Hi,
Having pretty much failed with three other valve amp ‘projects’ I thought I’d go ahead with one final attempt to build a SE power amplifier before I give up completely and accept that I’m too dumb to build a valve amp.
So I decided to build Bob Danielak’s DC Darling amplifier as it seemed simple enough for a newbie like me. Anyway, I finished it a few days ago but as usual there are problems
I built the amp as per attached schematic (except I didn’t share the cathode resistor/bypass capacitor.)
On testing the DC voltages were a bit low compared to targets on schematic but probably near enough?
B+ voltage = 400V,
Voltage at Pin 8 (1626) = 130V
Voltage at Pin 5 (1626) = 110V
Voltage at Pin 2 (8532) = 1.05V.
Heater Voltages were slightly low at 5.9V for 8532 and 11.9V for 1626.
However I had a big problem with very loud buzz on both channels without anything connected to the inputs. However, when I inserted shorted RCA plugs on the input sockets the buzz disappeared. Similarly with MP3 player connected (no music playing) amp is quiet but as soon as I disconnect the MP3 player the loud buzz returns.
My first guess was that the amp was oscillating so I put 220ohm grid-stoppers on pin 1 of 8532 but this had no effect on the buzz. Could it be the 1626 valve oscillating?
Also, noted that 47K/2W anode resistor (for 8532) had also discoloured (due to overheating?) Could this also be related to the problem?
Anybody out there experienced this problem and able to suggest a simple fix?
Cheers
Colin.
Having pretty much failed with three other valve amp ‘projects’ I thought I’d go ahead with one final attempt to build a SE power amplifier before I give up completely and accept that I’m too dumb to build a valve amp.
So I decided to build Bob Danielak’s DC Darling amplifier as it seemed simple enough for a newbie like me. Anyway, I finished it a few days ago but as usual there are problems
I built the amp as per attached schematic (except I didn’t share the cathode resistor/bypass capacitor.)
On testing the DC voltages were a bit low compared to targets on schematic but probably near enough?
B+ voltage = 400V,
Voltage at Pin 8 (1626) = 130V
Voltage at Pin 5 (1626) = 110V
Voltage at Pin 2 (8532) = 1.05V.
Heater Voltages were slightly low at 5.9V for 8532 and 11.9V for 1626.
However I had a big problem with very loud buzz on both channels without anything connected to the inputs. However, when I inserted shorted RCA plugs on the input sockets the buzz disappeared. Similarly with MP3 player connected (no music playing) amp is quiet but as soon as I disconnect the MP3 player the loud buzz returns.
My first guess was that the amp was oscillating so I put 220ohm grid-stoppers on pin 1 of 8532 but this had no effect on the buzz. Could it be the 1626 valve oscillating?
Also, noted that 47K/2W anode resistor (for 8532) had also discoloured (due to overheating?) Could this also be related to the problem?
Anybody out there experienced this problem and able to suggest a simple fix?
Cheers
Colin.
Attachments
Don't give up now, you must be close!
The voltages seem close enough. Though if the amp is oscillating at RF, it may be drawing more current, causing the voltages to be low.
You could add grid stoppers on the 1626 but it's not a very high Gm tube, so I doubt that it will fix things. Worth a try though, it can't hurt.
As for the discolored resistor... it's being run very close to the limits for a 2W resistor (1.8W in your case), so I'm not surprised. It will work but will have a limited life. At some point it would be best to replace it with a 5 watt resistor.
A few suggestions:
1. Verify for sure that the Rg resistors are connected correctly, well soldered, etc.
2. Make sure the input wiring (from RCA to grid stopper) doesn't go near the wiring on the 1626 plate.
3. Try a really big grid stopper - maybe 10k. If it still buzzes it's probably not the input tube oscillating. Make sure the stopper is really close to the tube.
If you have a camera, shoot a picture of the underside wiring and post it here. Maybe somebody will see something...
It would be worth finding an oscilloscope (or a friend with one) to have a look around.
Pete
The voltages seem close enough. Though if the amp is oscillating at RF, it may be drawing more current, causing the voltages to be low.
You could add grid stoppers on the 1626 but it's not a very high Gm tube, so I doubt that it will fix things. Worth a try though, it can't hurt.
As for the discolored resistor... it's being run very close to the limits for a 2W resistor (1.8W in your case), so I'm not surprised. It will work but will have a limited life. At some point it would be best to replace it with a 5 watt resistor.
A few suggestions:
1. Verify for sure that the Rg resistors are connected correctly, well soldered, etc.
2. Make sure the input wiring (from RCA to grid stopper) doesn't go near the wiring on the 1626 plate.
3. Try a really big grid stopper - maybe 10k. If it still buzzes it's probably not the input tube oscillating. Make sure the stopper is really close to the tube.
