Here is a photo of the Hiraga
IEC ground goes to chassis, and from chassis to the star ground.
Star ground is isolated from the chassis
RCA input grounds are tied together, and go to start ground.
Center of each of the two power supply boards go to the star ground, and to the power supply in on the amp boards from the power supply boards. It’s difficult to see from the closeup, but there are two wires from the center - yellow and green
Shield around the power supply boards is grounded to the chassis
IEC ground goes to chassis, and from chassis to the star ground.
Star ground is isolated from the chassis
RCA input grounds are tied together, and go to start ground.
Center of each of the two power supply boards go to the star ground, and to the power supply in on the amp boards from the power supply boards. It’s difficult to see from the closeup, but there are two wires from the center - yellow and green
Shield around the power supply boards is grounded to the chassis
It does indeed mean that! Problem is, the other amp - Hiraga - sounds better w the preamp.
I pulled the Cornwalls out of the basement so I could better hear the noise.
Speakers I normally have in place are small, 3ohm 79db efficient speakers…. So not nearly as noisy as the Cornwalls, but they require a lot more power to play at any kind of volume.
So the DIY Audio VFet amp has a power cord without safety ground.
This leads to the assumption you have a safety ground loop.
It may be safe to use your "noisy preamp" without power ground connection,
because the cabinet is made of wood. But perhaps you want to keep this ground
connection to the metal face plate, back plate etc. In this case remove all signal
ground from the metal parts, in other words keep your star ground or whatever
signal ground wiring you have isolated from the metal and safety ground. Then
connect these (power cord safety ground on metal and signal ground) with a
resistor of say 22 ohms. This way you break the ground loop.
This leads to the assumption you have a safety ground loop.
It may be safe to use your "noisy preamp" without power ground connection,
because the cabinet is made of wood. But perhaps you want to keep this ground
connection to the metal face plate, back plate etc. In this case remove all signal
ground from the metal parts, in other words keep your star ground or whatever
signal ground wiring you have isolated from the metal and safety ground. Then
connect these (power cord safety ground on metal and signal ground) with a
resistor of say 22 ohms. This way you break the ground loop.
Thanks
If I use the same power cord that is on the VFet (no ground) on the Hiraga, the noise returns at the same level as with a regular power cable.
Going to take me a second to digest the preamp grounding protocol you’re suggesting. As a visual thinker, I need to draw it out 🙂
If I use my Adcom GFA545 with the preamp, I have the same issue w noise - and it only has a two prong power cord.
If I use the same power cord that is on the VFet (no ground) on the Hiraga, the noise returns at the same level as with a regular power cable.
Going to take me a second to digest the preamp grounding protocol you’re suggesting. As a visual thinker, I need to draw it out 🙂
If I use my Adcom GFA545 with the preamp, I have the same issue w noise - and it only has a two prong power cord.
The signal ground is attached to the PCB in two places. The ground bus wire of the RCA input/output (single wire from bus to board), and the ground from the volume pot goes to the signal input on the PCB
The power ground is connected to the PCB from the chassis/star ground. The star ground has the front, top and rear panels connected to it, as well as the power/earth, the transformer grounds and the PCB ground.
The power ground is connected to the PCB from the chassis/star ground. The star ground has the front, top and rear panels connected to it, as well as the power/earth, the transformer grounds and the PCB ground.
Not interested to read the whole thread again, but it is bad practice to connect signal
ground and safety ground. Of course it is useful to keep metal parts connected to safety
earth, but not the signal ground (in more than one unit of the stereo set). But i you say
the noise remains without safety ground on the preamp the problem may be somewhere
else.
ground and safety ground. Of course it is useful to keep metal parts connected to safety
earth, but not the signal ground (in more than one unit of the stereo set). But i you say
the noise remains without safety ground on the preamp the problem may be somewhere
else.
Yeah, I get it. Long thread!
And I just confirmed, the cord without ground pin, plugged into preamp, does not remove the hum. It remains…
And I just confirmed, the cord without ground pin, plugged into preamp, does not remove the hum. It remains…
Consider using a ground lift like I had suggested several pages back. And rebuilding your preamp in a full aluminum anodized chassis.
Best,
Anand.
Best,
Anand.
Just tried connecting my Fosi V3 up to the preamp, and it’s dead quiet.
Tried the Adcom GFA 545, and it hums. Tried my Vista Spark, and it’s dead quiet.
Going to order the ground lift board today and see if it helps.
So, Fosi V3, VFet (with ground lifted cord) and Vista Spark II (with grounded cord) are all quiet.
Hiraga and Adcom both hum
Tried the Adcom GFA 545, and it hums. Tried my Vista Spark, and it’s dead quiet.
Going to order the ground lift board today and see if it helps.
So, Fosi V3, VFet (with ground lifted cord) and Vista Spark II (with grounded cord) are all quiet.
Hiraga and Adcom both hum
The schematic is freely there, and one can do it diy pretty easily ptp. I think Broski provides all parts, pcb, shipping, etc...I have a few pcb gerbers that are similar to this that I use for my personal use ordered from a chinese fab, which needs to be done in multiples not singletons.
That's why I wrote "CONSIDER", on post #228, not "YOU MUST."
Best,
Anand.
Yea but this is VTA/tubesforbifi not aikido; builders encounter hum on these sp-14 quite frequently, much more so than folks do with aikido, so I bet they’ve made changes.
Well, the two amps, Hiraga and SP14, were built to be a set. I’m already in so deep with this, the cost of these two boards is kinda inconsequential 🙂 I could order the parts, and put it together. But it’s just easier this way.
As I had three amps that were quiet w the preamp, I’m working on both amps together to try and get them to play nice with each other.
Between work and kids, time has not been my friend …
Tried the ground lift, didn’t make a difference to the noise unfortunately.
Removed all the signal wires, picked up some new wire and about to replace them all with twisted pairs. Fingers crossed this helps.
If this doesn’t help, then I’m going to remove the steel top plate and see if that makes a difference. If it does, I’ll be rebuilding it in a Hammond Aluminum chassis.
Tried the ground lift, didn’t make a difference to the noise unfortunately.
Removed all the signal wires, picked up some new wire and about to replace them all with twisted pairs. Fingers crossed this helps.
If this doesn’t help, then I’m going to remove the steel top plate and see if that makes a difference. If it does, I’ll be rebuilding it in a Hammond Aluminum chassis.
Rewired the preamp signal wires using twisted 22ga solid core wire.
Only wired in 3 of the 5 inputs this time - all I need - in an attempt to reduce the amount of wire in the preamp.
Sadly, it’s noisier now than it was previously…
Only wired in 3 of the 5 inputs this time - all I need - in an attempt to reduce the amount of wire in the preamp.
Sadly, it’s noisier now than it was previously…
If the frequency you're hearing is 120hz then it's power supply ripple.