Telefunken Lido: Repair (Day 6)

Day 5’s work can be seen here.

So, it was obvious that the speed regulation wasn’t working properly at the end of Day 5. So, last night was spent digging for information on how centrifugal speed governors work and I came across this excellent explanation.

So, my theory was that the disc was seized on the axel and not moving correctly with the rotational speed. This means that everything came apart again, and the axel had to come out.

In theory, as the governor spins faster, the three weights get pulled out. This in turn should pull the disc in to rub against the friction pad. When it came out of the motor, the disc was immovable – it was stuck to the axel as I guessed. So, the three springs+weights were removed from the axel and, after a lot of WD-40 and a little repeated gentle “persuasion”, I got to here:

This is after I polished the rust off the axel with sandpaper, starting at 400 and working up to 3200 (lubricated with more WD-40). I was sanding along the length of the axel, since that’s the direction of movement of the disc.

Then it was “just” a matter of putting it all back together again… However, before I put it back in the case, I checked that the governor was working, which you can see below. Notice how the disc moves sideways to meet the friction pad, keeping things at a constant speed.

Then it was just a matter of putting everything back together again… And I have a working Telefunken Lido for those Sunday afternoon garden parties!

Telefunken Lido: Repair (Day 5)

Back to Part 4.

This was nearly the last day of the restoration (sort of…)

The beechwood that will hold up the top plate. This is 21.4 mm from the lip of the casing, as are all of the other pieces.

The opposite side of the same part of the case. I’m hoping that the yellow leather will darken over time…

All of the wood in the case. Notice the bent wood at the top… Turns out that this didn’t work… There wasn’t enough room between the inside of the case and the horn, so it had to go.

The alternative solution, using large washers directly on the inside of the case.

The new mainspring, ready to be greased and wound into the barrel.

The mainspring in the barrel, with teflon grease applied. Notice that it winds clockwise. Also note that the hook on the inner sleeve is grabbing the spring end. This is important, and a little difficult to manage…

Closing up the mainspring barrel, rotating about 45 degrees each time, and tightening only a little at a time.

Teflon grease on all the inner parts. This was a good idea – except for the axels of the speed regulator. The grease was a little too viscous, so it was replaced with WD-40.

Everything’s back together. All those photos I took at the beginning helped a lot during re-assembly.

The thick rubber compression washers are used to help level everything later.

Motor’s back in… time to level things up.

The platter is a little high on the left (relative to the top side of the plywood) so two screws get loosened and two get tightened. The rubber washers keep things from vibrating, and allow for this adjustment.

The finished gramphone!

With the tonearm clipped back for transport. The crank is clipped into the lid on the right side.

Crank in place, ready to wind up the spring.

The tonearm out, but in its resting position.

Playing a record for the first time in a long time!!!!

Seems that I need to work on the speed regulator… But it works – which it hasn’t done, probably for many years…

Forward to Part 6 (The End!)

Telefunken Lido: Repair (Day 4)

Back to Part 3.

Some more bits and pieces of work this time, mostly leather work.

Yesterday was spent colour-testing the dye with some scraps first. The bottom piece is vegetable tanned leather without dye. The middle piece is with one light coat of dye. The top piece is thoroughly soaked with the same dye. The white balance in this photo is a bit weird – but the top one is the winner. It’s a yellow alcohol-based dye.

Then the remaining pieces were cut and dyed, the hardware is in, and the insert for the handle is formed. (At this stage, nothing was glued, since the leather was still wet.) The binder clips are there to shape the leather around the small piece of 2 mm thick leather inside the handle that creates the shape. The irregularity in the colour is due to the fact that the dye hasn’t finished drying yet.

All the stitching is done, and the handle is burnished. The handle and tabs are 2 mm leather, and the straps are 1.3 mm thick, give or take. I’ll punch the hole in the strap when it’s all assembled so as to ensure that it’s in the right place.

The above photo shows grease-proof paper glued to the inside of the bottom casing. This will protect the interior from any grease or oil that drops off the drivetrain. This is a pretty safe assumption, looking at the black grease stains that are there already.

The paper is cellulose-coated baking paper, and it’s glued in with water-based bookbinders glue. Once it’s dry (tomorrow), the white color will become transparent. Then I’ll put in another piece that wraps around the sidewall, since the player will often be set on its end.

