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London Power 3 channels amplifier project
#1
Greetings to all!

I've mentioned in some other threads that I'm in the process of building a 3 channels, 50w amplifier using London Powers kits. This is the 6th amplifier I'm building out of a kit but it is by far the most ambitious project I've started, I will take my time and try to do it right as this has the potential to be the ultimate amp for my need.

Here's a list of the kits I'll be using with this amp:

- LP-Pre 2 channels Preamp

- Z-Pre 1 channel high gain Preamp

- BFX Effect Loop

- 2xPA66 (4 power tubes capacity)

- PSU-TPA power supply

- 2x RLY Relay kits (for channel switching)

- SV1 Power Scaling

- GND Galactic Ground

Now for this project and the previous I've done (Ceriatone HRM100 MKII), I've done the layout on AutoCAD in order to make sure that everything will be drilled properly. The chassis I'm using is an Hammond 1441-32BK3 (17x10x3). Here's what the layout looks like as of today, since I'm not going home until next week I might tweak it a little bit but I think this should do the trick just fine

Front panel:
[attachment=14]

Back panel:
[attachment=15]

Top view (looking at the board on the socket side):
[attachment=16]

ISO Front view (didn't took much time on it, just to give a rough idea so the tubes and transformers look like crap):
[attachment=17]

ISO Back view:
   

If any of you think of any improvement or mistake I might have done, please feel free to share it. I'm not an electronic expert, just an hobbyist DIY guy.

Cheers!
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#2
Hi Vostre

The thing that catches my eye is the power switch right beside the input jack. These are normally as far apart as possible. One solution is to put the switch on the rear panel.

On the rear panel, I would swap the Send and Return s the signal flow on the rear is from right to left.

Power flow is opposite to signal flow, so the mains input should be on the other end, too, which really begs for the OT and PT to swap chassis ends, along with the PSU remaining under the PT. Overall, I would do this:

On the front, Input to left end as is with the selector switch above it.
OD channel below Clean channel.
To the right of this, PA stuff below Lead channel
PA stuff could include the mains switch as far right as possible

On the rear, Mains moved to opposite end
FX send/return swapped
foot switch jack on rear panel

External fuses? What are these for?

PSU has the mains fuses onboard. It is useful to add an OT fuse that is a fast-blow (mains are slow-blow), but none of these should be externally accessible.

The channel LEDs can do double duty as a power indicator, since one or another channel will always be selected. However, if you add now or later additional fusing for isolating the PSU or various circuits, a discrete power LED could be useful. Personally, I like to have a power LED right beside the mains switch as it is intuitive and expected.

You are obviously very good with autocad Smile
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#3
(11-21-2018, 04:00 PM)K O'Connor Wrote: Hi Vostre

The thing that catches my eye is the power switch right beside the input jack. These are normally as far apart as possible. One solution is to put the switch on the rear panel.

On the rear panel, I would swap the Send and Return s the signal flow on the rear is from right to left.

Power flow is opposite to signal flow, so the mains input should be on the other end, too, which really begs for the OT and PT to swap chassis ends, along with the PSU remaining under the PT. Overall, I would do this:

On the front, Input to left end as is with the selector switch above it.
OD channel below Clean channel.
To the right of this, PA stuff below Lead channel
PA stuff could include the mains switch as far right as possible

On the rear, Mains moved to opposite end
FX send/return swapped
foot switch jack on rear panel

External fuses? What are these for?

PSU has the mains fuses onboard. It is useful to add an OT fuse that is a fast-blow (mains are slow-blow), but none of these should be externally accessible.

The channel LEDs can do double duty as a power indicator, since one or another channel will always be selected. However, if you add now or later additional fusing for isolating the PSU or various circuits, a discrete power LED could be useful. Personally, I like to have a power LED right beside the mains switch as it is intuitive and expected.

You are obviously very good with autocad Smile

Thanks for the reply Mr O'Connor, very appreciated!

