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PostPosted: Wed May 09, 2018 11:29 am 
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Location: Denver, CO, US
Which ones of these are the right slo-blo fuse?

https://www.digikey.com/products/en/cir ... ageSize=25

Seems there are several variations of the 1.6a 250v, being that some are "breaking capacity" of 35a, 100a, or 150a?


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PostPosted: Sat May 12, 2018 9:50 am 
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Location: Calgary, AB, CA
Your upstream fuse is most likely 15A. So you should be fine with 35A for breaking capacity, as the 301 fuse even in dire circumstances should not ever see anything more than 15A


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PostPosted: Sat May 12, 2018 11:26 am 
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Ah. Thanks!


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PostPosted: Sat May 12, 2018 3:32 pm 
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dlodewyk wrote:
devon58 wrote:
Brooster wrote:
I had never come across this before. If you've read it already my apologies.
Not sure what its worth, but it does relate directly to the 301 MK 3
http://wallofsound.ca/audioreviews/ampl ... store-com/

Yep, that review is the reason I tried the Tung-Sol 7581-A, and I’m glad I did.
It’s a great tube in the MP301, bringing a blend of authority and musicality that bests the KT88, EL34, and 5881 that I have tried in my amp.



Thank you for the great link !

I have got a matched pair of the Tung-Sol 7581-A tubes on the way!


Did your 7581's arrive yet ? Any impressions ???? I'm getting itchy to try some new tubes in my 301.

So far I have rolled, Stock EL34, Pvsane EL34, JJ 6L6GC, RCA 1614, (My Favourite power tubes so far) SOVTEK-5881, KEN-RAD 6SH7, (Favourite pre-amp tubes) AND SED-WINGED-C


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PostPosted: Thu May 17, 2018 3:33 pm 
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Location: Calgary, AB, CA
Hey gents,

Finally settled in from moving and have my audio gear mostly setup again. Looking at trying to get on modding this amp while there are some cap sales going on.

As my previous links don't seem to be working, I'll redo them here if you could take a gander if things look correct:

Digikey:
2 x 450MXH470MEFCSN25X60 470µF 450V Aluminum Electrolytic Capacitors Radial
1 x PR02000201009JR500 10 Ohms ±5% 2W Through Hole Resistor Axial
1 x 225P10492XD3 0.1µF Film Capacitor 140V 200V Polyester Radial
2 x EEU-EE2E151 150µF 250V Aluminum Electrolytic Capacitors Radial

Parts Connexion (not 100% on these because of cost...)
4 x Mundorf Capacitor 0.22uF 1000Vdc Supreme SilverGoldOil

I've got a pretty basic soldering iron and higher content silver solder. Anything else I might need to do this correctly?

It was immediately noticeable but I have two other headphone amps at the moment to play with and this sucker hums like no body's business!! Hopefully the Digikey mods will fix that, it's hard to unhear now.


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PostPosted: Thu May 17, 2018 4:17 pm 
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msommers wrote:
It was immediately noticeable but I have two other headphone amps at the moment to play with and this sucker hums like no body's business!! Hopefully the Digikey mods will fix that, it's hard to unhear now.

Hey Matthew,
I found my amp hums unacceptably with either 6SD7GT or 6SH7 preamp tubes.
It is quiet with either 6SJ7GT or the stock 6J8P, go figure.
Good luck with your mods, are you planning to snip the cathode bypass caps?
Cheers,
David


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PostPosted: Sat May 19, 2018 11:39 am 
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Location: Calgary, AB, CA
Pete's power supply mods are essential for the amp. In stock form its pretty compromised, but the residual noise floor can be made dead silent even at max vol.


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PostPosted: Sat May 19, 2018 12:18 pm 
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Location: Calgary, AB, CA
msommers wrote:
Hey gents,

Finally settled in from moving and have my audio gear mostly setup again. Looking at trying to get on modding this amp while there are some cap sales going on.

As my previous links don't seem to be working, I'll redo them here if you could take a gander if things look correct:

Digikey:
2 x 450MXH470MEFCSN25X60 470µF 450V Aluminum Electrolytic Capacitors Radial
1 x PR02000201009JR500 10 Ohms ±5% 2W Through Hole Resistor Axial
1 x 225P10492XD3 0.1µF Film Capacitor 140V 200V Polyester Radial
2 x EEU-EE2E151 150µF 250V Aluminum Electrolytic Capacitors Radial

Parts Connexion (not 100% on these because of cost...)
4 x Mundorf Capacitor 0.22uF 1000Vdc Supreme SilverGoldOil


I've got a pretty basic soldering iron and higher content silver solder. Anything else I might need to do this correctly?

It was immediately noticeable but I have two other headphone amps at the moment to play with and this sucker hums like no body's business!! Hopefully the Digikey mods will fix that, it's hard to unhear now.


I think the parts list is fine. If I could make a recommendation, while the amp is apart, is to also change C7 and C7A and also consider at least 1 bypass on C8 and C8A. The cost is minimal, especially if you are considering the SGO's.
Matthew let me know if you would like to get together sometime.


