or Connect
Head-Fi.org › Forums › Misc.-Category Forums › DIY (Do-It-Yourself) Discussions › SOHA II Builders Thread
New Posts  All Forums:Forum Nav:

SOHA II Builders Thread - Page 24

post #346 of 1686
I replaced Q1P, and now TB+L and TB+R are both 60V. It also fixed the e12 tripping problem. However the left channel is much lower volume than the right channel. I assume this means I also screwed up a transistor in the amp circuit. And yes, the bias currents have been set.
post #347 of 1686
Thread Starter 
Since all of the gain comes from the tubes the bjts in the amp can't do much damage except to mess up the voltages. And since you can set your O/P current in both buffers and the e12 works ok then these bjts are almost certainly working properly.

So we have to figure out what's causing the left channel tube to not have enough gain.

Could you kindly check all the resistor values around the tubes. Particularly the two feedback resistors R8 and R7. Are they possibly reversed?

Also, what are your TPR and TPL??
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
Reply
post #348 of 1686
Well...I feel pretty dumb, after checking all the resistors several times, I figured out the problem with left channel. I had the headphone plug too far in, since I don't have the front panel on.

So I got to listen to it...sounds pretty good so far, however I'm noticing some distortion on certain notes, and on a particularly loud section of one song the e12 tripped. I thought this might have something to do with the bias current settings. I check the O/P and it was lower than I had set it, around 200mV so the current would be 90 mA. I tried to turn it up, but now I can't get it above 215mV before I run out of adjustment, I thought that was kind of odd, could it be causing the problems? The other measurements were fine, for the tail current and the difference between TP and TB on both channels.

Thanks for helping with all this
post #349 of 1686
Thread Starter 
Hmmm. Not good.

Is it possible that when the jack was in too far it was shorting the output?

In any case, there is a lot room on the bias pot to set the current properly. Please check all of the resistor values in the O/P stage.

If these are ok then the first question is does the distortion happen on both channels or just one? Are the rail voltages correct?

You might have to replace Q8 on the channel where you can't set the idle (or both if necessary). And then, possibly, Q7.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
Reply
post #350 of 1686
Quote:
Originally Posted by runeight View Post
Hmmm. Not good.
That's what I was afraid of.

It doesn't look like the input was shorting out, it was just making a bad connection (hitting the resistive bands). As far as I can tell the distortion is in both channels, also both channels act the same when setting the current. Unfortunately I am leaving in the morning, so I won't be able to work on it for a couple days. I'll post back when I've had a chance to check all of the resistors, etc.

Thanks again for the help, and happy new year
post #351 of 1686
Quote:
Originally Posted by bmwpowere36m3 View Post
Thanks, so far I'm really impressed by this amp. Definitely a lot better than the "SS" Hybrid and CMoY it has replaced. I've been listening to it with Senn HD580's and EH 12AU7 tubes thus far and I really enjoy the sound. The amp has been burning in for over now ~90hrs straight (have been listening here and there; at night letting it just run with a "test" set of headphones). I'll say the EH tubes have definitely settled in since when I first listened to them.

The build was straightforward and nothing really stood out as problematic. I only had trouble since I didn't install the pot before testing and was worried something had been damaged. WHen that was alleviated, I finished up the build no problem. Since I changed up my build, I had some "problems" getting everything to fit... eventually figured out the layout.

The EH tubes at first were a little harsh and very in your face, forward soundstage. As they burned in they've settled back, but still have a forward presentation. They have clear, defined highs, good midrange punch, and bass detail. I'd say the only thing they lack is maybe some more bass slam and midrange bloom, however like Holland has mentioned elsewhere they sound wonderful paired with "Metal".

I've listened to music ranging from Pink Floyd, Led Zeppelin to Metallica, Alice in Chains, In Flames, AC/DC, to some classical. It all sounds good and much more detailed than any other amp I've had thus far... when I start rolling tubes I'll be looking for something with a "warmer" sound (for Floyd, Classical, etc..), as the EH's are fairly neutral compared to my "SS" Hybrid which was very "tubey" sounding and a little overly warm.

I'm impressed and here are some pictures of it cased up for now, it'll stay like this till I get some more time to finish it up with a top. Also the knob is temporary, scavenged from my "SS"...
I missed this. It looks nice, bmw. I'm glad you're enjoying it. It's really no surprise it's better than the SS or a CMoy. It's a different class.

