Douk Audio Little Bear P7 headphone amp
Aug 27, 2020 at 11:44 AM Thread Starter Post #1 of 14

CADCAM

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I bought one of these on Amazon and it failed in a little less than a month.
I love the look and the sound was actually very good as well. Douk Audio has told me the power board is the issue and needs to be redesigned but they keep blowing me off on if and when they will address it.
Would anyone be willing to take a look at pictures I have of the internals and let me know if it's worth having repaired?
If so is there a member in the US that would be willing to repair it for me?
I really enjoyed this amp for the month I had it and would like to be able to use it again.
btw when it failed the tubes went off and the power button on rear of unit lite up red.
 

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Aug 28, 2020 at 10:41 AM Post #2 of 14

tomb

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You're always welcome to post pics of the internals here. If anyone sees anything useful, they'd be able to post right away. Be sure you have some good pics of that power board.
 
Sep 1, 2020 at 8:07 AM Post #3 of 14

CADCAM

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Here are some pics of the power board not sure what I'm suppose to be showing so if this isn't right please let me know.
 

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Sep 1, 2020 at 8:10 AM Post #4 of 14

CADCAM

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Couple of the main board When you first open it up.
Thing sounded great!
 

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Sep 1, 2020 at 9:11 AM Post #5 of 14

tomb

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Well unfortunately, there's very little that I can tell from looking at the photographs. You are probably SOL unless you can find someone to repair it. The transformer is completely covered with the steel shield. Other than that, there is nothing that looks burned. The standard procedure if you had the device in hand with a DMM, would be to plug it in and start measuring voltages. I would not advise doing that, however, unless you are very familiar with tracing line power and the dangers inherent with that sort of thing.

Some of the things you can do now:
  1. Check all of those connectors (wire in the white plastic blocks) for continuity. See if some of the wires are loose or broken inside the connector. Unplug and then plug back in each connector, making certain they are secure. Try the power after that and see if it changed anything.
  2. Search the bottom of the power module (you didn't include any pics of that) and see if there are burn marks anywhere. Check the rest of the amp for the same. If you can identify a burned part, that might be the issue.
  3. Likely parts that could fail are the power transistor (on the big silver heat sink), U5, the TO-92 transistor (directly below D5 and D6), or the transformer itself (all the junk under the yellow metal shield in the middle).
If it's the transformer, your amp might as well be junked.

One other thing to check is the IEC inlet itself. You remarked that the light changed to red on the back of the unit. This might be a fuse or something that came loose in the IEC inlet - the place where the power plug is attached. See if you can find something wrong with that area on the inside - something loose, burned, etc.

Just remember not to do any of this checking with the power on! Good luck!
 
Sep 1, 2020 at 10:14 PM Post #6 of 14

HiGHFLYiN9

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Tomb is correct there are unfortunately no obvious signs of issues like bulging caps, burnt resistors, or questionable connections. Since Douk knows the power board is the issue there is likely a design flaw, potentially a transistor that is running outside of spec because of the design and failing.

I've become very selective about what I purchase overseas now as I've experienced enough similar situations to give me a bad taste. When amps experience failures like this I become concerned regarding personal safety... I'd much rather build a well documented circuit or purchase from a trustworthy source than take an unnecessary risk.
 
Sep 2, 2020 at 7:26 AM Post #7 of 14

CADCAM

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I saw the amp on Amazon and thought it looked great and impulse bought it, I have a Little Dot MKIII and a Loxjie P20 already but something about the looks of this unit got me. After purchase I used it quite a bit and the sound was way better than expected. It ran it almost daily for just under a month and then silence.
I am not familiar with electronic repair so I'm not going to try anything with this unit and Amazon did refund me the purchase price and let me keep the amp so I'm not out anything. If I could get someone local to repair it for 100 to 150 bucks I'll probably do it because I did enjoy this little unit until it died. Shame on Douk for not doing due diligence with the design as this IMHO could have been a winner.
 
Nov 23, 2020 at 10:54 AM Post #8 of 14

CADCAM

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So... I dropped this little amp off at a guy over a month ago and he just reached out to me. He believes it is a power supply and is ordering a new transformer. He is going to try to get one that will fit in the chassis but if not will mount it externally.
He is going to have it back to me within two weeks so I'll post the results. I bought a Monoprice Monolith amp since dropping it off with him (plus many tubes) and they happen to have the same tube compliment so I'll have options on options for rolling tubes!
 
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Nov 27, 2020 at 8:26 PM Post #9 of 14

tomb

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So... I dropped this little amp off at a guy over a month ago and he just reached out to me. He believes it is a power supply and is ordering a new transformer. He is going to try to get one that will fit in the chassis but if not will mount it externally.
He is going to have it back to me within two weeks so I'll post the results. I bought a Monoprice Monolith amp since dropping it off with him (pulse many tubes) and they happen to have the same tube compliment so I'll have options on options for rolling tubes!
I can't picture in my mind how he would mount it externally and not have it pretty close to the tubes, given the size of the case, spacing of the tubes, etc. So, if he mounts the transformer externally, be sure he puts a steel shield around it. The tubes will probably pick up the 60hz from the transformer, otherwise.
 
Nov 28, 2020 at 5:09 PM Post #10 of 14

CADCAM

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I can't picture in my mind how he would mount it externally and not have it pretty close to the tubes, given the size of the case, spacing of the tubes, etc. So, if he mounts the transformer externally, be sure he puts a steel shield around it. The tubes will probably pick up the 60hz from the transformer, otherwise.
Thank you for the advise. He is an older guy who has a lot of experience with electronics so hopefully he will already know this. I did remind him that I will be listening through hp's (obviously) so noise is a big issue.
 
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Nov 29, 2020 at 3:47 PM Post #12 of 14

CADCAM

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so the problem was a fried power transformer?
[/Q
The unit is being repaired as I type this, I will post details of the repair when I receive the amp back and I get a full description of what was done.
 
Dec 1, 2020 at 11:46 PM Post #13 of 14

AudioCats

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how many different types of little bear P7 exist? I found this 2017 thread
https://www.head-fi.org/threads/little-bear-p7-mods-based-off-a-p8-thread.866649/
and it claims "The P7 has two separate internal switching power supplies one providing 180v (as labelled on the power input on the main PCB) and a single 6.3v for the 6n3 and 6n5 tubes whereas the P8 uses a single toroidal transformer with one 170v and two separate 6.3v outputs to the tubes." ??
 
Dec 9, 2020 at 4:32 AM Post #14 of 14

evonimos

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I think my DIY PCB unit, is basically a very similar design to the P8.
For anyone interested, I've posted a description along with pictures of the completed unit in here.

If it isn't an exact copy, from what I gather, it should be a very similar affair.
I have the schematics of it and might post them here or in the other thread linked above.
They may be of help to folks interested into that nice OTL design.
 
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