Passive Line Drive or Tube Preamp?

voltz

I recommend a Brimar Rectifier. maybe H9 has a spare?

mikeyb128

Brimars and super sweet, and don't get enough attention. Maybe that's a good thing. I have 2 brimars in my cary pre right now

jdjohn

It's great that you guys have already done all the research on the best (or most recommended) tubes I'm looking into the Brimars. It is very interesting to me how some of these old tubes originally made for military purposes have found a use in modern audio amps.

heiney9

The Brimar and perhaps a Bendix 6106 are the go to rectifiers by a lot, so don't mess with anything else.

I still have a small stash of tubes for the Dared, I might have something for you to get the rolling started.

I have (1) of the Brimar's left, but I'm keeping it. They are plentiful, make sure to get the coke bottle type with the waffle looking plates (holes). Those have the best tone vs. the short bottle type.

Be sure and buy some De-oxit cleaner and always clean the pins (before you use them) when you get tubes . It makes a world of difference. Once cleaned they don't need to be cleaned again for awhile. They may look fine to the naked eye, but.....

H9

jdjohn

Thanks, H9. I will procure a Brimar on my own, and just let me know via PM if you have any extra tubes to sell.

I received a message from the seller of the Dared with tracking info, but also some warnings about how sensitive the Dared is to grounding issues. Here's the message (I think English is his second language, btw):

"For tube SL-2000a preamp, someone may experience hum if house power outlet has ground loop issue. Please make sure your ground is correctly. Do not ground the preamp if your amp or CD player is grounded, and use sole outlet only. Plug your preamp to a power outlet without sharing with others. Use a power cord without ground pin or use an adapter to block the ground pin. Do not any power conditioner, etc such to plug into this preamp.

Tube preamp specially SET class-A tube preamp like this one is very sensitive to ground loop.

In your audio chain--- say: CD player --> preamp -- power amp. There is only one need to be grounded. If either your CD player or power amp is grounded, then you shall not ground the preamp."

My current setup involves just one outlet, with the McCormack plugged into one socket, and a Chang Lightspeed power conditioner plugged into the other socket on the outlet. I was planning on plugging the Dared into one of the sockets on the Lightspeed, but he specifically warns against that. Do you guys agree with the warnings, or have other advice? I could use a two-prong adapter to bypass the ground pin on the Dared plug if deemed necessary.

Now I know most of you probably have dedicated 20amp circuits with multiple outlets for your gear, but obtaining that in my case would involve removing stretches of drywall, so not practical. I could probably install a second outlet on the same circuit, right next to the one I have.

heiney9

I never had a single issue with my Dared. Mine was an earlier one with the nicer Auricap coupling caps.

I know some did have some issues with hum. I'd say cross that bridge when/if it happens as it seems to be system specific.

H9

heiney9

The only 2 minor annoyances I ever had with the Dared Sl2000A were the gain was too high (for my rig) and it's very hard to modulate the remote volume. You really have to practice to get it to go up and down smoothly.

I lived with it for awhile and ultimately I moved the Dared along because of the gain issue.

H9

Nightfall

Yeah the remote doesn't do small volume adjustments, don't hold down the button it will go up QUICK.

I haven't had any hum issues with mine either. All of my audio equipment has a ground plug and it's plugged into a strip, no choice on that. I have 8-9 things to plug in and only 4 outlets, the AVR and amplifier get their own outlet, everything else is on a strip.

jdjohn

I got the Dared...and it has hum. It's only in the left channel, though. I've tried two different speakers (and cables), two different power amps (and interconnects), different input sources (turntable and Squeezebox), but there's hum in the left channel each time. From my searching, it looks like a couple more folks here and elsewhere have had unresolvable hum issues with this Dared model.

I have some better tubes on the way, but I am doubtful they will fix the hum. It's really a shame because the sound is very nice in general. The hum is not noticeable while playing since the music drowns it out, and it doesn't go up with volume, but I know it's there since it reminds me during quiet passages and when the volume is down. Luckily there is a 14-day return policy if I can't get it figured out.

JPete

Good luck with it Jody. I've been contemplating a trial with a tube pre myself. If you get the hum sorted let me know how it sounds with the McCormack on those SDAs, yeah?

Nightfall

You need to experiment with ground delete plugs, not speakers and amps.

Nightfall

https://www.amazon.com/GE-14404-Polarized-Grounding-Adapter/dp/B00B7PK1TC/ref=sr_1_1?ie=UTF8&qid=1470344494&sr=8-1&keywords=cheater+plug

heiney9

Do a search as others have had this issue.

Nightfall

This guy reduced hum by putting a tube buffer between the preamp and amp.

http://forum.polkaudio.com/discussion/140043/sending-dared-sl2000a-in-to-repair-hum/p1

jdjohn

Thanks for the ideas, guys. I just wanted to try different speakers and amps as a process of elimination. The seller had noted that a grounding adapter might be needed, and that is my next step.

I did do some searches and found that thread where he used a tube buffer. Before trying that, though, he had even sent his preamp to a tech recommended by Dared, and that didn't help much, so eventually he got to the point of trying the tube buffer. But honestly, I would return this and buy a different/better tube preamp before spending the extra cash on a tube buffer...not to mention it adds another component in the signal chain. Ya know?

Hopefully the grounding plug adapter will help. In my reading, it looked like many folks just decided to live with the hum.