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PostPosted: Sun May 20, 2018 11:59 am 
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Thanks for the suggestions, Bruce! What would be interesting actually is directly comparing your modded 301 vs. my fairly stock one. After that, it would be more wise to see how much more to spend on this amp in way of output caps (the SGO's are fairly pricey...). I'll PM you about meeting up here soon. The move has been a bit of a clusterf*ck along with starting this new job but things seemed to have settled in here finally!

I believe the EEU-EE21E151 were for the C8/A and snipping the C6. I don't recall the C7/A....I'll have to go back.

Currently, I'm using the Tung-Sol 7581A and black metal JAN CRC-6SJ7 tubes, otherwise it's stock.


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PostPosted: Sun May 20, 2018 2:52 pm 
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Location: Calgary, AB, CA
msommers wrote:
Thanks for the suggestions, Bruce! What would be interesting actually is directly comparing your modded 301 vs. my fairly stock one. After that, it would be more wise to see how much more to spend on this amp in way of output caps (the SGO's are fairly pricey...). I'll PM you about meeting up here soon. The move has been a bit of a clusterf*ck along with starting this new job but things seemed to have settled in here finally!

I believe the EEU-EE21E151 were for the C8/A and snipping the C6. I don't recall the C7/A....I'll have to go back.

Currently, I'm using the Tung-Sol 7581A and black metal JAN CRC-6SJ7 tubes, otherwise it's stock.


The 150uf 250v are for the bypass caps. But I think its a good idea to also bypass those caps with poly films, to try and ameliorate some of the impact of that electrolytic in the signal path. The stock C7 & C7A are not very good technically. There are much better caps available, and the cost is very reasonable.


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PostPosted: Mon Jun 04, 2018 6:48 pm 
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Location: Edmonton, AB, CA
Brooster wrote:
1) Remove bottom plate of your amp.
2) Remove the 4 screws holding the front faceplate and rotate as in picture.
3) Disconnect the short jumper cable that runs from the daughter board to the " in " on the main board.
4) Take either of the input wires marked cd in or aux in and plug one of these directly to the " in" on the main board where the jumper cable was connected.
5) Reassemble. Everything works as before but the volume control and and input switching are out of the signal path. Only 1 input is active and no volume control.

Thanks for this Bruce, looks to be an easy switchover.
Any idea what the amplifier gain in dB would be as a power amp only?
I am considering trying the MP-301 to drive tweeters in an active tri-amp setup, and would prefer the gain be similar to the amps driving the woofers.
Cheers,
David


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PostPosted: Mon Jun 04, 2018 9:23 pm 
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Location: Calgary, AB, CA
devon58 wrote:
Brooster wrote:
1) Remove bottom plate of your amp.
2) Remove the 4 screws holding the front faceplate and rotate as in picture.
3) Disconnect the short jumper cable that runs from the daughter board to the " in " on the main board.
4) Take either of the input wires marked cd in or aux in and plug one of these directly to the " in" on the main board where the jumper cable was connected.
5) Reassemble. Everything works as before but the volume control and and input switching are out of the signal path. Only 1 input is active and no volume control.

Thanks for this Bruce, looks to be an easy switchover.
Any idea what the amplifier gain in dB would be as a power amp only?
I am considering trying the MP-301 to drive tweeters in an active tri-amp setup, and would prefer the gain be similar to the amps driving the woofers.
Cheers,
David


The gain of the 301 circuit is around 27.5 db ( a little less if you have removed C6,C6A)


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PostPosted: Tue Jun 05, 2018 5:52 am 
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Brooster wrote:
The gain of the 301 circuit is around 27.5 db ( a little less if you have removed C6,C6A)

Thanks, think I will give this a try in the near future.
My other power amps have switchable gain between 19 and 26 dB, in the high position this should be a close enough match.


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PostPosted: Tue Jun 05, 2018 3:19 pm 
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The removal of C6, C6A, is a valid option for dealing with the high gain of the 301 preamp stage. However IMHO there are sound quality issues involved when you remove those caps.
Cathode degeneration at the driver stage is an effect that can not be reversed further down the line. If you make a circuit decision at the driver stage its there at the output.
I find the amp more dynamic, and its overall transparency/extension/detail improve when the bypass caps are kept in place. The sound signature suits my system.

As an alternative to removing C6,C6A:
1) Replace C6, C6A, with low esr organic polymers. ( Rubycon)
2) Bypass C6,C6A with .1uf poly films ( Rubycon)
3) Replace resistors R2 & R2A with 7.5k ohm 2w metal films. ( These resistors lower the gain, and knock back the residual noise floor. Higher values can be used for more attenuation)


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PostPosted: Tue Jun 05, 2018 3:36 pm 
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...

Quote:
Thank you for the great link !

I have got a matched pair of the Tung-Sol 7581-A tubes on the way!


Quote:
Did your 7581's arrive yet ? Any impressions ???? I'm getting itchy to try some new tubes in my 301.

So far I have rolled, Stock EL34, Pvsane EL34, JJ 6L6GC, RCA 1614, (My Favourite power tubes so far) SOVTEK-5881, KEN-RAD 6SH7, (Favourite pre-amp tubes) AND SED-WINGED-C



I am really loving the TUNG-SOL 7581A Tubes in my system. They are excellent. Really great. I'd need to do a bit more recent listening to talk further on this but I really love these tubes so far.


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