• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

The amplifier itself whines

Most people may let this slide. My wife and several others simply can not hear the high pitch whine that my DC DArling emits, but it's loud enough for me (and a cousin) to hear from 20 feet away, maybe more. I really like this amp - it really shows off details and mates well to my horns. I'd like to know if there's an easy fix. I didn't build it and at best can offer photos.

It may help to know that if a tube blows the whine disappears. This leads me to think the tubes themselves are making the whine and I wonder how this could be ignored by so many listeners.

Also, I've never changed the power cable. Worth a shot?

-S
 
SY said:
Oscillation can make the caps sing. And cause tubes to blow out. Sounds like it's time to whip out that oscilloscope.
a whining amplifier is better than a whining wife. ;), their is no inexpensive fix for a whining wife.

that being said, any oscillation causes the output devices of an amplifier to draw a lot more current than spec'd. the first thing I would do is take a look for any components which have "turned brown".
 
more data

Well, here's my full experience:

This was my first tube amp. When I got it about a year ago, it came with the whine. After several weeks of use one 1626 tube started sparking when powered up. Not long after, that tube went out and the fuse blew. I replaced fuse and changed the 1626 pair for a different pair, but before long new tubes were sparking. Not knowing much about why a tube would spark at power up, I decided to roll 1626 for a spell and they all sparked. Evntually a cap got fried and it was sent out for repair. The tech replaced the cap with a larger cap, stated the previous cap was too small and also improved some of the ground connections.

Since then, I found that replacing the rectifier tubes (8xxx) really improved the sonics and seems to relieve the sparking 1626 problem. I know I powered up the amp to check if the tubes would spark before hooking up the speaker wires several times... I've learned that's a no-no. So, having rolled over to a new set up rectifier and main tubes and not powering up without speakers connected, I have no problems with sparks now.

Sounds like there's no easy fix. Maybe I'll move this over to the trade page.
 
SY said:
If you can link to a schematic, perhaps there's something simple that can be done to improve the reliability.


This is a DC Darling built in 2002 and the schematic can be seen here:

http://www.geocities.com/bobdanielak/jeremy.html

Unfortunately I can not locate the original builder to confrim the exact schematic, so I will endeavour to take some photos of the guts and post them. The intitials are MBH '02 are scrawled on the back of the brass plate and I think his name is Miles...

Please forward this to any MBH or Miles you may know and ask that he/she contact me at [email protected] and/or on this thread.

-Steven
 

SY

diyAudio Moderator Emeritus
2002-10-24 10:19 pm
Chicagoland
www.SYclotron.com
Probably oscillation, but... you could be suffering from a dying output tube caused by a flashover. This design does not have proper startup protection- I would definitely try replacing the output tubes, making sure the grid-stopper is physically right next to the grids, then connect a reverse-biased diode from the far end of the grid stopper to the output tubes' cathodes.
 
Sch3mat1c said:
Caps and/or resistors burning with whining sound and dying tubes = parasitic oscillations... tell the tech.

You don't have peizo tweeters by any chance?

Tim

No, I never had peizo electric tweeters - guess your suggesting this could had been bad for them? I have horn tweeters now. Should I remove the amp from the rig?

I've sent this amp to the same tech it was with previously when he put a Blackgate cap on the amp at the request of the previous owner. Seemed like a nice guy, but he has seen it twice and has not identified or mentioned this problem and my intiution is I should get myself a new tech. Incidently, I had him modify the amp so one gain knob controls both channels. Now, I can see reason to undo that modification.

Sch3mat1c, SY, or planet10, please PM me recommendations. It would fabulous to have this amp functioning to it's fullest potential. I'm not a DIYer but I like supporting DIYers. Someday, when my kids grow up we I can learn in parallel, I'll join the league.

-Steven
 
snilsen13 said:
No, I never had peizo electric tweeters - guess your suggesting this could had been bad for them? I have horn tweeters now. Should I remove the amp from the rig?

I ask because the last amp I built went ballistic, oscillating full power (50W) at 50kHz, when connected to some speakers with peizo tweeters.

FYI... I'm more concerned about the well-being of the tubes than any speaker. :p

but he has seen it twice and has not identified or mentioned this problem and my intiution is I should get myself a new tech.

No, this is again why I ask. Amplifiers with NFB are often very load-critical. The only load a tech is concerned about is a perfect resistor. Speakers are a really ... well, I can't use the verb here ... 'd up load to an amplifier. Eight ohms is a suggestion.

Even with simulated complex loads, you may not spot an instability.

Incidently, I had him modify the amp so one gain knob controls both channels. Now, I can see reason to undo that modification.

Unless the wires run near the output, causing feedback (your circuit has no loop NFB), this is not a problem. At worst, this will cause unnoticable crosstalk (I mean, your ears are in the same room, right?).

Sch3mat1c, SY, or planet10, please PM me recommendations.

FYI, the board's PM facility is disabled, and it's impolite to ask for e-mails on a public board. ;)

Tim
 
Sch3mat1c said:


FYI, the board's PM facility is disabled, and it's impolite to ask for e-mails on a public board. ;)

Tim


Okay. I won't do that again, but then, can I just point out how utterly inappropriate of me to ask for help on a DIY board?! :)

Seriously though. I suppose this may be futile, but I'd like to use a different tech and could use recommendations. I mean, until I get this sorted out, I'm listening to a tripath!!! fear and loathing in tubeland.

Thanks,
STeven