I got my pair of Sylvania Gold Label 12AT7 tubes in the mail today. Hoping things will come together!

jdjohn

A little update: The grounding plug adapter really helped with the hum...actually got it to an acceptably low level. The system has a really nice sound now, but maybe a touch grainy, possibly needing more burn-in time for the stock tubes (although it was a demo unit). But when I put in the Sylvania tubes, the hum comes back with a vengeance. These were sold as used 'low hours' tubes, so I'm doubtful that additional burn-in will help. They have a 30-day money back guarantee, so I guess I will be sending them back and try a different pair. My Brimar rectifier should be arriving today, so we'll see how that goes.

Do 'better' tubes reveal weaknesses like grounding issues more than the cheap Chinese tubes? Or do you think these Sylvania tubes are just bad?

heiney9

Wait until you get the Brimar. That Chinese rectifier is crap. The Sylvania's may have more gain than the Chinese tubes. The Sylvania's are excellent and would be rare to have them be faulty. But you never know how the previous owners treated them.

I'll send you a PM I have a pair of Siemens tubes for you, for cheap.

H9

jdjohn

Thanks for the PM, H9...very generous offer

The Brimar rectifier did help with the hum, I think. Interesting that it has five pins instead of four like the Chinese tube. I have now discovered the big gain the Dared has which you guys have mentioned. I didn't notice it when using the SqueezeBox since I kept the gain on the SB at about 33%. But when I hooked up a turntable last night, the gain issue presented itself very quickly! Adjusting the phonostage gain down to 40db helped, but still the Dared could only go to about 9 o'clock before getting too loud.

One solution I have is considered heresy in the audiophile world, but nonetheless, it involves using an EQ. I have a Behringer FBQ1502 graphic EQ that has adjustable defeat/gain, so by putting it inline between the Dared and the power amp, I can defeat the Dared's gain. Again, I know this isn't optimal, but IMO it is an example of how EQs can be helpful in certain situations. I still have a window of time to evaluate the Dared before the return policy runs out, so will have to see.

Having said all that, I do have an impression now of the sound using a tube preamp with the McCormack DNA. Jeremy, listen up IMO the biggest difference (at least with the tubes I am currently using) is the upper mid-range. The frequency curve has a significant bubble in that range for me and my setup (SDA-2Bs). It brings out details in that frequency (and there are many) that I never noticed before. With pure SS electronics, the frequency line is pretty flat and neutral on its own, at least with my rig. That's not necessarily a bad thing, but in order to hear those same sounds in the upper mids with SS, I would have to turn the volume way up, which of course would increase all other frequencies as well. With the tubes, the bass is more refined and detailed, but not as punchy or full. I'm sure this could change with other tubes, like maybe the Brimar 12AT7 Black Wing Plate O-getters...or so I have read. So in my limited experience with this setup, if you want to hear those mids really come alive, and don't necessarily *have* to have window rattling bass, the tube sound fits the bill. Again, the bass is detailed and lively, just not physically pounding.

Another impression of mine with the tube preamp is the cleaner sound at higher volumes. IME, I can turn up the volume higher with tube moreso than with SS, and it doesn't necessarily sound *louder*, but cleaner. But be prepared, because with strings on acoustic guitars/violins/mandolins/etc at the higher volume, that resonating steel string can pierce through your body right to the bone. You can envision the guitar pick or fingernail plucking, or the bow being dragged across. And with drums, you can picture the drum head or baffle pulsing, or the pillow inside a kick drum sliding around as John Bohham does his thing on The Ocean. Of course you have to listen pretty hard and maybe close your eyes, but you get the idea Usual disclaimers apply: IMO, YMMV, etc.

jdjohn

Ok, well I probably lost you guys once I mentioned an EQ, but anyway, I ran across this review mentioning the Dared SL-2000A at 6moons.com, and the reviewer had the same hum and high gain issues, but found a fix.

Here's an excerpt:

The Dared SL-2000A is perhaps the best tube preamp in the $500 category - with wooden remote control no less. In my Dared VP-20 review I pointed out that the gain of this preamp is too high to match the partnering VP-20 and produces audible hum unless the volume on the VP-20 is dialed down to mid position. Ever since then I sought advice from a technician and reset the gain of the SL-2000A to an universally acceptable level while the S/N ratio was further improved by replacing the factory 12AT7s with low noise 12AX7s. (Good 12AT7 are expensive but inexpensive 12AX7 are good!) Not only could the Dared SL-2000A now match my VP-20 to perfection, it became my favourite tube preamp. When added to the TA-10 bi-amp with battery power and coupled with the Klipsch Synergy F2, music was warm, passionate and involving. Soundstage and presence were 100% reminiscence of the La Scala.
Full article is here: http://www.6moons.com/audioreviews/trends/ta10_3.html

I tried to email the reviewer for more details, but it bounced back since I think he is no longer with SixMoons. I wonder how he 'reset the gain', and also what is involved in switching to low-gain 12AX7 tubes. Surely it's not just a straight swap...or roll?

heiney9

Yes, I would talk to a reliable tube technician to see what can be done. Not sure if anyone can help. If it's not working sufficiently in your rig because of the gain issue you might just have to chalk it up as not working well together.

Increase your budget and by the EE Mini Max .

You can't use 12AX7's unless the circuit is modified. I remember reading that review but 12AX7's have a higher mu than the 12AT7, so they have even more gain. I also don't agree with "inexpensive 12AX7's are good".

You can try a 5965, but the long plate structure almost always has some degree of microphonics. I was able to tame them with tube dampers, but honestly the gain wasn't that much lower.

Another problem is there is no room to work in that chassis, so that's another negative to finding someone willing to take it on. It's a good little unit but perhaps isn't compatible with everything on the planet.

Good luck.

H9

mikeyb128

Send it back. Buy the mini max. Lesson learned, we've all been there.