Dieselpunk Preamp of Doom and the Beast with Two Backs

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Irene Idler
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#136 Re: Dieselpunk Preamp of Doom and the Beast with Two Backs

Post by Irene Idler »

He's being modest, of course. It's shoddy. Very, very shoddy. You'll all have to come over and hear it yourselves.
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#137 Re: Dieselpunk Preamp of Doom and the Beast with Two Backs

Post by Cressy Snr »

Unbelievably shoddy! :D
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Dave the bass
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#138 Re: Dieselpunk Preamp of Doom and the Beast with Two Backs

Post by Dave the bass »

Technically that equates to Shoddy-bollux status.
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#139 Re: Dieselpunk Preamp of Doom and the Beast with Two Backs

Post by IslandPink »

Yes there was something about it when I saw the finished photos that I couldn't quite put my finger on.
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Irene Idler
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#140 Re: Dieselpunk Preamp of Doom and the Beast with Two Backs

Post by Irene Idler »

I have been given permission to quote Dave on this:

"I believe that I am entitled to be a bit smug. How smug am I? I am a smug bastard. A smug fucking bastard. Yes, I am."

And quite right too!
"Hey, you know the rules, baby. If you wanna PLAY funky, you gotta SMELL funky." -- Mike Troutman
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#141 Re: Dieselpunk Preamp of Doom and the Beast with Two Backs

Post by Ant »

There is so much shoddiness there that shoddy doesnt quite describe how shoddy it actually is!
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#142 Re: Dieselpunk Preamp of Doom and the Beast with Two Backs

Post by Thermionic Idler »

I now understand why people say it's impossible to photograph black cats. The same goes for black audio gear!

I played with the exposure settings this morning and managed to get this - this shows properly what the displays look like even though the case of the amp disappears into the darkness...

Image
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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#143 Re: Dieselpunk Preamp of Doom and the Beast with Two Backs

Post by simon »

Good photo Dave. Our eyes are a lot more tolerant of variation of light intensity than our cameras are, so it's very difficult to achieve the same effect.
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#144 Re: Dieselpunk Preamp of Doom and the Beast with Two Backs

Post by Thermionic Idler »

Having done some more listening, it's clear that the Alpha24 audio performance is truly exquisite and improves on my previous commercial preamp by some considerable margin. Wagner is very complex and dense music, and when listening to the first side of Rheingold, I was immediately a lot more aware of not only the main melodic lines, but also the structure and timing of the accompaniments underneath - which is the kind of thing that gives you a much deeper appreciation of the music. And wow does it play music!

Technically also, Ti Kan obviously knows what he's doing when it comes to grounding as the small amount of system hum I had before has vanished entirely - it is now completely silent at the speaker. Clearly I previously had some kind of grounding loop, I suspect some of the improvement can be put down to the elimination of that.

I took something of a risk with this because there was very little content online about the performance of the design, other than on the AMB site itself, so I couldn't independently verify how good it would actually be, subjectively. I was also slightly nervous going from tubes to op-amps. However Ti had posted a LOT of technical detail about the design, so I knew it had sub-70 ohm output impedance, bandwidth up to 1Mhz and almost unmeasurable distortion. I figured that with those credentials, it had to get as close to being a straight piece of wire with gain as an active stage can get. The stepped R-2R attenuation would give further benefits.

I have three minor 'teething' issues that I need to sort out - there's a visible orange lit-up line to the left of the display caused by the backlight sticking out, which just needs a bit of black tape putting over it. Also when installing the meters, I overtightened one of the bolts and fractured the plastic on the bottom left of one of the housings - some Araldite or something will fix that. And the meters themselves don't deflect fully, they stop at about -5dB even with increasing input level, so I think I need to swap out a gain resistor on the JLM buffer board. I'll address all that after the power amps are completed - at that point I won't need the unbalanced output, so I'll then convert that to a second balanced output which will be under LCDuino control. At that point I'll fix these other issues.

I recommend these boards very highly indeed, although soldering the SMD op-amps is not for the faint-hearted! The boards themselves are very small - only 2.5 by 1.4 inches, and can be stacked as well, so easy to accommodate into a compact design. Ti recommends putting the power supply into a separate chassis, but I've had no noise or hum issues with having everything in the same chassis.

This is my first build that has not been from a kit of parts, bringing it all together was a hell of a lot of work (far more than I'd anticipated) but it's been well worth it.

Onwards with the Beast power amps now.
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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#145 Re: Dieselpunk Preamp of Doom and the Beast with Two Backs

Post by Thermionic Idler »

Started populating a few parts on the Beast circuit boards last week but the bulk of my recent efforts has been on reworking the chassis layouts (again!). The preamp went through many reworks and the same is proving true of the power amps.

