I recently picked up what I consider to be a steal of a deal in 300B amps... the Musical Paradise MP-428. All top-notch discrete point-to-point components and wiring. Output iron is big, heavy and supposedly Japanese.
But more importantly, it sounds great.
My question is tube choice. It uses 6AC7s and 6SJ7 preamp tubes. Why would these tubes be chosen over, say, 6J5s? Also it seems that 99.9% of all 6AC7s these days are metal. I'm a glass tube kinda guy and sure would like to replace the metal 6AC7s with glass. But I understand there is no exact substitute for the 6AC7. Is that true for the audio range? Would 6SJ7WGTs work? 6J5s? Something else?
Thanks,
But more importantly, it sounds great.
My question is tube choice. It uses 6AC7s and 6SJ7 preamp tubes. Why would these tubes be chosen over, say, 6J5s? Also it seems that 99.9% of all 6AC7s these days are metal. I'm a glass tube kinda guy and sure would like to replace the metal 6AC7s with glass. But I understand there is no exact substitute for the 6AC7. Is that true for the audio range? Would 6SJ7WGTs work? 6J5s? Something else?
Thanks,
Wouldn't glass look a bit better?
An externally hosted image should be here but it was not working when we last tested it.
6AC7 and 6SJ7 are pentodes, and the 6J5 is a triode so you would have to redesign the stages to accommodate them.
Simplest answer is to look for some 6AC7/GT and 6SJ7/GT. The GT suffix indicates glass tube.
ESRC sells both.
Gary
Simplest answer is to look for some 6AC7/GT and 6SJ7/GT. The GT suffix indicates glass tube.
ESRC sells both.
Gary
I pulled the 6AC7s and replaced them with 6SJ7WGTs. Now I have glass all around and it still sounds great.
But does anyone know the downside of substituting 6SJ7s for 6AC7s? What changes would be expected?
But does anyone know the downside of substituting 6SJ7s for 6AC7s? What changes would be expected?
I also bought the MP428 recently. It is a great SET amp fpr the price. I had communicated with Garry, the designer and he informed me that the best replacement for both the preamp 6AC7 ( in the front) and driver 6J8P is the RCA red 5693. I realized you said you preferred glass, but according to him, this is the best.
Hi,
Nice amp, the building quality are very good
unfortunately 300B tubes are expensive in my country.
I wonder if the face plate and sides are wood or thin steel??
I look forward if MusicalParadise could made a 6C33 15W SET monoblock Integrated amp to fit audiophiles that like this Russian tube.
OBS.> MP site inform the output Trafos are made with Z11 japanese laminated steel.
Nice amp, the building quality are very good
unfortunately 300B tubes are expensive in my country. I wonder if the face plate and sides are wood or thin steel??
I look forward if MusicalParadise could made a 6C33 15W SET monoblock Integrated amp to fit audiophiles that like this Russian tube.
OBS.> MP site inform the output Trafos are made with Z11 japanese laminated steel.
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The sides are steel. It is well made, the transformers are heavy, and the components are not cheap stuff normally associated with some Chinese amps. Regarding the cost of 300Bs, there is a switch on the amp which allows you to change to 2A3 output tubes instead.
Thanks for informing. It is a great amp for the money asked.
Surely it had a good sound quality, by what I see on the under side photos on MP site.
Surely it had a good sound quality, by what I see on the under side photos on MP site.
I wish I could get the schematics of this amp...
I am interested in this amp but I wonder about the specifics of its architecture. The musical paradise site gives this description: "Filaments are powered by DC regulated circuit for cleaner background and longer tube life". There is a picture of the circuit on the bottom of the product page which indeed shows two separate circuits powering tube filaments. Even though it says "DC circuit", it looks rather like high frequency AC circuit (or is that just a relay in the plastic housing?). Anyway, regulated filament circuit is a feature rarely found on tube amps at such price. DC circuit is difficult to implement and sometimes doesn't provide desired results. I was wondering about the specifics of this particular design. Hope someone can give me an answer.
Also if I buy this amp the first thing to go is the internal signal wiring from RCA to the board - it looks like a real signal choke...
