[mlantinen]

Hi, so I finally recieved this little gem, but I'm having some difficulty. While I wait for my HD600's to arrive on Monday, I've got a couple backup pairs of lower impedance cans that don't seem to be operating right.

Both the Denon AH-D750 and the Senns HD428 are outputting unequal sound between the left and right ears. The left ear (which the headphone cord attaches to on both) is much louder than the right side, especially at low volumes. It gets to a point where if I turn them down low enough, only sound comes from the left phone and not the right.

As a test, I've tried both with the Beresford 7520 and my Motorola Droid without issue. They do not have this problem.

Could it be a defective tube? If so, do I simply wiggle them loose and try different tubes. The EL84's and the 12AX7B's glow orange with the EL84's being brighter. The cat's eye tube appears to be working fine.

Any thoughts?

 

[jsplice]

Where did you order this from? Did you contact the seller?

I guess if it were a problem with one of the tubes, you could find this out by switching the tubes between each channel. If you then find the problem with the channel is reversed, then it may be one of the tubes.

 

[Pricklely Peete]

Have you inserted the cable plug all the way (crazy and simple as it sounds) ? That kind of imbalance sounds like the plug isn't fully inserted all the way giving much reduced output in one channel. The jack on the amp may not be making good contact with the plug jack (is another possibility).

It's possible a tube has gone bad but make sure your cable is good to go before checking those tubes out (swapping drivers from right to left channels to see if the imbalance follows the bad tube for instance).

Peete.

 

[mlantinen]

Also, should the voltage of the unit be set at 115V or 230V?

edit: Ok, it should be on 115v.

 

[mlantinen]

Anyone else? I'm speaking with the seller. I bought this from a guy in China. Really good communication but it's difficult to understand him.

The problem does not seem to affect speaker output just the headphone output.

 

[mlantinen]

I tried reversing each the EL84's and the 12AX7B's to no effect. There still is less volume coming from the right phone. Again, it seems that the speakers work just fine. Here's the link to the product. http://cgi.ebay.com/ws/eBayISAPI.dll...d=442305418007

So I've been trying to get this resolved with the seller. I mentioned that everything is physically in tact, all of the RCA and power cord connections are solid and I've tried two different RCA connectors. I've opened the bottom and it appears all of the solders are intact, but I really have no idea what I'm looking for.

So, I mentioned to him that maybe it's a defective headphone jack. Here is his response:

"I just asked again, manufacturers, manufacturers say, this combined power amplifier is mainly a combined power amplifier, headphone amplifier part of which is incidental, so part of the headphone amplifier can not be perfect, so I convey to you, please understand that"

"If you like to listen to headphones, I send you an extra one headphone amplifier, but you need to buy a power adapter, because the original is a 220V voltage"

- lance6881888

So, from the sound of his response, he's saying that the headphone jack isn't meant to be perfect.....but he can send me a different headphone amp and then I need to buy a power adapter. Is this what everyone else's take is?

I would really prefer to get this fixed in the US and not have to open a paypal dispute since the product is not as described. The listing says nothing about the unit being primarily a speaker amp that coincidentally has a headphone jack that may or may not work correctly. At it's current state, I cannot use headphones, period.

Any advice? Happy Holidays.

 

[moodyrn]

That's bull!!! Sounds like he's trying to keep you from filing a dispute with paypal. I know you don't want to hear this, but you should gotten it from pacific valve. I know it's cheaper getting it from the Chinese sellers on ebay, but you never know what type of problems you might incur. And it's expensive and a hassle to send anything back to china. Pacific valve warrants and service everything they sell. And they also have a money back guarantee. They might be more expensive, you do get coverage and most of all peace of mind.

 

[mlantinen]

Thanks moodyrn, yeah, hindsight is 20-20. The only reason I ordered from this guy is because it was in stock and ready to ship. Pacific Valve is still showing that the item is out of stock even today. It wasn't about the extra few bucks.

So moodyrn, I take it that you have no issues with any of your headphones even at low volumes besides perhaps hiss with lower impedances?

I did send a fairly lengthy message back to this guy explaining that if he does not rectify this issue, I will file the paypal dispute. Even the title of the ebay listing explains that the amp is a Multi-Purpose Mini Tube Amplifier. It doesn't say Speaker Amplifier or Speaker Amplifier with Headphone Jack.

Ugh! Anyone else have any ideas? Thanks much.