I've worked on the layout a little today but I'll complete it tomorrow during my lunchtime (I'm using my work computer to do this so I've got to do it during my personal time ahah). I was kind of expecting that putting the power switch right next to the input might be problematic, I will put them on each end of the front panel to distance them as much as possible. I don't want it to be on the back panel, I've done it on my Ceriatone and I totally hate it, hard to reach when the amp is in my music room.

I shall post the modification tomorrow for a second review, my goal is to have the layout completed so I can print it on here before I go back at home (printer here can handle 11x17 paper size, which is perfect for the chassis)

Oh and thank for the compliment regarding AutoCAD, I'm using it everyday to draw mining stuff, still learnt to use it for some personal projects (guitars, cabs and amps). Ain't as useful as proper electronical knowledge, but at least it can has some uses for my hobbies ahah

Cheers!
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#4
Allright, here's version 2!

As M. O'Connor proposed, I've swapped the OT and PT, brought the clean channel along with the OD channel and put the PA section under the Lead channel. The two fuses that were on the back of the amp was a mistake, I knew that there was two fuses but forgot they were directly on the board. I've also swapped the Send and Return of the FX loop. Pilot light is out, I wanted to keep it but didn't found a place that would look good with the new layout, anyway as Kevin pointed out, the channel's led will show if the amp is on or off anyway.

Front view
   

Back view
   

Top view
   

Once again, thanks to M. O'Connor for the help!
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#5
Hi Vostre

Looks good!

The layout now has a smooth signal flow and power flow. There could be a little bit of a cluster between the preamp cards and the controls, but there's always something of that nature in every layout that is more complicated than a single-channel amp.

Remember that the OT and PT wires need protection from the edges of the holes through the chassis - deburr the holes as always but also use rubber grommets or nylon "caterpillar". Adding either requires a larger hole than just that needed for the wire. Unfortunately, the "approved" wire for transformer terminations has quite thick insulation.

Have fun
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#6
Thanks Kevin!

And yeah, grommets, I always forget how those little rubber donuts are called... and yeah "rubber donuts" doesn't give me much results on Mouser

Definitely getting some, along with some spacers for the boards and an ON-ON-ON dual pole switch for the channel switcher. Can't wait to work on this project, so much holes to drill, although I'm to blame for this I guess.

I'll move the preamp boards a bit more to the back and give myself more space around the front panel, given the amount of pots and switches they'll be a lot of stuff going around that area.

Cheers!
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#7
It looks like really cool and complex project! I don't have anything to add but I am eager to see it's progress. Good luck with the build!
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#8
Hi Vostre

I wouldn't use an ON-ON-ON switch as that is likely to be expensive or not exactly what is needed. The C&K 7211 can be wired as a 1P3T switch (like the T-U-Ps on my older amps), or as a A,A+B,B switch ala Gibson guitar pickup selector. It's a great quality switch, as are all the C&K 7000-series devices but it is very expensive.

I usually opt for a less expensive switch, such as a SPDT with centre-OFF (7103-SYZQE for panel mount and solder lugs). Depending on the circuit switching requirements, wiring the relay contacts in a specific fashion will give the 1-of-3 selection/muting as needed. More reliably, using a few BJTs to interface provides the distinct 3-way output needed. Instead of BJTs, one could use CMOS gates but you still end up needing BJTs to drive the relays. With any of these solid-state interfaces, it is a lot easier to build if it is on a PCB - even with just the relays a PCB makes things neater.
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#9
Looks like a fun and ambitious project. I would be tempted to try GMX (as a feel enhancer, as the LP site says) in place of the second PA66.
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#10
Hi Guys

Having the extra tube positions is much more versatile than replacing them with GMX. The tubes can be any type lending their tone character as well as the GmX effect.

In a super versatile format, each output tube can have its own level control, allowing any mix of the two sides of the circuit with whatever tubes are fitted. PA66 uses a tonally asymmetric splitter, so even in a same-tube situation, reducing the drive to one side of the circuit has a different sound than reducing it to the other. The panel control allows access to both sounds. Adding a Body control to only one side allows accessing the tone of the other side and dialling that sound all the way to an SE (single-ended) tone. But... if the Body control itself only works on one side and there is only one such control, only one range of tones is accessible (for same-tubes).

