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Any one with a Fostex 3050 delay?

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Any one with a Fostex 3050 delay?

Postby vinyl_junkie » Tue Jul 23, 2013 11:49 am

I recently got some random rack gear in a sale for next to nothing (£30) as there was a piece I wanted there (TX-81Z) included in the sale was also a Fostex 3050 Digital Delay but on closer inspection she's dead.

It appears the transformer is the fault, I have circuit tested the fuses, plug, switch etc and they are all ok but no voltage out from the transformer.

Any whom without a service manual I haven't got a clue what the voltage outs are from the transformer, bit annoying as I bet the rest works.
If any one has one of these can I be cheeky and ask if you can probe the output wires and see what voltages they are supposed to be?

Image
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Re: Any one with a Fostex 3050 delay?

Postby vinyl_junkie » Tue Jul 23, 2013 11:52 am

Errm I can't seem to edit this post to fix the overly large pic and make all the text fit in!
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Re: Any one with a Fostex 3050 delay?

Postby zenguitar » Tue Jul 23, 2013 4:04 pm

I'll flag it up in the Mods Area and ask an admin to fix it for you.

The forum software should resize the image automatically, but it it does suffer from the effects of old age and gets confused occasionally.

Andy :beamup:
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Re: Any one with a Fostex 3050 delay?

Postby Hugh Robjohns » Tue Jul 23, 2013 4:19 pm

Fixed the image problem for you.

You might be able to work out the likely transformer taps by finding out what the voltage regulators are...

H
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Re: Any one with a Fostex 3050 delay?

Postby vinyl_junkie » Tue Jul 23, 2013 5:53 pm

Hugh Robjohns wrote:Fixed the image problem for you.

You might be able to work out the likely transformer taps by finding out what the voltage regulators are...

H

Thanks for fixing the post Hugh and also for the info re power regulators, I'll have a look at it again soon
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Re: Any one with a Fostex 3050 delay?

Postby James Perrett » Tue Jul 23, 2013 7:41 pm

The fuses in the picture look like they're on the output side of the transformer. Is there an input fuse? Are you sure that this is a 230V unit?
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Re: Any one with a Fostex 3050 delay?

Postby vinyl_junkie » Tue Jul 23, 2013 11:00 pm

James Perrett wrote:The fuses in the picture look like they're on the output side of the transformer. Is there an input fuse? Are you sure that this is a 230V unit?

The only input fuse is the one on the plug. It is a 230v unit, sticker on the back says 240v 50hz so pretty sure it's not a 110v unit.

I checked with a multi meter and did a continuity test from the live pin of the plug to the input pins of the transformer and that was all good, did the same for the neutral too.
Fuse in the plug and on the unit are ok too
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Re: Any one with a Fostex 3050 delay?

Postby James Perrett » Thu Jul 25, 2013 9:54 am

Some mains transformers have integral fuses in the primary winding. Try putting your meter across the primary of the transformer and check the resistance. If it is open circuit the fuse in the transformer has probably blown.
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Re: Any one with a Fostex 3050 delay?

Postby nathanscribe » Fri Jul 26, 2013 7:17 pm

Hmm, if you can get that working it looks like a bargain! I've got a pair of Digitech RDS1900s that have a control voltage input like that - and I'm guessing that the Fostex will be similarly lo-fi and interesting. Nice find.

(I was also going to suggest looking at the regulators to work out the transformer requirements, but someone got there first :) )

Quick question - I can't seem to make it out in that picture, but what's the earthing like?
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Re: Any one with a Fostex 3050 delay?

Postby DGL. » Fri Jul 26, 2013 7:32 pm

nathanscribe wrote:Hmm, if you can get that working it looks like a bargain! I've got a pair of Digitech RDS1900s that have a control voltage input like that - and I'm guessing that the Fostex will be similarly lo-fi and interesting. Nice find.

(I was also going to suggest looking at the regulators to work out the transformer requirements, but someone got there first :) )

Quick question - I can't seem to make it out in that picture, but what's the earthing like?


If you are talking mains then none, clearly two core flex
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Re: Any one with a Fostex 3050 delay?

