Millett LR + TP Opus + AMB α24 reboot

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Thermionic Idler
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#61 Re: Millett LR + TP Opus + AMB α24 reboot

Post by Thermionic Idler »

Well bugger! I've realised that in the preamp, I have a PCB full of relays and no flyback diodes - apparently you need these to protect things from high voltage spikes on mechanical relay turn-off.

I didn't know about the need for flyback diodes when I designed this. Poo.

Hmm.

I know the ideal would be to have one diode per relay, but I'd have to completely re-do the PCB as there are quite a number of relays - five of the buggers. Maybe long-term I should do that.

So how can I bodge it. Looking at the circuit below, I believe I should have a couple of spare GP10Y diodes from when I added the protection to the 300B power supply. If I put one across J2 - solder it to the XLR4 connector which supples the power relays in the 300B's - that should cover the 300B relays and K3, K4 and K6. Another can be soldered to the LED connections in the front panel switch J3, to cover K5 and K7. This will have a 150R resistor in series with it but I don't think that will present a significant problem?

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Deck: Garrard 301 - Audio Origami PU7 - NW Analogue DH3S
Phono: Pete Millett LR, Lundahl SUT, AMB σ22 PSU
Linestage: Bruno Putzeys Balanced Pre + Hans Polak relay mod, LCDuino control
Power amps: 300B PP 'Symmetric Reichert'
Speakers: FF225WK Big Mets
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Nick
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#62 Re: Millett LR + TP Opus + AMB α24 reboot

Post by Nick »

If they are through hole relays just solder a 1n4148 or similar across the back of the coil pins.
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#63 Re: Millett LR + TP Opus + AMB α24 reboot

Post by Thermionic Idler »

Nick wrote: Tue Nov 02, 2021 10:57 pm If they are through hole relays just solder a 1n4148 or similar across the back of the coil pins.
They are indeed through hole relays and I didn't trim off the excess lengths so... good call Nick, that should be do-able, thanks! I should even have enough spare 1N4148's as I think I bought 10, and this circuit used 5.

Then in each 300B amp, I'll stick a GP10Y diode across each of the larger relays, the little PCB's that hold them have screw terminals.

EDIT - the 300B amp relays are on ready-made PCB's, and they already have back-EMF protection built in - so I don't have to worry about those. Another Saturday morning task awaits...
Deck: Garrard 301 - Audio Origami PU7 - NW Analogue DH3S
Phono: Pete Millett LR, Lundahl SUT, AMB σ22 PSU
Linestage: Bruno Putzeys Balanced Pre + Hans Polak relay mod, LCDuino control
Power amps: 300B PP 'Symmetric Reichert'
Speakers: FF225WK Big Mets
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Thermionic Idler
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#64 Re: Millett LR + TP Opus + AMB α24 reboot

Post by Thermionic Idler »

Well - it's not what one would call an aerospace-grade solution, but it's a solution nonetheless.

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Deck: Garrard 301 - Audio Origami PU7 - NW Analogue DH3S
Phono: Pete Millett LR, Lundahl SUT, AMB σ22 PSU
Linestage: Bruno Putzeys Balanced Pre + Hans Polak relay mod, LCDuino control
Power amps: 300B PP 'Symmetric Reichert'
Speakers: FF225WK Big Mets
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#65 Re: Millett LR + TP Opus + AMB α24 reboot

Post by Ray P »

Just need to be a bit careful scrubbing off the flux residue!
Sorry, I couldn't resist!
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#66 Re: Millett LR + TP Opus + AMB α24 reboot

Post by jack »

Don't scrub it off! IPA and a cotton bud...

Oh, and it's a perfectly acceptable solution.
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#67 Re: Millett LR + TP Opus + AMB α24 reboot

Post by Ray P »

Scrubbing in the loose sense of the word - I use an old soft toothbrush for any stubborn flux residue but mostly just wet with solvent and dab with some kitchen towel.

For the solder I normally use I find this much better than IPA, nice clean boards with very little effort.

https://uk.farnell.com/servisol/1000190 ... dp/3821470
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#68 Re: Millett LR + TP Opus + AMB α24 reboot

Post by pre65 »

Or a fine brass bristle wheel on a 1500W angle grinder, works wonders. (like a Double Diamond) :lol: :wink:

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#69 Re: Millett LR + TP Opus + AMB α24 reboot

Post by Thermionic Idler »

OK this is daft. I've noticed a few posts on other threads about disappearing down rabbit holes, I think I'm well past that into the vale of tears.

For about the last week or so I've been faffing about in Spice trying to see if I could engineer a time-delayed solution for muting the DAC whilst switching sources between the two I2S receivers, and "staggering" the power up/down of same (so that I'm not wasting power on the inactive receiver).

The critical interface is the USB one from the server, and I have the nice JLSounds board for that. The SPDIF interface is for the TV, as I've mentioned before. It's just a generic one from Banggood and is it honestly going to sound any better than say a cheap 2nd DAC like a Topping?

Why not just have the two DACs and switch the analogue audio with the preamp as normal? Because muggins here thought that would be less "elegant" than having the one DAC and engineering a whole lot of complicated infrastructure around it just to switch between two digital sources. :roll:

It also locks me into the AMB / LCDuino control system, which I'm also starting to see as a rather over-complex solution to a simple problem. All I was after originally was a means of remotely controlling volume on a stepped attenuator, and at the time I built it, the LCDuino was pretty much the only way I could find to do it, as the Bent Audio products were off the market. I would have been perfectly happy with a manual switch for power on/off and source selection as those operations are performed way less often, but I do like to tweak volume from the listening position. I don't like having to rely on the remote for so much functionality - if I were to, say, bring the system to Owston but forgot the remote, we'd have no way to change sources!

