[Zemo]

I purchased an amp from Shutakagi but I can't contact him because his PM box is full (shutakagi, if you're reading this CLEAN IT OUT!!!).
And sadly, there are problems with the amp. The idea was that it would drive my AKG K501s with plenty of authority, but I crank the knob all the way up, and it's STILL not loud enough! When the input is the 1/8th jack (it has that and RCA) the connection isn't solid, sometimes only the left channel will come through, and I have to jiggle the plug for it to work.

Another problem is that with 2 fresh 9v batteries in it, the LED will sporratically get really dim, and the sound will go out, or the LED will just turn off with the sound.

What am I supposed to do?! I can't contact Shutakagi cause I don't have any of his contact info other than his PM box (wich is full)! Is it possible to fix the amp?

The whole reason for me to get this amp was to have an amp that powered my headphones at a really high level....I can crank it and still want more volume...can this be fixed at all?

 

[JMT]

From Tangent's site:
Quote:

The Modified Linkwitz crossfeed circuit attenuates the signal going through it by roughly 6-10 dB, depending on the source you use. (The variance is probably due to different source output impedances.) You need to set the amp's gain 2 to 3x higher than you would if there were no crossfeed in the circuit to counteract this attenuation. Try 2x first, and only go up to 3x if the amp still won't drive the headphones enough in your setup.

Try sending him an e-mail through the link in his profile and see if he can up the gain to compensate for the attenuation. At the same time he can take a look at the jack issue.

 

[Zemo]

he has it set so that I can't send him an email through the message board, so I contacted the administrator, hopefully I can get through there.

So I'm going to have to send it back, huh? dang it, I waited so long for this.

What about the other problem? The sound just stops after about 1 minute of play, and the LED glows VERY dim. When this happens, I can switch it off then on again, and I get another couple seconds of sound before it stops. The longer I leave it off, the more sound I get when I turn it back on.

Help!!!

 

[Zemo]

for clarification:
The problems with this amp:

-Can't contact Shutakagi
-Output levels not high enough for AKG K-501
-Sound stops after about a minute
-Loose 1/8th connection (jiggleing it makes it work)
-volume pot isn't smooth
-scratch below 1/8th jack

 

[Zemo]

Another post by me:
The specs for this amp (for those of you who care):

-ad8620 opamp
-4 stacked el2001cn buffers / each output
-1 el2001cn for ground
-alps blue velvet pot
-jfet-cascode class-a biased
-modified linkwitz crossfeed
-black hammond 1455 case: 120x78x43 mm
-closed-circuit dc jack (for wallwart); 2 9v battery power
-rca in; 3.5 (1/8") mm input
-6.35 mm (1/4") output

pics are HERE

note: the pics don't show a scratch below the 1/8th jack, but the one I recieved has one....

 

[Zemo]

since this amp doesn't ACUTALLY work, like Shutakagi led me to believe, I see two options: Send it back to Shu and have him fix it, or fix it myself. How do I go about diagnosing and fixing my problems?

 

[Zemo]

since this amp doesn't ACUTALLY work, like Shutakagi led me to believe, I see two options: Send it back to Shu and have him fix it, or fix it myself. How do I go about diagnosing and fixing my problems on my own?

 

[10SNE1]

Does this amp run at all on wallwart power?

The behavior exhibited with fresh batteries suggests some kind of power problem where an excessive amount of current is being drawn.

Since you are running it class A, the power demand will be higher than if it was not. Also, the buffer config will demand more power than a single buffer per channel.

You are getting amplification, so the basic operation seems OK but as JMT suggested, the feedback and gain settings might need to be adjusted for your headphones, among other things.

Did this person build the amp, or is it a resale?

 

[Zemo]

it has a jack for a wall wart, but I don't know what kind of wallwart to get...how do I tell? So you're telling me that it stops after one minute of play because two 9v batteries can't handle it? So nothing is wrong with it, in that respect, it just can't run off of batteries? I don't believe it.

and how do I adjust the gain?