I am interested in this amp but I wonder about the specifics of its architecture. The musical paradise site gives this description: "Filaments are powered by DC regulated circuit for cleaner background and longer tube life". There is a picture of the circuit on the bottom of the product page which indeed shows two separate circuits powering tube filaments. Even though it says "DC circuit", it looks rather like high frequency AC circuit (or is that just a relay in the plastic housing?). Anyway, regulated filament circuit is a feature rarely found on tube amps at such price. DC circuit is difficult to implement and sometimes doesn't provide desired results. I was wondering about the specifics of this particular design. Hope someone can give me an answer.
Also if I buy this amp the first thing to go is the internal signal wiring from RCA to the board - it looks like a real signal choke...
An externally hosted image should be here but it was not working when we last tested it.
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Looks like a normal relay to me. There's nothing magical about a regulated filament supply, probably uses a LT1083 or similar chip.
the description of the amp also says that amp could use both 300B and 2A3C output tubes. I wonder how the designer of the amp managed to implement it, considering that these tubes have different plate voltages and output impedances.
I have received Musical Paradise MP-428 amplifier that I bought on Boxing Day sale. I listened to it, replaced Guigang 300b tubes that were humming with Shuguang 2a3c - much better, hum is reduced. I noticed some amount of idle white noise in the right channel. I sent an email about it and Garry Huang, the owner of the company, responded:
"The small amount of white noise shuld be caused by some wirings interference on the right channel. Since it is very small, it doesn't affect actual listening."
Small or not small, any difference in stereo channel topology is a serious matter in "hi-fi". It does affect actual listening since we are talking tubes here, and white noise (not tube hiss) in tubes that is not input signal related should be an indication that something may not be kosher with the amp.
Wiring interference is something that could be easily corrected, right? So I opened the amp and looked closely for differences in wiring between the channels.
There are several things that I found while looking at the construction of this amp.
My amp features Global Negative Feedback, which is implemented via simple wire tap and resistor from 8 ohm output transformer tap to the second signal tube. It is not there in the pictures of the MP-428 on the musical paradise website.
Here's Garry's post in reply to Joe Rosen's inquiry on 428:
"The MP-401 and MP-428 sound significantly better. The MP-428 is 100% zero feedback design." Hm...
So the THD figures (<2%) on the mp website for this amp - are those with or without GNF?
Looking for differences in channels I found them in filament DC supply modules - right channel module has fewer wires running in and out, and without detailed schematics it is difficult to say what is what. And then the wires led me to tube rectifier...
If you look closely at the centrally located rectifier socket you would see that pins 2 and 8 are connected (heater pins, so the tube glows), pin 4 attached to diode bridge (what?!) dangling in the air, and pin 6 is not attached to anything, pins 3 and 7 (empty ones) are used as soldering points for various wires...interesting. I would need some comments from the maker of this amp to help me understand the schematics. Is this some sort of hybrid half-wave rectifier?
here's pinout schema of this tube:
Logic tells me that pins 2, 4, 6, and 8 should be used if both sides of the tube are used (why use full wave rectifier for half wave rectification?)
No such crap is visible on the original pic from MP website:
I emailed Garry asking for schematics of the amp, here's his reply:
"Since it is all point to point wiring design, I don't have an electronic copy in my computer. I will try to redraw one by hand tonight and send it to you."
In my opinion it would cost almost nothing to include printout of the schema with the amp, it's not exactly a "secret information".
The best part of this amp is its chassis - really hefty one, very well made. Transformers are good quality as well (I did not open the output ones, but they sounded good). That's all the pros so far.
Soldering quality - you can see it yourself, - globs of solder everywhere, I scraped couple of solder splats off the sides of electrolytics. Wires are singed at the ends, some of them have burn marks at various points from careless handling of the soldering iron. Soldering looks more like beginners attempt rather than professional work. Quality of components - mmm...nah, wimas are sitting in the pools of glue, would be a challenge to replace. Internal signal wiring (from RCA) also begs to be replaced, it is dangling lose, contact points at the pot and input switch are exposed (shrink-tubing anyone?), wiring not secured, naked shield wires are millimeters away from exposed power tube heater resistors. Those resistors have exposed contacts right next to the plate, and this is high current area. Heater wires for the first signal tubes are hair-thin signal threads that will probably melt with use, touching grounded plate, pretty shoddy and possibly even dangerous.
