Hi all,
Well, I've done some measuring: I took an old interlink, and transformed it into a probe for my soundcard: Inserted a 0.47uF/640V cap to decouple.
Used it to measure some things, and found this:
(Please note that I used the gain in the input of my soundcard, so the levels shown are not exact: 0.02V/div is what ZelScope says, but it might be less, because of the gain).
Now: Here's a series of shots from the output: I've hooked my 'probe' onto the output, right after the decoupling caps.
Note that the Volume Pot is @ zero, and the timebase = 5ms/div
Unmuted 0.02V/div
muted 0.02V/div
muted 0.003V/div
Rather noisy, not?!?!?!!!
Here's a series opening the volume pot, all are at 0.2V/div:
Pot @ zero
Pot @ half
Pot @ full
AAAAAARRRRRRRGGGGGGGHHHHHHHHH!! What a mess!!!!
And finally my B+, please note that this line rather floats up'n'down a bit, might be the smallish decoupling cap:
B+
Paul
Well, I've done some measuring: I took an old interlink, and transformed it into a probe for my soundcard: Inserted a 0.47uF/640V cap to decouple.
Used it to measure some things, and found this:
(Please note that I used the gain in the input of my soundcard, so the levels shown are not exact: 0.02V/div is what ZelScope says, but it might be less, because of the gain).
Now: Here's a series of shots from the output: I've hooked my 'probe' onto the output, right after the decoupling caps.
Note that the Volume Pot is @ zero, and the timebase = 5ms/div
Unmuted 0.02V/div
muted 0.02V/div
muted 0.003V/div
Rather noisy, not?!?!?!!!
Here's a series opening the volume pot, all are at 0.2V/div:
Pot @ zero
Pot @ half
Pot @ full
AAAAAARRRRRRRGGGGGGGHHHHHHHHH!! What a mess!!!!
And finally my B+, please note that this line rather floats up'n'down a bit, might be the smallish decoupling cap:
B+
Paul
Is your input shorted? You're not feeding any signal (oscillator/sig gen) to it, right?
re: B+, well that's something i've seen on another preamp in the past (VTV variant). Play some music and it goes haywire even more.
I'd like to show you some pics I collected in the past. These were taken from the B+ and with music playing.
The two on top was taken from a PSU w/ CLCLC topology.
The bottom left is taken from my 12B4 with FR107-CRCRC.
The bottom right is taken from my 12B4 with MOSFET series pass PSU.
re: B+, well that's something i've seen on another preamp in the past (VTV variant). Play some music and it goes haywire even more.
I'd like to show you some pics I collected in the past. These were taken from the B+ and with music playing.
The two on top was taken from a PSU w/ CLCLC topology.
The bottom left is taken from my 12B4 with FR107-CRCRC.
The bottom right is taken from my 12B4 with MOSFET series pass PSU.
Attachments
Arnoldc,
Okay, so this B+ thing ain't not very important.
I did NOT shorten my inputs.... I'll do that (Plug in an iPod), and post some new images....
The output with no signal applied to the input (iPod on pause)
at first
Later
Looks like this after a while, I'm pretty shure this is HF oscillation, not? though I do have the 100Ohm gridstoppers right on the socket
Paul
Okay, so this B+ thing ain't not very important.
I did NOT shorten my inputs.... I'll do that (Plug in an iPod), and post some new images....
The output with no signal applied to the input (iPod on pause)
at first
Later
Looks like this after a while, I'm pretty shure this is HF oscillation, not? though I do have the 100Ohm gridstoppers right on the socket
Paul
Pot grounding
Hi,
(As you can see my my number of pots today, I'm having a day off...
)
Okay, I've put a little wire between one of the ALPS' screws, and grounded it via a tiny cap. (10nF).
Oscillation seems gone now, but I still have this 100Hz sines on my screen...
My DMM, in AC mode, measures 0.09V on the output.
Ciao, Paul
Hi,
(As you can see my my number of pots today, I'm having a day off...
)Okay, I've put a little wire between one of the ALPS' screws, and grounded it via a tiny cap. (10nF).
