Hello,
I am thinking about changing out the above mentioned International Rectifier Mosfets, mentioned above by Bob Crump, and replacing them with Harris or Fairchild Mosfets.
I could not find the part # that Mr. Crump mentioned.
Does anyone have this information and/or part number?
Also, could anyone tell me exactly where these Mosfets are located inside the amp?
Thanks. |
I've only seen the Rotel part of the review. I can't find the Parasound portion online. As far as the RB-1090 goes, I think it's pretty good for the cost.
Dre |
I just read the old January 2000 Stereophile review of the Parasound HCA-3500 the other day.
Bob Crump was right...they did measure pretty high levels of 2nd harmonic distortion, especially into lower impedances. This was also obvious by looking at most of the measurement diagrams.
The reviewer, Robert Deutsch, also commented on a "slightly forward sound, with a bit more upper-midrange/treble grain. These characteristics showed up as a somewhat etched quality on voices, massed strings, and the upper harmonics of trumpets, making the sound ever so slightly fatiguing over time." This was in comparison to the Rotel RB-1090.
Interesting! |
Nealhood: I agree with your comments although i would add that power cords should still be designed to resist RFI and pass plenty of current in an unrestricted fashion. After all, any exposed wiring / cabling can act as an antenna, so you've got to take that into account too.
Using heavy gauge conductors with a cable geometry that is naturally RFI resistant also presents a low nominal impedance and low series resistance. This allows current to be delivered in both a timely fashion and in the quantity needed. It also reduces the EM field around the power cord, so it is not inductively coupled into other signal or power cabling from other nearby gear.
As a side note, i'm using a unit that is similar to the Topaz mentioned above, but it is much larger, sturdier and heavier as it was designed for commercial applications. I've never weighed it, but when it was shipped into me, the weight on the bill of lading was listed as 450 lbs plus 30 lbs additional for the skid & packing materials. The 7.5 KVA unit that Neal made mention of weighs in at appr 116 lbs, so that should give you some idea of what i'm talking about.
On that topic, the Topaz T100H-7500 seems a little light to me at that type of power rating, so that tells me that it is lacking in core size. As such, i would consider this to be more of a 3.5 - 4 KVA unit in my opinion. Even at that level of output, you are talking about 30+ amps of continuous current capacity. Unless one is running very high current draw amps with very low impedance & low sensitivity speakers in a very large room, this should be adequate for most systems.
For sake of comparison, my old 2.5 KVA transformers clock in at over 100 lbs apiece, but they are WAY overkill on core size. I have seen 5 KVA and 7.5 KVA transformers that used smaller cores. That's the reason that i bought several of these, as i never had to worry about core saturation.
To take that a step further and for a more common point of reference, the old Tice Power Block / Titan iso transformers were rated for 1.8 KVA ( 15 amps ) and they clock in at appr 42 lbs each. Now you know why people running big amps used to complain about the Tice's ( and other "small core" iso transformers ) "squashing the dynamics ans smearing the sound at high listening levels" i.e. the core of the iso may have been temporarily saturating, introducing distortions and limiting peak current capacity.
This is why Tice came up with the Titan, as it simply used an additional yet identical transformer in parallel with the one found in the Power Block. This meant that you now had 84 lbs of core for the rated 1.8 KVA rating, which is obviously much better / allows more headroom during normal operating conditions. This is why i've said that you should look for an iso that was rated for almost double the max current draw of your components i.e. you have no chance of the iso distorting or saturating and the AC line impedance remains very low.
Obviously, power cords DO effect the sound of most components, but that's only because the components are still being fed "grunge" from the AC line and lack the proper design to deal with it. By going to the source of the problem and filtering the AC to a very high point of purity before feeding it to the system, you no longer have to rely on the guesswork of what power cord will "filter out the junk" the best on each individual component i.e. "The Super Vaporizer works best on digital whereas the AC Magna-Charger works best on amps". The only thing that power cord has to do at this point is deliver the proper voltage & current without allowing additional "grunge" & RFI to sneak back into the system AFTER the primary filter.