Here's overall look of my amp:
I trust Garry has no ability to check each and every amp that goes out the door of his company, but there should be no excuse for poor quality manufacturing, especially for the company that needs to establish a respectable name. I will probably return this amp as I feel it is not safe to use it as it is. Hope that production quality will increase and the name "Musical Paradise" will be synonymous with...well, musical paradise.
"The small amount of white noise shuld be caused by some wirings interference on the right channel. Since it is very small, it doesn't affect actual listening."
Small or not small, any difference in stereo channel topology is a serious matter in "hi-fi". It does affect actual listening since we are talking tubes here, and white noise (not tube hiss) in tubes that is not input signal related should be an indication that something may not be kosher with the amp.
Wiring interference is something that could be easily corrected, right? So I opened the amp and looked closely for differences in wiring between the channels.
There are several things that I found while looking at the construction of this amp.
My amp features Global Negative Feedback, which is implemented via simple wire tap and resistor from 8 ohm output transformer tap to the second signal tube. It is not there in the pictures of the MP-428 on the musical paradise website.
Here's Garry's post in reply to Joe Rosen's inquiry on 428:
"The MP-401 and MP-428 sound significantly better. The MP-428 is 100% zero feedback design." Hm...
So the THD figures (<2%) on the mp website for this amp - are those with or without GNF?
Looking for differences in channels I found them in filament DC supply modules - right channel module has fewer wires running in and out, and without detailed schematics it is difficult to say what is what. And then the wires led me to tube rectifier...
If you look closely at the centrally located rectifier socket you would see that pins 2 and 8 are connected (heater pins, so the tube glows), pin 4 attached to diode bridge (what?!) dangling in the air, and pin 6 is not attached to anything, pins 3 and 7 (empty ones) are used as soldering points for various wires...interesting. I would need some comments from the maker of this amp to help me understand the schematics. Is this some sort of hybrid half-wave rectifier?
An externally hosted image should be here but it was not working when we last tested it.
here's pinout schema of this tube:
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Logic tells me that pins 2, 4, 6, and 8 should be used if both sides of the tube are used (why use full wave rectifier for half wave rectification?)
No such crap is visible on the original pic from MP website:
An externally hosted image should be here but it was not working when we last tested it.
I emailed Garry asking for schematics of the amp, here's his reply:
"Since it is all point to point wiring design, I don't have an electronic copy in my computer. I will try to redraw one by hand tonight and send it to you."
In my opinion it would cost almost nothing to include printout of the schema with the amp, it's not exactly a "secret information".
The best part of this amp is its chassis - really hefty one, very well made. Transformers are good quality as well (I did not open the output ones, but they sounded good). That's all the pros so far.
Soldering quality - you can see it yourself, - globs of solder everywhere, I scraped couple of solder splats off the sides of electrolytics. Wires are singed at the ends, some of them have burn marks at various points from careless handling of the soldering iron. Soldering looks more like beginners attempt rather than professional work. Quality of components - mmm...nah, wimas are sitting in the pools of glue, would be a challenge to replace. Internal signal wiring (from RCA) also begs to be replaced, it is dangling lose, contact points at the pot and input switch are exposed (shrink-tubing anyone?), wiring not secured, naked shield wires are millimeters away from exposed power tube heater resistors. Those resistors have exposed contacts right next to the plate, and this is high current area. Heater wires for the first signal tubes are hair-thin signal threads that will probably melt with use, touching grounded plate, pretty shoddy and possibly even dangerous.
Here's overall look of my amp:
An externally hosted image should be here but it was not working when we last tested it.
