[tomb]

Quote:

Hey, my electronic parts just arrived so I'm going to start mounting this little guy very soon (still awaiting tubes and power supply).
 
I'm probably going to start working on the case. What would be the best material for the case? Is wood okay? My father's a carpenter so I could get some help there. I'm asking because I don't want to have noise or hum on the amp. Maybe a combination of wood and metal? Thanks.

While there is nothing wrong with a wood case, more metal is better for grounding and reducing hum.  If you use wood, you should probably add something similar to the copper ground plate that Pete Millett used in the original.
 

 

[tomb]

Quote:

Hi,  I just finished building my 12au7 amp per the instructions above. However I'm having some problems, when both channels are connected the amp sounds tinny and weak. When a single channel is connected sound comes out both sides of my headphones at equal volumes. I believe it might be a faulty RCA jack. Would a faulty RCA jack cause what I described?

It looks like no one responded to this.  If it's not too late, the symptoms you describe are a perfect example of wiring up the jacks or the heapdhone jack incorrectly.  Take a good look at your wiring and make certain that you didn't use an opposite channel's signal wire for the ground on one of the RCA jacks/headphone jack connections.

 

[Amatsu]

Hey, my tubes and sockets just arrived but I can't fit the tubes inside the sockets even though they align perfectly, the tube doesn't enter the metallic part of the socket and doesn't stay still... I'm starting to wonder if the sockets holes are too small or if they are different kind of sockets. I'd appreciate any feedback. These are the sockets I bought (a pack of 4): http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=300462903452&ru=http://shop.ebay.co.uk:80/%3F_from%3DR40%26_trksid%3Dp5197.m570.l1313%26_nkw%3D300462903452%26_sacat%3DSee-All-Categories%26_fvi%3D1&_rdc=1#ht_500wt_922The tubes are 17EW8, both socket and tubes are 9-pin.
 
Edit:
 
I tried widening the holes with a small screwdriver and now the tube enters fine.

 

[Ikarios]

So I've suspected that my 12AU7 SSMH has a higher-than-normal noise floor for quite some time. At my normal listening levels (which is generally quiet by most people's standards) I can hear some hiss with low impedance headphones like Grados and most portables. I don't really hear it with my K701 so I didn't really bother with it. I confirmed that my version does have a much higher noise floor than a stock kit 19J6 SSMH (but also has about 2x more volume/gain). Now that I'm beginning to diversify and getting a whole bunch of portables I figure I should tackle this issue sooner rather than later. What's generally the main culprit of a high noise floor?
 
For the components of my build I stuck to the TomB PCB BOM as closely as possible, only making changes for some of my switch implementations (gain, input, LED) and the 12AU7 version differences given by the_equalizer. I'm also using a GrubDAC wired to the input switch, which is my main input, but I've tried it with other inputs (through RCAs also connected to the input switch) and it's not the input that's the issue. I've considered cutting out C7 and C8 and instead attaching them to the gain switch (which currently switches between 50k and 150k resistors feeding into a 50k pot, but doesn't make a very big impact - only approx. 30-60 degrees of the volume knob). I'm also using a star ground with (I believe) no copper plane. Any ideas?

 

[holland]

1) bad tubes
2) poor grounding scheme
3) poor wiring/layout
4) oscillating mosfets
 
what kind of noise do you have?

 

[Ikarios]

With low impedance headphones, a low steady hiss that increases steadily as I turn the volume knob. I'm thinking it's a combination of #2 and #3 (lots of extra wire inside, no ground plane) but I haven't spend much time listening to the other set of tubes I have so I guess it *could* be the problem. Should I try adding a copper plate as ground?

 

[the_equalizer]

I seem to remember Beftus mentioned in a post that adding grid-stoppers helped with a similar noise issue. Maybe he can chime in.
 
cheers!

 

[walangalam]

Are you sure you're not hearing the hiss from your source?
 
Ground you inputs.  If you still hear hiss its from the amp.

 

[Beftus]

Quote:

I seem to remember Beftus mentioned in a post that adding grid-stoppers helped with a similar noise issue. Maybe he can chime in.
 
cheers!

I don't think we have the same noise issue : http://www.head-fi.org/forum/thread/319231/millett-starving-student-hybrid-amp/5310#post_6733980

 

[monkeyevil]

Any issue using these caps?
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&itemSeq=96055649&uq=634323643171191105
 
 
EDIT:
NM, Went with 
http://beezar.com/oscommerce2/catalog/product_info.php?products_id=73

 

[Ikarios]

Quote:

Are you sure you're not hearing the hiss from your source?
 
Ground you inputs.  If you still hear hiss its from the amp.

I'm not sure what grounding my inputs means, but I've tried two sources (USB -> GrubDAC -> switch -> SSMH, and X-Fi XtremeMusic -> RCA in -> switch -> SSMH) and the hiss exists. I will have a third source available by next week that I can try, but I doubt it will make a difference.