Two Body controls "fixes" the above inasmuch as the tonal range of each circuit half can be accessed. The same applies with a double-ended Body control, as I had on the later hand-wired amps. I have some custom pots on order for a newer version of the double-ended Body control to go on some amp designs in the works.

So, Vostre, maybe you need to make room for one Body control? Move the footswitch to the rear.
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#11
(11-23-2018, 01:49 AM)K O\Connor Wrote: Hi Vostre
I wouldn't use an ON-ON-ON switch as that is likely to be expensive or not exactly what is needed. The C&K 7211 can be wired as a 1P3T switch (like the T-U-Ps on my older amps), or as a A,A+B,B switch ala Gibson guitar pickup selector. It's a great quality switch, as are all the C&K 7000-series devices but it is very expensive.
I usually opt for a less expensive switch, such as a SPDT with centre-OFF (7103-SYZQE for panel mount and solder lugs).  Depending on the circuit switching requirements, wiring the relay contacts in a specific fashion will give the 1-of-3 selection/muting as needed. More reliably, using a few BJTs to interface provides the distinct 3-way output needed. Instead of BJTs, one could use CMOS gates but you still end up needing BJTs to drive the relays. With any of these solid-state interfaces, it is a lot easier to build if it is on a PCB - even with just the relays a PCB makes things neater.


Oh I think I see what you mean, for some reasons I forgot that the clean channel was in the N/O position of the first 2 relays, which means that the picture above should be the way this switch is wired, right? (I know that they actually connect to the footswitch's poles but its just to be sure I understand that part right)

Edit: Oh and yeah, drew that super fast and forgot that when the switch is on the "up" position, the bottom lug connects to the middle lug and vice versa. Meaning that the lead would be on the "up" position on that drawing and the overdrive on the "down" position.

[attachment=23]

Regarding the Body Control, I thought about it while reading the PA-66 documentation but decided to not use them because the amplifier will be versatile enough for my needs with all the controls that I have planned on it already.

Cheers and thanks again for the help!
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#12
Hi Vostre

Your figure shows conceptually what the 7211 does, but it looks like a DPDT and needs a jumper on the back to have this functionality - otherwise it defaults to the pick-up selector function.

Also, because the relays have two states, you have to decide on what the default state selects channel-wise, i.e.e, no relays on = clean, but could just as easily be over-drive. It depends also on what aesthetic you want for the switch positions, which are in a fixed order mechanically, but you can assign the result as "increasing gain" or whatever, if that is clear?
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#13
(11-23-2018, 03:45 PM)K O\Connor Wrote: Hi Vostre
Your figure shows conceptually what the 7211 does, but it looks like a DPDT and needs a jumper on the back to have this functionality - otherwise it defaults to the pick-up selector function.
Also, because the relays have two states, you have to decide on what the default state selects channel-wise, i.e.e, no relays on = clean, but could just as easily be over-drive. It depends also on what aesthetic you want for the switch positions, which are in a fixed order mechanically, but you can assign the result as "increasing gain" or whatever, if that is clear?

I think it is, but lets see if I understand you correctly ahah

Basically, if I connect:

Relay-1: ML-1 to NO and Clean Mute to NC
Relay-2: ML-2 to NO

Then the switch act like the picture below (I think my first one was confusing, hence this one being a bit more clear on what I wanted to show):

   

I've deleted the pictures that were not good as I've reached my attachment quota lol

Cheers!
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#14
Hi Guys

The attachment limit has been reset Smile

Thanks for finding that.
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#15
Well thanks for fixing it, will make my life much more easier when I'll be uploading my build progress

Cheers!
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#16
Well, ran into a small issue, will delay the project a bit ahah

Turns out that the Hammond's Steel chassis is one hell of a bitch to drill, everything was going well until I had to ream the tubes holes. I've got a step bit that I've used in past project and a Mastercraft (cheap) press drill that I'm using for the first time. Well, since the holes has to be big enough for the tubes to pass through the chassis (as opposed to my previous projects where just the socket would pop out) and that the chassis is much stronger than the aluminium ones I've used in the past, I can't do a clean job. The power tubes holes has to be as big as my step bit's biggest size and the drill keep on jamming (did I mention that I'm using a cheap press drill).

