London Power Pre-Amp

[SonicSonar]

Hi all.

My name is Peter and I am new to the site. I am not exactly sure how I stumbled on to this site, but I know it had to do with KOC and his London Power/TUT stuff. Here is the link I found -> http://music-electronics-forum.com/t244/

I am a software engineer by trade and a guitar player when I have time. The amp I have in possession is the (GT)Groove Tube D-75 and the (GT)Groove Tube Trio. Both are out of production and both a extremely grrreat . Love the sound I can get from it. My interest in building an amp is when I decided I need a back up. That is when I began my search. The only thing that satisfy my taste will be something similar to the Groove Tube. KOC provides the best possible answer imo.

Objective #1: Build a Pre-amp. 3 channel, switchable. Just like the GT Trio

My plan is to build a rack mount Pre-Amp from KOC London Power kits.

I expect this to take about 6 months. As time goes by, I will update.

FYI. KOC no longer sells the Standard. It is way over my head to do something that complex as my first build.


Bought the Quad, L-Pre, Z-Pre, Power Amp, and Line



Started to put them together.


Is this from the movie Iron Man?


Trying to mimic the Trio was a bad idea. I bought the exact same size Rack Mount chassis as the Trio and it turns out to be too small.

[Phostenix]

Cool. Look forward to seeing how this goes.

[voodoojaron]

Cool, I'll be keeping track - I want to do a similar project to go with my Dual 75.

VJ

[SonicSonar]

Hi all
Been busy doing other things and spent some time working on amp.
Here is my update.


I have it working, which is good. But there are things that must be fixed before I continue.

1.) Power-amp - ON, pre-amp -OFF. Without connecting the pre-amp to the Power-amp, when I power up the PRE there is this audible noise that last for about .5 - 1 seconds. Somehow the Power-amp is picking it up and amplifying it. Strange.

I have other issues, but this one needs to be done first because it has the least amount of things going on. There is no guitar plugged in.

Any ideas?

Thanks

[stormbringer]

I'd really like to see more of this build; I've considered the LP kits for a while, but there is so few threads showing the build process. Your last photo shows the preamp transformers (PSU-PRE), but there is the toroidal PT? Was it for a separate power amp?

[SonicSonar]

I moved away from the big toroidal PT to the PSU-PRE that uses a "semi-toroidal" design. http://www.hammondmfg.com/229.htm
The switch mostly did with curiosity and space issues in the mouser rack mount chassis. When I get the chance to start building the Power amp I'll use the big Toroidal.

Keep in mind I am building a stand alone pre-amp. I have to use my GrooveTube Power amp to test it with.
The build consists of
LP-PRE + Z-PRE + QRK + BFX + LINE + PSU-PRE


What I have learned.
--------------------------
0.) Chassis work sucks
1.) Build the PSU-PRE and test it alone. Then test it plugged into the Power Amp.
2.) Next add the LINE and test plugging in guitar into the LINE + PSU-PRE.
3.) Next add the LP-PRE or Z-PRE and test it.
.
.
.
.
Get those working together before adding the BFX and QRK.

Summary: Do it in pieces and slowly add once everything is working properly.

I've been real busy lately and haven't had much time to work on it, hence the reason why I haven't posted in a while.
Things are much better. Getting the ground to work correctly in the chassis helped.

[SonicSonar]

Hi all
But there are things that must be fixed before I continue.

1.) Power-amp - ON, pre-amp -OFF. Without connecting the pre-amp to the Power-amp, when I power up the PRE there is this audible noise that last for about .5 - 1 seconds. Somehow the Power-amp is picking it up and amplifying it. Strange.

I have other issues, but this one needs to be done first because it has the least amount of things going on. There is no guitar plugged in.

Any ideas?

Thanks

I found the problem, but not sure the exact cause of it. This problem happens when I turn on the fan, so it can't be the pre-amp. Electromagnetic waves and/or grounding in my home must be the root cause. The build is improving and sounding better.

[stormbringer]

Thanks for the updates and details. Do the kits come with schematics, layouts, and instructions? Do you have any new photos?

[SonicSonar]

Thanks for the updates and details. Do the kits come with schematics, layouts, and instructions? Do you have any new photos?

No new pics.

Ask Kevin about the kits. Don't worry he won't bite.

[stormbringer]

No new pics.

Ask Kevin about the kits. Don't worry he won't bite.

Just bought the TUT series (along with the other LP books). TUT1 covers the LP standard preamp and many other things. A tonne of info in those books.

How is your preamp coming along?

[SonicSonar]

2 steps forward, 1 step back.

When I have free time, and the summer didn't give me much, I worked on it.
I was consumed by other projects. The FishFive mic preamp and the 2 Nady 1050 mic modification. Both are done, and now I can get back to the amp.
Spent considerable amount of time working on the ERK getting it functional. In doing so, I found I had other issues that needed resolving.
Ended up buying a larger rack mount, and bought more parts from KOC to build a Power amplifier.


To answer your question. Slowly. But I am in no hurry. There isn't much free time these days.

[olddawg]

In general, when using separate preamps, power amps, etc with separate power supplies, it's a good its a good idea to turn the power amp on last after waiting 10 sec. Some amps are designed with a delay trigger and power up delayed after the main power is turned on. Some amps are also designed with an input mute for 5-10 sec. Both of these scenarios allow whatever is on the main amp input to stabilize before it can make any sound. There are a lot of ways to do it. It usually isn't a problem when the preamp and a power amp share the same power supply for tube amps. Tubes need time to warm up and work. Most SS amps have some kind of muting because they are instantly on.

[SonicSonar]

Here are some updates.


I went to a larger chassis. Much easier to work with and plenty of space.

Next I went to the PSU voltage regulated heater and source.
And finally started almost from scratch.
IN this pic, it is the PSU + the LINE


Tested. Works great, sounds clean and no fuzz.

Now From there, I added the pre-amp. All work except the Marshall tone is giving me some high pitch noise.
But before I tackle that, I need to get the QRK working. Those darn JFets are not working. I can use the relays, but I want the JFets for switching.



Since I am always adding and subtracting stuff and modifying the boards, I created those small eyelet boards to pass the power. It is now easier to remove a board if needed.

2 things are holding me back from completion.
1.) The Switching QRK (Jfets)
2.) The Marshall channel is messed up.

Getting closer....Once this is complete, I can start working on the Power amplifier.

[jmaf]

Just to add 2 cents, I was unable to identify any shielded wires in there. The squeal you heard on the hi gain Marshall channel may be due to coupling among the wires. Move wires around to see if it changes anything about the high pitch noise. Congratulations on your build, hope you get it all working soon!

[SonicSonar]

Finished the pre-amp. Finally.

There are some unfinished side projects that go with the pre-amp, but no need at the moment.
Inside it looks like this


Many of things I have learned over this project. Any questions, please ask.


I just realize this took more than a year.