I'm rolling 8416 and 6189 right now. Will roll some 5814s later. I'm finding I'd rather relax and listen to music than build my Bijou. I really hate casework.
post #352 of 1686
Quote:
Originally Posted by Ferrari View Post
Don't worry, that is a good reason for me to put this amp into this enclosure ASAP.
Ferrari I have a question about this build. I'd like to build mine "upside down" too so the tubes will stick out further. I like they way they look

My question is about heat. By doing this, aren't you dramatically affecting how well the heat sinks work? The heat would travel up and get stuck on the board.

Maybe it's not an issue, but it has me worried, so I thought I would ask how yours is working.
post #353 of 1686
^^ I missed that link too, Ferrari. Damn, you keep taking things further. That one is really badass.

I think you had better stop. I don't know about others, but I'm starting to feel inadequate.
post #354 of 1686
Is it true that there will be front and back panels available for the Hammound enclosure?
post #355 of 1686
Quote:
Originally Posted by regal View Post
Is it true that there will be front and back panels available for the Hammound enclosure?
I don't think there was enough interest in them. To be fair Runeight did put it to the test to to see if enough people would buy them but he got very little feedback.. I might be wrong though of course..
post #356 of 1686
Quote:
Originally Posted by Hayduke View Post
I'd like to build mine "upside down" too so the tubes will stick out further. I like they way they look
As an alternative to the “upside down” build, I mounted the tube sockets on a separate platform made from scrap aluminium. It slides into the second highest slot in the Hammond case, which leaves enough room for the stock heatsinks below if the amp itself is in the second lowest slot.



See here for how it looks with the lid on—the tubes stick out almost completely. Also very convenient for tube rolling, as I don't have to worry about putting too much pressure on the board.

I think Ferrari also made a similar platform for his other SOHA II build?
post #357 of 1686
Thread Starter 
Quote:
Originally Posted by onform View Post
I don't think there was enough interest in them. To be fair Runeight did put it to the test to to see if enough people would buy them but he got very little feedback.. I might be wrong though of course..
This is true. I have offered on several occasions to have these panels made and sold through GJA but there hasn't been quite enough interest. Partly, I suspect, because they are so expensive.

To make this worthwhile we need to make at lest ten sets. The price would be $18 for the front panel and $22 for the back panel. This adds $40 to the cost of the kit from GJA.

Jeff was going to look into having the stock hammond panels (since the hammond enclosure comes with the kit) punched out by a local machine shop, but I don't think there has been progress on that front.

That's all I know . . . let me know what I can do.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
Reply
post #358 of 1686
Quote:
Originally Posted by Hayduke View Post
Ferrari I have a question about this build. I'd like to build mine "upside down" too so the tubes will stick out further. I like they way they look

My question is about heat. By doing this, aren't you dramatically affecting how well the heat sinks work? The heat would travel up and get stuck on the board.

Maybe it's not an issue, but it has me worried, so I thought I would ask how yours is working.
Yes, you are correct that the heat would travel up and get stuck on the board… in a closed box.
The heat can simply not escape and will definitely accumulated in the enclosure, since there is no air convection.

But as long as there is sufficient air convection (air flows bottom => top), it should be fine.
The heat does travel up and then coming out the enclosure via the tube holes (28mm dia) and the vents on top of the enclosure.
The enclosure I used is very well ventilated (vents on both top and bottom).
On top of that, I have made 4 extra holes with 20mm diameter on the bottom plate, right under the area of the heatsinks.
By doing so, cold air can enter the enclosure exactly where it needed most.
The invisible hand of Mother Nature does the remaining part of the cooling job.
post #359 of 1686
Here's the nice panels runeight is refering to:
http://www.head-fi.org/forums/5120441-post699.html

Runeight I've read than some tubes like 6DJ8 are rated @ 365mA for the heather current. Does that mean I need to upgrade the transfo (+ remove a resistor in the PS) to use them or 300 mA would be sufficient?

reference:
The 6DJ8 / ECC88 / 6922 Tube
post #360 of 1686
Thread Starter 
There shouldn't be any problems if you make R3P 8R2. This value was changed during the prototype process, down from 10R, for just this reason.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
Reply
New Posts  All Forums:Forum Nav:
  Return Home
Head-Fi.org › Forums › Misc.-Category Forums › DIY (Do-It-Yourself) Discussions › SOHA II Builders Thread