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post #946 of 2213
I have reflowed Q3P, but I am still getting pin 6 number that are all over the place. When I measure between the anode of D1R and TB+ I get @2.5V. Bill sent me some transistors, but since I was looking in the buffer before, I didn't ask for Q3P. Anybody have an extra they would be willing to send?
post #947 of 2213
Quote:
Originally Posted by tacitapproval View Post
I have reflowed Q3P, but I am still getting pin 6 number that are all over the place. When I measure between the anode of D1R and TB+ I get @2.5V. Bill sent me some transistors, but since I was looking in the buffer before, I didn't ask for Q3P. Anybody have an extra they would be willing to send?
I am pretty sure I have a couple I can spare..let me check my inventory quick..

edit: Nope..looks like I have just enough for the upcoming build.
post #948 of 2213
Quote:
Originally Posted by tacitapproval View Post
When I measure between the anode of D1R and TB+ I get @2.5V.
This seems fine to me. The capacitance multiplier will drop voltage when loaded. The output voltage is 0.65v lower than the base voltage, which in turn is lower than the source voltage. A 2.5V drop with a 2mA current seems about right to me.

Voltage is steady and not fluctuating? Fluctuating voltage may mean a varying current load. The CRD should be regulating the current flow at that point.

The opamp is supposed to flow or pull current away from the cathode resistor to regulate the voltage at the plate.

I would probably look at replacing the CRD, if everything else looks good to you.

C1R is installed in the proper direction? What voltages do you measure at the cathode of the tube (pin 8 for the right side)?
post #949 of 2213
I think it has to be D1R. I measure 105v on the anode of it, but only 38v on the cathode. I also have witnessed the same fluctuations on it that I see at pin 6(I guess this would not be suprising), but the B+ and anode seem to be stable. Do others concur?

Polarity of C1R is correct and Pin 8 was at 1.3v.

Wiatrob-- Any chance I can trouble you again for a 1N5305 and MPSA42, so I don't have to put in a mouser order just for those?
post #950 of 2213
Quote:
Originally Posted by tacitapproval View Post
I think it has to be D1R. I measure 105v on the anode of it, but only 38v on the cathode. I also have witnessed the same fluctuations on it that I see at pin 6(I guess this would not be suprising), but the B+ and anode seem to be stable. Do others concur?

Polarity of C1R is correct and Pin 8 was at 1.3v.

Wiatrob-- Any chance I can trouble you again for a 1N5305 and MPSA42, so I don't have to put in a mouser order just for those?
It is probably Q3P (MPSA42) that is causing the low reading on Pin 6 and D1R, I had a similar problem with low voltage(55v) on Pin 1 and D1L, replacing Q4P fixed it.
post #951 of 2213
Quote:
Originally Posted by MrSlim View Post
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..
Email received, thanks much for pointing out the issue, and suggesting a fix!

Site updated!
post #952 of 2213
Quote:
Originally Posted by tacitapproval View Post
I think it has to be D1R. I measure 105v on the anode of it, but only 38v on the cathode. I also have witnessed the same fluctuations on it that I see at pin 6(I guess this would not be suprising), but the B+ and anode seem to be stable. Do others concur?

Polarity of C1R is correct and Pin 8 was at 1.3v.

Wiatrob-- Any chance I can trouble you again for a 1N5305 and MPSA42, so I don't have to put in a mouser order just for those?
You could I'll send you an email.
post #953 of 2213
Quote:
Originally Posted by MrSlim View Post
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..
Quote:
Originally Posted by danobeavis View Post
Email received, thanks much for pointing out the issue, and suggesting a fix!

Site updated!
MrSlim and danobeavis, just love it when communication works. Another perfect example when members share ideas and comments, things always end up as well as they do. Thanks to you both.

In terms of the A/B box, listening to differences in SQ, nuances, etc. between amps is my primary reason for wanting one but also for one other purpose. It may also become permanently connected to my source since there are many times I'm undecided which amp or tubes I feel like listening to at that moment, … perhaps I’m just way lazy to swap cables or amps/tubes sometimes
post #954 of 2213
Quote:
Originally Posted by wiatrob View Post
All- I'm out of town for a week so if anyone needs spares it'll take a bit of time. The first set of custom panels showed up in The mail minutes before I left. Thy look great.