So I'll either have to find someone locally who can save the chassis I'm using or I'm ordering an aluminium one so I can at least get something done. Unless someone has some ingenious way to deal with that issue
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#17
Hi Vostre

There is no need for the tubes to go through the chassis unless you put the parts on the same side of the board as the sockets.The usual mounting has the components and tubes on opposite sides, allowing just the tube socket to protrude slightly or be flush with the chassis outside surface. The other issue could be of using stand-offs that are unnecessarily long.

For the 9-pin tubes, it is about 0.75" if you are really precise, but 1" if you need some slack - this is also good clearance for the tube itself. The stand-off might be 1/4" here.

For the octals, 1-1/8 to 1-1/4" hole depending which part of the socket you have to clear. The stand-offs would be 1/4" to 3/8".

Step bits work well in thicker material than Hammond's chassis. The steel is actually not that thick but if you are used to aluminium then it will seem pretty tough - stainless could seem impossible! With most consumer-grade drill bits and cutters, the number of flutes and hence the number of cutting edges is usually minimal. For example, counter-sinking bits are most often three-flutes and sometimes only two for the smaller sizes. Good counter-sinks are five-flute. I had to order them from China recently because no one had them locally.

With the low-flute-count drill bits and a slightly wobbly drill chuck, it is difficult to get a smooth cut unless the drill speed is a bit higher. That can lead to an out-of-control situation pretty quickly, though, but one defence against it is to loosen the belt in the drill press. This will keep the bit from grabbing the piece out of your hand, or out of any jig or holder.

Another way to fix the holes is to use a nibbler. This is a single-tooth cutter that you use to nibble away material - great for making the IEC mins plug hole.
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#18
(12-04-2018, 06:23 PM)Vostre Roy Wrote: Well, ran into a small issue, will delay the project a bit ahah

Turns out that the Hammond's Steel chassis is one hell of a bitch to drill, everything was going well until I had to ream the tubes holes. I've got a step bit that I've used in past project and a Mastercraft (cheap) press drill that I'm using for the first time. Well, since the holes has to be big enough for the tubes to pass through the chassis (as opposed to my previous projects where just the socket would pop out) and that the chassis is much stronger than the aluminium ones I've used in the past, I can't do a clean job. The power tubes holes has to be as big as my step bit's biggest size and the drill keep on jamming (did I mention that I'm using a cheap press drill).

So I'll either have to find someone locally who can save the chassis I'm using or I'm ordering an aluminium one so I can at least get something done. Unless someone has some ingenious way to deal with that issue

I would encourage you to persist with the  Hammond steel chassis or get a non-hammond Aluminium chassis.  I've found the Hammond Aluminum chassis to be rather flimsy at only .04" thick.  With your drill press you may need to change the speed, use a newer step bit, and use metal cutting oil to ease getting through the larger holes.  I've used many Hammond Steel chassis and generally with a good bit and the proper speed you'll get though it just fine.  To clean up the burs I'll use a grinding stone on a hand drill for large holes and countersink bit on smaller holes. For the hard to reach spots on the panels I use a drill bit holding extension arm (what are they really called?) with the grinding stone.  You'll clean em' right up! 

If you prefer to go Aluminium I'd suggest that the chassis be .07" to .09" thick.  There's seller on Reverb that can make them custom sizes and make bottom plates if you need one. 


