are done.
DSC03123.jpg
DSC03123.jpg [ 258.93 KiB | Viewed 7995 times ]
File comment: Remove the 2 small capacitors (circled) and replace the large black 120uf (also circled) with a 180uF you took out of the top.
DSC03119.jpg
DSC03119.jpg [ 338.31 KiB | Viewed 7995 times ]
File comment: Large Filters Replaced !!
DSC03122.jpg
DSC03122.jpg [ 231.17 KiB | Viewed 7995 times ]
File comment: Digi-key 380uF @ 450V Capacitors
DSC03124.jpg
DSC03124.jpg [ 207.34 KiB | Viewed 7995 times ]
File comment: The finished product. Sit back and enjoy a 200% improvement in performance and sound quality.
DSC03027.jpg
DSC03027.jpg [ 210.77 KiB | Viewed 8021 times ]

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Last edited by petersch on Tue Jan 03, 2017 6:38 pm, edited 1 time in total.
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PostPosted: Tue Jan 03, 2017 6:36 pm 
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Location: london, ON, CA
Excellent! Thank you Peter. That's exactly the information I was looking for.


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PostPosted: Sun Jan 08, 2017 3:40 pm 
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Thank you Peter for the info on the upgrades to the MP-301 amp.
I have a version 2 and would like to make these changes on my amp to improve things.
I read that you said the changes would apply to all 3 versions of the amp.

Is the upgrade to the higher value caps easily accessable for soldering of the new caps once the bottom cover is removed?
I would like to avoid having to remove a circuit board, and all that it would involve.

Although not an upgrade, I have just recently repaired my amp which had distortion and finally no sound on one channel.
I'll post my fix in this thread, some may find it useful in the future.


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PostPosted: Sun Jan 08, 2017 5:05 pm 
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petersch wrote:
First off, on the original 6V6 version the filter capacitors were 390uF @ 450V, the later versions cheaped out here and went to 180uF @ 450V. It's a no brainer to restore the filtering back to 390uF. Digi-Key has them under part number 1189-2631-ND, order 2. Once you replace the filters take one of the old 180uF you removed and upgrade the other large black capacitor (120uF @450v) on the inside (circled in red). This had a major impact on hum, slam and power reserve.


Noob mod questions here. (the extent of modding I have done to a piece of audio gear was to re-solder a cold joint on my Mapletree headphone amp)
These capacitor changes, are they "plug and play", like removing a tube from its socket? If not, how does one remove and re-attach these capacitors?


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PostPosted: Sun Jan 08, 2017 5:12 pm 
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devon58 wrote:
petersch wrote:
First off, on the original 6V6 version the filter capacitors were 390uF @ 450V, the later versions cheaped out here and went to 180uF @ 450V. It's a no brainer to restore the filtering back to 390uF. Digi-Key has them under part number 1189-2631-ND, order 2. Once you replace the filters take one of the old 180uF you removed and upgrade the other large black capacitor (120uF @450v) on the inside (circled in red). This had a major impact on hum, slam and power reserve.


Noob mod questions here. (the extent of modding I have done to a piece of audio gear was to re-solder a cold joint on my Mapletree headphone amp)
These capacitor changes, are they "plug and play", like removing a tube from its socket? If not, how does one remove and re-attach these capacitors?


You are playing with high voltages here; clearly enough to curl your hair permanently. First thing first, you MUST ensure that the high voltage caps are fully discharged before proceeding. Next you must unsolder the old caps and replacing/re-soldering them with the new ones while paying special attention to the polarity.


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PostPosted: Sun Jan 08, 2017 5:29 pm 
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bikenut wrote:
Thank you Peter for the info on the upgrades to the MP-301 amp.
I have a version 2 and would like to make these changes on my amp to improve things.
I read that you said the changes would apply to all 3 versions of the amp.


The component changes only apply to the Mk2 and 3, the original version only needs the (V1 & V2) cathode resistors to be snipped.

bikenut wrote:
Is the upgrade to the higher value caps easily accessible for soldering of the new caps once the bottom cover is removed?
I would like to avoid having to remove a circuit board, and all that it would involve.