In addition to this, the blocks of wood are ready to be inserted – almost all of them cut out of 10 mm thick beech. Instead of the canvas, I plan on using a 5 mm thick strip of beech, but this will have to be steam-bent to follow the curve of the top. We’ll see how well that works out – never tried steam-bending wood before… these will all be held in place with M3 Chicago Bolts with the non-slotted nut on the outside of the case. This will look almost exactly like the original rivets, but it will mean that everything will be much easier to disassemble in the future – just in case…

The new mainspring arrived in the mail today from Lindholts; it looks like it might need a couple of small modifications to work, but it’s a much better fit than the one I had on hand. So the next big days will be spent re-assembling the drive train and inserting the wood parts.

One small setback today. I found the right-shaped screws (to replace the random ones that were holding it together) at Birger A. Handel in Slagelse. The right shape – but the wrong colour. They’re brass, and the originals are all either nickel- or chrome-plated. A found a nickel-plating company near here in Herning, but they emailed me today to tell me that they’re not interested in plating 30 tiny screws for me. Not much profit in that I guess… Oh well. Hopefully, some day, I’ll find replacement screws. Until then, my Lido will be a lovely chrome / brass burst of colour!

Forward to Part 5

Telefunken Lido: Repair (Day 3)

Back to Part 2

Today was spent doing a bunch of small jobs while I wait for some replacement parts to arrive.

For starters, I found two needles under the hinge on the bottom half of the case. They’ll come in handy later!

The interior of the case, showing the four wood blocks to which the top screws on. Funnily, these are made of three different types of wood: pine, birch, and beech. I suspect that this was not strategic – but just a question of using whatever was on-hand. The lining is a waxy paper – the black stains are grease that has dripped down from the drive mechanism.

The four pieces of wood are two different heights from the top edge of the casing, although I suspect that this would have been custom-fitted. They’re attached to the outer casing using either tacks (the largest piece on the right) or split rivets that were bent over to lock the wood in place. The wood parts are not glued onto the case. All of the rivet and tack heads of these are badly rusted – so they’re coming out…

One of the split rivets after the wood has been removed. The wood did not survive the removal process. The hole on the far left is the opening for the crank.

The wood in the process of removal. I’ll just make new blocks to replace these…

The handle and strap are a different colour than the case, and are in quite bad shape. In addition, the hardware is badly rusted. This will all get replaced with new parts.

The handle and strap are attached with the same split rivets, but bent around a canvas material that’s glued to the inside of the case, as can be seen in the photo above. The canvas is the dark square and rectangle. This canvas can’t be seen normally, because it’s covered by the wax paper. I peeled this off, because I’ll be replacing it with something a little more sturdy.

The rust on the exterior metal parts was cleaned up with a small wire brush on my Dremel tool. The before-and-after can be seen above. This took some time so as to not slip and carve into the case covering.

I used Simichrome to polish the metal tonarm. This appears to be plated brass. I’m not going to take apart the reproducer (the black part that holds the needle and contains the diaphragm).

If you look carefully, you’ll see a small set screw sticking out of the half of the tonearm on the right. That’s used to stop the front portion of the tonearm from making a full rotation when it’s swivelled back and forth onto the record, by hitting the portion of the threaded pipe that can be seen below.

So, if you’re dismantling the tonearm, remember to back off the set screw before separating the two parts.

I also started the leather work to make a new handle and strap. The replacement hardware and dye were ordered from laederiet.dk, near Aarhus (which is where I buy all my leather supplies).

Apart from all of that, I washed the exterior of the case with dish soap and a soft cloth – not too wet because there are some places where the covering is worn through and I don’t want water getting in there.

I also sprayed the interior fabric (maybe taffeta?) with an enzyme spray and rubbed it gently to remove some of the stains. Too much rubbing frays the fabric, so I had to be gentle…

Forward to Part 4

Telefunken Lido: Repair (Day 2)

Back to Part 1

Time to get inside and find out what’s wrong…

The cap comes off the mainspring barrel by tapping it with a hammer while holding onto the barrel itself. The inside shaft was already able to move up and down, so it was obvious it was no longer attached to the mainspring itself. The block of wood is used to prevent the hammer from damaging the cap edge. You hit the wood instead of the metal.

With the cap off, it’s easy to see that the mainspring is unfortunately broken. So, there are two options: Try to drill a new hole at the end of the remaining spring. This will mean heating it up to soften the steel a little… OR Try to replace it with a new spring.

