Building a BFDR-A Couple of Questions

TelZilla · July 2nd, 2007, 01:01 PM

I’ve got two questions regarding a potential BFDR build:

-I would never use the normal channel. Would it have any impact to just do the vibrato channel? What would I leave out?

-I have a general question about capacitors, particularly regarding the voltage rating. Is it ok to have a greater voltage rating? How about a lower one? For instance, can I use a 16 uF,@475 volt cap iwhen the layout and schematic call for a 16 uF @ 450

zook · July 2nd, 2007, 01:30 PM

Quote:

Originally Posted by TelZilla

I’ve got two questions regarding a potential BFDR build:

-I would never use the normal channel. Would it have any impact to just do the vibrato channel? What would I leave out?

It would not have any impact You would leave out one 12AX7 7 resistors and 5 capacitors. You would have to change the value of one of the cathode resistors (on the paired cathodes) from 820 to 1500 Ohms.

Quote:

Originally Posted by TelZilla

-I have a general question about capacitors, particularly regarding the voltage rating. Is it ok to have a greater voltage rating? How about a lower one? For instance, can I use a 16 uF,@475 volt cap iwhen the layout and schematic call for a 16 uF @ 450

Higher voltage is not a problem. If you have a 475 volt cap, measure the voltage going onto it. If it's less that 450 you'll probably do fine. Do not exceed the voltage rrating, however, Electrilytic caps can explode pretty spectacularly whn the voltage is exceeded.

Winnie

PhatTele · July 2nd, 2007, 03:08 PM

Don't give up on the Normal Channel. Just create something else fun to use. I use this Hot Rod mod from Blue Guitar all the time in Normal channels and in the Bass channels of Bassmans (BTW - I do not use the 750pF bypass cap in the drawing...too muddy):

http://www.blueguitar.org/new/schem/...d/bfhotrod.pdf

Suggestion: Even if you don't want the Normal channel, wire up your amp as the diagrams show. Make sure it works first as intended. Then, go about modding it...either by removing stuff you don't want or by changing values of components already there. I guarantee, if you take something out prior to making sure everything works as it should normally, you'll spend hours trying to figure out what needs to go back in to get it to work properly.

TelZilla · July 2nd, 2007, 03:28 PM

Quote:

Originally Posted by PhatTele

Don't give up on the Normal Channel. Just create something else fun to use. I use this Hot Rod mod from Blue Guitar all the time in Normal channels and in the Bass channels of Bassmans (BTW - I do not use the 750pF bypass cap in the drawing...too muddy):

http://www.blueguitar.org/new/schem/...d/bfhotrod.pdf

Suggestion: Even if you don't want the Normal channel, wire up your amp as the diagrams show. Make sure it works first as intended. Then, go about modding it...either by removing stuff you don't want or by changing values of components already there. I guarantee, if you take something out prior to making sure everything works as it should normally, you'll spend hours trying to figure out what needs to go back in to get it to work properly.

Yeah, that's probably what I'll end up doing.

What does that Hot Rod Mod do, anyway?

PhatTele · July 2nd, 2007, 03:51 PM

First of all, it separates the two channels. In the original design, the two channel's preamp tubes share a bias resister and bypass cap (that's why you can pull the V1 tube to drive the V2 tube a little more...the bias point changes). The mod also decreases the plate voltage to both side of the V1 tube making it establish bias at a hotter point (overdriving it a bit). The mod also uses smaller value bypass caps which throws away a bit more bass than you'd find in the normal setup (also good if you're driving things more...it won't get woofy on you...look at a Vox AC30 preamp). Finally, the mod changes the tone voicing just a bit, focusing more on the midrange. When it's all said and done, you get a hotter sounding channel. It's not runaway distortion. It just has a bit more hair to it. I've done this mod on at least 10 amps (again, without the 750pF bypass cap which makes it too muddy) and the guys who use these amps love them (country, R&B, soul, blues, rock...)

I actually beef this mod up a bit by putting in a 25K audio taper midrange control instead of the stock 6.8K resister coming off of the Bass pot.

July 2nd, 2007, 01:01 PM	#1 (permalink)
TelZilla Tele-Afflicted Join Date: Jan 2007 Location: Cleveburg, USA Age: 38 Posts: 1,736 6 Photos	Building a BFDR-A Couple of Questions I’ve got two questions regarding a potential BFDR build: -I would never use the normal channel. Would it have any impact to just do the vibrato channel? What would I leave out? -I have a general question about capacitors, particularly regarding the voltage rating. Is it ok to have a greater voltage rating? How about a lower one? For instance, can I use a 16 uF,@475 volt cap iwhen the layout and schematic call for a 16 uF @ 450 __________________ Thanks,Nick Go, cat, go!

July 2nd, 2007, 03:08 PM	#3 (permalink)
PhatTele Tele-Holic Join Date: Jun 2003 Location: Richmond, VA Posts: 688	Don't give up on the Normal Channel. Just create something else fun to use. I use this Hot Rod mod from Blue Guitar all the time in Normal channels and in the Bass channels of Bassmans (BTW - I do not use the 750pF bypass cap in the drawing...too muddy): http://www.blueguitar.org/new/schem/...d/bfhotrod.pdf Suggestion: Even if you don't want the Normal channel, wire up your amp as the diagrams show. Make sure it works first as intended. Then, go about modding it...either by removing stuff you don't want or by changing values of components already there. I guarantee, if you take something out prior to making sure everything works as it should normally, you'll spend hours trying to figure out what needs to go back in to get it to work properly.

July 2nd, 2007, 03:51 PM	#5 (permalink)
PhatTele Tele-Holic Join Date: Jun 2003 Location: Richmond, VA Posts: 688	First of all, it separates the two channels. In the original design, the two channel's preamp tubes share a bias resister and bypass cap (that's why you can pull the V1 tube to drive the V2 tube a little more...the bias point changes). The mod also decreases the plate voltage to both side of the V1 tube making it establish bias at a hotter point (overdriving it a bit). The mod also uses smaller value bypass caps which throws away a bit more bass than you'd find in the normal setup (also good if you're driving things more...it won't get woofy on you...look at a Vox AC30 preamp). Finally, the mod changes the tone voicing just a bit, focusing more on the midrange. When it's all said and done, you get a hotter sounding channel. It's not runaway distortion. It just has a bit more hair to it. I've done this mod on at least 10 amps (again, without the 750pF bypass cap which makes it too muddy) and the guys who use these amps love them (country, R&B, soul, blues, rock...) I actually beef this mod up a bit by putting in a 25K audio taper midrange control instead of the stock 6.8K resister coming off of the Bass pot.