ODS 124 - revisited for the 21C

[Stephen1966]

http://www.savinoluce.it/

Had a quick look (curious)

Everything in the storefront is for 120V primary. Perhaps they make 240V on demand. Looks like a website under construction!

[jazzbass]

Also, I should mention Musikding... they have a nice selection of knobs.

I'm happily married by the way

i didn't say about you that you were getting married but about erwin_we

Franco

[erwin_ve]

Also, I should mention Musikding... they have a nice selection of knobs.

I'm happily married by the way

i didn't say about you that you were getting married but about erwin_we

Franco

Thanks! Im happily married for almost 30yrs, no plans for a new wedding. I think you are referring to Norbury(Marcus).
Things are slowly getting better after lockdowns: I'm waiting on 3 different chassis run. Also working with a very talented Dutch member on something new, very exciting stuff...

Erwin

[jazzbass]

Hi Erwin_ve

I am happy to hear news from you and to know that you are not the one who is getting married, I have been married for 52 years and I would have to tell ... but each one has to have his own experience. I expect news from you on the chassis.

Franco

[Stephen1966]

I've been busy working on the layouts for the build... In the meantime, I have been thinking again about the 124 FX loop.

I'm building a Dumbleator separately and I'm keen to include switching in there which will allow me to run it in series or parallel. It occurred to me that I might do something similar with the FX loop onboard the amp.

Here's a sketch...

ODSR 124 Series-Parallel FX.jpg

It's just the addition of a couple of passive switches and a mixer pot all of which should sit on the back panel next to the jacks. The mixer pot could be in the region of 25k, looking at the similar schemes out there.

Has anybody tried anything like this before? Either way, the ability to keep the dry signal in parallel and not sending all the signal through the effect seems like a no-brainer!

Stephen

[Stephen1966]

So, the problem with that circuit in the first sketch is that with the DPDT switch to 'FX in' and the SPST switch to 'Series' with no effect plugged in, the circuit would be open - no sound from the amp!

This circuit solves that problem using a tip shunt jack (Switchcraft 12A - like the original) and moving the pot to the hot side of the series/parallel switch. With the circuit in parallel, the pot now only acts to attenuate the dry signal so should probably be renamed something like 'Dry level'. I might also increase the value to 50k. At least, this way if I leave the DPDT to 'FX in' and remove the effect jacks I will be left with an unattenuated bypass of the signal. Not too different from the original scheme.

ODSR 124 Series-Parallel FX2.jpg

Stephen

[rootz]

Stephen, are you planning to use this amp with a Dumbleator? There is a series/parallel Dumbleator in the files section.

[Stephen1966]

Stephen, are you planning to use this amp with a Dumbleator? There is a series/parallel Dumbleator in the files section.

Hi rootz, yes, I am - except when I'm not Indeed, I am putting together a series/parallel circuit for the Dumbleator and I realise that if I have S/P switching there, and S/P switching on the amp, I will need to run the amp in series before any switching in the Dumbleator.

This passive series/parallel on the amp is more for those times when I might run an effect without the Dumbleator hooked up. I'm trying to keep it simple and as true to the original as possible, but versatile as well. For the sake of a couple of switches and a pot it's worth trying.

Never seen this before though, so maybe there's a reason for that. Should I expect the villagers turning up at my door brandishing pitchforks and flaming torches???

Stephen

[Stephen1966]

So, it's been a while but I've been busy. I have the chassis layout figured out and everything - apart from me (work is always busy) - is just about ready to go.

I'm calling it the Skyliner, seemed an obvious choice in the end.

Cable runs are next, it'll help me figure out the assembly order. This study of the topology is both mechanical and theoretical, not harping on about my skills with Illustrator here but this thing is a work of art. The components in red are some of the experimental parts of the circuit. I'm sure you guys with a more derring-do attitude will think I am mad. My wife would agree with you

Skyliner chassis - 20-07-22.pdf

Stephen

[Stephen1966]

Okay, this might seem a bit esoteric, but does anyone have any thoughts about the DC lines between the voltage regulator and the relays along the front of the chassis and separate DC line to the jack at the far corner of the chassis providing a line (lines) to the LEDs in the pedal?

Looking back at the original, the relays are fed with parallel DC lines from the voltage regulator but many later examples reduce it to a single line, with relays in series (DC speaking). My thought is to run a branching line of DC for the pedal from the junction with the relays to the back and corner of the chassis where the jack for the footpedal is located. A shorter route.

The only threat to the circuit constants as I understand them in the original, is that a single line would be carrying the full charge for the relay coils, and two sets of LEDs (in the chassis and in the pedal).

The relays and the LEDs are all in the milliamps scale of things but if I can run a DC line for the pedal from the junction with relays I can use shielded multicore cabling under the boards to the back.

Is there any way to predict or measure the EMI? Or, is this really, of no consequence?

Stephen

[Stephen1966]

So I found it makes more sense to run the 12V DC lines almost the full width of the chassis front and back. If I can quote Blencowe: 'Noisy wiring should run close to the chassis wall or, better still, be pushed into the corners to maximise the capacitance to earth. The earthed chassis will then have a similar effect to a Faraday cage and will tend to draw the electric field towards itself, this often avoids any need to completely shield the wiring (especially the heater wires).' The heavily filtered 12VDC run through the voltage regulator isn't a likely source of magnetically induced hum but may provide a weak capacitance to earth which then propagates through the chassis and contributes a leaching effect which interacts with the general grounding scheme. There will be other reasons for the placement of the relay power ground (GND 5) but it seems no accident that it is as far away from the input side ground (GND 1) as it's possible to get.

This concludes my theorising for now (hurray, I hear you say) and it is literally time to get the iron hot.

Stephen

[Stephen1966]

Hi,

Does anyone have any advice for forming the caps when first applying power? The build is almost finished and I found plenty on reforming old caps but nothing clear on new caps already in circuit.

Cheers.

Stephen

[bepone]

do you have a variac? idea is to slow charge them to the full voltage and then slow discharge through 20min-half hour.. repeat the process few times to reform electrolyte inside dry electrolytic caps.

if you want to know more here is some paper https://library.e.abb.com/public/9f1bef ... 050629.pdf
but ABB is to radical and their resistor is to small

[bepone]

if you dont have nothing, no any regulated DC supply or variac or nothing, remove load from caps in the amp, put from cap + terminal to minus terminal 220k 2W resistor (for discharging) .. and charge them over rectifier diodes , insert from diode to the cap+ terminal resistor of cca 100k 2W in series and see the situation, how fast they will charge ..then sw. off. wait to be discharged.. sw. on.. . reduce resistor to 50kohms if too slow.. etc

[Stephen1966]

do you have a variac? idea is to slow charge them to the full voltage and then slow discharge through 20min-half hour.. repeat the process few times to reform electrolyte inside dry electrolytic caps.

if you want to know more here is some paper https://library.e.abb.com/public/9f1bef ... 050629.pdf
but ABB is to radical and their resistor is to small

Thanks, I have a variac. Current limiting lightbulbs as well if called for. Given an unknown time since their manufacture, is there any rule of thumb for the voltages and/or current dissipation we should be looking for with "new" caps? Having just finished building them into the amp's circuit I don't really want to start disassembling it. This power design will discharge itself when switched off though... Slow? Fast? I don't know, my other amp discharges through a snubbing resistor in about 30 seconds.