Beogram 8002: Transformer Block - A Comparison Between 120V and 240V Versions

I just sold a Beogram 8002 (Type 5633) that I recently restored to a customer in the UK. Unfortunately, the Beogram was a 120V US version. This meant it came with a transformer block specifically designed for the US power grid, which offers 120V at a grid frequency of 60Hz.

The Beogram 8002 (and 8000) were designed in a way that they could be converted for different power grids by simply swapping out the transformer block. This enabled B&O to use the same hardware globally with only the transformers adapted to local requirements.

So before sending this Beogram to the UK, I wanted to convert it to 240V/50Hz so that my customer could directly plug it in without needing an external voltage transformer. 

It is interesting to note that while the external transformer approach works well with most devices, the Beogram 8002/8000 have a design quirk that makes this approach less than perfect: They use grid frequency AC to run the linear 2-phase AC motor that drives the platter. Since the second phase is shifted relative to the first using a phase capacitor, the capacitor value is specific to the AC frequency used. This means that when a US 120V/60Hz Beogram is hooked up in the UK via a 240-to-120V grid voltage transformer, it sees the proper 120V, but it gets only 50 Hz. This means its factory phase capacitor does not have the proper value. This is the reason why B&O put this phase capacitor into the transformer block, so it would match the specific grid frequency the block is specified for.

I was able to buy a 240V/50Hz UK transformer block from a fellow Beolover in the UK. When I received it, I decided to explore the differences between the 240V and the original 120V blocks. Most importantly, I wanted to measure the voltages of the secondary windings of the two blocks to make sure I could swap them without issues. I had never done this before, so caution was on order!...;-).

This shows the original 120V/60Hz block:

And opened up:

The big can is the phase capacitor for the motor. It has a 27uF value optimized for 60 Hz. The fuse is a 300mA slow-blow type:

I had the fantasy that one might be able to convert 120V blocks into 240V types by changing the primary winding connections, but a look at the wiring of the primary side suggests this is not possible. This shows the primary connections:

Each winding has a solid colored and a transparent wire coming out. On the top side of the terminal board, the transparent wires are connected via a solder terminal:

The grey and black wires go into the power cable (the black one via the fuse). This means the two coils are connected in series. Since the turns ratio formula for transformers states that the ratio between the primary and secondary voltages (Vp/Vs) is equal to the ratio between the number of windings on the primary and secondary sides (Np/Ns):

Vp​/Vs​​=Np​/Ns.

​This means the lower voltage bloc should have the windings connected in parallel, and the higher voltage bloc in series if conversion would be possible. This is how the grid-voltage-switchable earlier Beogram 400x do it. Their voltage switch basically re-arranges the way the primary coils are connected to adapt the number of windings on the primary side so that voltages between 100 and 240V can yield the same secondary side voltages.

Anyway, lets have a look at the 240/60Hz block that I just received:

This shows it opened up:

There are small differences to the 120V version: The phase capacitor is a bit longer, hinting at a larger capacitance, and the terminal plate looks different:

The first thing to note is that the fuse is a 160mA slow-blow type, i.e., has about half the current capacity of the 120V fuse. This makes sense since the same hardware is powered, i.e., the current on the secondary side is the same. Since the primary voltage is double, the primary current will only be half for the same power (P=V*I). 

A look under the plate reveals that the primary windings are connected in exactly the same way as in the 120V block:

The transparent wires are again connected in a series configuration. This means the 240V transformer indeed has a different design than the 120V version. It has different winding counts on the primary coils.

The phase capacitor indeed has a larger value, 39uF:

After this inspection of the two transformer blocks, I set out to measure the voltages that they produce on their secondaries when plugged into the specified mains voltage. For powering the 240V version, I used my big old 0-250V variac 

I measured peak-to-peak (Vpp) voltages with my oscilloscope. Here is an example of how I connected my probes (to measure the coils for the ±15V rails):

This is what I saw on the scope:

I made this table after I measured all secondaries on both blocks:

The calculated ratios are about ±10% around 1, which is 'good enough' considering the circuit design. Since there can be significant grid voltage fluctuations, the power supply of the Beogram 8002/8000 is pretty forgiving regarding the secondary voltages it expects to make the stabilized 5V and ±15V rails.