I trust Garry has no ability to check each and every amp that goes out the door of his company, but there should be no excuse for poor quality manufacturing, especially for the company that needs to establish a respectable name. I will probably return this amp as I feel it is not safe to use it as it is. Hope that production quality will increase and the name "Musical Paradise" will be synonymous with...well, musical paradise.
I am going to be honest with you, I don't think these "Musical Paradise" amps are Canadian at all.
I think they are just run of the mill, lower quality Chinese amps with a North American name-plate.
That's why you can't get a schematic, I mean really, an amp company with no schematic, makes them out of his head? (I can see some companies wanting to keep schematics secret, I don't think this is the case here.)
I have no problems with anybody making anything, but for the price of these some might be mislead about the quality.
I think they are just run of the mill, lower quality Chinese amps with a North American name-plate.
That's why you can't get a schematic, I mean really, an amp company with no schematic, makes them out of his head? (I can see some companies wanting to keep schematics secret, I don't think this is the case here.)
I have no problems with anybody making anything, but for the price of these some might be mislead about the quality.
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It gets more interesting.
I spoke to Garry on the phone and asked him to explain tube rectifier design. He said that in version 2 of the amp they decided to use rectification tube as a "buffer" only, because it improved the sound quality!
Also the GNF in this SET amp was added to improve sound quality as well!
This amp is going back to Garry faster than you can say "Galapagos".
I spoke to Garry on the phone and asked him to explain tube rectifier design. He said that in version 2 of the amp they decided to use rectification tube as a "buffer" only, because it improved the sound quality!
Also the GNF in this SET amp was added to improve sound quality as well!
This amp is going back to Garry faster than you can say "Galapagos".
OT post deleted. Anything not relating to the amplifier being discussed should not be posted here.
The lack of equalizing/bleeder resistors across the series connected supply capacitors is also a big concern as it is not guaranteed that the voltage will divide equally across them due to differing leakage currents. One could be easily over voltaged and explode.. 
Far from the worst I have seen though, including some quite expensive high end gear made here.. This could be the starting point for tweaking, I would understand even at the relatively modest price point that many would be uncomfortable doing so. Not sure what anyone should expect for $700.00, my last amp design built from scratch cost more than 4X this much..
Note that they state that it is designed in Canada, so I would suspect that it is built by an OEM somewhere in China.
Far from the worst I have seen though, including some quite expensive high end gear made here.. This could be the starting point for tweaking, I would understand even at the relatively modest price point that many would be uncomfortable doing so. Not sure what anyone should expect for $700.00, my last amp design built from scratch cost more than 4X this much..
Note that they state that it is designed in Canada, so I would suspect that it is built by an OEM somewhere in China.
It is made in China. Generic chassis (good one) is sourced from the same source that DIY HiFi Supply has (at least they sell the same one), same for the transformers, even though MP website states that they "design their own transformers". Amp has a switch from 300B to 2A3, all it does is change filament supply voltage (5V - 2.5V), - bias, plate voltage and output impedance are left the same, not optimal design if you ask me. Description states that it is "self biasing" circuit...
Because of the price I was considering scrapping all signal components and rebuilding it to my own specs, but because of power supply issues and absence of schematics I shipped the amp back.
It's a good starter tube amp for someone to get a taste of tube audio without breaking a bank, although it is poorly designed with all the strap-on "upgrades" and tweaks. There are better SET Chinese amps out there for the same price.
Because of the price I was considering scrapping all signal components and rebuilding it to my own specs, but because of power supply issues and absence of schematics I shipped the amp back.
It's a good starter tube amp for someone to get a taste of tube audio without breaking a bank, although it is poorly designed with all the strap-on "upgrades" and tweaks. There are better SET Chinese amps out there for the same price.
There are many to choose from, not sure about if any one of them is "better" than the MP, since no one (AFAIK) has done a side by side test...
For example: ±¦¶û»úµ¨»ú, it's quite a bit cheaper, but cosmetically not so hot imo...
In the same price range, Sinovt's entry model looks nice: À·Æ¶ûµç×Ó¹ÜÒôÏ쳧
The schematics are available for both of these companies, so you have a pretty good idea of what you are getting...
Jaz
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