It requires removal of the main amp PC Board with entails removing all the tubes, board wiring and a choke, it's involved but not hard by any means. Just take a snapshot of the guts before you start so that you have a reference where everything goes.

bikenut wrote:
Although not an upgrade, I have just recently repaired my amp which had distortion and finally no sound on one channel.
I'll post my fix in this thread, some may find it useful in the future.


Well done! Thats the beauty of tube amps, they are usually repaired without much fanfare or experience. Please do let us know what you did as one of these days there will be others in the same predicament and it's always great to have an idea on where to start.

To any other folks as OBI mentioned, these amplifiers contain high voltages (HV) that are lethal and can cause serious injury. Please utilize caution when dealing with HV Capacitors as they can hold a charge for days at a time!! If soldering and HV work is not your forte' please ask for assistance. Myself, I'm more than willing to assist locally and have been doing these types mods for a long time. They were still teaching tube theory when I was in school so I've learned to respect HV and have been zapped many times as a reminder of what not to touch!

I just noticed that MP has some Refurbs going for about $100 less than retail. Here's a chance to grab a deal on a great little amp on the cheap! http://www.musicalparadise.ca/store/index.php?route=product/product&path=59&product_id=84

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PostPosted: Mon Jan 09, 2017 4:10 pm 
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This is not an upgrade, but describes a fix I had to perform. I did not want to send the amp in for service.

I own version 2 of the MP-301 amp. I'm not sure if this applies to the other versions of the amp.
The right channel started having distortion while playing, and finally went dead.
With a little troubleshooting help from Garry at Musical Paradise it was determined that a resistor and capacitor for the channel had gone bad.
He thought I had a bad tube that caused the problem, but the tubes tested good on my tube tester.

Garry offered to replace the parts for free if I paid the shipping cost, good deal.
I only needed one of each, but he supplied 2 of each, so I replaced the parts on both channels. New parts on both channels, sounded ok to me.

Garry at MP did not have the parts in stock and they were shipped on a slow boat from China, took over a month to arrive. When they did show up, the resistors were the wrong ones. I searched around and found probably better quality ones at Parts Connection and got them within a day or two. In the future I will just source the parts locally if they are generic standard parts, live and learn.

Bottom of amp with cover removed.
Cap that needed replacing is circled, I did both beside each other.
A bit tricky and tight but can be soldered without removing the circuit board.
Capacitor = Rifa PHE420 630v 0.22uf
Attachment:
inside cap.jpg
inside cap.jpg [ 150.94 KiB | Viewed 7817 times ]


Resistor locations circled in red, left and right.
Locations on board are R7 and R7A I believe.
Original resistors = Dale 301ohm 5w 1% RS-5
Garry requested I check connector in centre to ensure it was on tight, not the source of the problem.
These resistors were easy to access and remove, and solder in new ones.
Attachment:
mk.png
mk.png [ 546.84 KiB | Viewed 7817 times ]


Picture showing the wrong resistor shipped from China and the new one sourced from Parts Connection. I was a bit taken back with the size difference but after confirming things with Garry I went ahead.
New resistors are Mills make = 300 ohm, 5W, 1%, wire wound
Parts Connection part number = MILLS-66670
Attachment:
IMG_0923.JPG
IMG_0923.JPG [ 41.28 KiB | Viewed 7817 times ]


In the end, an easy fix and pretty cheap.
Amp works fine again.
This may help someone in the future.


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PostPosted: Fri Jan 13, 2017 12:40 pm 
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Location: Ardrosssan, AB, CA
petersch wrote:
Myself, I'm more than willing to assist locally and have been doing these types mods for a long time.


Hi Peter,

Based on your gracious offer, I sent you a PM for some DIY assistance but not sure if you have seen the message. Knowing you are active on this thread, thought I would try to reach out here to see if I can get in contact with you.

Thanks!


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