roland 808 drum machine u.s power conversion

[cod65]

greetings! I have a client who wants to convert his euro 240v import roland 808 drum machine to US 120v. I have a service manual and schematic and looking for appropriate transformer(s) to swap. Based on schematic I am looking for 120 primaries, 10vac and 23-0-23 vac secondaries. What I am confused about is current rating. the schematic seems to suggest 150ma, but im not certain. the euro fuses are rated at 250ma, th US fuses at 500ma, and further the schematic notes suggest later versions of this machine use 1/4 watt 10 ohm fusible resistors  in place of 500 ma fuses on the US version. there are no additional mods that i know of, so how can these ratings be so disparate ? Why wouldn't the euro and US version both have 250 ma fuses ? doesn't a 10 ohm 1/4 watt fusible resistor fed 23v blow at sqrrt(.25/10) = 158ma?
 what is an appropriate amperage based on the schematic  below?

Plse help me to find apropos transformer(s)- they cant be higher than about 43mm, so this, and figuring out amp rating has  proved challenging to me to find

[Swake]

My opinion is that if you don't know these basic things yet, then you should not offer 'transformer conversion' services to customers because you clearly cannot assess whether what you're doing is safe or not. Build some knowledge and experience first. Offering such services comes with responsibilities.

If you cannot identify suitably sized transformers, you might want to convert to SMPS power supplies as these are generally much smaller. Or move it to an external box.

[themadhippy]

you might want to convert to SMPS power supplies

And possible introduce lots of extra drum beats as the switching frequency is picked up by the rest of the circuit. Me id just use an external  120-240v step up transformer,and a little tip when dealing with musos toys ,whilst not applicable here ,watch out for things that are using the mains frequency as the clock source,they tend to be  out of tune if you try running a 50hz device on 60hz.

[Fraser]

I second the recommendation by “themadhippy”. It is desirable to use an external step up transformer that converts 110V to 220V. You then avoid any responsibility for changing the configuration of the musical instrument. Being accused (even if unfairly) of causing a problem with your transformer change would be no fun.

Regarding fuse ratings….. you need to consider the purpose of each fuse and what it is actually intended to protect. On the utility mains supply side of things the current rating of the fuse for a 110V configuration is often around twice that of the 220V configuration. This is simple maths and Power = Current x Volts. Half the Volts means twice the Current for the same Power. Fuse ratings are often not an exact science but sensible values should be used. Fuses take a relatively long time to open in an overcurrent situation so are often intended for protection against catastrophic failures where very high levels of over current occur. The fuse ratings on the secondary side of the transformer will not need to be changed as the secondary winding voltages will remain unchanged. In some products, fusible resistors are used in place of fuses and it would appear that this was introduced in this equipment at some point in its product life. It is not essential to change from fuses to fusible resistors however.

The input fuse “F1” is stated as being 0.5A on the 110V version of the equipment. This appears sensible. Changing the secondary fuses from 0.25A to 0.5A,as shown in the provided schematic, makes no sense at all, except maybe for the convenience of using a single fuse rating during manufacturing !

Fraser

[CaptDon]

First off, the 240 volt unit only draws half as much line current as the 120 volt model. Basic first day Power/Ohms law knowledge that is why the fuses are different. Second, there is no doubt the Roland 808 DID NOT use an 'off-the-shelf' transformer. It is certainly a custom designed part. IF indeed they used resistors instead of fuses then they MUST be flameproof!!! Buy or build an external 120vac in 240vac out 'transformer in a box' for your friend. That Roland unit is around 50 watts (actually less) and one solution may be to find a 50va rated transformer with dual primaries (120 / 120). The secondary windings are typically 12 / 12. Ignore the secondaries, we won't use those. Wire the primaries in series observing the proper phase relationship. Feed 120 from one end and the center point and get 240 across the far ends of the two primary windings in series. This may be way beyond the safe area of your current skill set?

[CaptDon]

Looking at the transformer diagram it seems to indicate something more like 220/240 primary NOT 120/240.

[cod65]

Thank you one and all for the information and concern for my personal safety . I really appreciate the prompt and thoughtful responses. There is obviously a wealth of information and I am still digesting much of it . This forum has already proven fantastic. If my post seems a bit elementary and it should be moved to 'Beginners' I certainly understand. If that is possible en masse with threads I would like to do that with help of admin.


