• 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.

TPAD Devices Kit

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Jump to Latest
philipbarrett

philipbarrett

Member
Joined 2005
So I built this kit (http://tpadevices.com/hifiproducts.html), price seemed fair & I thought it would be a good baseline to compare my own sorry phono-pre efforts against.

Although the preamp is working fine I am experiencing a hum (10mV) on the output. Obviously the first place I suspected was my PSU which is in a seperate chassis connected with a 4-pair cable & 4-pin XLRs.

My B+ is 320VDC and my heaters are at 6.8VDC. Both supplies look very clean on the 'scope. I have experimented with both tube & solid-state supplies for the B+ and with both full wave and bridge supplies for the heaters. All supply designs were checked with PSU designer and performed to the programs' specifications. None of the designs made a difference to the hum level.

I contacted T-PAD but haven't heard back yet. Any suggestions from the brain trust?

Thanks in advance...

PB
 
philipbarrett

philipbarrett

Member
Joined 2005
PSU is physically 2 feet from the preamp, audio connections are via shielded (one end tied to ground) audio cable. I tried locating a completely seperate B+ supply away from the heater supply, also bypassed my umbelical cable and ran direct wires to the pre, no change.

B+ secondary CT is tied to chassis ground as is incoming AC ground. I tried lifting the AC ground, no change.

Thanks for the ideas...

PB
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Top Bottom