AudioNervosa
Systemic Development => Amplification and Preamplification => Topic started by: Bigfish8 on December 05, 2009, 04:33:59 PM
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Guys:
Many of the local Raleigh Group have heard Sol Samet's I-60 amp in its stages of development. Well, I have to report that I heard it again today driving Richidoo's Usher BE-20 speakers. Since I last heard it a couple of weeks ago on my speakers Sol had made a couple of tweaks to the amp. When he first connected it and played several tunes on it today it had excellent bass control and a very detailed top end. However, I personally thought it sounded too lean in the midrange. Sol took the amp upstairs to the work bench, removed and soldered in some different parts. When he brought it back down for another audition. Wow! :thumb: All of the bass control and detailed top-end was still there and there was a full, beautiful sounding midrange. There was absolutely no distortion that I could hear - it just made beautiful music.
I am looking forward to hearing the I-60 drive my Usher Dancer Mini II's again with the latest modifications. I hate to admit it but I feel quite confident it will put my Odyssey Mono SE's and Mapletree Combo to shame. I especially think that will be the case with the ModWright Transporter, with it tube output stage, as the source.
Sol, how much are you going to charge for these little packages of dynamite?
Ken
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Thanks for the critique Ken. You and Shane are hard to please so I'm glad to hear you were able to dig it.
After you left he changed just the model series of cap, within same brand, same size and voltage to eliminate the last trace of edge on violins and brass, cymbals, 4k breathy vocal stuff. Smooth as silk now but still extremely detailed, alive and exciting. It's amazing to see the amp come so far since the first time we heard it more than a year ago. Can't wait for everyone to hear it.
We'll do a batch of PCBs next and build a couple prototypes for interested parties to give us some feedback.
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Sol came over today to work on the i60. He changed a resistor value that helped stabilize the bias current better, then we listened to a bunch of current settings. It was very surprising and eye opening the results. Bias started very high, so we kept turning it down and it got better. We finished with our jaws on the floor and a cooler amp. Tomorrow we'll go at it again, swapping in some output transistors that we've tried before, which may work better now with the other changes that have happened since. We also want to try to use computer sound card based distortion analyzer to see the spectrum of the distortion. If we can get it to work I will post the graph. That will be cool!
I am entering the schematic into the PCB software so we can start laying out the PCBs in the next week or so.
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Well first off good luck with this project. Souds like fun. SS, tubed, Hybrid ?
charles
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Thanks Charles. It is all solid state. A single pair of output devices per channel makes a very conservative 60W@8ohms.
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Single ended SS. Cool. As you know the output device choice is a big part of the final sound. I wonder what darTZeel, MBL or Pass uses.
charles
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It's push pull class AB. :-$
Yes, the output device makes a big difference, just like with tubes. And the bias has a big effect too. We tuned the bias a little more yesterday, the amp sounded perfect, magical. Then we took it apart to try some other output transistors, lower distortion, clearer and even more transparent, but not magic. So I think the i60 design is mostly finished now and will make some people very happy when they hear it.
Pass uses MOSFETs for now, they probably will switch to powerJFETs eventually. I don't know about DartZeel and MBL.
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make sure it has remote volume ;)
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richidoo, Any chance of Sol coming on AN and responding to questions. I am a little confused by your description of the I-60. It is unclear about how the amp operates. Is it single-ended or push-pull? Also is the front-end current mirror loaded and does he use active current sources? Inquiring minds want to know.
Scotty
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Scotty, It's push pull, not single ended, single pair per channel. He does use active current sources. I will ask Sol if the front end is current mirror loaded. When it is released for sale we will describe conceptual details more thoroughly. We will have an Audio Nervosa demonstration tour also.
Sol is determined to keep the base cost low so the 20-something crowd can afford it. But there will be several options available, including remote control. Thanks for the suggestion Shane! I'm with you on that one. :thumb:
Rich
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Scotty, The I-60 front end is mirror loaded. Class A buffer to Mirror Loaded Diff Amp to Vas to output stage. The Vas runs with high current instead of more transistors to add current gain in the output stage.
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It sounds like a pretty good design on paper. By limiting the output to 60 watts you can use lower voltage transistors in the front end which is a good thing. As it happens most of the best sounding transistors are lower voltage ones. This is one of the reasons that higher powered amplifiers suffer when compared to lower
powered amps from the same mfgr. My new amps development was held up by a lack of good sounding bipolar transistors to use in the diff pair of sufficient voltage to allow 110 watts/ch @8ohms.
Scotty
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Is this a dead project, or did I miss some new info?
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The design continues to evolve. It had a major change a year ago, went from 3 stage to 4 stage amp. I used it for a while, now it's back with Sol who is making some new minor updates. Bigger local decoupling caps and trying some new output devices with built in tem sensor that would be easier to mfg than T-03. No real progress towards commercialization.