But for now, some things I would like to clarify and gain further understanding of in my pursuit.
Firstly I am neither a learned professional nor a complete novice. I have less experience dealing with line level voltages, but I need to gain this experience(safely of course). I interpret  this Roland 808 as a Class 1 device- (i.e. the chassis and faceplate are metal and potentially dangerous without proper earth ground) - so I am not approaching this project without (I hope ) healthy  trepidation. My client is of the mind that 'its just simple transformer swapping' and I am not of that same mind- because of the dangers of doing it wrong( to myself and my client). That being said, I need to learn this stuff for personal and professional reasons. I have studied college level electronics through the first 2 years approximately, but not a lot of work with line level AC circuits. I do not go into this lightly by any means, nor sleepily. I also claim full responsibility for any outcomes of my attempt at this project. I also am well aware that this is a very valuable piece (around 5-7k US dollars!), so I really don't want to f#$%! it up!(I intend to disconnect the power supply board from all other electronics at the start of this venture to minimize possibility of damaging anything outside of power supply board ).

You may yet convince me that it is 'above my level of experience'. I am open to that. But if that is the case I still wish to learn the answers to some questions:


I have at my disposal an isolation transformer- if that reduces chance of  lethal shock . I realize it wouldn't negate its possibility- for instance  if I were to touch a hot and a chassis that was shorted to neutral. I'm putting that out there to discuss any other pros/cons regarding iso tranformers use during servicing this particular unit in this scenario.

My opinion is that if you don't know these basic things yet, then you should not offer 'transformer conversion' services to customers because you clearly cannot assess whether what you're doing is safe or not. Build some knowledge and experience first. Offering such services comes with responsibilities.

If you cannot identify suitably sized transformers, you might want to convert to SMPS power supplies as these are generally much smaller. Or move it to an external box.

Thank you Swake for your time and knowledge. I hear you and appreciate what you are saying regarding safety , professionalism and responsibility. I did not exactly offer my services, but rather I had worked on a DX7 for him previously and so he was somewhat insistent, even though I told him (and demonstrated)a 240-120 external step down transformer worked well with device) - he insisted he wanted it done internally. I told him I would look into it.

As for SMPS power supplies- this is an  analog device, highly coveted for its analog nature - wouldn't smps supplies possibly inject unwanted high frequency digital noise ? The

The original transformer was indeed bespoke, and unfortunately long gone. In its place I received unit in working 230v condition with two transformers in place of one, handling all secondaries. I have read that this is entirely acceptable for this unit and scenario.

here is a picture of current 230v transformers in situ:

https://drive.google.com/file/d/11WrQhLrSPqHEOq4iqC2CBpAN5PRqEnU-/view?usp=sharing

My intention was to replace this pair with a 120v suitable pair.

[cod65]

you might want to convert to SMPS power supplies

And possible introduce lots of extra drum beats as the switching frequency is picked up by the rest of the circuit. Me id just use an external  120-240v step up transformer,and a little tip when dealing with musos toys ,whilst not applicable here ,watch out for things that are using the mains frequency as the clock source,they tend to be  out of tune if you try running a 50hz device on 60hz.

thank you for your time and knowledge themadhippy. Yes, I explained this to him and demonstrated the working machine with my own step up/down transformer, but he wants the conversion internally.


As for this device being 'out of tune' , well it is a drum machine so I guess that might mean something on the order of this machine might sound slightly different  in voicings depending on what country it was wired for?. But the fact is it was designed to be used/marketed in Japan, Europe or U.S. no ?  The schematic suggests to me that the machine, with different transformers and fuses can be run from 100-240vac (and Japan does run at 100, 60hz.)
I don't think there are any differences with the main board in different countries, but I will read the whole manual and double check.
thanks again,apreciate your time and knowledge.

As I mention above this does not have the original transformer but 2 modern 230vac tformers currently

[cod65]

thanks Fraser. Your words sound wise and are swaying me. I did demonstrate the 808 to him using my own step up/down transformer but he wants it internally. But I hear you about causing problems or being blamed- makes sense and gives me pause- I may abandon this project as a result.

regarding fuses- yes! you have explained what was vexing me:

I understand the primary side change of value(110x.5 = 55watts, 220x.25 = 55 watts- same power), but the secondary made no sense to me!: 20 volts on a secondary is 20 volts- with either primary !- the load is the same ! why change the fuses? (manufacturing simplicity- makes sense!)

The fuses in this current 230vac config are unlabeled but I was assuming they had put in .250 amp . You are saying it doesn't really make a difference because their intent is to protect against a (probably) much higher current surge, and either would do the job- makes sense.
And also, thank you for explaining the switch to fusible resistors and that it is not necessary- I will stick with glass 500 ma.

but just to follow through - I calculate the fusible resistors to blow(start to blow ?) at 158ma - based on :

10 ohm 1/4 watt fusible resistor fed 23v
 √(.25/10) = 158ma

is my math/thinking  correct ? this seems awful close to the 150ma secondaries  the schematic references - is it that these fusible resistors are essentially analagous to 'slow bow' fuses and can actually handle more?

