New Preamp

[DaveC]

I'm happy to be finishing up my next project, a zero-gain preamp using Tortuga's LDR and Broski's Aikido tube buffer.

RDavidson helped with design and is getting one of them, his is made with spalted maple and natural aluminum metal parts, mine is maple burl with brushed copper front and top panels.

I needed a buffer preamp and this one turned out great, I'm super happy with the way it sounds.

 

[DaveC]

Here's the spalted maple chassis:

 

[amirm]

Wow, these are works of art! Did you do the woodworking yourself or farm it out?

 

[DaveC]

Wow, these are works of art! Did you do the woodworking yourself or farm it out?

Thanks! Yes, I did the woodworking, finishing and assembly...

The sound is really amazing though, I'd put this thing up against anything... My last preamp (a 6SN7 Aikido) was compared with a $10k+ Air Tight which resulted in the owner of the AT selling it along with the Fi 2a3 monos he was using with it... My EL34 amp was a bit better. This preamp sounds even better, the Tortuga LDR based preamp controller is a great sounding unit. And having a remote control is awesome.

 

[amirm]

Oh, didn't know I was speaking with a fellow woodworker .

So what is the pricing? Do you just build them one at a time as people request them?

 

[amirm]

And what is the digital board doing? Is it displaying levels and such on the front panel or is it also used to control bias and such? Is there a remote control? Inquiring minds want to know .

 

[DaveC]

I wasn't necessarily planning on it, but a lot of effort went into the design and I have all the CAM files so I could make a chassis for other DIY'ers or even offer a build service like many folks offer for the NCore NC400 modules. Pricing would be on a case-by-case basis depending on the details but the above preamps would be in the $5-6k range with the chassis being around $2k.

The Tortuga LDR is the digital board, it does a few things....

- calibrates the LDRs into a 70-step volume control with a 60 dB range so each step is a bit less than 1 dB. LDRs are not linear and differ from unit to unit so calibration is necessary.

- balance control

- input/source switching

- adjustable input impedance from 20-99k with 5 presets that can be changed as you listen

- uses an Apple remote control or the encoder dial on the front panel for controls

- the displays on the front panel are L and R volume but also change depending on what you're doing... balance, calibration, etc...

- displays can be adjusted for brightness in 15 steps

- USB input is only for updating firmware, no on-board DAC.

 

[kach22i]

They look great, almost (but not quite) too fancy.

One question.

 

[DaveC]

Power transformers for the tube buffer B+ and LDR boards. They are meant to resemble potted trafos but since wood is not a great conductor they are convection cooled. They are oversized and stay fairly cool. B+ uses a few watts and the LDR board uses about 2.5W. Both are 50VA toroids. The wood boxes and the chassis interior is coated in a carbon conductive paint for shielding.

 

[Joe Whip]

Looks well damped inside! Doing a similar thing to my DAC.

 

[amirm]

Dave, I noticed on the 175 uf cap you have double bolt holding the wire connector/lug. Is there a reason for that than just tightening them against the cap? Or do they come that way and there is no more threading past that point?

 

[DaveC]

Dave, I noticed on the 175 uf cap you have double bolt holding the wire connector/lug. Is there a reason for that than just tightening them against the cap? Or do they come that way and there is no more threading past that point?

They come with the double nut arrangement... the studs are fully threaded but the interface with the cap body is insulated so it doesn't really matter where on the studs the nuts are tightened. I've used theses caps in other projects and they didn't always have the double nut, I'd guess some folks overtorqued the studs and destroyed the caps. Those caps are very low ESR and make a huge difference in tube amp/preamp power supplies in terms of dynamics and also eliminating grain. These caps and the output caps, and to a lesser degree some of the resistors used, can make the difference between a fairly ordinary sounding preamp and one that sounds amazing. As long as the circuit design is up for it, and this one is... the Aikido uses one triode as a load for the other so the non-linearities cancel and distortion is reduced without a feedback circuit, and power supply noise is also nulled at the output as well. It's a very low-distortion, low-noise circuit that sounds more solid-state than many SS designs, but you still get the many sonic advantages of tubes as well. Combined with using the Tortuga VC, this preamp sounds awesome...

 

[DaveC]

Looks well damped inside! Doing a similar thing to my DAC.

Yup, while it's debatable that it does any good with some components it doesn't take long or cost much...

 

[Joe Whip]

Not it doesn't but I have heard it improve the sound of an Oppo 105 and a Yggy.

 

[TBone]

Stunning work ... curious, why the different type rca's (input/output 1), to match a specific interconnect cable/rca?

 

[DaveC]

Stunning work ... curious, why the different type rca's (input/output 1), to match a specific interconnect cable/rca?

Thanks!

The in/out 1 RCA jacks are top end rhodium plated Furutech, I didn't want to spend the money on the others as I only have one source for audio... the others will be used for video and I don't care so much about sq with video. They are still pure copper jacks, just not the same level (or price) vs the Furutechs.

I've been really happy with the preamp, love having a remote control too...

 

[TBone]

The in/out 1 RCA jacks are top end rhodium plated Furutech, I didn't want to spend the money on the others as I only have one source for audio... the others will be used for video and I don't care so much about sq with video. They are still pure copper jacks, just not the same level (or price) vs the Furutechs.

performed a similar mod long ago, amps rca's, and certain pre (phono&cd in, output) plugs were replaced w/Cardas rhodiums to match my GHex5C IC's.

I've been really happy with the preamp, love having a remote control too...

some time ago, considered replacing the pot w/a relatively popular motorized version which uses an ALPs Blue Velvet, a fine pot, but not within this specific application ... but that said, although doing laps all night long is healthy, on those late/lazy nights, I often reconsider.

 

[ACHiPo]

Beautiful! I'm guessing they sound as good as they look.