If you have a camera, shoot a picture of the underside wiring and post it here. Maybe somebody will see something...
It would be worth finding an oscilloscope (or a friend with one) to have a look around.
Pete
Hi Colin
As Pete said don't give up I'm not that bright either, most of the threads I read on this site go over my head and will probably never design any thing from scratch either and will be content to build other peoples designs and it doesn't matter either. I have just finished mine it took me two years I couldn't make a decision till I had read and reread until it sunk in and that was on simple things like positioning components and grounding techniques all the more complicated stuff is still magic to me . The thing that helped me alot was finding circuit diagrams and photos and comparing the two to see how works visually , mine worked so can yours.
Nigel
As Pete said don't give up I'm not that bright either, most of the threads I read on this site go over my head and will probably never design any thing from scratch either and will be content to build other peoples designs and it doesn't matter either. I have just finished mine it took me two years I couldn't make a decision till I had read and reread until it sunk in and that was on simple things like positioning components and grounding techniques all the more complicated stuff is still magic to me . The thing that helped me alot was finding circuit diagrams and photos and comparing the two to see how works visually , mine worked so can yours.
Nigel
Hi,
Firstly, thanks for the positive advice from Pete and Nigel to stick with the project.
Just a quick update following suggestions by Pete.
I thought this was likely to be the case - thanks for the tip! I'll look to change this to a 5 watter when I next place an order with Farnell or RS.
Pete, regarding your suggestions:
Checked this all connections seem good.
I think I'm ok with this also. See attached picture.
Put 10k carbon resistor as gridstopper on 8532 on one channel only to hear the effect of this change. Sadly, the buzz was still present on both channels - suggests input valve isn't oscillating.
Tried this a few days ago with a 1K5 carbon resistor but this had no effect on the buzz - maybe value was too low?
Posted a picture of the underside as suggested - it ain't too pretty so feel free to suggest changes to the layout
I agree but I was curious enough to want to remove the source of the buzz just in case this resulted in further issues a few months time.
Cheers
Colin.
Firstly, thanks for the positive advice from Pete and Nigel to stick with the project.
Just a quick update following suggestions by Pete.
I thought this was likely to be the case - thanks for the tip! I'll look to change this to a 5 watter when I next place an order with Farnell or RS.
Pete, regarding your suggestions:
Checked this all connections seem good.
I think I'm ok with this also. See attached picture.
Put 10k carbon resistor as gridstopper on 8532 on one channel only to hear the effect of this change. Sadly, the buzz was still present on both channels - suggests input valve isn't oscillating.
Tried this a few days ago with a 1K5 carbon resistor but this had no effect on the buzz - maybe value was too low?
Posted a picture of the underside as suggested - it ain't too pretty so feel free to suggest changes to the layout
I might be able to borrow an old oscilloscope from work but I haven't ever used one before so I need some serious advice in how to use it to track down the source of the buzz in this amp. Will look into this.
I agree but I was curious enough to want to remove the source of the buzz just in case this resulted in further issues a few months time.
Cheers
Colin.
Attachments
Hard to see in your photo, but it looks like you are using tag strips with components soldered to the tag that connects to the chassis. With those tag strips, make sure you don't solder any components to the tag that continues through to the chassis connection, otherwise it will be connected to chassis ground. If you wanted to have this component connected to ground, you might have a ground loop through the chassis. If you did not mean to connect the component to ground - then you have bigger problems!
Cheers,
Chris
Cheers,
Chris
DC Darling amp +buzzing
Do you have a capacitor between the chassis and the electrical ground?
I just built the capacitor coupled Darling (see Darling club) and it worked perfectly on power-up.
I am just getting back to tubes after a 50 year absence. My first amp buzzed. A friend suggested a capacitor between chassis (connected to the third AC plug wire) and the circuit ground. It cleared the hum right up.
Do you have a capacitor between the chassis and the electrical ground?
I just built the capacitor coupled Darling (see Darling club) and it worked perfectly on power-up.
I am just getting back to tubes after a 50 year absence. My first amp buzzed. A friend suggested a capacitor between chassis (connected to the third AC plug wire) and the circuit ground. It cleared the hum right up.
Hi,
Time to revive this thread after a long break!
I finally got around to checking this DC Darling amp over tracing possible source of loud buzzing. From previous replies the suggested source of the buzzing was that the choke was to close to the RCA inputs. Last night I disconnected the RCA inputs and moved them temporarily to the opposite side of the chassis as far away from the choke as the cables would allow. Unfortunately this made no difference – buzzing remained at same level.