[Swake]

Most and everything audio that is sold today is having SMPS power supplies in it. You're probably listening to audio/video from your mobile phone, laptop or desktop computer all the time, these are full of SMPS, not only in the power brick but also on the motherboards. Many great lab DC power supplies, with reputable low ripple far lower than what you need here, are in fact SMPS based.

Why is this working? I believe the main reasons is that the chopping frequencies used in those SMPS are much higher than the human audible field and then of course there is also a filtration stage to keep it away from the audio signal.

With that, I'm not saying you have to go SMPS, it is just an option in case not enough room is available for classic transformers. I do believe that are conversion with classic transformers would be more appropriate in this case as it respects the original product better.

The picture shows 9 V and 20 V with a 2x3 VA power rating for both, and that there is in fact plenty of room. You can certainly source them locally or find them on aliexpress, ebay and amazon.

From the schematic you posted there does not seem to be a 50 Hz or 60 Hz clock pickup, only DC voltages.

[cod65]

First off, the 240 volt unit only draws half as much line current as the 120 volt model. Basic first day Power/Ohms law knowledge that is why the fuses are different. Second, there is no doubt the Roland 808 DID NOT use an 'off-the-shelf' transformer. It is certainly a custom designed part. IF indeed they used resistors instead of fuses then they MUST be flameproof!!! Buy or build an external 120vac in 240vac out 'transformer in a box' for your friend. That Roland unit is around 50 watts (actually less) and one solution may be to find a 50va rated transformer with dual primaries (120 / 120). The secondary windings are typically 12 / 12. Ignore the secondaries, we won't use those. Wire the primaries in series observing the proper phase relationship. Feed 120 from one end and the center point and get 240 across the far ends of the two primary windings in series. This may be way beyond the safe area of your current skill set?

Thank you Capt Don for your time/ knowledge. Sorry I wasn't clear - as explained in other replies- I get why the primary fuse would double in value , but the secondaries made no sense to me- 20 volts either way, the load is the same. I got a good explanation above.

also should've mentioned earlier on that the original transformer is long gone and I included pic of current config with (2) 230vac  providing the 10vac and 23-0-23 I wish to replace.

[DimitriP]

As I mention above this does not have the original transformer but 2 modern 230vac tformers currently

"RS-Pro"  no less

RS PRO 6VA 2 Output Chassis Mounting Transformer, 9V ac, IEC 61558-2-6
https://docs.rs-online.com/cd7c/A700000008857656.pdf


RS PRO 6VA 2 Output Chassis Mounting Transformer, 20V ac, IEC 61558-2-6
https://docs.rs-online.com/9099/A700000008857672.pdf


one has two  secondary 9V windings 3VA each, the other has two secondary windings  20V  3VA each ..

It's right there on the label...

and I forgot what the original question was ....



(fixed quoted message)

[cod65]

From the schematic you posted there does not seem to be a 50 Hz or 60 Hz clock pickup, only DC voltages.

thank you Swake- can you elaborate on this last sentence a bit ?

[Swake]

Someone mentioned that some audio devices from that era use the 50 or 60 Hz Hz clock to tune sounds.
This device does not seem to do this as there is no pick-up of that 50 Hz (or 60 Hz) signal.

[Swake]

The 115V equivalent of the 9V 6VA transformer at RS is RS-stocknr.: 503-990, see datasheet attached

There is no equivalent for the 20 V version. There is a 24 V but that is probably a little too much (would have to check datasheets of the TA7179P, but anyhow you don't want to stress that one as it is old and probably unobtainium). The 15V is going to be too low.

[squadchannel]

Triad F3-10 for 10V and
Triad F4-36 for 23V.

f3-10:$7.43
F4-36:$9.52

What do others think?

dual output transformers were hard to find.
now that we know we can get two put in, anything would be possible.

[cod65]

As I mention above this does not have the original transformer but 2 modern 230vac tformers currently[/
quote]

"RS-Pro"  no less

RS PRO 6VA 2 Output Chassis Mounting Transformer, 9V ac, IEC 61558-2-6
https://docs.rs-online.com/cd7c/A700000008857656.pdf


RS PRO 6VA 2 Output Chassis Mounting Transformer, 20V ac, IEC 61558-2-6
https://docs.rs-online.com/9099/A700000008857672.pdf


one has two  secondary 9V windings 3VA each, the other has two secondary windings  20V  3VA each ..

