[Llama16]

you're right. Tomorrow is a new day.
I'm already very glad that it hasn't caused any (so it seems at least) non-temporary damage, and that the offset is good.
I shone a flashlight from the back and I didn't see anything coming close to the case at all.
I'm just really unsure what would happen if it does happen when listening to headphones.

Troubles for tomorrow.
I'd already like to thank you and equalizer alot for your support and help. You guys are pretty patient with me

 

[Fishline]

Since I have ordered enough parts to build two, I started (and finished) my second Starving Student amp with the caps specified in the modified schematic, this time even with WIMA MKPoutput bypass caps. However, I have a strange problem. The amp powers up fine. The junction between R1/R2 and between R7/R8 both reads around 46v as specified in the schematic. However, pin 3 in the right channel takes a couple of minutes to reach 19v (and the tube in that channel takes about that long to reach full brightness), while the left channel shows 19v right after power up.

I get no sound in the right channel, while the left channcel works just fine, even after the voltage at pin 3 reached 19v in the right channel.

Will post pics tomorrow. Any hints/clues? Thanks in advance!

Fishline

 

[tomb]

Quote:

Originally Posted by Fishline /img/forum/go_quote.gif Since I have ordered enough parts to build two, I started (and finished) my second Starving Student amp with the caps specified in the modified schematic, this time even with WIMA MKPoutput bypass caps. However, I have a strange problem. The amp powers up fine. The junction between R1/R2 and between R7/R8 both reads around 46v as specified in the schematic. However, pin 3 in the right channel takes a couple of minutes to reach 19v (and the tube in that channel takes about that long to reach full brightness), while the left channel shows 19v right after power up. I get no sound in the right channel, while the left channcel works just fine, even after the voltage at pin 3 reached 19v in the right channel. Will post pics tomorrow. Any hints/clues? Thanks in advance! Fishline

Try switching the tubes and see if it does the same thing.

 

[Fishline]

I did try swapping tubes, but the problem stays with the right channel, so it's not the tube. One more thing: the DC offset on the left is under 5mV, but the right will start at around 60mV and gradually come down to below 5mV, as the voltage on pin 3 of that channel climb up to 19V.

Here are some pics.

 

[Fishline]

Clarification: The problematic channel is the one near the top of the pictures in the first two pics, and the one on the left in the 3rd picture.

 

[Llama16]

I feel like interrupting again, but I just couldn't waite sharing my succes

I slid the amp back in the case and haven't yet screwed on the front and backplate, but as my DC offset was only 1.2mvolt after half a minute, I plugged in my HD650.
An amazing little amp

I understand it when some say that the caps need a burn in period because when I left it running for about 2 hours or so I recongised quite bit of difference from the first few minutes.

Allthough I do recognise that the right channel is significantly louder (not very very much, but you really feel it though, subtle). It becomes really clear when I compare it to my headphone straight from my ipod touch. I have set my rockboxed ipod for 13% more left channel volume to temporary kinda equalize them. Is there any way I can internally fix this? Because I don't really plan on using this solely with rockboxed ipods

.
Tomorow I'm gonna try some 'pinknoise' on it

, so I can get a more accurate idea of how bad the imbalance is. I also read that I should try switching the tubes, or see if the effect is less when the pot is turned up more (signs of an imbalanced pot, I read). I'll be switching the tubes tomorrow (If the channel switches with them, I'll sue my spare set of tubes, so no worries there). Allthough, as far as I improfessionaly tested it, I can't really say that the effect doesn't lessen when I switch from 'low ipod volume, high pot volume' to 'high ipod volume, low pot volume', so I don't think it's an imbalanced pot.
It's as if, when normally the singer is in the middle of my head, it's like as if he shifted more to the right.

Is there any other test I could perform before casing up the amp? And is there a way to internally fix this (I heard of adding a resistor to the right channel to balance it, but yet again, I should know the exact grade of imbalance), if so I'll wait before boxing up the amp

.

BTW: I forgot to say, could it be the cable? I'll explain why. Right now i'm not having a mini to RCA cable at hand so I'm actually using like 3 crappy cables to comensate: First I got an RCA cable from the television (male on each side) connected to the amp. Then I got a selfmade 'female RCAs to female mini connector' to connect to the first cable. As las I got a mini interconnect (two times male) to make the last step towards my ipod.
I was making a (yep even trying to braid it

) a mini male to RCAmales with some generic parts though, when I came to the genial idea to just use those 3 components for a while, to try the amp out. So maybe it's that.

Also, are there any 'professional' ways to test the imbalance? I'm gonna try the pinknoise demo, switch the tubes.. but that's about all I can imagine.

