Studiomaster Leadmaster

UPDATE 2-4-18: This thing finally went home a week ago-late January of 2018-after I fought it to a standstill.

The customer complained that the XLR out wasn't working and a trip to Kevin's recording studio proved that the owner wasn't using it properly, or it was not properly wired or both. Kevin tells me that there is no consistency or standard to how XLR plugs are wired.

So that solved one problem. A lot of parts are made of unobtainium, and the ones that are installed are not maintenance friendly.

The LED for the standby switch is one example. To service it the choke and power transformer must be removed. I'm not going to spend a couple of hours fooling around with this to fix a LED.

The pots are hard to come by, the pull switches are unavailable and obsolete, and making them work reasonably well consumed about half a can of Deoxit.

The plate load resistors were making a popping noise so I looked at it. The preamp board is backed up by a metal plate and the entire thing including the preamp tube sockets is riveted together, the gap between the two being maybe a quarter inch-plenty of potential there for shorts.

I was able to install one plate load and lucky me, that was the noisemaker.

Also, selectively dialing back the gain in a few places made the amp much more tractable.

All the preamp and power tubes needed replacement for noise, and I selected the preamps for lowest noise. I think there is a 5751 and a 12AU7 in there somewhere. The amp was full of ancient Chinese junk for tubes, and they all went in the trash.

The reverb was also on the fritz but a new tank took care of that. Luckily it is transformer driven ala Fender and uses a similar tank. It uses a stereo cable so I made do with what was there.

Every once in a while somebody brings in an amp that you've never heard of at all and wants some small thing taken care of. It usually turns into a shit show and this was no different.

Enter the Studiomaster, which looks something like a home made Boogie clone with the extra special unventilated tube section.

After going for a test drive, itemizing its many flaws and opening it up later I decided the owner may not know it but the first thing that was going to get done was a comprehensive power supply overhaul.

It's like a house. If you do not have a solid foundation, nothing else you do will be of lasting value.

Luckily enough the major components are on a board that's easily removed.

Here's what I've found so far. The schematic is courtesy of Nic Grabien, who was involved in the Studiomaster project as a consultant. Thanks brother.

The pics are of the power supply board and the raft of dodgy IC capacitors poorly installed, a/k/a Instant Crap.

Here's the after, with new diodes and balance resistors. The diodes were upgraded with 1N5062 2a .8kv genuine Telefunken diodes for the bias supply, and 1N5399 1A 1.5 kv in the power supply.

Much nicer with F&Ts, don't you think?