Oscillation seems gone now, but I still have this 100Hz sines on my screen...
My DMM, in AC mode, measures 0.09V on the output.
Ciao, Paul
G'd day.....
Well, there's something I don't get (Might be my lack of knowledge in tube biznezz).
When I measure at the point marked B+ in my schematics (Right BEFORE the Rplate(11K)) is get this. (Rather flat DC).
But when I measure AFTER the Rplate, thus on the plate, i get this, EVEN THOUGH there's NO input signal present and the cathode's clean....
Note: Green line = Output, Yellow line = measured thing...
Paul
Well, there's something I don't get (Might be my lack of knowledge in tube biznezz).
When I measure at the point marked B+ in my schematics (Right BEFORE the Rplate(11K)) is get this. (Rather flat DC).
But when I measure AFTER the Rplate, thus on the plate, i get this, EVEN THOUGH there's NO input signal present and the cathode's clean....
Note: Green line = Output, Yellow line = measured thing...
Paul
Hi,
Look like I'm talking to myself...
Cheerio for Shoog: Took my solderingrod, and whilst having the amp on, I got one side of the heaters off.
Guess what...
Remember that I went to AC heating, 'cause the voltage dropped to much with my heater PSU?
I haven't got much components at hand, and the shop is 1 hour drive, so what could I beat try at first:
I've got some (4) 1N4004's, one or 2 bridges (of unknown origin), couple of 16V electrolytics, and one or two low R's...
Loaded with the heaters, the PT gives: 6.55 V (Hey, that's too much!!), unloaded some 6.82V
Regards, Paul
Look like I'm talking to myself...
Cheerio for Shoog: Took my solderingrod, and whilst having the amp on, I got one side of the heaters off.
Guess what...
Remember that I went to AC heating, 'cause the voltage dropped to much with my heater PSU?
I haven't got much components at hand, and the shop is 1 hour drive, so what could I beat try at first:
I've got some (4) 1N4004's, one or 2 bridges (of unknown origin), couple of 16V electrolytics, and one or two low R's...
Loaded with the heaters, the PT gives: 6.55 V (Hey, that's too much!!), unloaded some 6.82V
Regards, Paul
"When I measure at the point marked B+ in my schematics (Right BEFORE the Rplate(11K)) is get this. (Rather flat DC).
But when I measure AFTER the Rplate, thus on the plate, i get this, EVEN THOUGH there's NO input signal present and the cathode's clean.... "
Thats what I have found to be fairly typical with hum problems. What it is telling you is that the hum isn't coming through the plate resistor but is been generated internally by the valve. It unfortunately tells you very little about the source of that hum. Means its either generated by the grid circuit or within the physical structure of the valve (ie heater hum).
I went back to the diyparadise site and looked at his hints. He uses AC heater which are grounded so the whole heater thing may be a red herring.Still at this stage its definately worth the small effort in trying.
Heres a question - does your choke vibrate at all ? Have you tried placing a 0.1uf cap before your choke. This is used to stop physical hum in choke input PS's and might stop any radiated magnetic field from leaking into your circuit. Its a simple thing to try without to much hassle. Probably won't help but might. Shouldn't effect final voltage.
Sometimes earthing the valve sockets themselves helps.
I'am clutching at straws here. All you can do is go through trying one stupid thing after another until something works. I am currently listening to my CCS 5687 and there is no hum at all despite my having ultra sensitive speakers. It can be done !!
Shoog
But when I measure AFTER the Rplate, thus on the plate, i get this, EVEN THOUGH there's NO input signal present and the cathode's clean.... "
Thats what I have found to be fairly typical with hum problems. What it is telling you is that the hum isn't coming through the plate resistor but is been generated internally by the valve. It unfortunately tells you very little about the source of that hum. Means its either generated by the grid circuit or within the physical structure of the valve (ie heater hum).
I went back to the diyparadise site and looked at his hints. He uses AC heater which are grounded so the whole heater thing may be a red herring.Still at this stage its definately worth the small effort in trying.