The fact that many "audiophile grade" PLC's still make "aftermarket power cords" somewhat of a "necessity" in order to achieve optimal results should tell you that the PLC itself isn't up to the task at hand. This could be why most of the "audiophile grade" PLC's don't provide meaningful spec's i.e. they rely on the thick metal chassis, fancy faceplates and snake-oil marketing departments to sell their mega-dollar units for them. Sean
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Mr. bill, no the Topaz 100 does not hum or buzz. It is not a true ferroresonant transformer like that employed in the Topaz model 800. So it's efficiency remains high and noise virtually non-existant. It will not degrade dynamics on a power amplifier assuming it is sized properly.
Although the model 800 may exhibit a small bit of hum, make no mistake it's conditioniong performance is second only to a true power converter/inverter and, only if the inverter is of the higher caliber type with a low THD sine wave output. Even then, the inverter is unlikely to ever equal the ferro system performance as far as the available current rating (short circuit impedance). Therefore the inverter solution stands to restrict harmonics much more than the ferro system.
The model 100 is plenty adequate for virtually all home systems and will beat the socks off any high zoot power cords and, probably most any competing power conditioner. |
Neal,
Is the MGE Topaz 100 a noisy unit - does it whirr or hum or make noise and does it restrict dynamics?
Is this the cheap effective alternative to a power regenerator or expensive audiophile product?
Thanks,
Bill |
"Sean" is correct, address your power line issues with a quality conditioner then use an ordinary power cable of sufficient size. And, a preamp doesn't burn much current. Don't waste money on some long-green high zoot cable because it will never provide the benefits of a good power conditioner such as the MGE Topaz 100.
http://www.mgeups.com/products/pdt120/powerc/tpz100/t100.htm
By the way, Pass is top notch. Their new amps included. |
The difference between the Ayre and Pass on vinyl might simply be a matter of the loading that is being presented to the cartridge via the phono stage. Unless you have identical settings on both preamps for the phono loading, one will sound "different" than the other. Even with identical settings, they can sound different due to parts tolerances and the variances in circuit design.
As to the power cords making such a noticeable difference, there's a lot to be said there. The purer that the power is being fed into the system, the less of an effect the power cords will have. If one is running some type of power line filter / conditioner and power cords are still highly influential in what one hears, that PLC or filter simply isn't doing much of a job.
On top of that, the better the filtration of the power supply within the component, the less of an effect the power cords will have. That's because the component itself is filtering out the hash and trash prior to applying any type of manipulation to the audio signal itself. While hi-fi components are quite costly, the power supply is quite often the first part of the component that is built to a price point. As such, this is why external changes to the AC supply side of each component can make such a drastic change in the audio side of what we hear.
Rather than spending hundreds and potentially thousands of dollars chasing various component / power cord combo's, why not take steps towards cleaning up the AC for all of the components simultaneously, and do so in a manner that is both measurable and highly effective? This is not that hard to achieve and the benefits will remain with your system regardless of the components used.
Once one does this in an appropriate manner, the use of inexpensive but well designed power cords will almost always deliver as good of results as far more costly cords that rely on marketing and snake oil to sound as good as they do. After all, their is nothing "magic" about 60 Hz power delivery, especially when one considers the design confines within a typical power cord / component configuration.
Spending hundreds / thousands of dollars on over-built & under-designed cabling and componentry that doesn't measure up, either audibly or electrically, is one of the greatest banes of audiophilia. All this on top of being a point of great frustration for the end user. Sean
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The Adcom sounded better than the Ayre with the Parasound HCA-3500 power amp ONLY.
With the JC-1's, its no contest...the Ayre wins hands down!
I had to let my friend have the Parasound HCA-3500 power amp back. It was just too fatiguing in the long run. Sure it sounded clear, lively, and transparent, but at the same time it was too bright.
I recently purchased a Pass Labs X-2.5 preamp.
It sounds VERY impressive. Make sure you ditch the stock power cord, however. I borrowed a Signal Cable shielded Magic Digital Reference [High Current] power cord with it and was very impressed with it, especially for the price...A REAL STEAL!
The Pass competes very favorably with the Ayre, believe it or not, and actually sounds better to my ears with digital than the Ayre. The Ayre can be too analytical with digital.
