[dgcrane]

I just received this information from Garry regarding the humm and lower impedance phones....
 
"
Hello Darren,
There is a simple mod to lower the gain for Grado. The hum will be way lower. Please take a look at the attached picture. You need a needle to solder out one leg first, and then use a plier to take out the resistor while applying the iron to the other leg. Very easy. You can keep those resistors. When you are going to use 600ohm headphones, you need to put them back. Just simply solder them back on the top of the PCB instead of the bottom.
 
The heat from the tubes are normal. They are very hot. When using 6L6, the power transfomer is just warm about 40-45C. When using EL34, it is hotter at around 50-55C, but your hand should still able to hold the transformer forever. These are the normal temporature status.
 
Thanks,
Garry
"
 

 

[willthong]

Would these pair well with the AKG K701s?

 

[eclein]

We shouldn't have to de-solder resisters to listen to a certain kind of headphone and then solder them back in if you listen to another kind...thats a design fail. Plain and simple if it was necessary to do something like that in the circuit then he should have added some type of High/Low gain switch. 
 
Modding something to make it better is one thing, modding something to make it work??   Thats another!!!

 

[dgcrane]

Agreed.... mine is on its way back this evening.....
 
Darren

 
Quote:

We shouldn't have to de-solder resisters to listen to a certain kind of headphone and then solder them back in if you listen to another kind...thats a design fail. Plain and simple if it was necessary to do something like that in the circuit then he should have added some type of High/Low gain switch. 
 
Modding something to make it better is one thing, modding something to make it work??   Thats another!!!

 

 

[Gubretti]

Well so far it seems like only bad news about this amp, and then those ebay links I posted kept me from pulling the trigger. Sigh, it looked so attractive

 

[Skylab]

It isn't all bad news.  I'm really enjoying this amp now that I found a set of tubes that are quiet.  It's driving the HifiMan HE-500 very well.  And remember, this isn't designed to be a headphone amp - it's more designed as a speaker amp. But with the right tubes and headphones, it's a very good sounding headphone amp.
 
That said, there are some concerns, for sure - it's unfortunate that it seems to be very sensitive to the tubes used in it.  Several of us have received bad power tubes (me included).  And while it is quietest with high impedance headphones, it delivers the least power to these.  Being transformer coupled should enable it to handle lower impedance loads, but it has the most hum issues with these...
 
 
 

 

[eclein]

Why put a headphone output then??? He took everybodies advice and added a switch for the speaker and moved the jack for what- 4 kinds of headphones????
1) He needs to:
a) Fix them
b) Send us a fix
c) Correct it for the next batch
d) Don't put a headphone jack in it if its not meant to do headphones-isn't that what Head-fi is all about???
 
2) And he needs to figure out a better shipping method.....mine was bought for me and the gentleman bought expedited shipping which got a unit shipped out weeks ago only to have it returned to China because they won't send vacuum tubes air, so then we have to wait a week and 1/2 for the standard shipment to arrive in Canada, then its ships, expedited shipping, its now going on almost two week to get the unit 1500 miles...5 days in customs...thats expedited????????????
 
He's going to losse his customer base, why send somebody a DIY fix via email to post for everyone, people are going to flip, cancel orders and flip....I am and it didn't cost me a dime. I feel really bad that my friend bought it for me, he keeps asking me did it arrive yet????

 

[gtube]

Hi Everyone,
Thanks for your feedback. The orginal design of the MP-301 MK2 is mainly for speakers and high impedance headphones. In order to satisfy customers' requirement regarding the background humming noise, I have made a notice on our website and made some changes to the ordering page. We provide the customers an option to select the version they need from now on. Customers can choose 50-600ohm (default) or 32-300ohm version when they place orders. We will add a mini switch in the future batches, so the user can select the impedance they like easier. For existing customers who use low impedance headphones and want to implement the change, we can supply the mini switch and instruction to add the mini switch for free. If you are not familiar with soldering, please contact me for RMA. If you don't like the amp for any reason, you can return it for refund.    
 
