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A Very Compact Hybrid Amp - Page 62

post #916 of 2213
I was wondering how much current is going to the e12 LEDs right now and if it would be possible to adjust this bias to get something like 10-15mA to better light up a tube LED?
post #917 of 2213
12AU7 tubes do need a little help in the glow department. Make it orange if you can, it only proper.
post #918 of 2213
thanks for spotting the error. that's why I always sort pics before turning on.
post #919 of 2213
Quote:
Originally Posted by zkool448 View Post
< snip > The SS has warm, tubey like sound and much deeper bass while the CTH sounds more detailed, accurate and good channel separation with very sharp mids/highs (but not bright).. am very happy with it.
One of the really nice things about this amp is the ability to contour its sound to your tastes/cans. TimJo & others have good posts in this regard.

Primarily this is done by rolling tubes. E.g. if more bass Amperex 6dj8 may do the trick (esp for rock/alt), while Siemens chrome plate seems more flat, detailed & accurate. Those are only a couple of my impressions, there are quite a few others in this thread & the CTH Tube & Tweaks thread.

Another way to change the sound of the amp is altering the only caps in the primary signal path; C4s. E.g. I've found Amperex 6dj8 w/Mundorf S+O C4s too lush/tubey/heavy/bassy for my fav D2000s (great for DT-880s tho) & plan to pull the S+Os & try Sonicaps.
So cap rolling is another option esp. in larger-than-stock cases. But due to the tight confines, the CTH may be sensitive to cap placement, lead length so tube rolling is primary.

IMO those used to "tubey" sound may be initially surprised by the detail, accuracy, etc. of this amp. And after getting used to that may not want to forgo it And options for contouring the sound are always there too.

Glad you are liking it.
post #920 of 2213
Quote:
Originally Posted by MrSlim View Post
Oops, my mistake, I looked at the schematic and didn't check the parts layout...
It might be worthwhile measuring the voltage on the input and output of C4L and R, the interstage coupling cap and compare the two channels. That might help determining if the input stage is at fault or it's something in the buffer.

Runeight would have to comment on this, but I'm wondering if a bad D2(R) might cause this? It is supposed to provide a constant current source for the upper half of the buffer, and the servo opamp is used to adjust the lower current source to compensate for variations between the parameters of the upper and lower transistors, to end up with close to zero DC offset at the output.

Also, have another look at all your solder joints, in case you have a cold/bad one that is causing you issues.
Thanks again. As to your first suggestion on C4, how would I accomplish this physically? Forgive my noobiness, but I am not sure how I would go about measuring these two. I did swap out C4R to see if that would help, but it did not.

On the D2, I measured both L and R and the readings are similar with the diode setting on my DMM. This was not under power. Is it possible that D2R is bad even though it reads near D2L. I mean the problem only occurs periodically, so the part must work most of the time, no?

I have tried to go over all the joints on the right side buffer. I also measured all the resistors there, and double checked all the wiring.

Earlier, Alex had mentioned swapping Qs in the splitter. I guess I will try this next, although I wonder that this would produce a problem only on the right side. I'm not sure.

What other parts would be worthwhile to swap as potentially problematic?
post #921 of 2213
Quote:
Originally Posted by zkool448 View Post
oh geez... as I mentioned I don't really have what you experts call "trained ears" not too mention a total hp noob ...but If you'll insists, i'll do my best and give an objective comparison of the two once I get the CTH fully burned in (just like my MSSH).

I also have to build me this A/B box by danobeavis first since it's probably that only way I can distinctively identify their similarities and/or differences.
I like clean and simple, and Beavis' box is certainly that, but I have to warn everyone about a change you will have to make to the build instructions to use it with the CTH (and any other amp that uses a VIRTUAL GROUND(in the CTH it floats at about +12V) on the output). His wireing instructions suggest that you connect all the grounds together. That would be a no-no, since you would be connecting real ground and +12 V together.
You should only connect the input ground to Buss A and Buss B Send, and connect the Output Ground to Buss A and B Receive. I'll email him about his also, so he changes his site..
post #922 of 2213
Quote:
Originally Posted by tacitapproval View Post
< snip >
What other parts would be worthwhile to swap as potentially problematic?
With the symbiotic/complimentary relationship of elements in this design, it's sometimes hard to pin down problems to specific component(s). A build error, short or bad/out-of-spec part can cause trouble elsewhere.

E.g. when I fried OB TO92s probing around tried limiting my replacements to what I thought could be bad. Was wrong & got to watch them fry again.

That's why I suggested wholesale replacement of sand in suspect circuits. Assuming the L+R tube servos are ok. Just a thought.

Me & my Proto PCB were getting tired of removing/replacing things so just went all out. Of course, it's worked perfectly ever since.
post #923 of 2213
Tacitapproval, If you don't have one already, get yourself one of these: Desoldering Tool Professional Solder Sucker Pump TSL017 - eBay (item 400045454976 end time May-24-09 05:12:13 PDT)
I've been in the tech field a long time, back in the day when we were fixing REAL computers in the field and we needed to be really good at desoldering components. Damaging a board was not an option. Using a desoldering pump like this will help reduce the damage done to the board through repeated component replacements. When I built my prototype, I put all (Yes all...) of the tombstone'd diodes in backwards. I was able to flip most of them around, and replaced a couple of other components (the 2595 didn't approve...) and its been singing nicely for me since without a problem.

