[rajacat]

Those look very interesting.  They look small enough to fit in my Tortuga's case. I'd probably want to use the highest output tube available. Can't beat the price! More DIY, although it looks to be fairly simple.   Unfortunately, the Aikido board is out of stock.

[rajacat]

I'll make a picture later.

Thank you.

[Folsom]

Dave, current is required but voltage determines volume. If you divide the volume you have less gain, no way to change that with current.

[tortugaranger]

Those look very interesting.  They look small enough to fit in my Tortuga's case. I'd probably want to use the highest output tube available. Can't beat the price! More DIY, although it looks to be fairly simple.   Unfortunately, the Aikido board is out of stock.

Simple board and tube buffer conceptually. It's the power supply that can get a bit messy and matters depending on how you configure things. If all you want to do is buffer the feed going to the Crown then not so critical. If you plan on buffering the output of the Tortuga going to both MainAmp and Crown then: #1 - power supply becomes key,  #2 - you'll have an active zero gain tube preamp with an LDR attenuator (which is ok....just saying).

[DaveC113]

Those look very interesting.  They look small enough to fit in my Tortuga's case. I'd probably want to use the highest output tube available. Can't beat the price! More DIY, although it looks to be fairly simple.   Unfortunately, the Aikido board is out of stock.

I'm using this one:

http://glass-ware.stores.yahoo.net/acpcbocandus.html

It has the PS incorporated in the PCB and it's a very good PS imo. I'd just replace the final PS filter caps with Clarity TC caps mounted outboard and call it good. There's a variety of trafos that will work but I like a toroid for the HV and a dedicated 12,6 V filament trafo with a 30 sec time delay relay between the heaters and B+ supply. With 12V heaters you can rig a switch to do either parallel or series so you can use 6V or 12V tubes.

[tortugaranger]

I'm using this one:

http://glass-ware.stores.yahoo.net/acpcbocandus.html

It has the PS incorporated in the PCB and it's a very good PS imo. I'd just replace the final PS filter caps with Clarity TC caps mounted outboard and call it good. There's a variety of trafos that will work but I like a toroid for the HV and a dedicated 12,6 V filament trafo with a 30 sec time delay relay between the heaters and B+ supply. With 12V heaters you can rig a switch to do either parallel or series so you can use 6V or 12V tubes.

This is very similar to the tube based buffer design we've been slowly working on. Bipolar B+/- supply to 6SN7's and no input coupling cap. Working on taking this one step further using an op amp servo to null out any DC offset on the output and thus eliminate the big soul-sucking output coupling cap as well. The trade off for no output coupling cap is an output relay and DC offset sensing circuit to protect against DC spikes during startup or in case of PS failure etc. A pure straight through DC cathode follower tube buffer. 

[DaveC113]

I thought about doing that (DC servo), and I would if I were you for sure to avoid the cost of a good output cap. A good copper foil cap like Jupiter makes is pretty transparent and neutral but costs a lot of cash, too much for a commercial item that's trying to meet a price point. And some amps are ok with a tiny bit of DC offset but you have to know for sure!

One thing to spend money on is Clarity TC power supply caps, try them out and you'll be amazed.    The ESR is so low you may be able to use smaller values vs electrolytics. They are not cheap but the difference in performance is incredible.

[rajacat]

Would this provide a solution by converting RCA's to XLR and increasing the voltage to the amp?
http://artproaudio.com/artcessories/audio_solutions/product/cleanbox_pro/

[kernelbob]

Don't those volume controls defeat the key attribute of the Tortuga preamps?  The point of the Tortugas is that there are no switches or potentiometers in the signal path.  There are only two light dependent resistors in the signal path, one in series and one as a shunt.

[DaveC113]

Would this provide a solution by converting RCA's to XLR and increasing the voltage to the amp?
http://artproaudio.com/artcessories/audio_solutions/product/cleanbox_pro/

It says 100 ohm input impedance but I bet the "k" is just missing. If you used it just before the Crown amp you get ~10x gain and and a 10x higher input impedance, if so that would definitely help.

I'd probably go with Folsom's suggestion of using the amp's output padded with resistors to the Crown's input though.

[tortugaranger]

I'd probably go with Folsom's suggestion of using the amp's output padded with resistors to the Crown's input though.

I second that.

[Folsom]

Let me know if you have any questions. I did this, found it somewhere... Probably a flaw, maybe different values or whatever, but it worked great. Also twist your wires. This is just a diagram. You can also measure the voltage on them before plugging them in while playing music. If you see over 4v besides maybe a peak, you need more resistance. 2V should be fine at the gain for XLR and hopefully 1/4in, but for the RCA I'd hope to see a bit more, even double. These are all rough, you'll clearly know when you plug it in. 

