mr.pee1 Posted July 28, 2016 Share Posted July 28, 2016 My friend built me a Dynaco st 70 with three 12at7 s driving kt77s . Any one have thoughts on a preamp ? I am using La Scala's. 1 Quote Link to comment Share on other sites More sharing options...
tube fanatic Posted July 29, 2016 Share Posted July 29, 2016 If your source has variable output, connect it directly to the amp and it should work fine. Alternatively, you can use a passive line stage if you need more than one input. Keep the interconnects between the passive unit and amp as short as possible. This one works well: https://www.amazon.com/Schiit-Audio-SCH-13-Passive-Preamp/dp/B00K6Q2A4C/ref=sr_1_1?ie=UTF8&qid=1469793784&sr=8-1&keywords=schiit+passive+preamp Maynard 1 Quote Link to comment Share on other sites More sharing options...
mkane Posted August 4, 2016 Share Posted August 4, 2016 http://www.enjoythemusic.com/diy/0611/slagle_autoformer_volume_control_modules.htm Quote Link to comment Share on other sites More sharing options...
NOSValves Posted August 4, 2016 Share Posted August 4, 2016 If the 3 -12AT7 front end is the one I am familiar with you'd be better off using a passive if you're not going LP's. Is there and name printed on the circuit board? Quote Link to comment Share on other sites More sharing options...
erik2A3 Posted August 4, 2016 Share Posted August 4, 2016 Another possibility is to install a volume control directly on the amp chassis, itself, which I have done in the past on the Dyna 70. There are a couple of ways of doing this, though slightly different depending on whether or not the grid leak resistor on the input to the first stage (which establishes the input impedance to the amplifier) is kept or removed. However, if you have more than one source, one can very easily make a simple switch box that switches two or more sources between a single output. For some reason I always find the majority of variable ouputs on digital sources to be sonically inferior to fixed line-level outputs. That's just my experience, though, and if there is one constant in this hobby it's that it's all completely subjective in terms of what sounds better or worse than something else. This essentially is the passive attenuator to which both above posts from Maynard and Craig refer - I'm in complete agreement with them. An onboard attenuator is also an effective way of variably knocking the gain down a bit if one insists on using a high ouput active line-stage. I performed this exact modification to a Dyna 70 (along with a pair of Heresy IIs) I gave my dad several years ago. He HAS to keep his linestage preamp because of the need to boost HF response as much as possible, but complained about the lack of volume control rotation on the preamp. The slight clockwise nudge was WAY too loud. I drilled a carefully placed hole on the deck of the amp, installed the pot he had on hand (he is a tube electronics wizard who taught me to solder when I was 5) and ran the inputs to that. Problem solved. Quote Link to comment Share on other sites More sharing options...
mr.pee1 Posted August 4, 2016 Author Share Posted August 4, 2016 I don't have the amp yet , he is running it to see if all is ok. Oh it's not kt 77s they are 6550 Russian . I will ask him who made the driver board, it was stuffed when he bought it. He went ss rectifer , the 5ar4 is lit but not being used as is the can cap . He has built 5 st 70s. Quote Link to comment Share on other sites More sharing options...
mr.pee1 Posted August 9, 2016 Author Share Posted August 9, 2016 So the Dynaco st 70 is setting there all lit up , and the audio seems "smoother" ? I have not listened a lot yet because my wife is home for a while, and she dosnt like my music. Quote Link to comment Share on other sites More sharing options...
mike stehr Posted August 10, 2016 Share Posted August 10, 2016 https://community.klipsch.com/index.php?/topic/157192-stepped-attenuator-level-control/#comment-1887544 Quote Link to comment Share on other sites More sharing options...
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