DC Mods that are easy to do!

Hi there
In regards to the bias mod on the DC-5
Can somebody please email me a picture of the resistor that needs to be changed for the bias mod? I can't figure out which one it is on the board. My email is sfx70 at yahoo dot com.
Thanks

Has anyone used a 12au7 as a inverter on a DC 3??

P.S.Monsta,did the output volume mod on the DC 3.Great easy little mod,thanks 8)

sfx70,
I don't have any pics, sorry. I thought I did, but my family and I moved about 5,000 this summer and I'm still unpacking.

bhsbhswarp,
I haven't tried an AU7. I don't really like what the AT7 did for the sparkle either. An AT7 to me, sounds best in Fender amps, but not that great in a Mesa.
Glad you like the MV mod, can't remember who came up with that here.

I'm going to have to get myself another DC after Christmas!

I have done the volume and fx loop mod to my DC-5b (it applies to DC-10 too). It works great. Here are some pictures of before and after the mod in case you have some doubts of how to do it.

Volume mod before:


Volume mod after:


Fx loop mod before:


Fx loop after:

I have found out other mods suggested in a Harmony Central review (http://www.harmonycentral.com/products/83434):

1. The Lead channel is too dark or muddy, lacks character & harmonics. This is caused by an unusually low input impedence on the Lead channel of about 319K ohms. To fix this simply remove the 470K ohm input grid to ground resistor on the Lead channel (V1b-7).

2. The Rhythm channel on the DC-5B version has too much presence for my tastes. Removing the 75pf brightness cap on the Rhythm Gain pot will take care of this. If it's still too bright for your tastes you can change the stage-2 anti-miller cap from 39pf to 20pf or 22pf. That's the cap that is in parallel with the 3.3M ohm resistor connected to V4a-2.

3. The Output Level pot comes on full at about 2 or 3. There is a 220K ohm pull-up resistor from the wiper to the CW pin that causes this. It's there for two reasons: to make this amp seem louder than the competition, and to dampen the effect of the 56K ohm + .005uF filter. You can simply remove the 220K pull-up resistor, which may be located on the circuit board depending on the revision of your amp. This will fix the taper, but it will also cause a lot of mid & high frequency reduction in the 5 to 7 range on the Output Level pot. If you do not like this then add a 300K to 330K ohm resistor from the Output Level pot wiper to ground (after you remove the 220K pull-up)."


Has somone tried the 1 and 2 mod suggested above :?:

The first mod looks a bit weird... I would say to increase it to 1M, but I'm a tube designer noob.

I haven't tried them, but here is my take, for what it's worth....


Removing the 470 ohm resistor to ground will probably (I'm saying probably because I haven't tried it) create a situation where you have no output on the lead channel. This resistor helps create the amount of gain the tube stage will have. The larger the resistor (within reason), the more gain it will have.
I built a Plexi clone about 10 years ago and forgot to put the grid resistor on the 1st gain stage. I had no sound at all until I figured out what I had done.


Removing the capacitor across the rythm channel's gain pot will work to keep treble down at lower gain stages. This is pretty much what the Bright switch does on Fender amps.

Not sure what removing the 39 pf cap across the 3.3 M resistor would do. The standard Fender value is 10 pf. You could easily experiment with different values.
I use this tool: CSUB_SMC from these guys: https://amptechtools.powweb.com/subs.htm
It only goes down to 47 pf, so it won't work for this particular situation. It works great for finding the tone stack treble cap and the bright cap on amps though!

polaris20 said:

PDF is now up on this page at my blog:

http://biesiadecki.org/?page_id=77

midway down.

Click to expand...

thanks for hosting that, and thanks to monsta-tone for all the mods!

What mod to increase reverb? or make it more useful...

Hello,

there is a lot of misleading information in this thread so i will post the results of my current DC-5a modification here, perhaps it will be of some help to someone in the future.

