Tube Amps / Music Electronics
For current discussions, please visit Music Electronics Forum. New: view Recent Searches.
New: visit Schematic Hell!
The sunn still shines online!

Listen to great tunes streaming live right now!

ampage archive

Vintage threads from the first ten years

Search for:  Mode:  

Steve...interesting find concerning your c30 mod

1/16/2005 1:53 PM
daz Steve...interesting find concerning your c30 mod
I just had to mention this because it really suprised me. Yesterday i decided to replace C4 with a silver mica. I had already replaced the 470pf with 820 as per your instructions, but i used a cheap cap and i wanted to put a mica there. I also had never changed C7 as you suggest with a 390pf in place of the stock value. So i decide while i was in there to do that too.  
long story short, the amp lost a ton of the tonal details that make it so good.It's frequency range seemed to be squashed and the mids lost major complexity and transparency. No comparrison ! I didn't know whether the micas caused it or the C7 value change, but i figured it was the value change. So i replaced C7 with the stock value and it all came back ! It seems this cap is extrememly important to the overall tone of the amp, and the 390pf just killed it. I swear i am not exaggerating when i say the amp literally lost 1/2 it's mojo with the 390pf compared to the stock cap. (470 if i recall)  
So i'd recommend anyone doing these mods to leave C7 alone or at the very least go back to the stock value after using the 390pf for a while to see if you're losing anything. Just for the record the mods i have are the cathode bias, the vintage style input, presence, tone stack caps, (replaced w/quality caps of same value) and the C4 swap to 820pf. By the way, i can actually hear the improvment of the 820pf mica over the 820pf junk cap i had in there.
1/16/2005 6:45 PM
Bruce /Mission Amps

I avoid these amps like the plague.  
Please endulge me, or any reader who might consider these to be some of the worst amps on the planet or in the history of mankind, .... what is C7 and what is it doing in the amp?  
1/16/2005 7:31 PM
Bruce /Mission Amps

OK I found C7 on the schem.  
I think if you heard that much difference with a 390pF vs 470pF in that spot, there is a good chance you had a bad cap or installation error.  
1/16/2005 10:08 PM
No installation error, as i am meticulous and even use an eye loop to inspect the joints. A bad cap....maybe. But while i'm not a tech as you, i find the suggestion that these amps are garbage rather.....well, i don't wanna start something here. But suffice it to say that when an amp evokes plenty of positive response from people as this one does, you might wanna re-think your feelings about them. After all, if many more people like them than not, then they obviously have worth. Because you don't doesn't make them bad amps. To YOU they aren't, but it's apparent from all the positive things i read about them that you are in the minority. Because you sell amps or kits or whatever you may have a bias towards inexpensive amps. But the fact is these amp can sound very good with some help, and according to a lot of people they sound great stock.  
Just today i was reading thru threads at many of the major forums and noticed a lot (yes, a LOT) of threads where this amp was mentioned and very few of the replies were negitive. And personally while i'm not a tech like you, my ears are probably at least as tweaked towards amp tone as you or most anyone after decades of gigging. It doesn't take being a tech to know good tone. I'll be blunt and say that my ears are very sensitive to amp tone and i KNOW what good tone is. At 51 with 3 decades of this behind me it's a no brainer. I've owned countless amps over the years and gigged with them. And while i obviously won't convince you, the classic 30 with simple mods that take an hour or 2 and a good speaker and tubes can easily compete with many other amps that are generally considered to be standards of good tone. I've been thru many of those amps, and i've been using and been totally happy with a modded c30 for years now. there are amps i've owned that cost far more that i wouldn't consider using over my cheap peavey ! Some i might consider in the same league tone-wise, but thier features might not be whatb i want compared to the 30. In any case it's a matter of taste, not nite and day tone quality.  
So to sum up, i find that statement offense because it reeks of pretentious attitude. And if i'm wrong i'd like to know why the C30 is one of THE most coveted low cost amps made and has been for years. If you don't agree with that then theres nothing more to say because i have read a ton of remarks/reviews on this amp for years online and theres no mistaking it's mass appeal, and NOT just from kids but seasoned players. Not to mention the tone that my experienced ears hear and know is great....modded yes, but never the less a great tone form an amp you marked as one of the worse ever made. If your amps are better, thats great. But whats that got to do with it? A c30 is much cheaper, and with a bit of work and a couple bucks of parts it becomes simply a matter of taste as to whats better. I know because i've played and owned several boutique amps and found more hype than better tone. Especially when you consider no matter how good an map's tone is, it's worthless if all the wonderfull details get lost in a live mix. My c30 doesn't, period. It's one of the best amps i've owned in that regard, and that makes it better than many "killer" amps. Worthless garbage or whatever you said? Whatever you wanna me thats a rediculous statement. You sure you weren't thinking of a gorrilla?
3/2/2005 1:54 PM
Steve A.

Bruce said:  
I avoid these amps like the plague.  
Please endulge me, or any reader who might consider these to be some of the worst amps on the planet or in the history of mankind, .... what is C7 and what is it doing in the amp?
    I guess that C4 would be more appropriate? (Call out the bomb squad!) ;)
1/16/2005 9:36 PM

I agree, 470 to 390 at C7 should brighten it up a little. Look at it, it is a cap to ground from the signal path. Lowering its value should reduce any rolloff effects. I vote you got a funny cap, too.  
By increasing C4, it is a series cap in the signal path, you lower the frequency it rolls off at. Essentially the larger cap lets in more mids so overall it is less high-centered. I suspect the C7 reduction is to compensate by making it more bright after C4.  
Increasing C4 should make the amp less trebly, less shrill. Lead channel only of course. Decreasing C7 should make it a bit brighter.
1/16/2005 11:51 PM
thats just what i got from enlarging c4 as steve mentions. But C7...i'm sure you're right about the frequency change you mentioned. But i swear it didn't just change the frequency but changed the voice of \  
midrange a lot. hard to describe it, but the midrange with the stock cap along with all the mods and tubes i've got happening (especially nthe GT mullard clones) give it this midrange that sounds like a real transparent and full marshall mid. With the 390 the mids totally changed to a compressed midrange that lacked all the ccomplexity it had before. Really suprised me how one cap could make such a difference. But as has been said, maybe a faulty cap. In any case i'm leaving a good thing alone !  
I wonder tho enzo....whats your take on replacing those resistor looking caps and the tiny yellow egg shaped blobs with micas or other quality caps? Seems replacing c4 with a mica of the same value improved the tone and makes me wonder if a total re-cap of all those cheesy ones might make a considerable improvment. The amp sounds so good now i'm a bit leary about doing that, but you know how that is. :)
   Page 1 of 3 Next> Last Page>>