A shot of the axel and the broken end of the spring. There’s a hole at the end of that spring that is caught by the hook that you can see on the axle. That hook is actually part of a sleeve that slides off the axel itself, as can be seen below.

The gap in the sleeve sits on either side of a pin that sticks out from the axel. This prevents it from rotating.

The rest of the mainspring is out of the barrel. This has to be done carefully to prevent it jumping out and either breaking something or punching a hole in me. One way to do this is to hold onto it on both sides of the barrel with two hands, and lifting one side of the spring out. This will push its way out until it gets stopped by your other hand, then you just alternate hands to let it out 180 degrees at a time. The only thing to be careful of at the end is to avoid bending the spring, since it will be caught on the pin on the inside of the barrel.

The bottom plate and the centrifugal speed regulator. The axel with the toothed gear just lifts out.

A close-up of the speed regulator and the clutch wheel, still covered in grease. Note that the pins on the end of that axel sit in brass bearings that are just holes drilled into pins. However, the holes are not centred. So, if you back off the set screws on the “front” of the vertical post, you can rotate the brass pins to change the height of the axel. Only the set screws are threaded.

The underside of the top plate. The spring that can be seen there is used to prevent the screw from rotating counter-clockwise. (Clockwise rotation loosens the spring. Counter-clockwise tightens it.) The portion that sticks out on the right is the part that the handle screws into from the outside. So, you can screw it on, tighten the spring, but then, when you reverse the rotation of the handle, it just unscrews because the rotation is stoppped by that spring grabbing the axel.

Another view of the same part. Notice the small cotten pad that sticks out of the arm connected to the tall rod in the back. That’s the part that pushes against the clutch wheel to slow things down.

The top of that same part. There’s still plenty of old grease in the worm gear… I didn’t take anything apart more than this. All of the degreasing was done in the state the you see in the photos above.

Degreasing started by just scraping off the goop with small wooden picks that I made from scraps I had lying around. The next step was to spray on WD-40 degreaser and start wiping things down with paper towels and a stiff plastic brush. That procedure was repeated until things were looking clean, but not necessarily shiny.

The photo above shows most of the bits and pieces degreased and cleaned up.

One last close-up of the cotton pad that is used for the speed regulator.

Back to the spring… I decided to not try to heat the steel, bend it to a smaller radius, and drill a new hole. Instead, I remembered that I might have some lying around. About a year or two ago, I bought a collection of tools and leftover parts from a guy who had planned to try watch and clock repair as a retirement hobby. He had bought the collection from a retired watchmaker.

In that collection, there were some old mainsprings for mantle clocks. Time to dig those out…

First thing is to measure the Telefunken’s mainspring. Turns out its roughly 23 mm wide, 0.5 mm thick, about 3.5 m long (this is just a rough estimate based on pulling it as straight as I could for as far as I could…) and the barrel interior is 78 mm in diameter. This means that I’m looking for a mainspring that’s 23 x 0.5 x 3500 x 78 – give or take…

A box of old clock mainsprings that I happened to have lying around…

I selected the spring that best matched, based on the width, and thickness and unpacked it. This is a delicate matter that involves holding the spring in a thickly gloved hand, cutting the wire, and then slowly releasing it under a towel. That way, if it does jump, you’ll only get hit in the face with a towel…

Sadly, the spring that I had on hand was too short. So, I’ve ordered one from lindholds.dk. The one that’s coming is also not as long as the original, but hopefully, it’ll do the trick.

Tomorrow: Greasing and reassambling as much of the drivetrain as I can, and starting to clean up the case.

Forward to Part 3

Telefunken Lido: Repair (Day 1)

I recently bought a well-used Telefunken Lido portable gramophone. It’s in reasonable shape, but it certainly needs quite a lot of repair and/or restoration. For starters, it doesn’t work – probably because the drive spring is either broken or disonnected inside the barrel.

The plan is to get as much fixed on it this weekend… however, that plan may change as the work progresses.

I’ve already made use of this page, this page, and this video to get ready for the project (including learning from the mistakes of others…) My documentation might be of similar use to others – in addition to providing some info on how gramophones worked…

The lido, as-is before I start…

The platter just lifts off.

The diagonal arm is the speed control that adjusts a clutch mechanism that can be seen in photos below. The needle and membrane are locked in the “travel” position, which sits them down into the mouth of the horn (the dark rectangular area at the “back”).

