[dsavitsk]

Quote:

Originally Posted by Nonchalance /img/forum/go_quote.gif Just to be absolutely sure, I wire all of into the case right?

You can do that, and it is a common way to wire guitar amps, but I think the better option is to use a terminal strip

and connect it to the case in one place and connect all of your ground connections to it. Google for "star grounding" for more details. The resistance of the case itself may be a little too high to use it as a ground plane which may lead to some noise.

 

[Nonchalance]

I was wondering what those things were in the SSMH pics! I see now. The article recommends 2 strips and separating certain components, and I actually see 3 terminal strips in the PMillet site that are interconnected. What's the recommended setup? Edit: found on mouser, haha.

Thanks a lot!

 

[bpr]

I finished building my Starving Student last night, and as this was my first DIY audio project of any kind, I was thrilled when I flipped the switch and heard music instead of silence. Everything seems to have worked as it should - the amp sounds great and I couldn't be happier.

The only very small problem seems to be a slight channel imbalance. Centered audio material, like vocals I know to be in the dead center of the sound stage, are favoring to the right channel ever so slightly. This happens over a variety of music and three different pairs of headphones.

I know there could be a number of possible culprits - a problem in the gain stage, or output stage, or the volume pot tracking error mentioned two pages back, etc. What I don't know is where and how to start looking for the error.

I'm a real beginner here, so any assistance anyone could provide would be immensely helpful. Truthfully, even if I can't find or fix the problem, I'm so happy the amp works and sounds so great that I could live with the imbalance, if I HAD to.

Thanks.

 

[dsavitsk]

It's most likely a pot imbalance issue. But if it is consistent at all volume settings, then it might be mismatched resistors elsewhere -- most likely the input resistors, possibly the plate loads. It is probably not the tubes, but it is worth swapping them to see if the problem switches sides.

 

[bpr]

Quote:

Originally Posted by dsavitsk /img/forum/go_quote.gif It is probably not the tubes, but it is worth swapping them to see if the problem switches sides.

Thanks for the fast reply. It might actually be the tubes. I swapped them as you recommended, and the channel imbalance switched sides. The difference between channels isn't huge, just enough to be noticeable and mildly annoying. It seems like the soundstage is moved just past center. Everything else about the amp sounds great.

Aside from looking for more tubes, are there any remedies to this problem that are (easily) performed?

 

[tomb]

Quote:

Originally Posted by bpr /img/forum/go_quote.gif Thanks for the fast reply. It might actually be the tubes. I swapped them as you recommended, and the channel imbalance switched sides. The difference between channels isn't huge, just enough to be noticeable and mildly annoying. It seems like the soundstage is moved just past center. Everything else about the amp sounds great. Aside from looking for more tubes, are there any remedies to this problem that are (easily) performed?

I've had a feeling for awhile now that many of the complaints about pot imbalance are actually the tubes. Did you request/pay for tube matching? Tube matching is the answer. If you did and you got them from Beezar, I'll swap them out.

 

[revolink24]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif Check that center standoff for a short on the LED resistor trace. The power supply has an automatic cutoff in case of a short. If you can measure 48VDC from the power supply connector when it's not connected, then you've got a short that developed when you re-assembled the case.

Ha, that was my first problem, I was silly enough to use a washer size too big

 

[PJPro]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif I've had a feeling for awhile now that many of the complaints about pot imbalance are actually the tubes. Did you request/pay for tube matching? Tube matching is the answer. If you did and you got them from Beezar, I'll swap them out.

Was tube matching provided as part of the kit or was it something extra that one had to request?

 

[bpr]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif I've had a feeling for awhile now that many of the complaints about pot imbalance are actually the tubes. Did you request/pay for tube matching? Tube matching is the answer. If you did and you got them from Beezar, I'll swap them out.