 

[walangalam]

Grounding the inputs means shorting the ground lug to the signal lug in the RCA jack.  Its like the minimum position of the volume pot, where essentially the wiper of the pot is shorted to ground.  But because of production tolerances, its only "almost" shorted, not completely shorted, so there is some signal still present.
 
The reason I ask is because of your comment that the hiss increases as you rotate the volume pot.  Since the amp components sit behind the pot, then increasing the volume should not increase the hiss at all.  So I suspect that you are hearing the source hiss.
 
 
 

 

[Ikarios]

Quote:

Grounding the inputs means shorting the ground lug to the signal lug in the RCA jack.  Its like the minimum position of the volume pot, where essentially the wiper of the pot is shorted to ground.  But because of production tolerances, its only "almost" shorted, not completely shorted, so there is some signal still present.
 
The reason I ask is because of your comment that the hiss increases as you rotate the volume pot.  Since the amp components sit behind the pot, then increasing the volume should not increase the hiss at all.  So I suspect that you are hearing the source hiss.
 
 
 

Okay. I did some experimenting.
A couple things:
1) My RCA inputs are always noisier than the GrubDAC inputs (when off).
2) If I don't ground the RCA inputs and turn up the volume all the way max, I get a buzzing sound in the left channel (and only really noticeable in the left channel). This is interesting, because I've always thought my pot had a channel imbalance between leftmost turn and ~8-9 o'clock (where the left channel would be louder than the right).
3) If I ground the RCA inputs and turn up the volume, the hiss will be less evident, but still more than when I have the GrubDAC selected (and off).
4) With the DAC selected the hiss does increase with the volume, but only slightly. Most of the hiss is still present at zero volume (maybe about twice as loud going from zero volume to max volume).
5) with the GrubDAC on and volume to max, I definitely hear computer noise, as it gets worse when I move my mouse. This is not something I hear at normal listening levels.
6) With the RCAs selected and the inputs not grounded, most of the noise/hum (mostly evident in the left channel) (not the background hiss) is attenuated when I put my hand on the metal case of the amp, then completely disappears when I lift the amp off my desk. My case is isolated with little rubber feet, and placing some paper underneath the amp doesn't get rid of the "lift" effect. I suspect my tubes are slightly susceptible to vibration.
 
So while I can definitely hear some input noise depending on what it's connected to, the "hiss" I hear with Grados is definitely coming from the amp. I don't think it's a ground plane issue, because my star ground is linked to the case, which should be good enough. I have a lot of excess wiring; could that be a major contributor to noise/hiss?

 

[monkeyevil]

 
Just because I had a hard time figuring out what parts I needed, I'll post this.
 
For the 9 pin and 17EW8 or similar the only real substitution from the original parts list (besides any of the optional stuff.) is the 390omh resistors in R2 & R8. Correct?
 
This is the current parts list I have on order for mine.  I subbed 63volts 470uF 20% general caps for the audio ones suggested because they were back orderd.  Not saying it's all correct, but I had a hell of a time figuring out what I needed and what I didn't from the 370 page thread
 
http://www.evilmonkeymedia.com/dl/SSamp.htm

 

[holland]

 
Quote:

Okay. I did some experimenting.
A couple things:
1) My RCA inputs are always noisier than the GrubDAC inputs (when off).
2) If I don't ground the RCA inputs and turn up the volume all the way max, I get a buzzing sound in the left channel (and only really noticeable in the left channel). This is interesting, because I've always thought my pot had a channel imbalance between leftmost turn and ~8-9 o'clock (where the left channel would be louder than the right).
3) If I ground the RCA inputs and turn up the volume, the hiss will be less evident, but still more than when I have the GrubDAC selected (and off).
4) With the DAC selected the hiss does increase with the volume, but only slightly. Most of the hiss is still present at zero volume (maybe about twice as loud going from zero volume to max volume).
5) with the GrubDAC on and volume to max, I definitely hear computer noise, as it gets worse when I move my mouse. This is not something I hear at normal listening levels.
6) With the RCAs selected and the inputs not grounded, most of the noise/hum (mostly evident in the left channel) (not the background hiss) is attenuated when I put my hand on the metal case of the amp, then completely disappears when I lift the amp off my desk. My case is isolated with little rubber feet, and placing some paper underneath the amp doesn't get rid of the "lift" effect. I suspect my tubes are slightly susceptible to vibration.
 
So while I can definitely hear some input noise depending on what it's connected to, the "hiss" I hear with Grados is definitely coming from the amp. I don't think it's a ground plane issue, because my star ground is linked to the case, which should be good enough. I have a lot of excess wiring; could that be a major contributor to noise/hiss?

Pictures.  You need to ground your case.  It sounds like you may have a ground loop as well.