Cleaning out old paperwork.

Hiwatt Dr 103 kind of too quiet in max volume situations...

We corrected a simple error in our modding the amp at the gain stage just before the tone stack.

Mellotron 400 has a high level, low frequency tone (probably 60Hz) coming out the output..I am thinking there is a dead electrolytic somewhere. Checked the PSU for terrible ripple. Going to check the audio head preamp board, and motor drive amplifier tomorrow.
When I opened up the preamp/line amp box, and inspected the pc boards, I found no bad caps, or failing parts. When I powered it up, the mellotron worked fine. While I had everything open, I -Cleaned the insides, Adjusted the capstan motor positioning, which was off a bit. The motor is mounted on a piece of plywood which was flexing a bit under the weight of the motor. I placed a wood shim to push the plank back to vertical. Made minor adjustments on the keyboard for sensitivity, etc. Cleaned the heads

Finished another EAPreoto. This has an anodized bronze faceplate with yellow legend. It is very visible in low light. The old black on bronze was cool looking in normal light, but illegible in studio light.

greg wrote:Finished another EAPreoto. This has an anodized bronze faceplate with yellow legend. It is very visible in low light. The old black on bronze was cool looking in normal light, but illegible in studio light.Started building another one.

greg wrote:studio light.

Neotek Series II,

Channel 31 working intermittently. More specifically, the audio to the fader would cut out, but sends to busses and pre-fader solo worked.

Found a cold/broken solder joint on an audio jumper wire to the mute relay (part of our in-place solo mod).

Installed 1/4" speaker jack on our Traynor TS-10, so it could be used with other cabinets. Waiting on a replacement pot for the "Master" volume. (Kevin)

Epiphone practice amp (EP800r) has a broken mid eq pot.

When removing knobs to work on this thing. The other pots fell apart. I might toss this toy into the river, or use the carcass for a mini tube amp project.


Neve B002 Mixer. Intermittencies and loud noises caused by the polarity switches.

Ordered parts to upgrade the mixer. The polarity reverse switches are showing their ass after 15 years of toggling. I'm going to replace them with sealed relays, controlled by similar switches. I'm also moving them from the input side of the preamp to the output. It is much quieter to switch things there.

More Preamp work, and testing...

steve wrote:

greg wrote: I'm also moving them from the input side of the preamp to the output. It is much quieter to switch things there.

That may have been done so the polarity switch will work on signals mixed through the busses. If you're just talking about a polarity switch on the channel output transformer that won't do that.

Oops,Thanks for reminding me. I forget that it gets used this way, and not just as 6 discrete preamps... and this after using for summing tom mics a couple of weeks ago. Stupid. We'll deal with the clicks. It should be much quieter with the new relays regardless.

greg wrote: I'm also moving them from the input side of the preamp to the output. It is much quieter to switch things there.

That may have been done so the polarity switch will work on signals mixed through the busses. If you're just talking about a polarity switch on the channel output transformer that won't do that.

Is the phantom what causes the click? Is there a way you can use a DC-blocking cap on each leg so the Phantom doesn't hit the switch?

steve wrote:Is the phantom what causes the click?

It shouldn't be worse with the phantom on since the mic is directly powered buy the drop resistors prior to the polarity switch, and input transformer is floating (nowhere for DC current to flow). If pin 2 reaches the transformer before pin 3, it shouldn't matter since the primary will already be at 48 volts before the second connection.* The transformer can only provide an AC load to the mic. The intermittent lifting, and re-applying of the source load (mic) seems to be why a "click" occurs, much like when you plug/unplug a dynamic mic with the preamp gain up. I've noticed this with other transformer i/p preamps where there is a mechanical polarity switch in front.

Is there a way you can use a DC-blocking cap on each leg so the Phantom doesn't hit the switch?

I don't think this would solve the "click" as described above. The problem we're having with this is the switch making degraded, intermittent contact. Sometimes, when you flip the polarity, the signal cuts out, or distorts. *Is it possible to create a signal on a secondary without current flowing through the primary? In this scenario, applying DC voltage (theoretically pure DC) to one leg of the primary, with the other leg floating. It seems like there shouldn't on paper, but in the real world ... could happen?
I'm going to do some tests and get back to y'all...

Audio Technica Pro37 intermittent output.
Missing screws not grounding the main body to the connector barrel. Ordered replacements, should lock paint them into place...
Later- Got them. Tightened things down nice, and everything worked. No locking paint.