Greetings, friends, I'd like to build a Power amp with a toroidal PT, the Antek AS-1T250. Amp is based on the Dynaco ST35 with circuits on a pair of PCBs, SS CRC power supply, Edcor CXPP25-MS-8K and everything bolted to an Aluminum top plate:
Toroidal PT will be mounted to the underside of the plate:
Will I have hum with the output transformers mounted in such proximity to the power transformer? Is this baby gonna fly?
thanks for taking a look
will
Toroidal PT will be mounted to the underside of the plate:
Will I have hum with the output transformers mounted in such proximity to the power transformer? Is this baby gonna fly?
thanks for taking a look
will
I have used that layout and not had an issue.
Another option is to fix it in the chassis, using the same space, so the top plate is not too cumbersome. Where is the power socket, power switch, indicator lamp and fuse? If they are not on the top plate it is simpler to not have the toroid there.
I have also used in line fuses from the secondary to minimise wiring complexity.
Another option is to fix it in the chassis, using the same space, so the top plate is not too cumbersome. Where is the power socket, power switch, indicator lamp and fuse? If they are not on the top plate it is simpler to not have the toroid there.
I have also used in line fuses from the secondary to minimise wiring complexity.
Oh good. I'd like to use an all-in-one plug socket, fuse holder and switch directly behind the PT. Looks like I'll have room for that and the speaker connections on the back of the plate, inputs on one side, or split, and a volume knob down center.
Might have to look at 3mm top plate, or a bulkhead to accommodate the weight of all that iron. Or maybe some 35mm brass standoffs connected to feet below the bottom plate.
Might have to look at 3mm top plate, or a bulkhead to accommodate the weight of all that iron. Or maybe some 35mm brass standoffs connected to feet below the bottom plate.
Not a problem with the Toroid.
But you will have hum if . . .
You do not take care of ground loops:
B+ first capacitor (needs a controlled local ground loop, center tap, or bridge negative out)
RCA inputs and input tube circuitry (needs a controlled local ground loop of isolated RCA return, volume control, Rg, Cathode bias resistor ground, all together)
Central ground point
Chassis Ground
Example, do not connect the ground returns of any of these directly to the central ground point: isolated RCA return, volume control, Rg, Cathode bias resistor ground. Connect them together first, and then connect a single wire from there to the central ground.
Keep ground loops short.
Do not let any signal wires pass in parallel with the B+ first capacitor local ground loop.
This is the nastiest ground loop, with many upper harmonic noise (hash) for any capacitor input filter.
A choke input filter has much less hash, but creates a magnetic field (try that with single ended air gapped E-I transformers, you must give proper spacing and proper orientation).
Shoot for less than 100uV hum from the loaded 8 Ohm tap (before negative feedback is applied).
That is a tough one.
You will need far less than that much hum for certain headphones, even though you use a load resistor, and an attenuation resistor to the headphones.
Just my opinions.
Have fun designing, building, and listening!
But you will have hum if . . .
You do not take care of ground loops:
B+ first capacitor (needs a controlled local ground loop, center tap, or bridge negative out)
RCA inputs and input tube circuitry (needs a controlled local ground loop of isolated RCA return, volume control, Rg, Cathode bias resistor ground, all together)
Central ground point
Chassis Ground
Example, do not connect the ground returns of any of these directly to the central ground point: isolated RCA return, volume control, Rg, Cathode bias resistor ground. Connect them together first, and then connect a single wire from there to the central ground.
Keep ground loops short.
Do not let any signal wires pass in parallel with the B+ first capacitor local ground loop.
This is the nastiest ground loop, with many upper harmonic noise (hash) for any capacitor input filter.
A choke input filter has much less hash, but creates a magnetic field (try that with single ended air gapped E-I transformers, you must give proper spacing and proper orientation).
Shoot for less than 100uV hum from the loaded 8 Ohm tap (before negative feedback is applied).
That is a tough one.
You will need far less than that much hum for certain headphones, even though you use a load resistor, and an attenuation resistor to the headphones.
Just my opinions.
Have fun designing, building, and listening!
Thanks for all the good advice. I plan to use a 3A 4 pin bridge rectifier. Because the PT has 2 each HV and LV windings I could power each channel with its own windings at a minimal cost of one extra BR + filter cap set. Tempting.
As much as I dislike the front panel mounted jacks on the Dynaco, it does allow the builder to keep signals away from power. As a top-plate-based amp, there's no reason to put the input jacks in the back.
As much as I dislike the front panel mounted jacks on the Dynaco, it does allow the builder to keep signals away from power. As a top-plate-based amp, there's no reason to put the input jacks in the back.