I'm looking at this newly custom built tube phono preamp. It has a separate power supply. It has a bit of hum.
Here's some pictures.
The first thing I'm suspicious of is how there are two ground points. Most tube amps I've seen have a single ground connection to the chassis and it is at the input terminal ground.
Does this seem like a good starting point? Does anyone notice anything else?
EDIT: no further replies required.
Here's some pictures.
The first thing I'm suspicious of is how there are two ground points. Most tube amps I've seen have a single ground connection to the chassis and it is at the input terminal ground.
Does this seem like a good starting point? Does anyone notice anything else?
EDIT: no further replies required.
Last edited:
Connect TT to earth of pre amp.
Maybe use a resistor.
But ground continuity is essential.
Also to wall earth.
Maybe use a resistor.
But ground continuity is essential.
Also to wall earth.
I noticed a few things
-Heater wires not twisted.
-Black Transformer and inductors not 90-degrees angle
-two big "audio" capacitors 🙁
-enough power supply capacitors for a big power amplifier: big current pulses from rectifier.
-Heater wires not twisted.
-Black Transformer and inductors not 90-degrees angle
-two big "audio" capacitors 🙁
-enough power supply capacitors for a big power amplifier: big current pulses from rectifier.
Whoever built that MESS, certainly doesn't know a single things about critical lead-dress or proper layout of components.
Plus, the soldering job is sloppy as though a 7 year old did it.
It might look "pretty" on top, but that's superficial crap that people have been trained on.
FAIL.
Twist the heater wires tightly.
I would use cap multipliers instead of inductors for filtering duties.
I would use cap multipliers instead of inductors for filtering duties.
Also noticed the chassis is not a proper faraday cage. Top and bottom are metal but they are not connected. Sides are wood.
That's not good, right?
That's not good, right?
😀
Trust Matt (@wiseoldtech) to tell it like it is...
Too many fancy pants half wits around posing as experts....
Trust Matt (@wiseoldtech) to tell it like it is...
Too many fancy pants half wits around posing as experts....
I'm more of a fixer than a designer. Though I've done design tweaks on tube gear with the help of forums before.
Nothing worse than trying to clean up a bad build though. All bets are off. At least when I'm cleaning up a bad repair job I know exactly what potential something has in its original form.
I was hoping to open this thing up and find a couple simple things to optimize. No such luck.
The wiring looks like the practice work done by a trainee.
Component quality looks average.
So I would politely return it to the customer, with an inspection charge, if desired.
You will end up with a lot of hours in it, and it may not work.
So you will be unable to satisfy the customer....so a wasted effort.
Component quality looks average.
So I would politely return it to the customer, with an inspection charge, if desired.
You will end up with a lot of hours in it, and it may not work.
So you will be unable to satisfy the customer....so a wasted effort.
Measure the frequency of the hum, is it 50/60 Hz. or 100/120 Hz.?
If it’s 50/60 Hz. try DC for the heaters (I cannot see if it has DC or AC based on the power supply picture).
Regards, Gerrit
If it’s 50/60 Hz. try DC for the heaters (I cannot see if it has DC or AC based on the power supply picture).
Regards, Gerrit
As a start
1. twist the heater wires together tightly and wire them daisy chain style to all the heaters
2. make sure there is one and only one ground point to the chassis
3. rewire the inputs so that all the front and signal cables from the input connectors run together to the selector switch and cable tie them tightly together. (from what I can see, the input connector grounds are wired with tinned wire together and the signal wires then run separately to the switch - this is a large loop area and prone to hum pickup)
It certainly looks cool from the outside - would be nice to get it fixed
1. twist the heater wires together tightly and wire them daisy chain style to all the heaters
2. make sure there is one and only one ground point to the chassis
3. rewire the inputs so that all the front and signal cables from the input connectors run together to the selector switch and cable tie them tightly together. (from what I can see, the input connector grounds are wired with tinned wire together and the signal wires then run separately to the switch - this is a large loop area and prone to hum pickup)
It certainly looks cool from the outside - would be nice to get it fixed
The maker is www.soundaries.com
First change the heater wiring for twisted pair! Use DC heating and elevate the heaters (if not already done). That should go a long way.
Break one of the two connections between signal ground and PE. What happens?
Shielding at least the input tubes is worth a try.
That should take care of a good chunk of issues. Also take a look at the current loops and minimize loop areas as much as possible.
How much hum did you measure with shorted inputs?
First change the heater wiring for twisted pair! Use DC heating and elevate the heaters (if not already done). That should go a long way.
Break one of the two connections between signal ground and PE. What happens?
Shielding at least the input tubes is worth a try.
That should take care of a good chunk of issues. Also take a look at the current loops and minimize loop areas as much as possible.
How much hum did you measure with shorted inputs?
Thanks for the website link.
Just to make sure, that I never by accident buy anything from that company 😎
Just to make sure, that I never by accident buy anything from that company 😎
I see lots of boutique components, but what I don't see is proper twisted heater wiring, a screening chassis, or a 0V bus bar. In the absence of those good signs, I'd be astonished if the designer managed to get the RIAA equalisation correct. Fixing it would be a complete rebuild and probably redesign. And the remote supply needs to be remote (2m away). Hand it politely back to the customer with some very carefully chosen words. It's not going to have a couple of silly faults that are bringing it down, it's going to have lots of faults, some major. It would be a real headache to fix.
Yep, I'm going to pass on the job. I'd rather start with a well known tried and true design and just build from scratch.
Fixing a bad build is the worst kind of job because all the bets are off.
Did the device always hum or has it started to hum recently?
If it did not hum previously layout and wiring are not the issue - a component could have gone funny (power supply or smoothing cap?) or the device has an earth loop when connected to whatever you have it connected to.
If it always hummed then layout/wiring/earthing are probable faults.
High gain preamps, especially with external supplies, are very prone to earth loops and much experimentation is required with tonearm, turntable, signal grounds and mains earth connections. Often devices will be dead quiet in one environment but hum when connected to different equipment/setups. If the device is a commercial effort and many are sold there is a high probability it does not inherently hum….
If it did not hum previously layout and wiring are not the issue - a component could have gone funny (power supply or smoothing cap?) or the device has an earth loop when connected to whatever you have it connected to.
If it always hummed then layout/wiring/earthing are probable faults.
High gain preamps, especially with external supplies, are very prone to earth loops and much experimentation is required with tonearm, turntable, signal grounds and mains earth connections. Often devices will be dead quiet in one environment but hum when connected to different equipment/setups. If the device is a commercial effort and many are sold there is a high probability it does not inherently hum….
- Status
- Not open for further replies.