On vinyl however, the Ayre sounds alittle better than the Pass, IMHO. |
This is going to look like a "love fest", but kudo's to you again Bob. Giving credit where credit is due is why you get the respect that you do. Honesty and friendliness are some of your best features : ) Sean
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PS... Crump is too big for me to say anything but nice things about him : ) |
Audio girl,
I too own JC-1s and although I've never heard the 3500 seems to me the synergy with the rest of your system might be the deciding factor in what you are hearing.Also I believe true "transparency" should never be accompanied by etch and grain.You state that the bang for the buck Adcom 750 preamp(designed by Pass if i'm not mistaken)sounded even better than your Ayre(recommended by many as a top notch line stage and one I would consider if I were to get the itch to change my Pass X1,unless I should have the good fortune to actually be able to afford a CTC Blowtorch).Does that mean that the Adcom is BETTER than the Ayre?tThough it may be possible,I doubt it.Most likely the 3500 and the 750 combination of strengths and weakness-es better complemented each other.
On a sidetrack i see you are using au24 speaker cable.I'm currently looking to replace my recently sold AZ Hologram II SCs.My ICs are either Analysis Plus Solo Crystal 8 or Cardas Golden Reference and besides these two brands i'm considering the Audiences for SCs, even though i don't have the ICs.Unfortunately there is no local dealer.Before buying the au24s what did you compare them with and what was it that determined your final decision?it's been said that au24 SCs are comparable to anything out there,regerdless of price.my speakers are dynaudio c4s.
Your observations will be most helpful I'm sure.
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Hey Sean, thanks for the kudos, but Curl was the one who found the problem when he started testing the JC-1 prototypes and luckily there was a second source for the part originally developed by IR that didn't have the curve tracer drawing circles :-) Thought I would add my 2cents as a couple dollars of parts will make the HCA3500 a much better sounding amplifier....... |
Rcrump: Isn't it crazy how an individual component ( semiconductor ) that measures "flat" in terms of the primary amplitude linearity can actually alter the tonal balance of what one hears due to lower level distortions inherit to the part itself?
This is the kind of stuff that fools a lot of people even though the most commonly taken and interpreted specs look to be quite good. This is part of the reason why many components that "measure the same" sound "different" from one another. Without the proper test equipment and knowing how to really interpret the data, it would be easy to make such assumptions.
Kudo's to you for taking the time to both share this info and offer a detailed explanation as to the why's and how's. On top of that, you even made others aware of how they can easily upgrade their own components to a higher level of performance. Not many in the industry would be willing to do something like that, especially when they themselves offer similar services. Ya gotta respect that in an industry professional. Sean
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Hey Plato, International Rectifier makes some mosfets that are set up as switches and strangely enough Harris makes a replacement part that works well and does not spew a ton of second harmonic......Second harmonic comes across as a bright etched quality in the upper midrange and seems to be what audiogirl likes and dislikes in the two amps.......My partner has a nice test rig for checking out the spectral analysis. Funny, IR changed the parts from the introduction of the HCA3500 to the point in time we had prototypes of the JC-1s and we specified the change after Curl ordered fifty of each, IR and Harris, to test........Nothing is particularly easy, but changing over to Harris parts took care of the problem.......I posted the part no here a couple weeks ago for those with 3500s that wanted to fix the problem......... |
Audio_girl,
It appears you've conducted your evaluation very well. Thank you for sharing the details; it's always helpful to be aware of such things. I don't take anything for granted these days.
Rcrump, what, in your book, equates to "a ton" of 2nd harmonic distortion? I thought it was mainly tube amplifiers that were guilty of that. Shucks, now I have to wonder whether I like my solid-state amps because they are accurate or because they also mimic tube distortions. |
Audio girl, the HCA 3500 has a ton of 2nd harmonic distortion compared to the JC-1 and that is probably what you like and dislike about the 3500........I changed out a couple of mosfets and the 2nd harmonic dropped dramatically and the two amps sounded quite a bit more like each other with the JC-1 being a significantly better amplifier for long term listening.......faster, cleaner and things that a better layout will allow in the JC-1...........The etched sound of the HCA3500 sure can be addictive as several folks have reported liking the old war horse better than the JC-1s, but once the 2nd harmonic is reduced it can become a much better amplifier........ |
Plato,
I have extensive experience setting up gear for comparisons.
