AudioCircle
Industry Circles => Empirical Audio => Topic started by: audioengr on 1 Apr 2004, 11:23 pm
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I promised to update the readers on the progress on this mod, so here we go:
The mod is working well. The only feature that I have disabled is the level meter LED's on the front panel. The path is down to three op-amps and the gain is similar to other amps. All of the AC-coupling has been eliminated, except for that to the Tripath module. The only complaint that I have is the hiss, which is louder on this amp than others that I use, even stock. It seems to come from the Tripath module itself. There is a small pop or thump on power-up as well. The DC offset is -.75 mV RMS on one output and about +12 mV on the other output. Both acceptable. The Papst fan is quieter than the stock fan, but still audible with the top cover off. I am using the speed-control version and directing it out the back, opposite of stock.
For the last mod, I replaced the output inductors with air-core types that I use in crossovers etc.. and this make a HUGE difference. This thing is really musical now. Still not quite up to my reference amp, but getting close. One more inductor change might do it.
I am trying several types of air-core inductors. The problem is: they are getting VERY hot after only 1/2 hour of music playing. Seems like I need an inductor with in integral heatsink. I have contacted the manufacturers to see if they can help. It makes sense that these inductors are stopping more of the RF and thereby turning it into heat.
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Steve, seems you have renamed the ZR-1600 to the ZR-1200. I assume this was a typo or is there some reason? :)
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Just a typo.
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Fixed :wink:
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Did you duplicate the stock value of the output inductor, 11uH, and if it is larger what is the new filter pole. The original pole is 80kHz,12db/oct,
before the addition of staggered networks which appear to be Carvers work. Have you confirmed that the amp is not oscillating at RF frequencies
as this will also heat up the output inductors and mosfets. With the new output inductor in place is the amp still flat to 20kHz without loudspeaker load interaction that would alter high frequency response characteristics.
The pop at turn on is a result of the mute line not being properly toggled
[slow turn-on,quick turn-off]. The hiss is a mystery, my DIY Tripath based amp has no hiss problems, even with the 96db efficient speakers in my system. I don't think the hiss is intrinsic the the module. Good luck with your mod, getting rid of the extra parts in the amp looks like a real challenge. According to Tripath the toroidal shape of the original ferrite inductors was also chosen to suppress RF radiation as well as having low DCR,other inductor shapes are much worse radiators of RF. Some sort of shielding may be necessary around the new inductors.
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how does this amp compare to aragon 2002, i'm auditioning one right now and i like the tight bass of the 2002, the highs are much better than my hk 7200 receiver, cleaner and more involving to listen to.
my pricepoint is around ~$1000, is that close enough to a modded zr1000?
thanks,
angelo
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The amp is around $700 new and the mods will be around $1500.
I am not changing the filter poles, but I did remove one pole completely. This may be the reason for the hiss.
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Steve seems to be near completing the mod on the ZR-1600. He has corrected the hiss coming from one channel and seems to have eliminated the popping on power up. The wife gave him the thumbs-up on sound quality. His last e-mail to me was "very promising indeed!"
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I have found that it is very difficult to probe anything in the chassis with a scope. Even with 0.5" scope ground stub to the board, the noise pickup is several volts AC squarewave. The electric fields inside must really be intense. Not sure I like working on a powered-up unit - kind of like sticking your head inside a microwave oven....
I have also discovered that the hiss is mostly due to the intense fields and funky power delivery. I am devising ways to break-up the ground-loops and isolate things.
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audioengr - any updates :)?
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Hi AE, Thank you for the advice on the Jensen line transformers! My 1000 is now stone cold silent with the mains ground intact, non-lifted and safe. Granted, this isn't what you're dealing with, but may be a great boon to others not going after the ultimate mods. http://www.markertek.com/SearchProduct.asp?item=JEN%2DCI2RR&off=2
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Gordy - can you update that link or list the cataloge number? The link didn't work.
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Hi Chris, try this one http://www.comtran.com/ Click on distributers and then Markertek, they have the stereo CI-2RR-RCA or XLR's discounted from $170 down to $120. Use as is or better yet, remove 'em from the casing and install where the input board was. Hope this one works for you...
Gordy
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Latest ZR1600 mod update:
The hiss is under control now and the sound is approaching my reference amps. I have a few more parts on order to try. The fan cannot be unplugged - gets too hot. I have the variable speed Papst installed - it buzzes like a bee even at low speed. Very irritating with the cover off - better with it on, but I can still plainly hear it between tracks. Have the single-speed Papst on order - I may need to ratchet this one down as well. The current inductors still get hot, but they can still be touched, so they should be okay. I will be mounting heatsinks to the final versions.
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Latest ZR1600 mod update:
The hiss is under control now and the sound is approaching my reference amps. I have a few more parts on order to try. The fan cannot be unplugged - gets too hot. I have the variable speed Papst installed - it buzzes like a bee even at low speed. Very irritating with the cover off - better with it on, but I can still plainly hear it between tracks. Have the single-speed Papst on order - I may need to ratchet this one down as well. The current inductors still get hot, but t ...