Last weekend the software completely bricked itself at switch-on and I had to re-flash the chip to get it to work again. In the process it nearly cooked the Darlington arrays that control the relays - I was rather perplexed at the smell of hot plastic accompanying the display with garbage characters on it. When it's first switched on, all the branches default to "high" state which puts relay switching current through all the arrays, and the software "resets" them to low. Unfortunately if the software locks up, that doesn't happen!

If the Millett LR phono turns out to have legs, it's inevitable that I'm going to want to follow it up with the Bench LR. And if that were to be a success, I'd probably want to re-do the linestage with valves, to get an all-valve signal path back for LP's. And if I were to do that, I'd probably do away with the LCDuino, as we now have simple solutions like the Khozmo remote attenuator.

I realise I'm getting way ahead of myself, but thinking this through illustrates the folly of assuming anything in this hobby is ever going to remain static. I'm pretty sure my amps, speakers and turntable will remain a constant as I'm perfectly happy with those, but the 'stuff in the middle' is still under R&D, so I'd be wise to make sure future change can be accommodated without too much faff.
Deck: Garrard 301 - Audio Origami PU7 - NW Analogue DH3S
Phono: Pete Millett LR, Lundahl SUT, AMB σ22 PSU
Linestage: Bruno Putzeys Balanced Pre + Hans Polak relay mod, LCDuino control
Power amps: 300B PP 'Symmetric Reichert'
Speakers: FF225WK Big Mets
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#70 Re: Millett LR + TP Opus + AMB α24 reboot

Post by pre65 »

Wow.

In a way I'm glad I'm not clever enough to attempt anything "complicated".

But, hats off to those who can, and do. :)
The only thing necessary for the triumph of evil is for good men to do nothing.

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G-Popz THE easy listening connoisseur. (Philip)
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#71 Re: Millett LR + TP Opus + AMB α24 reboot

Post by Thermionic Idler »

Just got notification that Schaeffer AG are increasing their prices from 1st December by quite a bit due to hikes in the price of aluminium - eek! I think I'm going to have to bring forward the chassis work - I think as long as I get the holes in roughly the right place to hold a back-plane PCB in both builds, we should be okay.
Deck: Garrard 301 - Audio Origami PU7 - NW Analogue DH3S
Phono: Pete Millett LR, Lundahl SUT, AMB σ22 PSU
Linestage: Bruno Putzeys Balanced Pre + Hans Polak relay mod, LCDuino control
Power amps: 300B PP 'Symmetric Reichert'
Speakers: FF225WK Big Mets
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Thermionic Idler
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#72 Re: Millett LR + TP Opus + AMB α24 reboot

Post by Thermionic Idler »

Chassis for LR Phono and TP Opus DAC now designed and ordered, got in there before the price increase.

I'm heading oop north this weekend to audition Dom Harper's cartridge. If I decide to go for it, I'll need to swap out the step-up transformers I bought for the LR phono...
Deck: Garrard 301 - Audio Origami PU7 - NW Analogue DH3S
Phono: Pete Millett LR, Lundahl SUT, AMB σ22 PSU
Linestage: Bruno Putzeys Balanced Pre + Hans Polak relay mod, LCDuino control
Power amps: 300B PP 'Symmetric Reichert'
Speakers: FF225WK Big Mets
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#73 Re: Millett LR + TP Opus + AMB α24 reboot

Post by Ant »

Doing some mileage lately dave!
Feel free to call in for a pitstop if we are on your way back, its a long old drive up to see nat and dom
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#74 Re: Millett LR + TP Opus + AMB α24 reboot

Post by Thermionic Idler »

Ant wrote: Wed Nov 17, 2021 8:09 pm Doing some mileage lately dave!
Feel free to call in for a pitstop if we are on your way back, its a long old drive up to see nat and dom
Cheers Ant - as long as I get off by 9:30 - 10:00 on the Sunday, it should be do-able if the traffic's not too bad. I will need to keep an eye on the time and make sure I don't land back in Southsea too late as Meredith is planning a rather lovely oxtail stew! :D I will actually have some LPs with me this time.
Deck: Garrard 301 - Audio Origami PU7 - NW Analogue DH3S
Phono: Pete Millett LR, Lundahl SUT, AMB σ22 PSU
Linestage: Bruno Putzeys Balanced Pre + Hans Polak relay mod, LCDuino control
Power amps: 300B PP 'Symmetric Reichert'
Speakers: FF225WK Big Mets
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#75 Re: Millett LR + TP Opus + AMB α24 reboot

Post by Nick »

FWIW, I used these https://www.ti.com/store/ti/en/p/product/?p=ISO7240MDW to isolate and switch signals between the various inputs of the dac I made. Not that the word seems to have any you can buy at the moment.

I also think you are making things much more complex by tryng to bolt together existing bits instead of just designing and building what you want from scratch.

I think I mentioned the idea of a watchdog elsewhere, that would be how I would solve the no startup problem. If the processor is not running isolate and shutdown the supply's to the system.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
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