The first step was to unscrew the locking lid stay on the left side of the horn opening. The next step is to unscrew the lid hinges from the main case. Both the lid stay and the hinges are riveted to the lid, so they stay on.

The next step was to remove the three screws that hold the pipe + membrane + needle assembly onto the wooden top plate in the top right corner. After these have been removed, it all just lifts off.

Next is to remove the 5 small screws around the outer edge of the wood top plate. These hold the entire assembly into the bottom part of the case.

The next step is to disassemble the mechanism from the wooden top plate. In order to do this, the speed regulation arm has to be disconnected from the pin that connects it to the clutch underneath. This is done by loosening at least one of the two set screws that grab the pin.

The photo above shows the control arm after separating it from the pin that goes down into the mechanism.

Once this is done, there are four large screws the have to come out. Those are the four holes near the right-hand yellow “Fona” sticker.

In order to remote the drive mechanism, it has to be gently angled to slide it out without the spindle hitting the wood, and snaking it out around the horn.

The mechanism after removal.

The underside of the wooden plate, showing the entire horn. This is probably made of lead by the looks of things…

The two vertical rods are the main spindle (on the left) and the clutch control (on the left). Turning the clutch control pushes a soft pad against the vertical clutch wheel that can be seen on the same axel as the centrifugal speed regulator weights.

There are four 11 mm hex nuts holding the top plate of the mechanism to the four posts. First, the rubber washers needed to be removed using a knife to separate them from the top plate. Then the four nuts are loosened and the top plate can be lifted off. This will take the clutch rod and the main spindle with it.

The photo above shows the bottom plate with the speed regulator and the spring barrel.

The two last photos, above, show the underside of the top plate, holding the main spindle on the left, the clutch rod in the middle, and the screw entry for the winding handle.

That’s it so far. Tomorrow will probably be spent disassembling the spring barrel and seeing whether it’s fixable. Then de-greasing and cleanup of the drive mechanism, re-greasing and re-assembly.

Forward to Part 2

Speed Math

Two math puzzles:

#1: You have to drive to a meet someone at a specific time. Let’s say that you only have to drive on one road to get there, and the speed limit is the same the whole way. You calculate the time it will take to get there on time, and you start driving – but there’s traffic. So, you wind up driving half the distance at half the speed, then the traffic disappears.

How fast do you have to go the rest of the way to arrive at the meeting on time?

#2: You’re driving on a two-lane highway where the speed limit is 70 km/h. You are driving 100 km/h, and you pull into the left lane to pass someone who is driving the speed limit. Everything about the car you’re passing is identical to yours – even the driver weighs the same as you do. At the instant that you are side-by side, a train appears across the road in front of you and stops. You both hit the brakes at exactly the same time to try and stop from hitting the train.

Luckily, the person in the other car stops just as his bumper touches the train, let’s say 1 mm before touching it… But, because you were driving faster, you cannot stop in time.

How fast are you going when you hit the train?

The answers

#1. Most people instinctively say “double the speed limit” to make up the lost time. However, this is not the right answer.

Let’s say that the meeting is 100 km away, and the speed limit is 100 km/h. Therefore, it should take you 1 hour to get to the meeting.

If you drive half the distance (50 km) at half the speed (50 km/h), then at the moment the traffic clears up, you should have been at your destination. So, you would have to drive infinity km/h to get there. However, since teleportation doesn’t exist yet, you might as well just call and tell them you’ll be late.

#2: This one is a little tougher, but it should be pretty intuitive for someone working in audio. A car’s brakes work by taking the energy in the car’s momentum, and converting that to heat in the brake discs. The key word there is energy.

So, the question is: if you consider the amount of energy removed from the car going 70 km/h, and take that out of the energy in the car going 100 km/h, how much energy is left?

The answer is 70 km/h. For someone in audio, this might look like a familiar answer, since 0.7 V has half of the power of 1.0 V (assuming identical loads). In the case of the cars, it’s because the amount of power (the amount of energy that’s transmitted over time – in this case, to heat the brakes) to bring the car from 70 km/h to 0 km/h is identical to the amount of power it takes to bring the same car from 100 km/h to 70 km/h. (An audio geek might joke that 70 km/h is 3 dB slower than 100 km/h.)

The conclusion

Slow down. You’re not going to make it to the meeting anyway, and driving a little bit faster means you’re going to hit the train much harder than you think.

Translating Q to Q

As I’ve talked about in a previous posting, when a reciprocal peak/dip filter says “Q”, there’s no knowing what it might mean, because there are at least 7 different definitions of Q (3 for boosts and 4 for dips).