Thanks
Dries

AND A HAPPY NEW YEAR EVERYONE (4 hours to go here though

)!!! You guys made my holiday

My best wishes, a good health, lots of luck and have fun the next year!
*draws a partyhat*

 

[Juaquin]

I'd say 90% of channel imbalance comes from the pot used in this amp (Tom or someone can correct me, if wrong). As such, the way to fix this (short of using a better pot) would be to adjust the input resistors.

 

[the_equalizer]

Quote:

Originally Posted by Fishline /img/forum/go_quote.gif Since I have ordered enough parts to build two, I started (and finished) my second Starving Student amp with the caps specified in the modified schematic, this time even with WIMA MKPoutput bypass caps. However, I have a strange problem. The amp powers up fine. The junction between R1/R2 and between R7/R8 both reads around 46v as specified in the schematic. However, pin 3 in the right channel takes a couple of minutes to reach 19v (and the tube in that channel takes about that long to reach full brightness), while the left channel shows 19v right after power up. I get no sound in the right channel, while the left channcel works just fine, even after the voltage at pin 3 reached 19v in the right channel. Will post pics tomorrow. Any hints/clues? Thanks in advance! Fishline

Quote:

Originally Posted by Fishline /img/forum/go_quote.gif I did try swapping tubes, but the problem stays with the right channel, so it's not the tube. One more thing: the DC offset on the left is under 5mV, but the right will start at around 60mV and gradually come down to below 5mV, as the voltage on pin 3 of that channel climb up to 19V. Here are some pics.

Strange behaviour indeed. So if you've swapped the tubes and get sound from the left channel, I think we can discard a bad tube as the cause.

So that leaves us with the MOSFET. It's either fried or badly polarized. What's the voltage at the junction of R2 and R4 ? It should be around 23 volts (4 volts higher than the tube heater voltage). If it's not, check the values of the resistors, they should both be the same value.

HAPPY NEW YEAR EVERYONE !

cheers!

 

[tomb]

X2 on what equalizer and Juaquin say. If you've confirmed that swapping the tubes has no effect, then it's in the circuit. You have to decide if you can live with it, or whether you need to make a change. I'd rather boost both input resistors to a higher value so that you can get the pot into a more channel-matched regime. IMHO, trying to assymetrically offset the input resistors is an exercise in futility - the balance will vary with the tracking of the pot.

 

[SteveC89]

Ok, so I am about to start my build, but I just realized I ordered 220uF capacitors instead of the 150uF specified. I noticed in the original BOM notes it says any value > 150uF. I was just wondering how the higher value caps might effect the sound.

 

[Fishline]

My first SS has 220uF caps. If you look at the "modified" schematic, the caps have even higher values (470uF and 680uF). Some had gone as high as 1000uF.

Anyone has suggestion for my problem with no sound in one channel (posts 4381, 4383 and 4384 above)? I'd really appreciate the help!

 

[Fishline]

Quote:

Originally Posted by the_equalizer /img/forum/go_quote.gif Strange behaviour indeed. So if you've swapped the tubes and get sound from the left channel, I think we can discard a bad tube as the cause. So that leaves us with the MOSFET. It's either fried or badly polarized. What's the voltage at the junction of R2 and R4 ? It should be around 23 volts (4 volts higher than the tube heater voltage). If it's not, check the values of the resistors, they should both be the same value. HAPPY NEW YEAR EVERYONE ! cheers!

Apologies: Don't know how I could have missed this post. Also, it really should be the left channel in the schematic that's giving me problem. I measured the voltage between R8 and R10, and again, it slowly rose to 22.6v, while between R2 and R4 the voltage is at 22.8v at power on. Both heatsinks get hot, too. If a MOSFET is fried, it wouldn't heat up, would it? Any way to test the mosfet? I do have a couple more spare MOSFETs, but swapping it would be quite a bit of work...

Happy New Year to everyone, too!!

 

[Fishline]

Found the problem. After looking over the schematic again, I noticed I soldered the positive lead of C6 to the junction between R8 and R10, instead of R7 and R8. After correcting that, bingo!

Thanks to all for helping!

 

[Fishline]

Found the problem. After looking over the schematic again, I noticed I soldered the positive lead of C6 to the junction between R8 and R10, instead of R7 and R8. After correcting that, bingo!

Thanks to all for helping!

 

[the_equalizer]

Quote:

Originally Posted by Fishline /img/forum/go_quote.gif Found the problem. After looking over the schematic again, I noticed I soldered the positive lead of C6 to the junction between R8 and R10, instead of R7 and R8. After correcting that, bingo! Thanks to all for helping!

Great news! Enjoy your new amp!

cheers!