Postby nathanscribe » Fri Jul 26, 2013 7:45 pm

That's what I thought it looked like. What's the recommended way to replace these things, copy the original or add an earth lead?
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Re: Any one with a Fostex 3050 delay?

Postby DGL. » Fri Jul 26, 2013 9:09 pm

so long as the wires are sealed into the traff then keep it as is, if you have exposed terminals on the traff then technically there may be a need for an earth to the chassis as it would then become a class 1 item.
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Re: Any one with a Fostex 3050 delay?

Postby Hugh Robjohns » Fri Jul 26, 2013 9:16 pm

If its designed as class II (double insulated) then it should stay that way.
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Re: Any one with a Fostex 3050 delay?

Postby vinyl_junkie » Fri Jul 26, 2013 9:56 pm

Thanks for all the input guys, I'll get a look at this again at the weekend along with some other bits.

Got a broken Emagic AMT-8 I've had under my bed for about 2 years I think I fixed.
Originally paid quite a bit for it off ebay, worked for about a month then it had some mega power issues so I got pissed off and threw it across the floor and shoved it out of sight for years.

Had a closer look the other week and I think it's a fried TVS diode, got the part today and will fit it tomorrow and also have a close look at the Fostex.

Other bits that need doing is my MOTU 828, that thing I pulled my hair out so many times with... Any way that's another story.
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Re: Any one with a Fostex 3050 delay?

Postby vinyl_junkie » Sat Jul 27, 2013 9:45 pm

Okkk AMT-8 fixed today woo happy about that.

On to the Fostex delay.. I don't get any reading of any kind on the primary

The power regs are the following:

7912
78M12
78M05

So that's basically a +/-12v rail and a +5v but there are 5 cables coming from the secondary..

Took the board out so I can see the underside and it looks like both Yellow ones are going to the 5v reg hmmm, need a better look at this in the morning.
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Re: Any one with a Fostex 3050 delay?

Postby James Perrett » Sat Jul 27, 2013 10:06 pm

The transformer you are replacing isn't a toroid so no need for one as far as I can see. What are the voltage ratings on the large capacitors? That will control the maximum voltage you can use (together with the power rating of the regulators). It would be worth drawing out the circuit - just in case they use an unusual way of deriving the + and - rails.
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Re: Any one with a Fostex 3050 delay?

Postby vinyl_junkie » Sat Jul 27, 2013 10:14 pm

James Perrett wrote:The transformer you are replacing isn't a toroid so no need for one as far as I can see. What are the voltage ratings on the large capacitors? That will control the maximum voltage you can use (together with the power rating of the regulators). It would be worth drawing out the circuit - just in case they use an unusual way of deriving the + and - rails.


Hi James,

Reason I initially mentioned the toroid was mainly just out of preference.
Can't say I'm a fan of those square ones which usually just start buzzing after a few years... Ok mainly the cheap ones do lol

Any whom the caps are two 25v and one 16v for the 5v rail
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Re: Any one with a Fostex 3050 delay?

Postby DGL. » Sun Jul 28, 2013 7:09 am

vinyl_junkie wrote:
James Perrett wrote:The transformer you are replacing isn't a toroid so no need for one as far as I can see. What are the voltage ratings on the large capacitors? That will control the maximum voltage you can use (together with the power rating of the regulators). It would be worth drawing out the circuit - just in case they use an unusual way of deriving the + and - rails.

Hi James,

Reason I initially mentioned the toroid was mainly just out of preference.
Can't say I'm a fan of those square ones which usually just start buzzing after a few years... Ok mainly the cheap ones do lol

Any whom the caps are two 25v and one 16v for the 5v rail

We'll be talking around 7-10v for the 5v supply (78xx and 79xx regs need at least 2 volts above the regulated output to function), and around 15 for the +/-12v supply.

The 5 wires from the current traff will be something like 15-0-15, 7-0.
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Re: Any one with a Fostex 3050 delay?

Postby vinyl_junkie » Sun Jul 28, 2013 11:12 am

Superb info DGL!

What do you think the size of the trafo should be? 20va adequate?
This is old 1982 delay so at a guess not very power efficient may need more juice, there is the digital circuitry, the analogue side and it also has a analogue limiter and compressor before the input.