I tried to help some US customers to receive the MK2 faster, so we shipped those orders from China by China Post. However, a few of them was returned by the Chinese customs. They don't allow tube amps shipped by Air anymore. Canada Post expediated is the most afforadable way to ship parcels to the US. Express Post is way too expensive. There is no other option.
 
Any question, feel free to email me
 
Thanks,
Garry

 

[gtube]

AKG K701 can work well in both setup. It is 72ohm.

 
Quote:

Would these pair well with the AKG K701s?

 

 

[gtube]

Anyone who received a bad 6L6 power tube, please contact me. I will ship you a new one.
 
Thanks,
Garry

 

[eclein]

Thanks Garry for responding so quickly. Please send me the mini switch fix and I'll have someone local make the change or try to do the fix myself- I use mostly Grado's and very easy to drive cans.
Let me know if you need any other information from me to make that happen. 
 Thanks again.

 

[Rockyhill]

My concern is with the extreme sensitivity to other tube types that are listed as replacements for this amp. The RCA 6SD7GT and National Union 6SJ7GT I've tried sound lovely except for the incredible amount of hum. The stock tubes are OK, but is OK satifactory? I think not. I believe the stock tube selection should have focused on building demand for this product. As it stands now, I'm trying to figure out how to keep from spending an equivilent amount of money to find tubes that compliment this amp.
 
My 2 cents.
 
Edit: I am primarily a speaker user.

 

[gtube]

In order to shorter the lead time and provide the best pricing to our customers, we used almost the same case as the one you showed on eBay which is made by the same case manufacturer. The face and back plates are completely redeigned to meet our customers' requirement. The circuit, all transfomers and components are totally different. If you don't believe, buy the one on eBay, listen to it, and open it, you will know the big differences in terms of design and quality if you are familiar with electronics.   
 
Quote:

I wasn't sure if those had the same tubes, but then I found this one as well http://cgi.ebay.com/Brand-New-AC-EL34-Tube-Amplifier-Headphone-Amplifier-/320684340427?pt=LH_DefaultDomain_0#ht_2113wt_1139 , who cloned who

 

 

[Skylab]

Quote:

Hi Everyone,
Thanks for your feedback. The orginal design of the MP-301 MK2 is mainly for speakers and high impedance headphones. In order to satisfy customers' requirement regarding the background humming noise, I have made a notice on our website and made some changes to the ordering page. We provide the customers an option to select the version they need from now on. Customers can choose 50-600ohm (default) or 32-300ohm version when they place orders. We will add a mini switch in the future batches, so the user can select the impedance they like easier. For existing customers who use low impedance headphones and want to implement the change, we can supply the mini switch and instruction to add the mini switch for free. If you are not familiar with soldering, please contact me for RMA. If you don't like the amp for any reason, you can return it for refund.    
 
I tried to help some US customers to receive the MK2 faster, so we shipped those orders from China by China Post. However, a few of them was returned by the Chinese customs. They don't allow tube amps shipped by Air anymore. Canada Post expediated is the most afforadable way to ship parcels to the US. Express Post is way too expensive. There is no other option.
 
Any question, feel free to email me
 
Thanks,
Garry

That is excellent customer service, Garry!
 

 

[gtube]

The stock tubes are NOS Shuguang 6J8P(6SJ7) from the 1970s. They are great tubes although not the best. May I know what headphone do you use?
 
The output of those new National Union 6SJ7GT is too strong. They required some burn-in period I think. I will try a couple of the RCA 6AC7 with my HD580 tonight. 
 
Quote:

My concern is with the extreme sensitivity to other tube types that are listed as replacements for this amp. The RCA 6SD7GT and National Union 6SJ7GT I've tried sound lovely except for the incredible amount of hum. The stock tubes are OK, but is OK satifactory? I think not. I believe the stock tube selection should have focused on building demand for this product. As it stands now, I'm trying to figure out how to keep from spending an equivilent amount of money to find tubes that compliment this amp.
 
My 2 cents.