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A Very Compact Hybrid Amp - Page 51

post #751 of 2213
so I hear tell that it's a bad idea to mount the tube off the board by a few inches with wire. Is this correct and why?
post #752 of 2213
Thread Starter 
It's simply that any extra wire between the tube and the board introduces opportunity for E/M to get into the signal circuit. And since the buffers in this amp have very high input impedance they will be sensitive to this, including the burst of radiation that occurs when the e12 relay turns on and off. Keeping the tube close minimizes the chances for problems. But there is no hard a fast rule.

There is also a switching regulator on the board which generates some noise too. The closer the tube socket is to the ground plane on the board the less opportunity there is for this noise to get into audio as well. Although, IIRC, the oscillating freq of the regulator is 150kHz.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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post #753 of 2213
Quote:
Originally Posted by MrSlim View Post
goes up to 1 3/8", which is plenty large enough for the tubes used in the CTH.
In fact, it's just the right size to use a ring from a tube protector to "finish" it up, like the last pic here:
Unfortunately I have something that will go around the hole which needs a 1 1/2" hole..

Quote:
Originally Posted by sachu View Post
Congrats on your first build...That was really fast considering the components had to be shipped to australia..
Cheers. I had all the parts ordered a few weeks ago as I needed a bunch of other stuff from Mouser, just had to wait on the PCB's. But Mouser's shipping is pretty amazing, I had a US$500 order on my door in 71 hours from when I ordered.

Now to go buy the cables I need to actually hear this properly!
post #754 of 2213
Quote:
Originally Posted by runeight View Post
It's simply that any extra wire between the tube and the board introduces opportunity for E/M to get into the signal circuit. And since the buffers in this amp have very high input impedance they will be sensitive to this, including the burst of radiation that occurs when the e12 relay turns on and off. Keeping the tube close minimizes the chances for problems. But there is no hard a fast rule.

There is also a switching regulator on the board which generates some noise too. The closer the tube socket is to the ground plane on the board the less opportunity there is for this noise to get into audio as well. Although, IIRC, the oscillating freq of the regulator is 150kHz.
Thanks for that, I think I'll try it see if it's workable or not, I can always stick it on the board if there are problems.

Thanks
post #755 of 2213
Quote:
Originally Posted by runeight View Post
OK. Is the 2227 a jfet input opamp? I have forgotten.

Next text is to meaure all of the pins on the buffer opamp with respect to SG and report back. And you said that OG is 12V (or very close)?
Actually, I was wrong 2227 is a low offset bi-polar. Anyway, I know the tl082 is functional because I dropped in a cmoy and it played fine. OG is right near 12v.

Buffer opamp pins are as follows:
1 8v
2 10.8v
3 11.9v
4 0v
5 11.9v
6 10.8v
7 5.8v
8 23.8v

These numbers are with the tl082, by the way.
post #756 of 2213
Thread Starter 
These are interesting numbers, but I can't yet tell what is broken.

Pins 2 & 6 are connected to the splitter, OG. They both show the 11.9V that you measure there.

Pins 3 & 5 are connected to the buffer outputs. The opamp will try to adjust its own output voltage (pins 1 & 7) so that the voltages at 2,3 and 5,6 are identical.

We can see that the voltages are not identical, however. They are off by 1V (11.9V vs. 10.8V). This typically happens when the opamp slams against one of its rails and can't adjust any farther. But in this case the opamp outputs are very far from the rails. They are at 8V and 5.8V. The opamps have plenty of room to maneuver, but they are not equalizing their inputs.

So, with no headphones can you please measure the voltages on both leads of R18 on both channels.

Hate to run you through this but I don't know what's wrong yet.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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post #757 of 2213
Quote:
Originally Posted by smeggy View Post
Thanks for that, I think I'll try it see if it's workable or not, I can always stick it on the board if there are problems.

Thanks
Smegster,

your board is about 95% complete..took me about an hour and 45 mins. guess those 4 beers helped speed up my pace...
post #758 of 2213
Holy crap Sachu!

now you're not just putting these bits in place with Blutac are you...
post #759 of 2213
Quote:
Originally Posted by smeggy View Post
Holy crap Sachu!

now you're not just putting these bits in place with Blutac are you...
heh..a few components are not flush to the board..pesky diodes and resistors seem to fall out sometimes..



Will go get some resistors that are missing, the DIP sockets, tube socket from the surplus store...should be ready to fire up along with my second board later tomorrow.
post #760 of 2213
Awesome!!!

It's so cute!
post #761 of 2213
Quote:
Originally Posted by smeggy View Post
Awesome!!!

It's so cute!
Heh..not as pretty as I could have made it...but I was moving fast on this one.
Btw,

DO you want me to install the BOM standard coupling caps? OR do you want me to get some fancy caps for them? Basically C4L and C4R which are 0.22uF polypropelene caps.

There are many options...let me know. I might socket the caps in case you want to try different caps later
post #762 of 2213
eagerly awaiting my package to show up so I can get started. Best finish my buffalo build first so I have a source though!
post #763 of 2213
Quote:
Originally Posted by Nebby View Post
eagerly awaiting my package to show up so I can get started. Best finish my buffalo build first so I have a source though!
heh..my DIY DAC has been languishing for over 4 months now...waiting for 4 Jung super regulator boards to arrive from Sweden first...but man..I would love to snag a buffalo DAC
post #764 of 2213
Quote:
Originally Posted by sachu View Post
Heh..not as pretty as I could have made it...but I was moving fast on this one.
Btw,

DO you want me to install the BOM standard coupling caps? OR do you want me to get some fancy caps for them? Basically C4L and C4R which are 0.22uF polypropelene caps.

There are many options...let me know. I might socket the caps in case you want to try different caps later
I dunno, whatever is good. I have no idea what the bigger caps etc do so can't really say. I'll leave it in your drunken hands

Oh, did you ever win that tube auction you were going for or should I just order the $30 one from wherever it was?
post #765 of 2213
Quote:
Originally Posted by smeggy View Post
I dunno, whatever is good. I have no idea what the bigger caps etc do so can't really say. I'll leave it in your drunken hands

Oh, did you ever win that tube auction you were going for or should I just order the $30 one from wherever it was?
Heh..will socket them and install the BOM caps for now..That's what m original one has.

Naa that tube auction didn't go well ..another time perhaps
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