[rajacat]

Let me know if you have any questions. I did this, found it somewhere... Probably a flaw, maybe different values or whatever, but it worked great. Also twist your wires. This is just a diagram. You can also measure the voltage on them before plugging them in while playing music. If you see over 4v besides maybe a peak, you need more resistance. 2V should be fine at the gain for XLR and hopefully 1/4in, but for the RCA I'd hope to see a bit more, even double. These are all rough, you'll clearly know when you plug it in. 

Great! I'll give this a try.
Thanks for your time.

[steve f]

Ed Schilling was the guy who came up with resistor loading to mate the Crowns that way. You can check the values on either his website Hornshoppe, or Bruce Rozenblits Transcendent Sound in the DIY section. Unfortunately, Ed is banned here so he can't directly reply.

steve

[Folsom]

Ed Schilling was the guy who came up with resistor loading to mate the Crowns that way. You can check the values on either his website Hornshoppe, or Bruce Rozenblits Transcendent Sound in the DIY section. Unfortunately, Ed is banned here so he can't directly reply.

steve

He didn't invent it. I assure you, I did this before Crown XLS existed. I got it from someone else. It's not rocket science... or beyond electronics 101.

[steve f]

LOL. Should I have written popularized?

[rajacat]

In case anybody's still interested , I've decided to use a tube buffer/active with the Tortuga for volume control.  My system is going to be active with separate amps for the tweeter, midwoofer and multiple subs. It's  too complicated to use a passive pre. because it severely limits my choice of amps and sources. I guess you can divide the voltage only so many times. I fooled around with the speaker level cable, resistor implant to the Crown with mixed results and since this is for the critical midwoofer, not a sub, I'd like a more straightforward implementation.

One issue I'd like to make sure I get right is the buffer vs. active choice. Do I need an active unit because of  splitting the voltage to multiple amps? The buffer adds to the current capacity but does nothing for the voltage. Definitely don't want to build a buffer and then find out I still can't power my midwoofer (AE TD15m) with the Crown or similar amp. I hope that the positive attributes of the Tortuga won't get lost with the addition of an active buffer.
It's unfortunate but I'll probably have to rebuild my nice enclosure so that there will be enough room to house the pre + the Tortuga. Fortunately, I have enough redwood to build an expanded faceplate. I'll reuse the side pieces but the top, bottom and rear panel will have to be replaced.
Now I'll have to decide which line stage to use. Dave, the Aikido kits look interesting. I'm open to suggestions as to which kit would be the most suitable for my application. The 12Vac PCB and parts kit http://glass-ware.stores.yahoo.net/aikido12vac.html might be the simplest to implement and I could use my Astron power supply. Of course, if Tortuga comes up with a buffer I'd be interested in that too.

[DaveC113]

I went with the ACF-2 kit, basically the last half of the Aikido... it also has a bipolar power supply so you can use a DC servo or an output coupling cap. The Jupiter copper caps are so good I just went with them instead of adding more circuitry. Also used the LV-Regulator kit to power the Tortuga LDR. The ACF kit is negative gain, it's a cathode follower so you lose a few dB. But if you're using a 2V source you should have enough voltage for any modern amp, most are around 1.5V. The Crown XLS is 1.4V. I have an Aikido and even using low-mu tubes it'll have 20 dB gain or 10x voltage, it's way too much for most amps. I'm going to retire it from preamp duty and just use it as a driver for my EL34s or other amps. I think there's a lot of merit to having a preamp doing the voltage amplification separately (with it's own power supply) from the power output section. The lack of standards has left tons of people with noisy systems because they have way too much gain...

I'm building chassis for the Tortuga, ACF-2 and LV-Reg combination... if you want one let me know, I'm already building two. They are awesome. 

I think, if you build the ACF with good parts that it'll sound better than without, but that's just my experience... My Aikido with decent but not totally top end parts had no problem keeping up with or beating a $10k Air Tight preamp at a friend's place. Mostly in the area of drive, dynamics and delivering a full tone. The keys are proper resistor selection, using film caps for the final RC filters in the PS, and good output cap or DC servo.

[rajacat]

The problem is that Mhdt DAC only puts out 1.8V. Next it goes to the Tortuga where it is split to the compression driver tweeter amp, midwoofer amp and it sends low level to the sub amps. A source that outputs greater than 2.5V would sure make it easier to integrate my active system. This is the problem with a multi amp system. You're limited in your choice of amps and sources.

[DaveC113]

The problem is that Mhdt DAC only puts out 1.8V. Next it goes to the Tortuga where it is split to the compression driver tweeter, midwoofer and it sends low level to the sub amps. A source that outputs greater than 2.5V would sure make it easier to integrate my active system. This is the problem with a multi amp system. You're limited in your choice of amps and sources.

That'll still work for almost any amp. You could go with a 2:1 output trafo rather than a cap but good ones are expensive.