Cheers,

Martin
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Re: Any one with a Fostex 3050 delay?

Postby DGL. » Sun Jul 28, 2013 11:24 am

vinyl_junkie wrote:Superb info DGL!

What do you think the size of the trafo should be? 20va adequate?
This is old 1982 delay so at a guess not very power efficient may need more juice, there is the digital circuitry, the analogue side and it also has a analogue limiter and compressor before the input.

Cheers,

Martin

We will be talking at most an amp for each of the voltage regualtors (standard 78/79xx series will give out up to 1 amp, also the current draw will be at the voltage supplied to the regualtors so if 15v then it will be 1 amp (15w/15va) (the voltage drop is expelled as heat)), so 20va sould be fine.
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Re: Any one with a Fostex 3050 delay?

Postby vinyl_junkie » Mon Jul 29, 2013 10:46 am

Managed to score the schematics! :-)

Click on pics for higher res

Image

Image
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Re: Any one with a Fostex 3050 delay?

Postby James Perrett » Mon Jul 29, 2013 12:35 pm

DGL. wrote:
The 5 wires from the current traff will be something like 15-0-15, 7-0.

Don't forget the RMS to peak conversion - a 15-0-15 transformer will give you something like 21V on the input to each of the regulators which will mean that you're wasting a fair bit of energy as heat. A 12-0-12 would probably be better.

James.
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Re: Any one with a Fostex 3050 delay?

Postby vinyl_junkie » Tue Jul 30, 2013 7:50 pm

James Perrett wrote:
DGL. wrote:
The 5 wires from the current traff will be something like 15-0-15, 7-0.

Don't forget the RMS to peak conversion - a 15-0-15 transformer will give you something like 21V on the input to each of the regulators which will mean that you're wasting a fair bit of energy as heat. A 12-0-12 would probably be better.

James.


Sorry for the stupid question but I'm a little confused by this, care to expand?

The voltage out specs for the transformer are they peak to peak or RMS? Or are the specs for the v-regs peak to peak or RMS hence the conversion being needed?
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Re: Any one with a Fostex 3050 delay?

Postby DGL. » Tue Jul 30, 2013 10:18 pm

vinyl_junkie wrote:
James Perrett wrote:
DGL. wrote:
The 5 wires from the current traff will be something like 15-0-15, 7-0.


Don't forget the RMS to peak conversion - a 15-0-15 transformer will give you something like 21V on the input to each of the regulators which will mean that you're wasting a fair bit of energy as heat. A 12-0-12 would probably be better.

James.



Sorry for the stupid question but I'm a little confused by this, care to expand?

The voltage out specs for the transformer are they peak to peak or RMS? Or are the specs for the v-regs peak to peak or RMS hence the conversion being needed?


I believe that once the voltage is rectified and smoothed the actual voltage out will be higher than the rms voltage and will be the peak voltage (as the ac-dc conversion is based on the peak voltage. Therefore you will need a transformer that delivers a PEAK voltage of at least +3v more than the required regulator output (i.e. At least +/-16v and +8, this should also give you enough to allow for variations in mains voltage)

Hope it helps.
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Re: Any one with a Fostex 3050 delay?

Postby James Perrett » Wed Jul 31, 2013 11:26 am

vinyl_junkie wrote:
Sorry for the stupid question but I'm a little confused by this, care to expand?

The voltage out specs for the transformer are they peak to peak or RMS? Or are the specs for the v-regs peak to peak or RMS hence the conversion being needed?

AC voltages are normally quoted as RMS values and that's what the output of the transformer will be specified as. Due to the way the rectifier and smoothing capacitor work, the output voltage after the smoothing capacitor will be close to the peak voltage. When you are working with voltage regulators you need to ensure that their input voltage will never drop below their threshold voltage but you don't want the voltage to be too high as you will only waste power and end up with the famous Behringer ADA8000 power unreliability problem.

James.

PS - peak voltage and peak to peak voltage are two different things. The peak voltage is the maximum voltage between the 2 conductors while the peak to peak voltage is the difference between the maximum positive peak and the maximum negative peak voltage.
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