I am still borrowing and using my friends Parasound 3500 as we speak. He did say that he had removed the stock Vishay 47K feed-back resistors and replaced them with Holco 47K ones. He said this was the only deviation from the stock units.
I have tried various cables and vibration control devices on both amps, and the results are basically the same. I use dual dedicated lines for the amps. I use a Shunyata Research Hydra 8 power distribution device as well.
I also tried out an Adcom GFP-750 preamp with the HCA-3500, and it matches up really well with it! Actually the 3500 sounds better with the Adcom than it does with my Ayre preamp! Low volume detail, transparency, and openness is remarkable with this combo. It is great at higher levels as well, but really shines at lower volume levels.
While I overall prefer the OVERALL sound of the JC-1's, the 3500 is remarkably clear, transparent, and has extremely extended highs. It also have remarkable image depth. Again, the main drawbacks are a slight etch and some slight grain on certain cd's. LP's sound marvelous on the 3500. |
Audio_girl,
Excuse me, but since I don't know you or your experience level, I have to ask:
Did you use all the same power cords, interconnects, and speaker cables when you performed your evaluation? Or, did you try different things to try to optimize the performance of each amp? Were they plugged into the same AC line? Through an AC conditioner or not? Did they use the same mechanical-coupling methods or vibration control? Heck, I've heard some gear sound appreciably different just by setting the component on a different surface or by using different footers.
On the surface, one would think that performing the evaluation keeping everything exactly the same would be the fairest possible methodology. In my experience I have found that this is not always to be taken for granted.
These days, when I make such comparisons, I try to optimize the installation for each amp (or other component) so that each piece will sound as good as I can possibly tweak it to sound. What works best for Amp A may put amp B at a disadvantage (and vice-versa). So what, on the surface, would appear to be an impartial evaluation or observation, may be (unintentionally) slanted due to factors that simply may not have been considered. Your comments about the 3500 sounding "grainy" or "etched" might be right on the money -- but they could also be telling you that the 3500 does not like the same cabling or footers (or whatever) that work well for the JC-1's.
If you haven't had the amp to play with and tweak over a period of time then you probably have not heard it at its best. Brief shootouts can be misleading. Extended evaluations over time are more reliable indicators.
I don't own either amp you're speaking of, so I have no stake in the outcome one way or the other. But I do like to see things done fairly and competently. For sure, there are a lot of variables to consider.
It's just food for thought... |
I've not compared the two but am on my second HCA 3500 after trying a Marsh A400s in between. On my VMPS Rm 40's which are extremely transparent I find the 3500 performs excellently from the bottom to the top. This in contrast to the Marsh A400s which is also a good amp and I think it was REG of Absolute Sound who claimed it to be as good as anything upto 20k. The Marsh did have some good qualities but overall I went back to the 3500. It seems to do everything right and with ease. My pre is an ARC LS 16. My room is dedicated LEDE with bass traps. If there's any serious shortcomings it doesn't get in the way of the music. |
Has anyone had the chance to compare the JC-1 vs HCA-3500
after Steve (Empircal Audio) has done mods to both? |
Russ- He can't answer right now, drooling shorts out the keyboard. |
Drhst20- Uh, is there an answer in your response to Audio girl? |
Hello Audio_girl
I just viewed your stereo system ... "WOW"
I am single, late 30's, love all genre's of music, fine dinning, and long walks on the beach at sunset ...
If your interset's are similar, please forward pictures of the Linn Unidisc and the Mono Blocks ;-)
Rgds Dave |
This is the take that Steve at Empiracal Audio has always had. If you have read his posts in the past, he has alwasy said this. I am most likely going to have his mods done (This will be the first time I have givne any equipment to Steve). He has both units, and said taht after the mods, the jc-1 is superior in every respect. If I had to complain about my jc-1 (they are a great amp, but not perfect...what is?), my complaints would almost perfectly align with what Steve has written. Alot of it has to do, imho, with a lack of enegy in the mids and highs (and perhaps a little less transperancy), compared to other amps I have liked. In most ways, the jc-1's are a phenominal amp for the price(I must think so..I own them), but as with any product it has it's short comings. If steve can really do what he says (I confirmed what he says with one of his customers who had the mod done and was floored by the improvments), then it really might be my permanenet amp for a long while.
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