This thing has three big toroids in each monoblock - 500VA, 250VA and 100VA, and a thermistor for inrush current limiting. I've been reading the Rod Elliot pages where he warns against this practice (apparently thermistors can make an impressive bang if there's a fault), although my main motivation is the removal of this inevitably varying impedance (depending on load) from the mains line.

So I've bought a couple of Rod's soft start PCB's which use fixed resistors and two relays (second relay bypasses the resistors after 100ms), they are currently on their way from Oz. I chose them because they also nicely integrate 12V remote trigger switching which I specifically built into the preamp, and said switching only draws a few milliamps so I won't run the risk of overloading the regulator in the preamp's 12V power supply.

I also want to incorporate Rod's DC blocker circuitry - those big toroids will hum (and potentially saturate) if there's DC on the mains, running the risk again of choking the power supply.

I've been spending the last few days trying to solve the problem of making this PCB, the small 9V transformer that runs it, and the DC blocking circuit, all fit into my existing design whilst keeping it electrically safe, not having to make the chassis bigger, and not bringing AC too close to signal circuitry. I believe I have it figured out but I'm going to need to make my own turret boards to do it (thank you Ampmaker). I'll post the finalised CAD drawings when done.
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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#146 Re: Dieselpunk Preamp of Doom and the Beast with Two Backs

Post by Thermionic Idler »

Finalised CAD drawing for the soft-start and DC blocking assembly. Both Rod Elliot circuits, although I've upped the capacitance a bit on the DC blocker by having three 2200uF caps in parallel per side (makes more efficient use of the available space than having one big cap per side). Also includes a turret board for connecting up and distributing power to all the transformer primaries, and connection points for the secondaries. I'll explain the colour coding if anyone's interested, it's for my later reference really.

Image

And here's how it fits into the larger scheme of things (bottom right)

Image

I swear it takes me longer to plan these things in CAD than it does to build them.
Last edited by Thermionic Idler on Sat Dec 16, 2017 12:42 pm, edited 1 time in total.
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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#147 Re: Dieselpunk Preamp of Doom and the Beast with Two Backs

Post by jack »

Thermionic Idler wrote: Sat Dec 16, 2017 12:29 pm Finalised CAD drawing for the soft-start and DC blocking assembly. Both Rod Elliot circuits, although I've upped the capacitance a bit on the DC blocker by having three 2200uF caps in parallel per side (makes more efficient use of the available space than having one big cap per side). Also includes a turret board for connecting up and distributing power to all the transformer primaries and secondaries. I'll explain the colour coding if anyone's interested, it's for my later reference really.
...
I swear it takes me longer to plan these things in CAD than it does to build them.
Doing the CAD is fun - very professional!

Having multiple caps in parallel has another benefit in that you parallel the ESR - it's a cheap(er) way of getting a really low ESR into a smaller space, normally at a lower price too (ultra-low ESR caps tend to be very expensive and big - the 2,200uF @ 500V PEH169/200 RIfas/Kemets I use would cost 70 quid + VAT each if bought from Farnell...).
Last edited by jack on Sat Dec 16, 2017 1:10 pm, edited 3 times in total.
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Thermionic Idler
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#148 Re: Dieselpunk Preamp of Doom and the Beast with Two Backs

Post by Thermionic Idler »

jack wrote: Sat Dec 16, 2017 12:35 pm Doing the CAD is fun - very professional!
Thanks very much - it's quite relaxing mostly, although a lot of yesterday was spent staring at my screen and scratching my head trying to fathom out how to arrange all the standoffs so as not to end up with a catch-22 situation at build time - where fitting component A gets in the way of fitting component B, but if I then fit component B first, it'll block the fitting of component A. I checked it by creating another version and re-arranging the layers in build steps, so I could see it 'go together' on screen. This will then guide me when I come to build it for real.

The preamp went together without any major hitches so I know this works. That said, I still have a fair bit more work to do including the tedium of working out what nuts, bolts and spacers I still need to get. Aaaand I also have to draw out the 'mirror image' version. Realistically, I don't think I'll be ordering anything from FPE until the New Year.
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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Ray P
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#149 Re: Dieselpunk Preamp of Doom and the Beast with Two Backs

Post by Ray P »

Hi Dave, I dunno whether this will inspire you or distract you but this is a pretty neat Beast project...

http://sharksphotos.yolasite.com/

Ray
Sorry, I couldn't resist!
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Thermionic Idler
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#150 Re: Dieselpunk Preamp of Doom and the Beast with Two Backs

Post by Thermionic Idler »

Hi Ray - I couldn't get the site to respond this morning but if it's the one I think it is, yes I have seen it before and I like it a lot! (apart from the blue LED's).

The look of mine was inspired more by the Atmasphere amps. Figuring out the construction detail is proving very tedious and time consuming though!
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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