• DC-coupled Foreplay - Saul P 10:57:03 02/16/05 (3)
  In Reply to: you're close posted by zarniwoop on February 15, 2005 at 15:44:48:

  OK, since I don't have the parts to implement the cap-coupled stage correctly yet, I gave a try at DC-coupling the Foreplay to the Ella. When measured with a DVM with no load, both the SRPP stage of the Ella and the Foreplay stage had a little less than 70 VDC on the outputs. So, I figured, why not? And, it seems that the sound is a little fuller, with more bass. I suppose this is because the 6sn7s are running a lot closer to their optimum. Anything I should watch out for here? It seems like there are probably circuit optimization issues to worry about... Any good sources of information to learn about this? Thanks,
  Saul
  
  

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  • Re: DC-coupled Foreplay - zarniwoop 17:25:45 02/17/05 (2)
    In Reply to: DC-coupled Foreplay posted by Saul P on February 16, 2005 at 10:57:03:

    You can use your preamp that way (DC to Ella 2nd stage), but the way I look at it, the stock 3 stage Ella is prefferable to using an external preamp (with 70VDC ICs). The attenuator and srpp stage does everything the foreplay does and its built right in. If you need more sources you could add those to the ella without too much trouble.

    Other things that may be interesting. I changed the 6922 stage to a 6cg7 (mini 9pin 6sn7 approximately), which I like better than either the 6922 or the 12au7. You can also hook this first stage up in several ways. Don't have to be limited to srpp, though its not bad.

    then you can improve the splitter/driver stage by forcing better balance with a constant current source. An easy way is using depletion mode mosfets in cascode. I like triodes for outputs, but you may have luck with the UL mode and no global feedback. I think I mentioned this before, but careful when you disconnect the feedback. If you disconnect it from OPT 2ndary side you will also disconnect a RC zobel network (.22uf +24R) that may be beneficial to sound when running in UL mode. Just my guess, but maybe someone can confirm..

    a pretty good designed PP amp, fwiw. Let us know if you come up with any big improvements. I guess nobody wants to try the interstage coupled version I drew up a while back.
    
    

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    • zobel on OT - mccormick 11:59:43 02/19/05 (0)
      In Reply to: Re: DC-coupled Foreplay posted by zarniwoop on February 17, 2005 at 17:25:45:

      I have to agree that the OPT seems have some high frequency ringing. In triode, it is there but not in your face as is UL. The zobel seems to help, don't recommend speakers with a flat treble response.

      I have considered the interstage trans., but do not want to put any more $$ into this amp. I did the P-P rewire not too long ago and am pleased with the sound. The resistors are on the sockets, the amp images better and there seems to be more detail. Also added another cap for a CLC power supply filter. Tried various changes to the SRPP stage as well.

      I might opt for a 2A3/300B project if I can find a speaker I like to mate the amp with. I seem to have an affection for 87db speakers.

      Mark

      
      
      

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    • Re: DC-coupled Foreplay - Saul P 19:29:44 02/17/05 (0)
      In Reply to: Re: DC-coupled Foreplay posted by zarniwoop on February 17, 2005 at 17:25:45:

      The Foreplay must sound pretty close to the SRPP stage, and the only real reason I wanted to try it is because I have the Anticipation CCS installed on that. The only other possible advantage is the larger chassis space to add stuff in. My ideal implementation would be to switch those CCS boards from the Foreplay to the phase splitter stage, but I seem to have lost the manual which details how to alter the CCS specs. Maybe its time for a post in the Bottlehead forum!
      Did you have to adjust many things in the first stage to convert to 6cg7?
      I think that I will be sticking with triode mode and no NFB for now, as my new Fostexes allow that.
      
      

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• Cool! - Saul P 21:48:38 02/15/05 (0)
  In Reply to: you're close posted by zarniwoop on February 15, 2005 at 15:44:48:

  This is exciting, my first foray into real circuit design. I think I understand what you are talking about, but I am going to do a little research to make sure and then try the circuit adjustments tommorrow. I suspected that it wasn't optimal, the sound is really sweet in the mid and highs but the bass seems lacking ( I first thought that was due to my new DIY Fostex's). I'll let you know the progress.
  Saul
  
  

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