I'll get some pics posted when I return. Good luck with your builds...
Hi Bill, just wondering if you had a chance to post some pics of the custom panels. Hoping to see a sneak peek of what they look like. I'm currently modeling the casework (still undecided on the design) so I'm curious if I might/should rough them in. Thanks!

post #955 of 2213
Quote:
Originally Posted by Forte View Post
It is probably Q3P (MPSA42) that is causing the low reading on Pin 6 and D1R, I had a similar problem with low voltage(55v) on Pin 1 and D1L, replacing Q4P fixed it.
It would be fairly easy to test, though with a steady voltage drop across it, I'm not sure.

Anyhow, with the amp turned off, set your DMM to diode test. Put the red probe on the base (middle pin). Put the black probe on each other leg (collector and emitter). It should measure about 0.6V for both. Reversing the probes should yield nothing.

An NPN can be viewed as two diodes, back to back, for this test. With the anode at the base and the cathodes at C and E.

If it passes, the transistor is good.

You can do a similar test for the CRD, i.e., one way only.
post #956 of 2213
Quote:
Originally Posted by holland View Post
You can do a similar test for the CRD, i.e., one way only.
One thing tho that concerns me about out-of-circuit testing for the more complex parts is I'm not sure it's really testing it (e.g.performance under load & temp conditions.)
CRDs for example are more complex creatures than std diodes.
Again, piecemeal replacements may hit the problem but it requires some patience (& luck) IMO.

P.S. Boy, wiatrob is sure going above & beyond in his support of the kits - Good man.
post #957 of 2213
Thanks for everyone's patience with my flailing attempts to troubleshoot this problem. I have yet another hypothesis about the source of the trouble. I think Alex is right, there is something physically dodgy going on. If I push up and down with the probe while reading pin 6, it seems I can get the voltage to change. I have gone over the joints on the right side input yet again. This hasn't solved it. Maybe there is damage to the board? Ughhh...

Q3P tests out ok, by the way.
post #958 of 2213
Quote:
Originally Posted by cfcubed View Post
CRDs for example are more complex creatures than std diodes.
True, but if you can test a transistor you can test a CRD. A CRD, can be modeled as a JFET with gate and source shorted. The quick test is to make sure the diode is still functional. If it's shorted out or broken completely, it won't function as the basic junction is gone/toast. Any of the testing won't show in circuit failures, best would be to pull the end of the CRD and put an ammeter in series to measure the current flow. That's a bit of work, and might as well just pull the part completely instead of testing that.

I would rather try and test some parts in circuit instead of blindly replacing parts. Brute force works, but it doesn't help the knowledge base in the long run.
post #959 of 2213
Quote:
Originally Posted by tacitapproval View Post
Thanks for everyone's patience with my flailing attempts to troubleshoot this problem. I have yet another hypothesis about the source of the trouble. I think Alex is right, there is something physically dodgy going on. If I push up and down with the probe while reading pin 6, it seems I can get the voltage to change. I have gone over the joints on the right side input yet again. This hasn't solved it. Maybe there is damage to the board? Ughhh...

Q3P tests out ok, by the way.
Got a loupe? Examine the traces and joints. It's possible, sometimes it happens, that there can be an errant trace from the fab house, or bits left over shorting something...or a small wire floating around when you wired it that makes contact somewhere.

When you say push up and down, you mean with the probe contacted in both cases and just applying pressure? Or are you breaking contact and making contact? There can be some flux with contact make and break, especially repeatedly. I use a small clip (mini hook clips), to clip onto the leg of the socket, which connects to my DMM. With that in place, flex the board around the area you suspect. Push down on the tube, and release, for example.

http://www.tequipment.net/FlukeTL940.html

Edit: You may want to reflow the tube socket as well, it could be a bad joint around that area. The loupe will show it though, I use a min 10x, sometimes 20x.
post #960 of 2213
Yes, I mean applying more or less pressure on the board while maintaining contact. I have reflowed the socket, as well as anything that looked like it could be at all suspect. I don't have a loupe, but I do have a magnifying glass. I will look it over carefully. I also have some alligator clips, so I can try that.
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