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Hi all,
Thinking of building a C3m-300b amp. All of the schematics I have seen call for a .47uf coupling cap. Would a .22uf work?
Thank you
Follow Ups:
In all cases of amps I have built, the lower the value of the final's grid resistor, the better the sound. It is quite possible to go too low however, and load up the preceding stage too much. I use this logic to justify grid chokes...LOL No resistor has yet outperformed one yet...:)
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
Thanks All.
After doing the calculation a .22uf resistor and a 330k grid resistor would be 2.2hz for the -3db. so the .22 uf would do well in this circuit.
A 200k grid resistor would be fine too.
.
Have Fun and Enjoy the Music
"Still Working the Problem"
If you're working from a proven schematic, I wouldn't change anything at all. Build it as designed, then experiment if you think it might need improvement. FWIW, a proven schematic is one that's been used to produce good measured performance as well as successful builds and listening tests by a number of people. There are a lot of designs floating around out there that don't meet this basic criteria.
--------------------------
Buy Chinese. Bury freedom.
I made these amps with conventional power supplies back in the 90's, and they sound great. With the C3M's and Tango outputs they don't have the stereotypical limitations of SE 300b amps at all. Very fast and dynamic, with tight bass. I now use .47uf Jupiter copper HT caps, also grid chokes. I am about to install a couple of Tentlabs regulated DC filament supplies on the 300b's. David
Hi David Lawrence do you use the grid choke on the input tube or the finals tube? What brand and value?
Also did you use AC on the heaters of the 300b before switching to DC?
Are you using AC or DC on the C3M? Did you raise this tube above ground using a the center tap of the 20V filament transformer?
thanks
The grid chokes are for the 300b's. I forget the brand, maybe Stevens and Billington, and the value. Brian Cherry sold them to me many years ago when I was living in Hong Kong.
I once had DC filament circuits, following the Audio Note 300b Quest schematic (the amp's previous diy incarnation), and then switched to AC. I like the AC except have found the hum bothersome in the long run, especially with very sensitive speakers.
I forget what I did on the C3M filaments, but I just followed Thorsten's schematic.
Perhaps I'll have more to report as I hope soon to find time to open the amps again for the Tentlabs filament supplies...
David
Why don't you breadboard it first? Then you can try a bunch of different parts (tubes, caps etc,) to see which ones give you the sound you want. Easier to do it before you do an actual build.
Full agreement! Breadboarding is an amazing learning experience and the chance to see what affects what.
Yes.
will a .22 hurt the bass response compared to the .47?
That will depend on the value of the grid resistor on the 300b.
_-3db point = 159155 / (cap value in uf X resistor value in ohms)
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Didn't thorsten end up subbing a el84? I think his posts would be worth searching for if you wanted to save a lot of trial and error.
Thorsten's Legacy uses the C3m which he liked best. His schematic uses .47uf coupling cap.
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