 

[Zemo]

I believe that Shu built the amp, by the way, I don't think it's a resale, but I don't really know.

 

[tangent]

Quote:

the LED will sporratically get really dim, and the sound will go out

Sounds like bad connections internally. If you leave it in this state for a while, do the batteries get warm? If you turn the amp on without headphones attached, does the LED stay on long-term?

Quote:

How do I go about diagnosing and fixing my problems?

Without learning electronics? You keep answering our questions while we lead you around remotely. It's pretty inefficient, but so is you learning electronics before starting troubleshooting.

Quote:

how do I adjust the gain?

To increase the gan, you lower R3 or raise R4. It's simpler to lower R3, because you can do that just by piggybacking an additional resistor on R3. To raise R4, you'll have to desolder it and put a new one in its place.

 

[Zemo]

Quote:

Sounds like bad connections internally. If you leave it in this state for a while, do the batteries get warm? If you turn the amp on without headphones attached, does the LED stay on long-term?

No, the batteries do not get warm. Yes, the LED gets dim without headphones plugged into it, but at a MUCH slower rate than with headphones in.

Quote:

To increase the gan, you lower R3 or raise R4. It's simpler to lower R3, because you can do that just by piggybacking an additional resistor on R3. To raise R4, you'll have to desolder it and put a new one in its place.

What value resistor do I want to piggyback onto R3? I belive I can get resistors and soldering equiptment here at OSU (I have an EE professors intrest).

How will I remove the board from the case? What seems to hold it in is the nuts screwed in to keep the jacks on. the nuts on the RCA jacks are on the inside in a tight area with lots of wires and junk....

FYI, I will be checking here every hour or so, so don't hesitate to leave a post!

 

[tangent]

Quote:

the LED gets dim without headphones plugged into it, but at a MUCH slower rate than with headphones in.

Okay, so a load only makes the problem worse, it doesn't fix it.

Quote:

What value resistor do I want to piggyback onto R3?

The simplest change would be to use another resistor of the same value as what is there now. This will give 2x the current gain value. This may be technically "too much", but the pot is there to cut the volume down before amplification -- use it. If you wanted to get just a bit more gain but not too much, make it 3 or 4x the current value. Resistors are cheap...you could get a bunch to try.

If you're lucky, your builder used resistors with color stripe coding, which you can read in any orientation. If you're less lucky, he used resistors with numeric codes, but the resistors are mounted with the number visible. If you're unlucky, they're mounted with the code toward the board; you'd have to pull the resistor off the board to measure it in this case.

Quote:

How will I remove the board from the case?

There are four screws on each end panel, in the corners. Click over to my "Not a headphone amp" thread -- the top picture shows the front panel of a Hammond 1455K12 case with the panel mounting screws plainly visible. The board is probably mounted to the front panel via the pot. Remove the knob, usually with an Allen wrench. Then you can remove the pot mounting nut, and the board can be removed from the panel. The board will still be attached via hookup wires to panel components, but you can work on it in this state. There should be no need to desolder stuff.

 

[Zemo]

alright, so the problem now is the thing about the LED going dim and sound stopping....I can solve the gain problem, and I fixed the not-smooth volume pot (it was just a loose allen screw)....

The other problem that still needs attention is the 1/8th jack cutting out on the right channel, unless the cord is jiggled...how can I fix this?

 

[eyevancsu]

I had the same problem with the 3.5mm jack, and its cutting in and out, i also had to jiggle it. After much troubleshooting, and purchasing different jacks, i realized that i had not isolated the dc jack from the case, so the dc ground and I/O grounds were getting mixed. If your case isnt metal, then..., if it is, try to isolate and insulate the jacks.

ivan

edit: also, maybe the wire is messed up, my old interconnect had to be adjusted to just the right position to get the sound out, apparently, one of the wires was cut, try the amp with different cables.