yaffstone Posted October 23, 2005 Share Posted October 23, 2005 I just got a Dynaco ST-70 in original shape. Plugged it in and listened for a while. Not bad but not good either. It had a humm in both channels, a bit muddy, and just not any better than the solid state unit I was hoping to replace. So... I replaced the original 7199 driver board with a VAC all triode design and auricaps. New EL-34 driver tubes, new GZ-34 rectifier, and finally a Curico quad cap replacement board. The unit now sounds awsome on the K-horns. Detailed, punchy bass, really warm. Now the question: If I shove my ear in the tweaters I can still hear a slight hiss. Is this residual from the GZ-34? I could hook up the diode rectifier on the Curico board, but I'd have to loose the GZ-34 and I hate to have an empty socket on the top of the amp. Any suggestions? I could just stop being rediculous, turn up the sound and listen happily, after all, how many hours can one hold their ear to a horn with no sound but a slight hiss? Thanks, David Quote Link to comment Share on other sites More sharing options...
33klfan Posted October 23, 2005 Share Posted October 23, 2005 I have no experience with that amp or any tube amp for that matter, but i'll tell u one thing, if u have to shove ur ears into the tweeter to hear the hiss, then that's normal. Any electronics with speakers hooked up, u will hear a slight hiss. If u can't hear it from listening position when it goes from song to song then it's ok. Klipsch are sensitive so they can produce more hiss because of their sensitivity. My speakers make a hiss under stereo. It's fine. Quote Link to comment Share on other sites More sharing options...
sfogg Posted October 23, 2005 Share Posted October 23, 2005 David, If you have to be right up to the tweeter to hear the noise don't worry about it. Just about all amps. have some amount of hiss to them. Shawn Quote Link to comment Share on other sites More sharing options...
NOSValves Posted October 23, 2005 Share Posted October 23, 2005 A little hiss with you ear up to the speakers is 100% normal! Play some music and forget it. If anything the SS rectifier would make it worse by the way. Also It would also be much harder on your tubes. Craig Quote Link to comment Share on other sites More sharing options...
Daddy Dee Posted October 23, 2005 Share Posted October 23, 2005 Congrats on the rebuild and upgrade. You've got a fine amplifier there. How about some pics? Quote Link to comment Share on other sites More sharing options...
garymd Posted October 24, 2005 Share Posted October 24, 2005 Agreed. Some hiss is normal. My SYSTEM has a slight hiss and you don't even need to shove your ears up to the tweeters to hear it. Sit back and enjoy the tunes. Quote Link to comment Share on other sites More sharing options...
NOSValves Posted October 24, 2005 Share Posted October 24, 2005 Gary, You need to rephrase that. Your system has a hiss and you don't need to have your ear up to the speaker to hear it. I bet if you unhooked all associated components from the Mark III insert some shorting plugs to illiminate stray RF sneaking into the open RCA jacks you would indeed have to stick your ear up to the tweeter to hear a thing. A small amount noise in a high resolution system is the nature of the beast Tube or SS. Craig Quote Link to comment Share on other sites More sharing options...
garymd Posted October 24, 2005 Share Posted October 24, 2005 Gary, You need to rephrase that. Your system has a hiss and you don't need to have your ear up to the speaker to hear it. I bet if you unhooked all associated components from the Mark III insert some shorting plugs to illiminate stray RF sneaking into the open RCA jacks you would indeed have to stick your ear up to the tweeter to hear a thing. A small amount noise in a high resolution system is the nature of the beast Tube or SS. Craig Better? Yes, it's the ENTIRE SYSTEM, not just the amps that cause some hiss. Quote Link to comment Share on other sites More sharing options...
Guy Landau Posted October 24, 2005 Share Posted October 24, 2005 Better? Yes, it's the ENTIRE SYSTEM, not just the amps that cause some hiss. It's probably caused by these cheap resistors that Craig uses in his rebuilds [] Quote Link to comment Share on other sites More sharing options...
Allan Songer Posted October 24, 2005 Share Posted October 24, 2005 And all those old commie parts too. Remember when Communists were the "enemy?" Oh, how I long for those days . . . Quote Link to comment Share on other sites More sharing options...
Audio Flynn Posted October 24, 2005 Share Posted October 24, 2005 And all those old commie parts too. Remember when Communists were the "enemy?" Oh, how I long for those days . . . My once a month oppurtunity to agree with Allan. A little bit of hiss to me means the speaker is pretty high resolution, if source aand amplification are above average. My tube system is not the end all for bass weight and control (maybe just a bit "bloomy") but the "black quiet background" between CD tracks is amazing. And soundstage is far superior to any SS amp I have owned. With a trip to a qualified technician the ST-70 should get even better. Quote Link to comment Share on other sites More sharing options...
jrt Posted October 24, 2005 Share Posted October 24, 2005 put some shorting plugs in the amp- if the hiss goes away, it's the preamp (or earlier). A slight hiss is pretty normal, though. Quote Link to comment Share on other sites More sharing options...
yaffstone Posted October 24, 2005 Author Share Posted October 24, 2005 Thanks for the notes. I figured I was being overly critical. I got home tonight, turned on the system and couldn't hear a thing from my usual chair. Absolute silence. Now Wayne Shorter is playing and it's just great. Quote Link to comment Share on other sites More sharing options...
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