I hope that helps!
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#19
(12-04-2018, 06:56 PM)K O\Connor Wrote: Hi Vostre
There is no need for the tubes to go through the chassis unless you put the parts on the same side of the board as the sockets.The usual mounting has the components and tubes on opposite sides, allowing just the tube socket to protrude slightly or be flush with the chassis outside surface. The other issue could be of using stand-offs that are unnecessarily long.
For the 9-pin tubes, it is about 0.75" if you are really precise, but 1" if you need some slack - this is also good clearance for the tube itself. The stand-off might be 1/4" here.
For the octals, 1-1/8 to 1-1/4" hole depending which part of the socket you have to clear. The stand-offs would be 1/4" to 3/8".
Step bits work well in thicker material than Hammond's chassis. The steel is actually not that thick but if you are used to aluminium then it will seem pretty tough - stainless could seem impossible! With most consumer-grade drill bits and cutters, the number of flutes and hence the number of cutting edges is usually minimal. For example, counter-sinking bits are most often three-flutes and sometimes only two for the smaller sizes. Good counter-sinks are five-flute. I had to order them from China recently because no one had them locally.
With the low-flute-count drill bits and a slightly wobbly drill chuck, it is difficult to get a smooth cut unless the drill speed is a bit higher. That can lead to an out-of-control situation pretty quickly, though, but one defence against it is to loosen the belt in the drill press. This will keep the bit from grabbing the piece out of your hand, or out of any jig or holder.
Another way to fix the holes is to use a nibbler. This is a single-tooth cutter that you use to nibble away material - great for making the IEC mins plug hole.

Greetings Kevin,

Regarding the tubes, I probably misinterpreted the mounting diagrams that were included in the kit, really thought that the tubes had to have their base through the chassis, which required the largest size of the only step bit I own ahah. And yeah, that step bit only has two straight flutes (I guess the "flutes" are the vertical grooves) so an upgrade wouldn't be too extravagant I guess. Need to get myself a steel nibbler too so I'll get an Amazon order ready for my next time off.

Oh and yeah, I experienced the out-of-control situation pretty quickly, pretty sure that this chassis is screwed now. Won't cry over it, I'll use it to do some more test and get a better hand before doing the next chassis try.

(12-05-2018, 01:22 AM)makinrose Wrote: I would encourage you to persist with the  Hammond steel chassis or get a non-hammond Aluminium chassis.  I've found the Hammond Aluminum chassis to be rather flimsy at only .04" thick.  With your drill press you may need to change the speed, use a newer step bit, and use metal cutting oil to ease getting through the larger holes.  I've used many Hammond Steel chassis and generally with a good bit and the proper speed you'll get though it just fine.  To clean up the burs I'll use a grinding stone on a hand drill for large holes and countersink bit on smaller holes. For the hard to reach spots on the panels I use a drill bit holding extension arm (what are they really called?) with the grinding stone.  You'll clean em' right up!
If you prefer to go Aluminium I'd suggest that the chassis be .07" to .09" thick.  There's seller on Reverb that can make them custom sizes and make bottom plates if you need one.

I hope that helps!

Greetings!

Well I totally understand what you mean, reason why I wanted to try the steel chassis this time is because I've used Hammond's Aluminium in my previous build and I can feel the transformer "bounce" a bit when I carry the amplifier around. I'm sure that the amp will be fine in the long term but I really wanted something sturdy for this project. Guess I'll bit the bullet and as I said a little earlier, I'll use this chassis to perform some test (since I screwed up quite bad) and I'll get a new one of the actual project.

And yeah, some cutting oil is a good idea too, tried to work without it as my "workshop" is actually my adjacent garage with my summer car parked in it (which takes most of the space). Even though I'm putting a cover over it, I don't want oil going all around the place ahah

Cheers and thanks for your inputs guys! Sorry for the late reply!

EDIT: Oh and quick question, anyone tried a metal hole saw for those kind of jobs? Just curious as multiple flutes step bit seems to be quite rare as Kevin mentionned
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#20
Hi Vostre

Hole saws are designed for wood. I tried one on aluminium many years ago and it makes a ridge around the hole as the metal heats up, then you have to file off the ridge. Through steel it should be cleaner since steel has a grain where Al is particulate.

In the SVT project in TUT3, a stiffening plate is added to support the very heavy transformer set. The extra metal is just a Hammond 19" rack face plate that is 0.125" aluminium. Really, this will flex, too, with the extreme PT and OT weight and what is really needed is a right-angle piece or two underneath.
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