[runeight]

Quote:

Originally Posted by lacrossebowe8 /img/forum/go_quote.gif I just finished everything and am listening to some music. Sounds good. I will post some impressions later. I am using sr-80's but usually use sr-225's and I am hoping to pick up some senn 650's soon. Pictures and more to come. Thanks for a great amp design.

OK. Great to hear this and will look forward to further results. Don't forget that you can freely adjust the B+ on the tubes.

 

[runeight]

Quote:

Originally Posted by shellylh /img/forum/go_quote.gif Just ordered a SOHA II kit from Jeff at glassjaraudio.com. What a nice guy. Since this is my first REAL project, I am sure I will be asking a lot of questions as I go. [At this point, I have only made a cmoy, guitar hp amp from a kit and modded my X-can (installed new caps/diodes).] I figure that this will be a real learning experience. Anyway, I hope I don't kill myself or catch anything on fire. It would be even better if the amp actually works and sounds good at some point in the future.

Welcome aboard shellylh. It's great to have another Texan building one of these.

 

[pabbi1]

Quote:

Originally Posted by shellylh /img/forum/go_quote.gif Just ordered a SOHA II kit from Jeff at glassjaraudio.com. What a nice guy. Since this is my first REAL project, I am sure I will be asking a lot of questions as I go. [At this point, I have only made a cmoy, guitar hp amp from a kit and modded my X-can (installed new caps/diodes).] I figure that this will be a real learning experience. Anyway, I hope I don't kill myself or catch anything on fire. It would be even better if the amp actually works and sounds good at some point in the future.

Marry me! A woman building amps and getting a hd800 - what more could any man want?

Seriously, did you get to listen to my SOHA II in Houston? It will be at the DFW meet thanks to the nasty dust conditions in Afghanistan. It is good enough that Marc is building one...

 

[luvdunhill]

Quote:

Originally Posted by pabbi1 /img/forum/go_quote.gif It is good enough that Marc is building one...

yes, I'm plotting to get all Japanese transistors in mine

 

[bmwpowere36m3]

Quote:

Originally Posted by lacrossebowe8 /img/forum/go_quote.gif I just finished everything and am listening to some music. Sounds good. I will post some impressions later. I am using sr-80's but usually use sr-225's and I am hoping to pick up some senn 650's soon. Pictures and more to come. Thanks for a great amp design.

I curious as to your listening impressions, I have extensively listened to the SOHA II w/ HD580's and recently auditioned a pair of Grado SR-80s on it...

I also picked up a set of Amperex/HP 6DJ8 tubes to complement the EH 12AU7's I've already got.

 

[lacrossebowe8]

I will need a few hours of listening time to get some good impressions. The 80's are great, fun, cheap cans. Right now I am using beckman tubes that came with my glass jar kit at 6.3 volts. One day i will do some tube rolling.

What B+ are most people using?

 

[shellylh]

Haha... That depends on whether the KGBH/HE60 will be in the prenuptial agreement! I am not so sure the significant others would be too happy though.

Seriously though, I didn't get to listen to the SOHA II in Houston. There was too much gear and not enough time. I hope to get enough work done in the next week or so to make a road trip but it is not looking good.

Quote:

Originally Posted by pabbi1 /img/forum/go_quote.gif Marry me! A woman building amps and getting a hd800 - what more could any man want? Seriously, did you get to listen to my SOHA II in Houston? It will be at the DFW meet thanks to the nasty dust conditions in Afghanistan. It is good enough that Marc is building one...

 

[Ferrari]

Quote:

Originally Posted by lacrossebowe8 /img/forum/go_quote.gif What B+ are most people using?

I can’t speak for all, but on my builds the B+ voltage is sitting close to the limit of the HV section:
120V on the proto version on the first page of this thread and 90V on the balanced version I’m working on.

 

[holland]

I am using 95V.

 

[Uncle Bob]

My SOHA II has developed the infamous hiss problem

However, it's only in one channel......

1. I'm positive, the hiss problem was not there when the amp was 1st built
2. The problem appeared when I accidently caught the headphone cable and knocked the amp off the shelf it was sitting on. It didn't fall far as the shelf is quite low and the amp was tethered with the power and signal cables, but immediately afterwards I noticed the noise.
3. I suspected I'd damaged the valve but swapping them around beween channels or leaving them out, or changing them for a different type doesn't affect the noise.
4. It's not volume dependant - i.e it's not affected by moving the pot, and is only heard once the E12 relay engages.
5. It's still present if the inputs are disconnected.
6. It's not noise in my ear, if I reverse the headphones, the hiss moves to my other ear.
7. I can only hear it with my Grado's. It may or may not be present with the Sennheisers but if it is, it's just below my hearing threshold.

There's a possibility I might be able to do some checks with a friend's oscilliscope. I'll keep you posted.

 

[Hayduke]

Maybe it's relate to the headphone jack? You determined it was the tubes and it was a tug on the cord that triggered the problem. Maybe the headphones got damaged or the jack did since it took the brunt of the force. I would probably reflow the joints on the output jack and give the jack itself a visual inspection. Of course I have no idea how this could cause a "hiss" sound

My instinct just says to follow the source of the trauma.

 

[Alcaudon]

Quote:

Originally Posted by Uncle Bob /img/forum/go_quote.gif 7. I can only hear it with my Grado's. It may or may not be present with the Sennheisers but if it is, it's just below my hearing threshold.

Maybe the problem is in the headphones. Where they pluged when the amp fell? Have you tried them with another amp?

Hope you can fix it

Edit: Hayduke it's faster than me

 

[runeight]

Quote:

Originally Posted by Uncle Bob /img/forum/go_quote.gif My SOHA II has developed the infamous hiss problem However, it's only in one channel...... 1. I'm positive, the hiss problem was not there when the amp was 1st built 2. The problem appeared when I accidently caught the headphone cable and knocked the amp off the shelf it was sitting on. It didn't fall far as the shelf is quite low and the amp was tethered with the power and signal cables, but immediately afterwards I noticed the noise. 3. I suspected I'd damaged the valve but swapping them around beween channels or leaving them out, or changing them for a different type doesn't affect the noise. 4. It's not volume dependant - i.e it's not affected by moving the pot, and is only heard once the E12 relay engages. 5. It's still present if the inputs are disconnected. 6. It's not noise in my ear, if I reverse the headphones, the hiss moves to my other ear. 7. I can only hear it with my Grado's. It may or may not be present with the Sennheisers but if it is, it's just below my hearing threshold. There's a possibility I might be able to do some checks with a friend's oscilliscope. I'll keep you posted.

Hmmm. Since this was physical stress on the amp, it's probably a mechanical problem. But it doesn't appear that the amp took any kind of concussion, just a dangling from its various cords. Is that right? Or did it actually hit the floor?

In any case, the first electrical thing to do is to measure all of the testpoint to find out if the voltages are correct. And then measure the O/P idle current and the tube tail currents.

If these are all correct then we almost certainly have a mechanical problem somehow.

 

[mdabro]

Ferrari, You have connected tubes to PCB board with long wires. Did not it cause any hum ?

 

[Ferrari]

Quote:

Originally Posted by mdabro /img/forum/go_quote.gif Ferrari, You have connected tubes to PCB board with long wires. Did not it cause any hum ?

Not that I can notice.

To avoid possible bad effect, keep the wires as short as possible and use shielded cable for the sensitive input signal path (pin 2 of tube socket) and connect the shield to GND.

(Shielded cable was not implemented when I post pictures here, but it was implemented short after that).