It's right there on the label...

and I forgot what the original question was ....

thanks Dmitri. Some other details I would like to add(should have added earlier): I have a remote 'mentor' that I asked about this project. I told him the same information you pointed out - that the existing transformers had ratings of 3VA,6VA. I calculated that the transformer current max  then must be:

9vac:
2(3VA) = 6VA(parallel config) so I = (VA)/V = 666ma

and 20-0-20:

I = 3VA/20 = 150ma each leg

I says 'why dont  I just get some similar 3VA 120vac transformers ?'

he insists a couple things: that the fuses, being 500ma imply that the transformers have to handle at least 150% of that, or they will blow first. Hmm I says- and then i look for weeks realizing that nothing would fit in the 1.7" space I have to work with !  Frustration ensues.

He says: you dont know the current based on the schematic - it seems to say 150ma secondaries , but you dont know if that is peak , etc. not fully clear, and because you don't know the current you need to rate above the fuses by 125-150%

I says OK.  And, of course not many transformers of that rating fit in a space no more than 1.7" high. I figure maybe I use toroidal. Then I figure maybe I will ask more people before I proceed.

He also says he doesn't use voltamp ratings for transformers becasue he considers them to be a kind of gimmick among manufacturers and not a reliable way to go -stick with max current rating - hmmm.... OK. He is way smarter than me so I listen. But then I realize many manufactures only list voltamps. I read up on voltamps and it seems pretty straightforward to me - I even see that these transformers CLEARLY SAY 3VA. But now hes got me vexed , and I want to ask more people , etc. This is partially why I am here.

so, yeah, I was initially under the impression I would just look for appropriate 3VA rated transformers and be done.  But he got me all scared and I want to understand what all the experts are telling me 110%

thank you for your knowledge and time!

[cod65]

I would also like to mention I chose early on for 9vac secondary , and have on hand , Hammond 187B10. It has ratings of 115vac ,10Vct, 6VA. It would fit well . does it look copacetic ?


https://www.hammfg.com/part/187B10

[squadchannel]

no problem i think.

if hammond, 23V choose 187A20 or 187B20.

187A20 is slightly lower current rating. maybe insufficient.

Toroid are overkill and a waste of money.

[cod65]

i measured a max height of 1.7" available  inside case, this hammond is similar to existing at 1.37"

looks like 187b20 will fit also ! thank you !

[cod65]

Toroid are overkill and a waste of money.

yes! the only reason I was considering them was becasue nothing else seems to fit 1.7" high  if I had to find a 20-0-20 at 750ma+750ma

[cod65]

oh wait, no i need 20-0-20 so that would be 40Vct, or thereabouts.

So I dunnoo .... 187B36 or 187C36


https://www.hammfg.com/part/187C36

the 808 manual on page 2 seems to suggest the dual regulator TA7179P will work between VIN(18-30v), so I assume after rectification my 18vac secondary should be what .... about 24vdc ?

[squadchannel]

oops, sorry yes needs 187B36.

[Swake]

VA and watt is indeed not entirely the same, but in this case it is going to be negligible.

Practice and theory are 2 different things. They're close but the difference is 'experience' and 'wrong information'. Let me explain with this example: The schematic says that between yellow and yellow there is 10 VDC, well good luck with that, if a transformer has DC on its coils then it is more a magnet than a transformer.

The given is that the 2 existing 2 x 3VA transformers make it work. Chances are this is enough power. If you want to make sure then you have to measure. I think this is a good exercise for you because it will give you certitude and explain the theory in practice and build some experience

What do you measure:
First
A/ AC Voltage of each secondary winding in operation, with the synth powered on and preferably making music.
B/ DC Voltage of each secondary winding. Obviously this should be very near to 0, but just in case there is new physics out there or a very big issue that needs repair
C/ AC Voltage of each secondary winding 'open' (= not connected to the synth, so you have to disconnect the wires)
By comparing this you can see how much of a difference the load the machine gives on the transformer. If the voltages in A are dropping heavily compared to C then the transformer is not big enough. I suspect this will not happen as there are no complaints now.

Second
- AC current on each winding while playing full blown music.
Now you can multiply this current with the above voltage in A and you know how much it really needs in VA. You can size the transformers accordingly. Here you indeed take some margin . In this case 'the biggest you can fit 'comfortably' in the case. Else as this is a small power supply, 150% is just a tad overkill but why not. If it was a very big power supply then maybe 110% is already enough.

[cod65]

hmmm wouldnt 187b36 be only 170/2 = 85ma per side ? do i need to go to 187C36 ?