Heres a question - does your choke vibrate at all ? Have you tried placing a 0.1uf cap before your choke. This is used to stop physical hum in choke input PS's and might stop any radiated magnetic field from leaking into your circuit. Its a simple thing to try without to much hassle. Probably won't help but might. Shouldn't effect final voltage.
Sometimes earthing the valve sockets themselves helps.
I'am clutching at straws here. All you can do is go through trying one stupid thing after another until something works. I am currently listening to my CCS 5687 and there is no hum at all despite my having ultra sensitive speakers. It can be done !!
Shoog
Shoog said:
Hi Shoog, the heaters on both the 12B4 and 5687 is AC.
Yesterday, I did a little shootout between the two. Use my usual suspects test CDs which include Hayley Westenra, Sheffield Labs Jazz Experience, Blue Man Group Complex, Vanessa Rubin.
Thing that are consistent with the || 5689:
- Seems to go lower (Vanessa Rubin)
- Seems to have more air/ambiance on vocals (Hayley Westenra)
Both the 12B4 and 5687 did well on the Sheffield Labs. But on complex music as in the Blue Man Group, the 5687 seems to me confused. Instrument separation is not as good as the 12B4.
Well,Shoog said:
I'm currently listening to MY 5687, and ain't no hum neither!
It turned out to be a rather crappy bridge, who couldn't deliver enough current, and dropped the voltage: Found another 5A rated bridge, hooked it up,a s well as the CRC filter as stated in the schematics, and: GOTCHA! 6.1V DC after heating up, and NO hum anymore!
There's just a slight hiss, but that might be the grounding: Hooked the screen and the Power earth to the chassis, and all this rather close to the rectifier & PT, so....
(Could I decouple that or so?)
Arnoldc,
Good you seem to like it: The lower end suprised me as well, and for the overall I seem to like it, but I must admit I haven't got so much reference. It sounds better than with just my yamaha AX-470 amplifier (It's hookup simply before that amp)
Have you tried seperating the sections, as I did?
Listened to blowzabella (Missed their concert fryday, cause I was fiddling with this amp...
) and liked it!I mainly listen things like Pink Floyd, (modern) mainly french folk, like Stéphane Delicq but jazz (Keith Jarret, Erik Truffaz, Art Farmer, Jamahl) as well, and all seem to 'enjoy passing through' this amp...
Now, what could I build to be driven by this linestage? I have not so senitive KefKit speakers (These large ones, KefKit 3 or so? B139, B110 + tweeter).
And I don't have buckets full of pennies to spend....
Regards, Paul
I'am glad we got there in the end.
I have found that I like my 5687 preamp, but its not quite as good as my homebrew FVP5. The bass is deeper and stronger but the overall sound is a little to full. I have heard it said that the 5687 sounds a little "dark" and I would tend to agree with that. The FVP5 definately betters it. My 5687 is operating at -4.3V bias LED bias, with a CCS on the plate and a plate voltage of about 130V. Could be that there is a more leaner sounding operating point. Any suggestions would be considered.
Shoog
I have found that I like my 5687 preamp, but its not quite as good as my homebrew FVP5. The bass is deeper and stronger but the overall sound is a little to full. I have heard it said that the 5687 sounds a little "dark" and I would tend to agree with that. The FVP5 definately betters it. My 5687 is operating at -4.3V bias LED bias, with a CCS on the plate and a plate voltage of about 130V. Could be that there is a more leaner sounding operating point. Any suggestions would be considered.
Shoog
The sound of the 5687 is going to depend on how its built.
Considerable time could have been saved if the 5687 had been built to the schematic that diyparadise had. The power supply they specified used two chokes and the outcome was zero hum in the one I built with no DC heaters.
I personally thought the 5687 sounded very open and uncluttered but lacked somewhat in the low end when compaired with the 12B4. The 5687 was probably one of my favorite line stages after adding some VR tubes in the power supply.
Considerable time could have been saved if the 5687 had been built to the schematic that diyparadise had. The power supply they specified used two chokes and the outcome was zero hum in the one I built with no DC heaters.