1. Bias mod: It is possible to replace the 22k resisitor, but i would recommend to built it fresh (i will post pictures and schematics on request). It's a typical Smith-circuit and the 220uF capacitor is rated 63Vdc, with around -70Vdc after the 1K/(22k parallel 82k) voltage divider! Mine is still working, but i recommend to replace that capacitor with a 100V type (100uF is still enough).

2. Power-tubes: without the biasmod talking about Power-tubes doesn't make sense. The PT is a 561155 also used in the rectoverb so it's safe to say that there is enough reserve regarding the heater current. My DC-5a is working with 5881, 6L6 (-43V) and EL34 (-38V). I recommend to measure the cathode-current over a 1Ohm resistor (info everywhere on the net) and bias to ca. 70% of Pmax.

3. There might be an option to do a modern voicing mod on the gain-channel, i will test this and post the results.

@Monster-tone: the 470k input resistor on the gain-channel is not a fundamental part of that channel. To be precisely, the 1M 500pf combination of the clean channel is still active when the gain channel is activated and the additional 470k in parallel will indeed result in a 391k 500pf combination. This may sound dull. One could remove it or replace it with a 5M resistor.


Max

Thanks Max for chime in.
Looking forward to hear from you soon. Regards.

Teleman said:

Looking for DC3 bias mod and suggested bias current.

Click to expand...

Quick fix -Piggyback a 470K on the 120k in the bias circuit. This will bring the bias voltage down to a more tube friendly -14vdc instead of the insane -11 with 400vdc on the plates.

Adjustable? Replace the 120K in the bias supply with a 100k pot and 20K resistor.

Bob

Right on Bob!
Wish I had a DC-3 to try this on now!

The Serial EFX loop mod will work fine on a DC-10 right? Probably a stupid question but thought I'd ask before I tear the amp apart.
Thanks in advance!
Also, has anyone modded the reverb with a larger value pot or any other reverb mod for that matter? What were the results?

Yes it works with the DC-10. I've done it to a DC-3, 5 and 10 with good results.

Yeah, it works for any DC!
Like I said before, I usually make all of the connections on the Send jack (after replacing the Send jack with a Switchcraft 12A jack) and then use the extra hole for something else.
Once the connections are done on the Mix pot, you will notice that only 1 tab is being used and the thing is just taking up space.

As for the Reverb mod, you can do just about anything with it. I would have to look through my notes for specifics, but I'm pretty sure I changed the circuit to the same Reverb as the Maverick on my old one.

Serial EFX loop and master volume mods completed. Amp sounds great and my Boss DD-3 is no longer
distorting. Thanks for the info everyone. Now, the reverb on the lead channel is barely audible even when
the reverb is cranked. Is that just the nature of the amp? Will the larger value pot fix that or is there something
else I should try? Also, how hard is the more gain mod to do or is that something I need to send the amp for?
Thanks again!

The reverb will just not be as present on the dirty channel.

As for the more gain, there is a little you can do and still retain the clarity of the lead channel. Basically, if you add too much more, it will get mushy.

The higher the gain is set the less reverb you get. I put a very high gain Sylvania long plate in my reverb position and that gave it a bit more. Bob

Ughh! My Boss delay is still making that noise. Maybe the pedal is bad? It is powered by a Voodoo Labs PPII.
Thanks for the info. I think I'm going to forgo any gain mods and get a Xotic EP booster. That thing works great.
I can't seem to stick with a set up though and keep selling EP booster's. This would be my third one. There is also a
humm to the amp. I can hear it a little in standby too. I can feel the transformer vibrating at the same freq
as the hum. What does that mean?
Thanks a million. Boogieboard is awesome!

Well, tried the DD-3 with just battery power and changed cables with no joy. Still sounds garbled. The repeats sound distorted and garbled
like the input of the pedal is being overdiven. When I did the EFX loop mod I just snipped the white wire and capped then moved the red wire
to the center lug of the mix pot with the two orange wires. Did I miss something?