 

[moodyrn]

Since the problem is with the headphone out, it must be a solder problem with the headphone jack. I know you have already taken a look at the insides. I would suggest taken another look. Sometimes the solder joints can appear to be solid, but a closer look may reveal a loose solder connection. You can check the solder joints on the headphone jack, and a closer look at the wiring that runs from the headphone jack to the speaker headphone switch. Good luck. I hope you can get this resolved. The ming da is really a nice sounding amp for both speakers and headphones.

 

[mlantinen]

Ok. Here are some photos to see if anyone can spot a problem.

Shows RCA and HP/Speaker switch

Shows tube area

Shows hp jack

Closer hp jack. Do these look like good solder joints?

 

[mlantinen]

Well, my uncle, who's been an electrical engineer for 40 years and evidently used to be quite an audio enthusiast, ended up coming over to my house for Christmas. We monkeyed around with the amp for awhile and after about 10-15 minutes he came to the conclusion that it's the dual volume POT (potentiometer). I'll try to paraphrase what I remember him saying, but essentially said there are two disks within this dual volume POT which are not aligned perfectly which is why at lower volumes there is an uneven output.
I had my computer volume maxed because I wanted the amp to do all the work, but once we turned the computer volume down to about anywhere less than 50%, I was able to get even output at low volumes using the amp's volume nob. So, he said that if we have the seller just send us a replacement volume POT, he'll solder it in.

But for the time I can tweak my computer volume (not the way I prefer it) to temporarily fix the issue.

Hope this helps others.

 

[mrarroyo]

Glad the solution will be so simple. If you want to you can also buy a better potentiometer locally, good luck.

 

[moodyrn]

That will be a better solution. They're not expensive at all. I would definitely leave negative feedback for that seller. All he did was lied to you and gave you the runaround. I'm glad everything worked out for you. One thing I'm courious about. If the problem was the pot, why didn't it affect the speaker out? I remember you reporting that the speaker outs were fine. Oh well, but again, glad everything is working out for you.

 

[mlantinen]

@moodyrn
Quote:

If the problem was the pot, why didn't it affect the speaker out?

Ya know that's a good question. I think the speakers did have the same issue, but it was more difficult to detect. With the speakers I have to use a higher volume, and the uneven-ness was only really noticable at lower volume levels with the headphones.

Quote:

I would definitely leave negative feedback for that seller. All he did was lied to you and gave you the runaround.

In all fareness, the biggest problem was the language barrier. The guy was great at getting back to be asap and was sending me messages regarding the status of the item and how testing was going prior to shipping it out to me. He did eventually say that if I sent it back to him (I pay for shipping) then he'd get it checked out and send it back to me (he pays shipping back). So I think he was generally concerned with my problem, but yes, the comment about how the unit is primarily a speaker amp and if the headphone amp is borked then you're SOL was pretty bad.

On the bright side, I really like the sound even with the stock Chinese tubes. In a few weeks I'll maybe grab some better tubes and give them a whirl.

Another semi-funny thing that may help others is, if you're using this in conjunction with a Creative X-fi card that is capable of DTS output, make sure to turn it OFF. Initially, I had this feature turned on when I first started listening to the amp. So for the first few days the sound was rather muffled and distant. I was really disappointed so I thought I had better double check the sound card settings via the Creative Console Launcher feature of the X-fi software. Glad I did!!! Now I'm really hearing what this amp can do. That was definitely a "Oh Duh" moment.

 

[mlantinen]

Update:
Recieved the replacement potentiometer from the seller who obtained from the manufacturer. Not in a real hurry to replace since I have an easy work around, but I will definitely replace in the future, when I can find time to enlist my uncle to do so.

But, overall I'm very happy with this unit. Still haven't rolled tubes, but I'm also planning to do so in the near future. I have a pair of older KLH 8ohm (I think 88db sensitivity) floorstanding speakers that are driven very well with this unit. I just have to turn the volume up abit more than when using headphones. I could easily drive them to ear bleeding levels. Still trying to find the best bookshelf speakers/subwoofer for the job. Going to retire the Z-5500's pretty soon.

My newly acquired HD600's sound terrific. I'm really curious to see what the changes will be once I start rolling tubes to vintage NOS tubes.

If anyone has any questions regarding this unit or the experience I had with the ebay seller just give me a shout. I'm more than happy to help in any way that I can.