For many people, this doesn’t really matter. If you’re just playing with an EQ to make things sound better right now, then the values on the display really don’t matter: it’s the sound that counts.

If you’re like me, you need to be able to navigate between different pieces of software and hardware, and to get the same EQ response from them, then you’ll also need to know firstly that you can’t trust the display, and secondly, how to “translate” from device to device when necessary.

For example, take a look at Figure 1

Figure 1: The magnitude response of two peaking filters, both with Fc=1 kHz, Gain = +12 dB, Q = 2

This shows two magnitude responses, however, these are the measurements of two equalisers with identical settings:
Fc = 1 kHz, Gain = +12 dB, Q = 2.

The black curve shows the response of an equaliser that uses the -3 dB points to define the bandwidth of the filter, and therefore the Q is based on 1/(2 zeta). The red curve shows the response of an equaliser that uses the mid-point (in this case, +6 dB because the Gain is +12 dB) to define the bandwidth of the filter.

The difference between these two plots is shown below in Figure 2.

Figure 2: The difference between the two curves in Figure 1.

We’d have a similar problem if we were cutting instead of boosting, as shown in Figure 3.

Figure 3: The magnitude response of two peaking filters, both with Fc=1 kHz, Gain = -12 dB, Q = 2

You have to think upside down in this case, because the 1/(2 zeta) filter is actually using the 3 dB UP points to measure bandwidth; but we’ll ignore that and move on.

If you need to translate between the two systems shown above, there’s a pretty easy way to do it.

I’ll assume that you are implementing your filter using the mid-point definition of the bandwidth, so you need to convert into that system rather than out of it. (I’m making this assumption because it’s the one that Robert Bristow-Johnson used in his Audio Cookbook, which was freely copy-and-pasteable, which means that you find it everywhere these days.) Get the parameters from the filter you want to copy.

We’ll call these parameters Fc (for centre frequency, in Hz), G_{dB} (Gain in dB), and Q_{z}. I’m calling it Q_{z} because it’s a Q based on 1/(2 zeta) and we’ll need to keep it separate from our other Q, which I’ll call Q_{rbj} (for Robert Bristow-Johnson).

Convert the gain into linear.

    \[G_{lin} = 10^\frac{G_{dB}}{20}\]

Then do the following:

IF G_{dB} > 0

    \[Q_{rbj} = \frac {Q_{z}} {\sqrt{ G_{lin}}}\]

ELSEIF G_{dB} < 0

    \[Q_{rbj} = Q_{z} * \sqrt{ G_{lin}}\]

ELSE
your filter isn’t doing anything because G_{dB} = 0

END

Example 1

If you have a -3 dB-based filter with the following parameters:
Fc = 1.0 kHz
G_{dB} = +12 dB
Q_{z} = 2

and you want to implement that using the Bristow-Johnson equations, then you’ll have to use the following parameters:
Fc = 1.0 kHz
G_{dB} = +12 dB

    \[Q_{rbj} = \frac {2} {\sqrt{ 3.9811}} = 1.0024\]


Example 2

If you have a -3 dB-based filter with the following parameters:
Fc = 2.0 kHz
G_{dB} = -9 dB
Q = 2

and you want to implement that using the Bristow-Johnson equations, then you’ll have to use the following parameters:
Fc = 2.0 kHz
G_{dB} = -9 dB

    \[Q_{rbj} = 2 * \sqrt{ 0.3548} = 2.3826\]


Two Extra Things…

If the filter that you’re translating FROM is based on Andy Moorer’s design (which is based on the gain mid-point if the gain is within the ±6 dB range, but based on the 3 dB points if it’s outside that), then you’ll have to write your own IF/THEN statements.

If you’re implementing a filter that was specified for RBJ’s equations in a system that’s based on 1/(2 zeta), then you’re probably smart enough to figure out how to do the above in reverse.

One additional addendum

IF
you don’t like IF/THEN statements for some reason or another (code optimisation, for example)

THEN
you could do it this way instead:

    \[Q_{rbj} = \frac{Q_{z} }{ \sqrt{10^\frac{\lvert G_{dB} \rvert }{20}}}\]

What I’ve done there is to fold the decibel-to-linear conversion into the equation. I’ve also converted the gain in dB to an absolute value before converting to linear. That way, it’s always positive, so you always divide.