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DIY Millet 307A build thread ? - Page 2

post #16 of 24
I bought the cheapie regulator kits off eBay, but no chance of them performing at 1A. I looked at Pete's circuit, and couldn't find some of the parts, much less do the p2p. Finally, the 4x $200 for Tent Lab regulators, iirc, took me well past $2k in parts for this, so I (half) pulled the plug, and sold the James 2508 OPTs and my beautiful NOS UTC 10h chokes (4 of them).

Even sillier is that I got the interstage stuff, knowing I wasn't splitting SE but building differential from the get go.

Nope, this is where my journey stops. I admire Nate for going where I can't (and gladly adding to his 307a collection), but man enough to admit this is my limit, expecially until other things get cleaned up. Maybe some day down the road, but, not today.
post #17 of 24
Quote:
Originally Posted by pabbi1 View Post
Nope, this is where my journey stops. I admire Nate for going where I can't (and gladly adding to his 307a collection), but man enough to admit this is my limit, expecially until other things get cleaned up. Maybe some day down the road, but, not today.
It's been a painful journey and I haven't even started on the chassis yet. Someday soon hopefully, if I can keep from getting further distracted by other projects.
post #18 of 24
Quote:
Originally Posted by n_maher View Post
It's been a painful journey and I haven't even started on the chassis yet. Someday soon hopefully, if I can keep from getting further distracted by other projects.
Well, kitting up one project really doesn't distract from another... or, does it?
post #19 of 24
Quote:
Originally Posted by regal View Post
I can't seem to find a datasheet for this tube.
Really? Did you try TDSL?

http://www.mif.pg.gda.pl/homepages/f...136/3/307A.pdf

There are some triode curves floating around, too that you can calculate rp, mu, and S from -- rp is ~1500 ohms and dissipation is somewhere between 15w and 20W. Overall, the triode curves look almost exactly like 6L6 triode curves, so you can pretty much design from there and then tweak. (they are below, but you may need to be logged in at DIYAudio to see them)



Quote:
Originally Posted by regal View Post
I guess based on my experiments with Grados (MS1's, HF2's, and MS-Pros) I found a strong correlation to low output impedance to less congestion. For example the 5842 SET OPT amp doesn't compare favorably to my HV-properly biased Tube + SS buffer hybrid amp that has an output impedance of 2 (with zero NFB). It isn't so noticeable until a complex passage hits and to me it is obvious that the driver is out of control. Escpecially a SET amp damping plays a critical role because the damping factor changes as the tube output voltage goes up/down with the music.
That isn't damping factor -- that sounds like clipping, or blocking distortion, or IM distortion, or something of the sort.

Yes, damping factor changes with voltage, but not by that much, certainly not be enough to hear easily, and, unless you are listening unbelievably loud, and using an enormous stepdown, voltage is not swinging that much on the plate.



Quote:
Originally Posted by regal View Post
Before recommending this, you should build one and put a scope on it -- LM317 based current sources have a bad habit of oscillating. The measures typically needed to stop these oscillations involve an AC bypass that defeats the whole point of a CCS by providing a low impedance at AC. It can be made to work, but I've never had much luck, even at moderate currents. The tent labs stuff is probably a little overpriced, but in designing ones own it is easy to spend more -- though that's always the case with DIY, right?
post #20 of 24
I had huge issues with LM317 current sources as Doug mentioned. In fact, I had one on a PCB that I finally just moved a trace or two in order to just to drive a LED, I was so fed up with it.... that's a more appropriate duty in my opinion.
post #21 of 24
Quote:
Originally Posted by dsavitsk View Post
I built, for instance, a pentode based transconductance amp with a Zout of ~300 ohms that is turning out to be one of my favorite Grado amps I've heard.
Personally, that's the only way I can listen to Grados. To me, Grados are painfully shrill with a low source-impedance driver.

But that's just me.

BTW, the 307A amp on the web page is a push-pull speaker amp. The TTVJ 307A is a single-ended headphone amp. As was mentioned, the TTVJ 307A uses an input transformer to allow balanced line input as well as galvanic isolation to lower ground-induced noise (when/if needed).

Pete
post #22 of 24
Thread Starter 
I've learned a great deal from this thread, thanks for sharing your knowledge gained.

I need to take another look at the grado impedance thing. I guess I like the sharp guitar strikes of Grados, and they seem to fall in the background with a low damping factor.
post #23 of 24
Quote:
Originally Posted by pabbi1 View Post
Well, kitting up one project really doesn't distract from another... or, does it?
It does when the kit looks like this. And that's a partial, incomplete set of parts...

post #24 of 24
Thread Starter 
Quote:
Originally Posted by dsavitsk View Post
Really? Did you try TDSL?


Before recommending this, you should build one and put a scope on it -- LM317 based current sources have a bad habit of oscillating. The measures typically needed to stop these oscillations involve an AC bypass that defeats the whole point of a CCS by providing a low impedance at AC. It can be made to work, but I've never had much luck, even at moderate currents. The tent labs stuff is probably a little overpriced, but in designing ones own it is easy to spend more -- though that's always the case with DIY, right?

Thanks for the advice, Have you tried battery powering the LM CCS:


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