After this measurement, I felt confident that I could plug this 240V transformer block into the Beogram and give it a spin! But before I did that, I updated the phase capacitor with a Beolover Motor Capacitor for Beogram 8000 and 8002:

Note that for my initial test, I connected the 27uF capacitance for 60Hz grid frequency as shown above. My variac only changes the grid voltage but not the frequency. Ah, physics!...;-)

After installing the new phase capacitor, I plugged the 240V transformer block into the header on the main PCB of the Beogram and plugged it into the variac. Then I ramped the voltage to 240V, and the Beogram showed the usual red dot in the display! I pressed START, and it ran like before! Beolovely!

Of course, I was curious if the platter motor of this unit would still run properly if the 39uF/50Hz capacitance were used for the motor while running at 60Hz. Sort of a test of "can one use a standard grid 120V/240V transformer in a pinch if there is no proper transformer block available?".

I changed the capacitor setup to 39uF/50Hz:

I reinstalled the block and plugged it back into the variac. Then I pressed START. And everything seemed to work properly. The platter ran as usual, and the Beogram was able to lock onto "33.33" on the display, which means the microcontroller was measuring the proper speed and had no trouble maintaining it.

I played a few records, and it seems there is no practical penalty for using the 'wrong' phase capacitance.

So why use different capacitors for 50 and 60 Hz in the first place? I think it comes down to 'efficiency'. If the phase shift between the two motor coils is a bit off the optimal value, the motor consumes a little more current since it is less efficient. This does not matter much in this design since the RPM is feedback-controlled. So the control circuit simply compensates by giving the motor a bit more power to get the specified RPM.

I will now play this Beogram a bit more, and then it will be time to send it to its new owner in the UK!

Beogram 4002 (5503): Replacement of a Loudly Humming Transformer with a Modern Universal Power Supply

Oh well, after playing the lovely Beogram 4002 (Type 5503) that I recently restored I had to realize that the transformer made a pretty loud humming noise, which was quite noticeable during lower volume music passages. Especially, when placing the unit on a wooden sideboard the resonance of the wood amplified the hum to quite annoying levels.

I decided this definitely needed fixing before I could possibly sell this unit. A welcome project since I thought the initial crop of AC motor Beograms also needed a universal power supply upgrade similar to what I recently developed for the later DC motor models. 

Modern monolithic universal power supplies have several advantages over the original transformer/rectifier based setup: They are usually short circuit proof, they do not hum in any audible way and they mostly are designed to run on grid voltages ranging from 100V to 240V, i.e. can be plugged in anywhere on this planet. This feature also makes them brown-out resistant and they will also reliably protect the Beogram circuitry from voltage spikes etc...

The reason why my solution for the DC motor Beograms cannot be used in the AC motor models is these have a more than 3x higher power rating. DC motor Beograms are rated 15W, while the AC motor models are rated 50W. This difference is mainly caused by the AC platter motor, which is a power hog. This explains why the older Beograms get much warmer than the later ones.

It means that the 25W Meanwell supply I utilized for the DC motor Beograms is not powerful enough to run an AC motor model. Further investigation yielded that similar supplies rated for higher output had a too large footprint and would not fit into the space vacated by the transformer.

After a bit of poking around I found a more advanced design made by Traco that combined a small footprint with a 30W output: The TPP 30-D Series, which is a high-quality medical power supply. It is fully encapsulated and the output voltage can be adjusted (a rarity among this type of power block). The specific TPP 30-124-D (24V nominal) type can be adjusted to a maximum output of 26.4V by connecting an external resistor. This was great, but 30W is still not enough for the standard setup of an AC motor Beogram.

However, when combined with the Beolover Efficient 22.8V Power Supply and Main Capacitors for Beogram 4002 (Types 550x) 30W is enough. The Beolover 22.8V supply reduces the power consumption of the AC motor models significantly since it replaces the other power hog of this 1970s design, the linear voltage regulator, with a buck converter that has a high efficiency.

This shows the Transformer Replacement Kit for Beogram 4002 (Types 550x):

It includes the TPP30 supply mounted on the breakout board, the adapter necessary for bolting it to the enclosure bottom, the jumper for connecting it to the fuses assembly, the mounting bolts and a set of fresh fuses.

Let's see how I implanted the Traco TPP 30-124-D supply in this Beogram!