I personally thought the 5687 sounded very open and uncluttered but lacked somewhat in the low end when compaired with the 12B4. The 5687 was probably one of my favorite line stages after adding some VR tubes in the power supply.
Attachments
I think the need for DC on the heaters will be dependent on two things.
1- the sensitivity of your amp, a little bit of hum on an insensitive amp may fly under the radar.
2- the brand of the 5687.
It obviously has proved essential in some case
I think I am operating my 5687 with not enough voltage over the CCS, I am currently making adjustments. I expect things to open up and the sound to improve.
Shoog
1- the sensitivity of your amp, a little bit of hum on an insensitive amp may fly under the radar.
2- the brand of the 5687.
It obviously has proved essential in some case
I think I am operating my 5687 with not enough voltage over the CCS, I am currently making adjustments. I expect things to open up and the sound to improve.
Shoog
Speaker sensitivity is not the same as amp sensitivity, though you may have a very sensitive amp as well.
How do you explain it that when Bibster finally went DC the hum went, if its not from the heaters. There maybe another path that the heaters are using to introduce hum, but an explanation of what that might be would help eliminate it in the first place.
Shoog
How do you explain it that when Bibster finally went DC the hum went, if its not from the heaters. There maybe another path that the heaters are using to introduce hum, but an explanation of what that might be would help eliminate it in the first place.
Shoog
I fully understand where you are coming from. With a sensitive commercial amplifier only requiring .775 volts in to obtain full output mine was 100% quiet. I understand the meaning of sensitivity of both amplifiers and speakers.
I don't doubt that DC heaters might have helped his situation. I also feel there is more than one path to follow. Why should I try to speculate on the outcome of a line stage I cannot see or measure? As you certainly know wire placement can play havic with hum and therefore it might have not been the DC heaters that totally removed the hum. I suggest that just for s*its and grins you build one with the power supply specified and see what happens. I think you will end up with a hum free unit dispite the choice of tubes.
We could argue over this till the cows come home, and its rather pointless. The main thing is that Bibster is happy with his preamp now.
I personally had similar issues with my first 5687 preamp and went down the path of DC heaters in the end. The thing that I find a little usual is that with the same techniques against induced hum, my attempts with the 6922 have had little hum problems despite having a much higher gain. My FVP5 clone uses AC heaters, as do all of my power amps. I always default to AC heaters over DC. The 5687 has been my exception.
Changing the operating point of my 5687 to 115V on the plate with 10mA and -4V bias has indeed opened up the sound a great deal.
Shoog
I personally had similar issues with my first 5687 preamp and went down the path of DC heaters in the end. The thing that I find a little usual is that with the same techniques against induced hum, my attempts with the 6922 have had little hum problems despite having a much higher gain. My FVP5 clone uses AC heaters, as do all of my power amps. I always default to AC heaters over DC. The 5687 has been my exception.
Changing the operating point of my 5687 to 115V on the plate with 10mA and -4V bias has indeed opened up the sound a great deal.
Shoog
I just had a closer look at Bibsters layout photo. It does appear that his original heater wires were probably to big and not braided tightly enough. In this form they pass directly under the cathode components and "could" very well account for transfer of hum from wires to cathode resistor.
Shoog
Shoog
Ow yes they could....Shoog said:
But they'd NEVER account for the amount of hum I had. You might haven noticed I posted some 'scope' images off the cahode as well (Flat as they were).
This hum was just to present, too much. There's stuff left, and NOW, and only NOW, I am to take into account things like layout, wiring and the such.
I'll make a new housing later this summer, when my mate comes over, and I'll try a brass cover, if ever I manage to find one. and I'll take way more care in the layout.
(Hints still welcome n this thread)
Having said that, I'd like to thank Shoog and Arnoldc for helping me out: Thank you! Merci! Bedankt! ¡Gracias! Danke! Tige dank!
A+, Paul
PS: Does someone learn just as much from followins projects as from their first? I mean: I learned more than in college here, these last weeks!
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.