• 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.

Rundmaus at work - PP1C without sand

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Hi there,

I am beginning to realize that this project will probably be nominated for the 'Slowest DIYaudio project ever' award. :D

But again, a little progress has been made, the cathode resistor assembly with the EL34 cathode resistors and the large bypass electrolytics is finished:

cathode_res_bypass.JPG


And last month the output transformer for the test setup has arrived from Lundahl:

LL1663.JPG


So now everything is ready and waiting to complete the one-channel test setup, I hope I manage to do this in the next weekends, if there's not too much other work to be done...

Greetings,
Andreas :)
 
WHOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO! :D:D

It works!

itworks.JPG


Powered the test circuit up for the fist time after completing it this afternoon.
Very nice, seemingly undistorted sound via a single 8ohms fullrange driver.

A slight hum is audible when listening close to the driver, and it does not disappear instantly when switching off the mains. So I would think there is some grounding/shielding problem with stray noise picked up via the long, unshielded interconnects, not heater-related or too much ripple on B+.

Ideas for troubleshooting, anyone? :)

Greetings,
Andreas
 
....
A slight hum is audible when listening close to the driver, and it does not disappear instantly when switching off the mains. So I would think there is some grounding/shielding problem with stray noise picked up via the long, unshielded interconnects, not heater-related or too much ripple on B+.

Ideas for troubleshooting, anyone? :)

I assume you are joking. Having only a slight hum with a breadboard circuit is very good. The first thing to do is use shieled wire. I use RG-174 but anything would work if it can take the voltage. The RG-174 is rated for tube-type voltages and is not expensive. Of course yu only ground one end of the shield and use heat shrink on each end to prevent the shield from shorting to something. I use coaxial cable for EVERY signal that feeds a high impedance. It really will keep out environmental EMI.

Next step after that is to get a chassis with six metal sides. I go as far as to use star washers to close off the bottom cover plate to ensure the aluminum to aluminum conducts.

then be sure and use those aluminum tube shields over the preamp tubes.

Replace the IEC connector with an inlet filter. These are cheep and keep noise from getting in via the power cable
Welcome to Delta Electronics, Inc. - Components

But hum on a breadboard is to be expected. If it is only slight feel lucky.
 
Slowest diyAudio project ever...

The slowest diyAudio project ever known to audiophile mankind has made another small step... :D

The main chassis has arrived from the CNC workshop. It will carry the power TX, heater TX, OT and a number of subchassis with phase splitter, final stage, input selection and so on.

Proud! :)

main_chassis_image_.JPG


Regards,
Rundmaus
 
Dear Rundmaus,
I'm impressed by your power of endurance! This necessarily means that this amp must sound really, really good!
In one of your earlier mails you mentioned another "time-sink" you had to deal with. Your PhD.
May I ask -completely off topic- mission accomplished?
In case not yet: all the best!
Ulrich
 
Hey there,

couldn't wait and started assembling the first pieces today. Shown is the main chassis with the mains input panel and the heater transformer in place for testing purposes. The metal brackets at the chassis corners allow easy access to both sides of the chassis during assembly.

Mains input panel closeup:
IMG_1005.JPG


Overview from the bottom side:
IMG_1006.JPG


Regards,
Rundmaus


@ui2: Mission accomplished - had my PhD defense in January 2015, 'official' degree has been given in May. Finally!
 
I just finished the mains input and switching stuff right up to the transformer secondaries.

IMG_1031.JPG


The image shows the chassis (bottom view) with the heater transformer (left), heater distribution and interlock circuit (middle) and the HV transformer (right) installed.

The DPST mains switch connects the heater transformer to the mains. Then one of the relays (2nd from right, orange for 230VAC coil) is used for a latching circuit, it allows the HV to be enabled by a momentary pushbutton next to the mains switch, see post above. The second 230VAC relay switches on the heater lines for the B+ rectifiers when HV is enabled.

The two blue relays will be operated from the B+ of both channels. This interlock activates the rectifier for the negative rail only when both B+ rails are present.

IMG_1034.JPG


The view from the other side shows the connector blocks (black) which are used for heater distribution.

Up to now, everything works fine! :)
 
The modular idea is inspired by the Morgan Jones book. The phase splitter / preamp stage and the final stage of each channel will be sitting on separate subchassis, as well as the rectifiers. So later changes to the amp will not render the whole chassis useless, I simply change out the corresponding panel.

Regards,
Rundmaus
 
Hey there,

another step forward has been made: The aluminum panels for the chokes (bottom side of chassis) and the rectifier tubes (top side of chassis) have arrived. All power supply components are in place now, but there's still some wiring to be done before firing the PSU up for some testing.

Chassis view from the top side, the rectifier sockets are visible in the center:
IMG_1042.JPG


Chassis view from the bottom side with all PSU parts mounted:
IMG_1040.JPG


Will report back as soon as the PSU is up and working.

Regards,
Rundmaus
 
Good news,

one channel is now completed and running. No magic smoke exited any component upon powering up. Everything works nicely, including seemingly good, undistorted sound from the test speaker!

No trace of hum audible, even with the ear being close to the speaker. Without signal, only a slight buzz can be heard close by, coming from the power transformer and the isolation transformer below the workbench.

Component / wiring side of completed channel:
IMG_1077.JPG

Note: Signal input and speaker output are connected 'quick and dirty' for testing purposes only. The I/O connector board, source selector and volume pot are not present yet.

Top side of the completed channel:
IMG_1086.JPG

Note: In the completed amplifier, all subchassis will be covered by a single, powder-coated cover plate with the corresponding cutouts for tubes, switches and connectors.

Regards, and a happy new year to all diyAudio people out there,
Rundmaus
 
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