I also noticed that the centre tap for the heaters was not attached to anything (maybe an oversight by me) and this could well result in the buzz I’m hearing? For all my previous projects I have always attached the CT to ground. So my question is should I connect the CT ground in this case or is this the one situation when this shouldn’t be done?
I’ve attached power supply schematic from ‘Bob Danielak’s DC Darling’ web page to help. Amp schematic is in post#1 above.
Any help would be appreciated.
Cheers
Colin.
Time to revive this thread after a long break!
I finally got around to checking this DC Darling amp over tracing possible source of loud buzzing. From previous replies the suggested source of the buzzing was that the choke was to close to the RCA inputs. Last night I disconnected the RCA inputs and moved them temporarily to the opposite side of the chassis as far away from the choke as the cables would allow. Unfortunately this made no difference – buzzing remained at same level.
I also noticed that the centre tap for the heaters was not attached to anything (maybe an oversight by me) and this could well result in the buzz I’m hearing? For all my previous projects I have always attached the CT to ground. So my question is should I connect the CT ground in this case or is this the one situation when this shouldn’t be done?
I’ve attached power supply schematic from ‘Bob Danielak’s DC Darling’ web page to help. Amp schematic is in post#1 above.
Any help would be appreciated.
Cheers
Colin.
Attachments
Hi,
Anyway, I decided to go ahead with connecting centre tap to ground. No smoke - but buzz reduced significantly. Not sure why I didn't do this in the first place. There is still some very small amount of buzzing present but I can live with it.
Back to my EL34 SE amp now.......
Cheers
Colin.
Anyway, I decided to go ahead with connecting centre tap to ground. No smoke - but buzz reduced significantly.
Not sure why I didn't do this in the first place. There is still some very small amount of buzzing present but I can live with it.Back to my EL34 SE amp now.......
Cheers
Colin.
DC Darling amplifier --buzzing on both channels
Colin,
Did you ever do what I suggested in Post # 10 (and what Danielak implied by showing the mains ground connected to earth --i.e., the chassis in this case) and the circuit ground seperate from the chassis ground. I am suggesting that you bridge the chassis ground to the circuit ground with a small capacitor -- say a .01 or so). There is no reason to have hum or buzz in an amplifier and Bob Danielak's circuit is a very good one.
Dick Ames KI6NOX
Colin,
Did you ever do what I suggested in Post # 10 (and what Danielak implied by showing the mains ground connected to earth --i.e., the chassis in this case) and the circuit ground seperate from the chassis ground. I am suggesting that you bridge the chassis ground to the circuit ground with a small capacitor -- say a .01 or so). There is no reason to have hum or buzz in an amplifier and Bob Danielak's circuit is a very good one.
Dick Ames KI6NOX
If you have buzzing you have an earth loop problem. Someone else posted very recently with a buzzing Darling amp. They followed the advice given and fixed the problem. Even if you do not understand how a valve circuit works, you must have an understanding of how and why to hook up the earth (zero volt) wiring if you are going to have any success. Read this http://www.aikenamps.com/StarGround.html it explains things very well.
Hi,
Richard: I tried your suggestion of attaching a small cap between chassis gnd and circuit gnd but this had no effect on the buzz.
Chris: Thanks for the link. I need to spend some time digesting this information before I take the amp apart and redo my earthing scheme. I must say in all my previous amp projects I haven't had any earthing issues - perhaps I got lucky with them!
Cheers
Colin.
Richard: I tried your suggestion of attaching a small cap between chassis gnd and circuit gnd but this had no effect on the buzz.
Chris: Thanks for the link. I need to spend some time digesting this information before I take the amp apart and redo my earthing scheme. I must say in all my previous amp projects I haven't had any earthing issues - perhaps I got lucky with them!
Cheers
Colin.
Hi Chris,
My previous failures have not been grounding related but down to other reasons e.g. motorboating on 5687 pre-amp, poor sonics + hiss on ECL82SE and excessive gain on EL34SE (still ongoing probs with this) - you can read about them all on diyaudio!!
Anyway, I appreciate the link you sent me - it deals with grounding schemes in a very thorough way. I must admit though that I haven't spent much time planning my grounding schemes on previous projects so I must have been lucky with the way they have turned out.
Cheers
Colin.
My previous failures have not been grounding related but down to other reasons e.g. motorboating on 5687 pre-amp, poor sonics + hiss on ECL82SE and excessive gain on EL34SE (still ongoing probs with this) - you can read about them all on diyaudio!!
Anyway, I appreciate the link you sent me - it deals with grounding schemes in a very thorough way. I must admit though that I haven't spent much time planning my grounding schemes on previous projects so I must have been lucky with the way they have turned out.
Cheers
Colin.
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