Bob - thanks much for the tips. I will definitely try the Harris part on the next one that I mod.
BTW - I decided to replace all of the bias pots with sealed Bournes units in the 3500 and eventually, the JC-1's to avoid creeping bias and future warranty problems. Also made some other changes to minimize warranty issues. I appreciate your "war-stories" on this. |
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Steve, sorry but suggest you measure it........We did and found a ton of 2nd.........Glad you and your customers like the brightness this imparts on the sound as it saves $5 or so in parts for the revisions along with maybe ten minutes of work........Really glad you fixed the horrible problems in HF extension and dynamics in the JC-1s and suggest that once your amp is out you send it here so that we can criticize it and perhaps offer mods to fix the problems as we see them.............Sorry, but without changing the emitter resistors the 3500 will never be pristine and you will have the same problems we did as you'll run out of heatsink before you get it pristine.......
Bob Crump
CTC Builders |
Talked it over with Curl and might as well give the information to make the 3500 a better amp for those still using the old war horse....Replace Q-5 which is an IR part with Harris IRF9610. This along with the AC polarity and feedback resistor we have published before will get you down the road pretty well......These can be replaced without even taking off anything but the top as they are close to the top of the boards......To get any more serious with the 3500 includes replacing the emitter resistors and then the rectifiers, both of which are a real job involving almost complete disassembly.......It was a five day job to rebuild the 3500s into the CTC BBQ and much of the metalwork was redone as well as used circuit breakers in lieu of the 6a switches and surgisters for turn-on........
Best,
Bob Crump
CTC Builders
Bob Crump
CTC Builders |
Bob - I get what you mean now.
My customers and I both find the "brightness" of the 3500 to be exceptional clarity once it is modded. I had to go back to the JC-1's after CES and improve the HF extension and dynamics to match that of the 3500. I actually used the modded 3500 most of the time at CES/THE Show as opposed to the JC-1's because of this pristine, clear high-end. It's hard to believe that this is distortion.... |
I'll get with John later in the day and post the number as easier than tearing the top off my 3500 :-) Funny thing is the Harris is the second source for the Mosfets as they are IR/Fairchild parts, but they don't exhibit the weird behavior and brightness of the IR/Fairchild parts......
Bob Crump
CTC Builders |
bob what 2 parts can i replace.and im running the legacy focas with arcls3 b |
Steve, we are talking about different things.......The IR devices that need to be repaced with Harris are not rectifiers, they are Mosfets used in the input section and this is the cause of the huge amount of 2nd harmonic distortion in the 3500 over the JC-1.......This amount of 2nd harmonic comes across as brightness in the upper midrange which can be tamed with two parts and about ten minutes of work.........The Harris diodes used as rectifiers in all three bridges in the 3500 will allow for improved bass tightnesss as well as a much better stage......
Bob Crump
CTC Builders |
"You are never going to get the 3500 as smooth as the JC-1s due to the devices as well as the layout."
Bob - I have to repectfully disagree. These things can all be fixed with the right mods. The 3500 and JC-1's end-up very close IMO. The 3500 has replaced rectifiers in it, although this seems to mostly improve the bass tightness. |
I have to disagree with Downunder, I have heard the JC-1 at a friends house multiple times and owned the SIM W-5, and there is no comparison in my mind. The bass authority and the 25watts of Class A make for a very musical amplifier, versus the detailed stark presentation with lite bass (sorry it couldn't drive or control my NHT 3.3's (4-6ohm speaker) to 21hz.
The JC-1 is more refined than the 3500 or two 3500's |
The 3500 is a stereo JC-1 is about the only difference worth noting in the electronic design. The 3500 has a ton more 2nd harmonic due to the International Rectifier devices in the driver circuit in lieu of the better mannered Harris devices in the JC-1 so the JC-1 is a much smoother amplifier without the glitz and glimmer in the 3500's sound. You are never going to get the 3500 as smooth as the JC-1s due to the devices as well as the layout.
Bob Crump
CTC Builders |
try and audition the Simaudio W-5. I have heard both and for coherence and musicalilty the W-5 sounds better. Admitedly the JC-1's had not had there 1400 hours of break in time.
One of the dealers has both amps and he is of the same opinion. |
A stock 3500 is not in the same league as broken-in stock JC-1's. However, with mods the 3500 is very close to modded JC-1's. Bass control is slightly better with the JC-1's. They are both my personal favorites. The 3500 is actually a very good design and outperforms most amps on the market with mods. For the money, it is hard to beat. See this review:
http://www.audioasylum.com/forums/amp/messages/61129.html
Steve N.
Empirical Audio
Manufacturer |
Which spkrs do you want to biamp? More importantly, does the manufacturer provide for active (or passive line-level) biamping? If so, you'll need a second stereo amp. |
Having just read the review of the original 3500 from 5 years ago, they say the bass is its strong suit and the mids and highes are where the improveent should be.(Jan.00) |
I do ,im wondering if i should buy another 3500 for byamp or the jc1s |
Apart from being differently boxed (as you note) they're NOT supposed to be identical circuits, either. They have a site that talks about that.
As to what differences you'll hear -- in simplistic terms, the JC1 simply sound better in all respects... (IMO)
BTW, why don't you like your present amp?
Cheers |