*********************************************************************************************************

Safety first: Potentially lethal voltages can be present during the installation of this part. Unplug your Beogram before installation. Ensure that the supply is bolted firmly to the adapter plate, and that the fuse box cover is in place before powering the unit up after installation.

*********************************************************************************************************

This shows the original setup:

The first step is unbolting the transformer and the (fake) voltage selector/fuse box housing. This shows the four bolts that need to be removed:

After removing them

the transformer and fuse box assemblies can be 'flipped' out of the enclosure:

The next step is disconnecting the transformer from the fuse box assembly and the rectifier. This shows the fuse box after removal of the fake voltage selector dial:

The grey wires come in from the power plug and the red/yellow wires go to the transformer primary windings:

I unsoldered the red and yellow wires and pulled them out of the fuse box assembly:

Be careful when you try this at home to not melt the plastic fuse box housing with the soldering iron. The next step was unsoldering the wiring from the rectifier (mounted beneath the floating chassis leaf spring next to the transformer):

This shows the unsoldered wires:

and the extracted transformer:

Now it was time to bolt the 3D printed adapter plate to the enclosure. It uses the same bolt holes that were used to hold the transformer in place:

This shows the adapter bolted in:

The next step is soldering the provided wire jumper to the fuse terminals previously connected to the red/yellow wires towards the transformer. This shows the wire jumper inserted from the bottom into the fuse housing:

And on the top side soldered to the fuse terminals. Left

and right:

It is a good idea to leave the fuses in place while doing the soldering. It will keep the fuse terminals in the proper orientation while they get hot.

Once the wires are soldered in, they need to be fed out of the fuse assembly through the 'exit channel' along with the grey power input cable:

Then the fake voltage selector can be stuck back onto the assembly,

which then can be bolted back to the enclosure:

This shows the fuse holder assembly back in place:

The next step is soldering the leads to the in- and outputs of the TPP30 supply's breakout board. First come the leads to the fuses housing assembly. They solder to the terminals "Input 100-240V AC~". Polarity does not matter since these wires carry AC:

Then the red and black wires originally connected to the rectifier output are soldered to the terminals labeled "Output 26.5V DC=". Make sure the red wire is soldered to the "+" labeled terminal and the black to the "-" labeled one:

Now the TPP30 assembly can be turned around and bolted to the adapter with the three provided screws:

Make sure that the in- and output wires are properly fitted into the cutouts on the adapter.

The final step is replacing the original fuses with the new 1.6A fuses provided with the TPP supply. It is easy to remove the original fuses by pushing them out with a suitable screwdriver:

 The new fuses provided with the kit can easily be pushed into the holders with a finger:

The final step is replacing the fuses cover. If it is not in place there will be potentially lethal voltages on the fuse terminals once the Beogram is plugged in. This shows the completed setup in place:

I plugged the Beogram in for a function test, and everything worked very nicely! Absolutely no noise from the supply! Beolovely!

Next I measured how much current the supply draws under the various operational modes of the Beogram.  As expected, the maximum current was drawn under 'play condition', i.e. platter motor running, solenoid engaged and the carriage moving towards the center of the platter. This shows the measurement:

The multimeter is connected between the fuse terminals on one side and set to its 10A range. In this setting it essentially acts as a small current sensing resistor in-between the fuse terminals, and the voltage drop across this resistor is converted into a proportional current reading.

The display shows 0.2 Amps RMS. This corresponds to about 24W power at 120V. In other words, the supply runs at about 80% of its maximum capacity of 30W. 80% is the usual engineering safe margin for reliable long term operation. All good in the power supply department! I should point out again that this new power supply only works in tandem with the Efficient 22.8V Power Supply and Main Capacitors for Beogram 4002 (Types 550x), which significantly reduces the power intake of the Beogram compared to the original setup. Therefore, please do not use the TPP30 supply if your Beogram runs from its original linear voltage regulator based 22.8V rail. It would not be safe and the fairly expensive TPP30 might suffer premature retirement...;-)

Beogram 4002 (5513): Replacement of a Dead Transformer with a Modern Universal Power Supply

****Note added in proof: This solution will not work in earlier AC-motor Beograms (Types 550x). The Meanwell power supply used in this post is not powerful enough for those. There is now a dedicated solution available for the earlier Beograms. Please, see here.****

I am making good progress with the Beogram 4002 (Type 5513) from Louisiana. The unit had a short circuited transformer that needed replacement. During my initial inspection of the unit I found blown fuses and that some grey slime had leaked out from the transformer.