Thanks, Tom. There is an imbalance in my volume pot at very low volumes, as you mentioned a few posts back, but it evens out before the pot is at listening levels. Once at listening levels though, a slight channel imbalance persists, and seems to change channels if I swap the tubes back and forth.

I did get my tubes from Beezar and I did pay for the tube matching service, so I'll take you up on your swap offer if it's not too much trouble. The tubes I rec'd were both Raytheons, and marked 75/100 and 85/100 on the tops of the boxes respectively. Let me know how best to proceed.

 

[Nonchalance]

Did anyone here follow the wiring diagram posted here a while back? It's probably neater than anything I can come up with, but does it work?

 

[tomb]

Quote:

Originally Posted by PJPro /img/forum/go_quote.gif Was tube matching provided as part of the kit or was it something extra that one had to request?

It was definitely included in the kit. Your problem sounded like the pot, though - it varied with the volume knob position.

Quote:

Originally Posted by bpr Thanks, Tom. There is an imbalance in my volume pot at very low volumes, as you mentioned a few posts back, but it evens out before the pot is at listening levels. Once at listening levels though, a slight channel imbalance persists, and seems to change channels if I swap the tubes back and forth. I did get my tubes from Beezar and I did pay for the tube matching service, so I'll take you up on your swap offer if it's not too much trouble. The tubes I rec'd were both Raytheons, and marked 75/100 and 85/100 on the tops of the boxes respectively. Let me know how best to proceed.

Well, heck - those numbers prove that they're imbalanced. Either average those two numbers or add them together - same thing, that's the total output of the tube that must match the other one - so 175 vs. 185. Not much of a difference, but some of you guys are persnickity, I know.

Anyway, I apologize if I did that and you truly paid for matching. Although, things are getting tough right now for tube matching - there's almost not enough tubes left to assure this anymore. I'm going to remove the matching option on beezar pretty soon.

 

[tomb]

Quote:

Originally Posted by Nonchalance /img/forum/go_quote.gif Did anyone here follow the wiring diagram posted here a while back? It's probably neater than anything I can come up with, but does it work?

Actually, I think it may look OK - seems like everything matches up.

 

[n_maher]

For what it's worth I have never have volume level differences translate from whatever I measured on my tube tester. One tube would have to be dead (or near dying) to have the gain that it provided be different.

 

[tomb]

Quote:

Originally Posted by n_maher /img/forum/go_quote.gif For what it's worth I have never have volume level differences translate from whatever I measured on my tube tester. One tube would have to be dead (or near dying) to have the gain that it provided be different.

Well ... far be it from me to disagree, but the effect is subtle. It's not a volume level difference, per se - it's more of a feeling that the headphones are less responsive on one side compared to the other. Now, depending on the music with which one's listening, that could translate into a perceived volume difference, too. I find a pretty close correlation between what I measure on the tube tester - at least with the 658 - and whether a pairing ends up with one side of the headphone sounding lively and the other side sounding dead. It took a lot of listening with Milletts before I was able to distinguish this difference - and it pre-dated my experience with tube testers. The testers seem to confirm it, though.

Obviously, there are circuits that are more susceptible to this than others. Ones with paralleled plates and fixed bias such as the SSMH tend to be less noticeable than with a Millett Hybrid, for instance. There, one might adjust the manual bias to center the volume by ear for the final touch - but if the tubes were mis-matched, then the dead vs. lively headphone can difference would assert itself, regardless. This effect was less for lower gain tubes than the higher ones, however.

 

[bpr]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif It's not a volume level difference, per se - it's more of a feeling that the headphones are less responsive on one side compared to the other.

This is the exact problem I'm experiencing. I know we're talking about possibly mismatched tubes, but this IS my first DIY audio build. I'm sure that my inexperience may have contributed to this problem, especially if you guys think that the mismatch in tubes wouldn't contribute to a very noticeable balance difference.

Before I send the tubes back, are there any measurements or checks I can make on the board and components to determine if I screwed something up?