I tend to agree with CF about replacing all the transistors in the right buffer.. They are cheap anyway.

I still think the DC swing has got to be coming from the buffer. C4 should block any DC coming from the input stage, and since it's only happening on one channel, I can't see how one of the common circuits(power supply, splitter) could be causing it. Of course everyone is entitled to MY opinion , but Runeight was the one who designed this beauty, along with CF, so they would have the best one's to help diagnose your issues..
post #924 of 2213
I have replaced transistors in the right side buffer and TL082. This leaves D2R, which measures okay, in the right buffer, right? I have transistors, so I can swap them in the left buffer(worthwhile?), e12, and splitter. I don't have the diodes. Perhaps Bill will be willing to send them? Anything else?

Cf -- How do I know the tube servos are correct?
post #925 of 2213
@tacitapproval. I'm not sure if my problem is gone or not. It has disappeared the last I checked, but I do not know why. The problem was happening, I put a socket saver on thinking it was heat on Q9R, Q6R, and Q7R that causes the problem as it builds up over time, and the problem went away. Removing the socket saver, to try and analyze further, and it didn't reproduce.

I had replaced all the transistors in my right side buffer a while back.

As for your question, the tube servos. Monitor the DC plate and cathode voltage of the tube pins. For the right side, the pin 6 and pin 8. Mine are fairly steady. The cap should be blocking the DC going through, anyway. The only thing that gets through would be AC. I would be surprised if it's the opamp on the tube, but it wouldn't hurt to test.

Edit: I haven't looked at the amp for a few days, after the problem disappeared. I will try again when I finish the casework.
post #926 of 2213
Quote:
Originally Posted by MrSlim View Post
< snip >
I tend to agree with CF about replacing all the transistors in the right buffer.. They are cheap anyway.

I still think the DC swing has got to be coming from the buffer. C4 should block any DC coming from the input stage, and since it's only happening on one channel,< snip >
Actually, I suggested *all* TO92s in OB & splitter & e12. I even did CRDs in OB & had OPAs to swap in.
Radical for sure, but as a rifle wasn't working I reached for the shotgun

Cf -- How do I know the tube servos are correct? - Think measurements you had for runeight could prove this but think removing C4s would really isolate DC offset to the OB (as MrSlim suggests, Edit: pulling the tube may achieve same iso as pulling C4s). Whenever I'd offset issues during prototyping I think it was always the settling down of the buffer (temp-wise, etc) that caused them. I may have presented OB w/1M to ground in place of C4s, to give them an input ref, but don't remember.
Runeight knows best here tho.
post #927 of 2213
Quote:
Originally Posted by cfcubed View Post
Whenever I'd offset issues during prototyping I think it was always the settling down of the buffer (temp-wise, etc) that caused them.
When I was hunting my offset issue, I blew on the buffers and tripped the e12 immediately. I put a fan on it to see if things varied and it settled down, removing the fan and the DC started to move in a large fashion. That's what lead me to believe it's the temperatures and knowing BJTs increase current as temp increases.

I honestly don't know what happened now, but the ambient temperatures are wildly different than when I initially had the problem (read cold now with temps in the 60s and 70s instead of 80s). Since I don't want to pull out a heater, I'll wait for warmer days.

@tacitapproval, if you've got a socket saver, give that a try. I'm at a bit of a loss right now, as to explain what happened for me.
post #928 of 2213
Quote:
Originally Posted by zkool448 View Post
I brought mine up and with a bit of luck on my side lately my CTH came to life without any issues.
Quote:
Originally Posted by Coreyk78 View Post
Fixed mine. Switched the caps around and its working beautifully now thanks guys!
Congratulations guys. Now the fun starts!

@Adumus - let us know how your amp is doing after you swap caps...

I'm just loving my amp. Meanwhile I'm saving my pennies to build a Bijou next.
post #929 of 2213
Quote:
Originally Posted by zkool448 View Post
haha, it's quite easy to make that mistake, I almost did it too -- perhaps need to make one of the caps Nichicon


nope, sorry didn't mean to leave that impression. I wanted to say was i first need to build a true A/B device that allows to switch amps 'on-the-fly' easily before I can subjectively hear their differences. My initial impression though is that the CTH and SS millett do not sound alike to my ears. The SS has warm, tubey like sound and much deeper bass while the CTH sounds more detailed, accurate and good channel separation with very sharp mids/highs (but not bright).. am very happy with it.

I'm currently using a Russian 61NP NOS tube which I'm going to let burnin for a bit.


.

your observations are quite inline with mine..i did have the presonus central station acting as the DAC as well as an A/B box..

The bass in the CTH got better with different tubes, worse with others. I have an amperex 6DJ8 that I want to try and also have a Seimens ECC92 coming in..so we'll see how those two perform.
post #930 of 2213
Quote:
Originally Posted by MrSlim View Post
Hey Bill, I wanted to let you know my package arrived this week, and I installed the perf top on my proto.. It looks great and runs much cooler too...
Great to hear - BTW - I installed a perf top on my proto and it still runs on the warm side... it does have a frankensteined 24V reg, should get in there and put a good one in at some point, and double check the sink.
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