The single speed Papst is the way to go. It works great. I would recommend small neoprene washers between the fan and metal windtunnel, this makes the fan silent for all intents and purposes. And the air flow of this model is more than sufficient to keep the amp cool at any load.
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8th nerve - thanks, I will try the neoprene washers.
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The single speed Papst is the way to go. It works great. I would recommend small neoprene washers between the fan and metal windtunnel, this makes the fan silent for all intents and purposes
The washers worked for me too.
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The single-speed Papst fan did the trick. Very quiet now.
I just installed the last power delivery improvements and the dynamics are matching my reference amp now. It really rocks the place now with dynamic music. The HF extension is identical now as well.
There seems to be a little phasiness or slight lack of dynamics at the highest frequencies that is preventing it from being identical to my reference. The difference is quite small however and not noticable except with certain musical pieces. This may just be a limitation of the Tripath module or the fact that the output filtering just causes this as a side-effect. I was not able to use my preferred inductors on the main output filter as they get too hot. I was forced to use the next-best I could find. This could be the reason. The module switches at around 650 kHz, so the filters are sub-1MHz to 2 MHz. If the thing switched at over 2 MHz, this would be a big help here, but it is what it is. I have improved the power delivery to the Tripath module as much as possible. Most people will not notice this subtlety unless they hear my reference amp and compare them head-to-head. The Carver definitely has the magic now - very punchy and above-all, musical.
I will keep the pressure on to get a better output inductor that does not overheat, which should make it identical to my reference, but I don't think many amps on the planet will touch it even now. Certainly none that I have heard, including the Parasound JC-1's and the PASS labs.
I have some final inductors on order to try and some heatsinks to install on them next week and then it should be ready for primetime...
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I discovered what it was - a hiss filter was causing it. This filter is before the Tripath module. I removed the filter and the hiss increased a little, but the imaging to the back wall got much better and now the high-frequency room echoes are audible. Very very close to my reference now. The bass is actually a bit better than my reference amp, but my reference is only 300W/chnl into 8 ohms.
The biggest problem with this amp is that the op-amps pick-up some radiated RF from the output MOSFETS, causing some hiss. If the op-amps were isolated, the hiss could be reduced significantly. The hiss is not audible from my listening position, but may be barely audible with some ribbon tweeters. I believe the hiss is a good tradeoff given the improvement in sound.
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Steve-What is your "reference amp"
or "amps?"
Also what exactly is your system
like. It would be most helpful if you could
list all the components you are using
in your system for your comparison
of your reference amp with your moded
version of the Carver ZR1600...
especially your speakers.
Thanks for your help and patience in this.
-Richard-
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My reference system:
Sony DVP-S7700 with Turbomod
----------Bitmeister digital cable
Perpetual Technologies P-3A DAC with Turbomod
----------Holophonic-PC unbalanced IC's
Mark Levinson #38 Pre with Turbomod
----------Holophonic-PC unbalanced IC's
Adcom GFA-585 amp with Turbomod
----------Clarity7 speaker cables
KEF 104/2 speakers with Turbomod
My backup amps are Parasound JC-1's, currently unmodified
My backup speakers are Soundline SL2's - currently unmodified
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I discovered what it was - a hiss filter was causing it. This filter is before the Tripath module. I removed the filter and the hiss increased a little, but the imaging to the back wall got much better and now the high-frequency room echoes are audible. ...
I'm not sure what a hiss filter is, but isn't this filter to keep all the radiated switching noise from getting into the input to prevent im and such? It does seem that just changing the content of the noise floor or im components will make the amp more lively.
steve
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This filter was there to roll-off the high-frequencies because the original design was so noisy. Removal of this filter with the orginal design would probably have resulted in too much noise. The new design is much quieter, so most of the filters have been removed.
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Received new inductors - they are smaller and get hotter, but I have epoxied a heat-sink to them. Next we'll see if this is good enough.
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Steve: This amp sounds like it is a design nightmare. From what you're saying here, i've gathered that little thought was given to internal lay-out or in-circuit / on-board impedances. If you laid the amp out more appropriately and took those factors into account, you could probably minimize the amount of RF radiation drastically. As you know, this would improve sonics and stability, but you'd have to design from the ground up, making it an all-new amp. As it is now, it seems like you've got your hands full, but are enjoying the challenge :)
Out of curiosity, what gauge are the output inductors that you're using? Sean
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Sean - it has turned-out really good actually. The mods are complete and I'm ready to mod more of them. It is very close to my reference, which beats the Parasound JC-1's.
The inductors are at least 12 AWG.
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Steve,
Can you now compare the sound of the modded Carver vs your Turbomodded Adcom. What differences (across the board) do you hear between the two amps ? Thanks !! :) [/list:u]
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Chris - the Turbomodded Adcom still beats it for high-frequency extension and air, but the Carver beats the Adcom for bass control.
I have a new inductor design that I will use in Spectralman's mod and I believe this will narrow the differences between the Adcom and the Carver.