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Discussion in 'Amp Central Station' started by cacibi, Jan 23, 2008.
Looks great. When you run it into a JC-120 is the internal speaker defeated?
Yes, I would LOVE to hear why ALNICOMAGNET replaces a 22 uf cathode capacitor that fully bypasses the cathode resistor of the output tube with a cap almost 50 times larger.
No, the internal speaker is always active,[the line out is a speaker tapped line out]. I run it easy so its not breaking up and then get volume from the big solid state amp.Its a great clean tone! I kinda see it like its a tube preamp at the end of my pedal chain
As for the 1000uf cap in c4, I have no idea why that would be part of a kit if it has absolutely zero benefit. I think hundreds of people have done this so I'm not alone. I guess I'd be more preterbed if his other mods didn't work like a charm. But its quiet as a mouse on 10,the standby switch is extending the life of my RCA's and the H.T. fuse already saved me from a possible catastrophy, so all is good in my world.
Still not really fond of buying/swapping parts that arent necessary...:neutral:
Well, I received this reply from Nigel aka ALNOCOMAGNET regarding the 1000uf c4 cap...
''Hi, when I experimented with 12" cabinets, and found it gave better low end grunt. The cap is the same physical size as the stock 22uF/450V item, so why not? Regards, Nigel''
Good enough for me,no harm no foul.
Ah, yes. Amp modification by parts substitution with no thought given to what the actual design impacts are. If Nigel had bothered to do the math, he would have realized that the -3 dB point of the power amp with the stock 22 uf cap is already about 37 Hz. Given that the lowest note on the guitar is 80 Hz, lowering the -3 dB point even more serves no useful purpose.
Oh well, as long as you are happy and he didn't charge too much for the unneeded part, I guess that makes it OK.
In support of ALNICOMAGNET I have done most of his mods to my 600 and they have transformed this amp into another beast entirely. I have a BDRI, Blues Jr III, Super Champ XD and have owned a silverface Pro Reverb, Peavey Deuce and I don't know how many other amps and the best sound I have at the moment is my ALNICOMAGNET modded 600 through the BDRI speaker. This is a guy that knows his stuff.
I'm sure some of his mods have some value, such as the conversion of the heater circuit from AC to DC. Replacing the 22 uf C4 cap is not one of them, however.
I concur, this amp sounds killer!
"I'm sure some of his mods have some value" - now that's a back handed compliment if ever i heard one!
Ok. I'll say it. Replacing the 22 uf cap in C4 with a 1000 uf (or even a 100 uf) makes me question the validity of the mods made by this person. Why? A simple circuit analysis proves that replacing C4 with a cap that big is worthless.
There are 4 caps that define the overall frequency response of the C600: The coupling cap, C2 (0.022 uf), the V2A cathode bypass cap, C3 (22 uf); the V1 cathode bypass cap, C4 (22 uf); and the V2B cathode bypass cap, C10 (22 uf). The tone stack can be ignored since we are talking about the impact on the overall -3 dB low frequency cutoff point of the amp.
Circuit analysis shows that the gain though V2A and V2B is flat from 82 Hz to 10 kHz with the low frequency -3dB point below 10 Hz. The coupling cap sets the -3 dB low frequency point at about 25 Hz (again, the circuit is flat from 82 hz to 10 kHz). Finally, C4 sets the -3 dB point of the 6V6 at about 37 Hz, one full octive below the lowest note on the guitar. Increasing C4 to 1000 uf results in a -3 dB low frequency point at the 6V6 so low, my cathode bypass calculator cannot determine it.
Given that the overall frequency response on the low end is limited by C4 and is set at less than 40 Hz by the stock cap, increasing C4 by any appreciable amount results in no additional gain at the 82 Hz value of the lowest guitar string.
Bottom line: Replacing the 22 uf cap at C4 with a 1000 uf serves no useful purpose and is a poor design choice in my opinion.
I certainly don't question your knowledge on the change of this component but does that really validate "Amp modification by parts substitution with no thought given to what the actual design impacts are" ?
Seems a little harsh with regards to someone with a proven record on the improvement of the 600 don't you think?
When it comes down it, if I read it right, ALNICOMAGNET may or may not have, as you say 'didn't do the math' but did experiment, surely this has some empirical value? Anyway as someone who has actually done the ALNICOMAGNET mods on a 600 I can heartily endorse them as a vast improvement on stock. Ducking out of this thread now!
Other than the AC to DC heater mods, I am not that familiar with all the mods included in that kit. However, when I read about the mod that replaces one value cap with another much larger value that serves no useful purpose, it raises questions in my mind regarding the thought that went into that and the other mods.
Harsh? Maybe so, but when someone is making money off of something that serves no useful purpose, they deserve to be called out.
If ALNICOMAGNET came here and explained his rationale behind this particular mod I would welcome it.
I experiment too when I mod an amp, but I also rely on an analysis of the circuit to determine the range of parameters that would have a chance of producing useful results.
Bluesky636, I'm sure the mathmatical calculations are most certainly correct regarding C4. But I play guitar by ear,build and tweek pedals by primarily by ear,tweek my guitars,pickups,electronics and amps primarily by ear. Is my method the optimum approach? Certainly not and If I could do it all again I would have studied music AND electronics in a formal enviroment.
Nigel, on the other hand, is a player and electronics wiz. His kit has transformed my little 600 into maybe my alltime favorite bedroom/practice/recording amp, and actually made it usable on large stages,something that wasnt possible prior to the mods.Thats a big success in my book.
If one component change in his kit is deemed mathmatically un-neccassary, well, I'm out a buck for the component and 10 minutes of my life are gone forever. But yes,I agree that ultimatly folks should be called out if they are profiting on some snake-oil service. However that is not the case here.
I think your approach to wielding your knowledge kinda comes across a bit elitist,even if your intentions are good.Its like you cant wait to prove the guy is a fraud or something.My Champion 600 says otherwise....
Its kinda like the whole Monte Allums thing.Some analog guru finds a component or two that make no mathmatical sense in his kits and they circle the wagons en-mass to prove that he has no buisiness being in thier elitist electronics club.
I enjoy your posts though, and am learning alot from folks like yourself on this forum, so thanks for sharing your knowledge.
Every mod I have posted in this forum and other forums I have analyzed and explained why I made it. Every question that someone has asked about a mod, I have explained why it is good or bad. This is the first time I have openly questioned a mod that someone sells as part of a kit designed to make a profit. I do not sell my mods, I simply share them with others. I will not recommend a mod unless I can back it up with a rational explanation and good engineering design. If that is elitest, so be it.
I am very glad that you are happy with the performance and sound of your C600 (and that is an honest statement).
I really should step back a bit.I guess I'm just defending the guy cause my experience was quite positive,but I dont know him and am not affiliated with him in any way. I'm not calling you elitist but pointing out it can be mis-interpreted that way. The fact that your sharing your knowledge free of charge says alot about you.
Keep posting and I'll try to keep learning!
Ok final mods done! Went back to the stock tone stack,as this speaker doesn't fart out like the stock speaker.
And this was a nice surprise, I changed out the stock heater wires with a longer,solid core twisted pair and the amp is now virtually silent on 12.
You can change these out from on top of the board,just dont leave any wire hanging below.The longer wire allows you to move them away from the pcb more and it works great.
The wire replacement/relocation seems like a cool and easy mod to cut down on noise.
Fender schematic link down?
Anyone got the schematic for this? Old links posted here are no longer active and when I go direct to the Fender support page (http://support.fender.com/schematics/guitar_amplifiers/Champion_600_schematic.pdf) all I get is a blank screen...