I decided to install a Meanwell RS-25-24 universal power supply like I did it recently with a couple of Beograms that I sent to the UK and Australia. Such modern supplies have a few advantages over the original transformers. They run on any input voltage between 100 and 240V and are short circuit protected. They also do not hum much, unlike some of the original transformers that often produce a noticeable 50/60 Hz hum when they are plugged in.

This shows the final result of my efforts:

The Beolover Transformer Replacement Kit for Beogram 4002 and 4004 (Types 551x/552x) is shown ere:

The Meanwell supply is shown flipped over with the adapter plate facing up. The plate allows the supply to be bolted to the same bolt holes that are used to hold the transformer in place. 

The wire harness connects the line-input of the supply to the fuses box. The additional solder lugs are used to connect the blue or blue/green wiring to the Beogram circuit to the Meanwell 24V output. The two screws are used to bolt the supply in place.

The provided 500mA fuses need to be installed in the fuses box of the Beogram. This ensures that the inrush current of the new supply does not overwhelm the fuses. The original 250mA fuses are not strong enough if the supply is plugged into 220/240 outlets.

Let's discuss the installation process:

*********************************************************************************************************

Safety first: Potentially lethal voltages can be present during the installation of this part. Unplug your Beogram before installation. Ensure that the terminal cover of the universal power supply and the fuse box cover are in place before powering the unit up after installation.

*********************************************************************************************************

This shows the primary wiring of the original transformer. Some cataclysmic event caused grey slime to emanate from the wiring orifice:

I removed the screws that fixed the transformer and the fuses box to the enclosure bottom. This released both components:

I first unsoldered the primary wires of the transformer from the fuse box terminals (be careful to not melt the black fuse box housing with the solder tip). Then I cut off the green and blue secondary wiring at the transformer housing. Next I installed 3 mm solder lugs on the secondary wires so they can be bolted to the output terminals of the new supply:

Make sure that the solder lugs connect to one green and one blue wire each. Both green and blue wires connect to rectifiers, i.e. their polarity is not important. Note that there are Beograms that have only the blue wires. In this case simply connect one lug to each of the blue wire ends.

The next step was soldering the grey wires to the fuse box terminals:

This is how it looks from the bottom side of the fuse box:

Both of the in and out wiring of the box need to be routed thought the 'exit channel' of the box:

Then the bottom cover of the fuse box can be stuck back on:

The next step is bolting the fuse box back to the enclosure:

Now it is time to connect the power supply terminals. The first step is removing the bolts from the two terminals on the left and the two on the right:

Then the wiring can be bolted to the terminals with the solder lugs:

The line-in wiring goes to the terminals labeled L and N.  and the gree/blue wires to the -V and +V labeled ones. The polarity of the wires is not important. Note that the ground connector in the center of the power supply does not need to be connected. The Beogram is a floating design based on galvanic separation via the power supply. 

Important: Make sure that the white trimmer potentiometer next to the terminals is turned all the way clockwise. This increases the output voltage to about 27-28V, which is beneficial for the operation of the arm lowering solenoid. In case you are worried about the performance of these modern supplies with regard to driving the solenoid, please, see here for some measurements that I did when I developed this upgrade.

Once the terminals are connected the new supply can be bolted in. The two small holes in the adapter plate fit to the original mounting holes of the transformer:

Just hold the new supply in place and put in the supplied screws from the bottom:

Then tighten them:

This shows the bolted in supply. Make sure the terminals cover is in place before plugging in the beogram!

This photo shows how the line input wire is routed from the cable gland at the enclosure orifice around the adapter plate to the fuses box. Also note how the green/blue wires go around the floating chassis and transport lock assembly towards the Beogram circuit board and Beolover reservoir capacitor assembly.

After the installation I made sure the terminals of the new supply were covered by the supplied plexiglass cover and that the cover was back in place on the fuses box. Then I plugged the Beogram in and pressed START. The carriage started moving and the arm dropped at the LP set down point! All good again in the power supply department of this Beogram!