Tube pre with SS HT

Yogi · 03-24-2003, 01:48 PM

Well finally I was able to integrate a cheap tube pre (2ch) with my SS HT gear. The tube pre was an ASL2004DT integrated with a Denon 3802 hooked to a Proceed AMP 2 for the mains and a B&K Ref7250 for the rest. The speakers are all Vienna acoustics. Out of the box the tube pre sounded fantastic with clean highs and taut bass and a lush midrange. The real kicker came in when last weekend we were watching a DD movie in 2 channel via the tube pre and on a restaurant scene my wife tells me that it looks like the neighbours are having a party since she can hear their music play. I too thought the same until I paused the movie and the neighbours music went away. And we both were wowed by the immense soundstage this preamp was projecting considering that our nearest neighbours home is about 100 feet away. The soundstage was completely three dimensional and extending beyond the physical speakers. I am a tube believer now. No questions.

There is however a problem. Just for kicks I cranked up the preamp all the way and although I couldnt hear any distortion the sound broke up during heavy transients. I listened to some classical scores and when ever there was a drum beat I could hear a crackling noise. I always believed that tubes never go into hard clipping and always distort gracefully so that is something that didnt make sense to me. Whats more baffling is that I hooked up the tube pre directly to my Tape and MD player and I couldnt hear any crackling at any volume level on my preamp. So it baffled me as to why this problem was source dependent. I also tried some higher quality interconnects and while the crackling is reduced to a minimum it still is there on transients. I only have two explanations for that.

1) Either the tubes are defective or highly microphonic.
2) Or there is some kind of impedance mismatch between the source DVD player and my tube preamp. I am thinking its the later as the DVD player is supposed to output 2V RMS and my preamps input impedance is 100K. since I dont know the output impedance of my DVD players analog outs I am only assuming that its in the 10K range, which means my tube pre is seeing almost 20V at its input and on heavy transients some of the internal components are getting saturated leading the the crackling sound. Does that make sense? Any expert opinions on this? I have a set of new tubes ordered so I'll be able to check for tube defect and microphonics tomorrow.

Any input would be greatly appreciated.

Chu Gai · 03-25-2003, 02:44 AM

How exactly do you have your system hooked up Yogi?
I'll just offer the following general comments. I think you'll find the distortion characteristics of tube preamps to be different from tube amps. As you get into saturation and hence distortion with the preamp the sound tends to get buzzy, or gritty sounding. It seems to lack dynamics if you will. Tube amp distortion is entirely different. We might be talking about the same thing. So just back off the gain on the preamp. Another thought Yogi, and you'd really need the vendor to give you the info on this (assuming they can since I believe they're primarily importers), is that you just might have a preamp whose distortion characteristics are not only non linear with gain, but result in odd-order (3rd I'd guess) harmonics.
On the other hand, the output of your preamp is on the order of 10 volts, fully cranked. You just might be giving headaches to your amp which has an input sensitivity of 1.6 volts for full output. I've no idea what the output impedance of your tube preamp is but i'd suspect it to be on the high side. Ever thought of giving that Behringer a try that Brett's been messing with? Less than 1/2 the price of those ASL's!

Yogi · 03-25-2003, 08:31 AM

I have the DVD players analog outs going to the 2004DT's inputs and its output going directly to the external inputs of my 3802. The 3802's preouts are going to the Proceed amp. Whenever I listen to music I put my 3802 in ext-in mode. That way it just acts as a straight gain without any DSP. I dont know the output impedance of my 2004DT

Chu Gai · 03-25-2003, 09:28 AM

well then if the 3802 is being bypassed entirely so that it's passing the signal of the tube through unscathed, then it sure sounds like you're overdriving the amp. maybe you'll bounce your findings off of ASL and see what their position is.

Yogi · 03-25-2003, 09:39 AM

I dont have an email for ASL but I did shoot off an email to Divertech (their NA distributor) and still havent heard a thing from them. You might be right I might be overdriving the amp.

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Chu Gai · 03-25-2003, 10:07 AM

well it's potentially over 5x the voltage needed for the amp...something's got to give!

Darrel McBane · 03-25-2003, 10:30 AM

I've been thinking of adding a 2 channel tube preamp into my system for about a year or more. I've had my eyes open on Audiogon for a VTL 5.5 preamp. I just love the sound of this piece. I'm not sure how it will match up with my Revel F-30 and Rotel 1090 SS amp. I've seen several come and go through Audiogon and their has alway been some other HT piece of equipment that has steered me away. But, I added two of the last piece into my system recently ( Aragon Stage One and Sensory Science OTA HD receiver) and this may be the year I pick one up. Then a decent turntable so I can play the vinyl LPs I've had in my closet for the last 15 years.

Good to hear your impressions of adding a tube preamp to a HT setup.

Scott_N · 03-25-2003, 11:55 AM

You could also look for a Rogue Audio Magnum 99 a Cary SLP-2002 or a Audio Research LS16. All solid tube preamps in the same price range. Myself I want a Cary SLP-98L and Cary V12i combo.

Ricky T · 03-25-2003, 12:08 PM

Darrell,

I use a Rogue 66 magnum tube preamp with HT bypass unity gain with my NHT 3.3s and Parasound 2200II amp...love it! You can even buy a used Rogue 66 (magnum or non-magnum) on audiogon and send it to Rogue for the $150 HT bypass option.

Yogi · 03-25-2003, 12:58 PM

I actually had been thinking about the Rogue 66 or 99 (or CJ PV14) as my next upgrade. Actually it would be a completely separate 2 ch cd/sacd music setup with Vienna Acoustic Beethovens (I luv VA speakers and dont want to change to another brand). I would then move my Proceed amp to this setup. I dont want to go to tube amplification as I feel there are somethings better left for transistors to do

I will then get a separate B&K 2 ch amp for my mains. I would still keep the 2004DT for my two front channels in the HT setup to soften some of the harshness in digital movie tracks. But all this not for another few years (hopefully). Untill then its 2004DT for my music and HT needs. I just got some new tubes for it and I cant wait to get home to do some tube rolling

.

Martin Rendall · 03-25-2003, 01:07 PM

When you say "external inputs", are you referring to the 5.1 (or perhaps 7.1) direct inputs?

So your chain is:

DVD Player -(RCA)-> ASL2004DT -(2 of 7.1 direct inputs)-> 3802 -(preouts)-> Proceed (yum, by the way).

If you replace the DVD player with another device, you don't get the distortion? Are the speaker volumes comparable? Do you have an SPL meter?

OK, regarding impedences. Impedences should be at least an order of magnitude greater as you go from source to target. More is even better. So, the DVD player will have a low output impedence (around 600ohms?), while the ASL2004DT has a 100K input impedence. This is actually very optimal. I have a DIY tube pre I use with a CD source (and tested with a DVD