Search found 169 matches

by d95err
Fri Feb 21, 2020 3:08 pm
Forum: Marshall Discussion
Topic: Relays for 2-channel 2204
Replies: 25
Views: 6989

Re: Relays for 2-channel 2204

Having the fx loop after the master volume is a bad idea, IMHO. It means the looo level is dependent on the current MV setting. In practice, this means you will get terrible signal-to-noise ratio if the MV is low and/or you’ll have way too high signal level when the MV is high. Move the MV to after ...
by d95err
Wed Jul 31, 2019 6:09 am
Forum: Marshall Discussion
Topic: Marshall 2205 Extra Gain
Replies: 17
Views: 3876

Re: Marshall 2205 Extra Gain

There are two different versions of the 2205, which are completely different amps with different topology. I assume you have the later 2205 (the type used by e.g. Schenker and Norum). In this version, the boost channel has a 10k with a diode in parallell. This stage is diode biased and is already at...
by d95err
Fri Nov 02, 2018 6:37 pm
Forum: Technical Discussion
Topic: Jet City JCA22 Attenuator Mod
Replies: 1
Views: 436

Re: Jet City JCA22 Attenuator Mod

You need to be aware that these things get really hot. Even though the L-Pad itself may be able to take 100W, things around it may not. I used a 100W L-Pad with a 30W amp once and the insulation to the connecting cables started melting. Eventually the solder started melting. Ventilation for the L-Pa...
by d95err
Wed Apr 11, 2018 7:40 pm
Forum: Marshall Discussion
Topic: Master volume mod
Replies: 16
Views: 5543

Re: Master volume mod

Do the mod I posted and now when your amp is all the way up it's it's actually turned up to 6 ( half way). The master volume taper is logarithmic, so when the master volume pot is turned up halfway, the resistance divider is something like 900k/100k. Use a 900k series resistor and 100k pot if you w...
by d95err
Mon May 04, 2015 6:44 pm
Forum: Marshall Discussion
Topic: Wanted by internal images of JMP1H or C
Replies: 7
Views: 4002

Re: Wanted by internal images of JMP1H or C

RockinRocket wrote:After seeing the schematic for the jtm 1 I lost all interest. Of course it was a reversed engineried schematic but its nothing like the real deal.
Can you explain how it was "nothing like the real deal"? What would be needed for you to consider a 1 Watt amp to be the "real deal"?
by d95err
Tue Apr 14, 2015 6:45 pm
Forum: Technical Discussion
Topic: power scaling on Carvin x100B ?
Replies: 11
Views: 2069

Re: power scaling on Carvin x100B ?

Remember that the switch will see the difference between the selectable PI voltages, not the full PI voltage. E.g. 400V on one side and 200V on the other, meaning the voltage across would be just 200V. A big heavy-duty switch would be overkill. I would use something like this: http://www.tube-town.n...
by d95err
Thu Apr 02, 2015 9:02 pm
Forum: Technical Discussion
Topic: bright switch to Airbrake? Update:Tone POT?
Replies: 7
Views: 1185

Re: bright switch to Airbrake? Update:Tone POT?

jamme61 wrote:what about adding a tone pot? why they don't put one on all the attenuators?
Because the tone pot would have to be able to handle (almost) as much power as the whole attenuator.

The Weber MASS Lite attenuators actually has this (labled Mids-Highs). It is a 50W pot for the 50W version.
by d95err
Tue Mar 24, 2015 9:15 am
Forum: Technical Discussion
Topic: 5E3 farting out sound and VVR
Replies: 6
Views: 1779

Re: 5E3 farting out sound and VVR

Technically, I believe "farting out" is when you have to much bass going into a distorting stage (try playing palm muted heavy riffs with a fuzz pedal...). From your description, it sounds like extreme sag. The 5k dropper to the screen supply should cause significant sag, regardless of rectifier typ...
by d95err
Wed Mar 11, 2015 1:59 pm
Forum: Technical Discussion
Topic: There's a new Randall Smith in town
Replies: 77
Views: 13448

Re: There's a new Randall Smith in town

I think this says a lot about the state of patents these days...

http://www.cs.virginia.edu/~gfx/Courses ... Patent.pdf

:D
by d95err
Thu Feb 26, 2015 10:39 pm
Forum: Technical Discussion
Topic: Mesa boogie king snake and the mid/boost control
Replies: 31
Views: 5955

Re: Mesa boogie king snake and the mid/boost control

http://www.mesaboogie.com/amplifiers/electric/mark-series/king-snake/index.html Kind of funny how they first claim the amp to be an "exact replica" of Santana's old amp and then go on to describe all the changes made from the original... :D I'd be willing to bet that the mid/boost function is just ...
by d95err
Mon Jan 26, 2015 10:15 pm
Forum: Technical Discussion
Topic: 100 ohm resistors for filament ground reference burning up
Replies: 18
Views: 3498

Re: 100 ohm resistors for filament ground reference burning up

What type of resistors are you using? 2W? 1/4W?
by d95err
Sat Nov 15, 2014 10:07 am
Forum: Technical Discussion
Topic: First-Time Tube Amp Design
Replies: 43
Views: 4649

Re: First-Time Tube Amp Design

As it is your first build, I strongly recommend sticking to old prooven designs. You don't have to copy a particular design, just use bits and pieces of them as building blocks.

Old Fender schematics from the 50s and 60s is a good place to start.
by d95err
Thu Oct 23, 2014 11:28 am
Forum: Technical Discussion
Topic: Taking an RMS control out of a circuit
Replies: 15
Views: 2301

Re: Taking an RMS control out of a circuit

On the schematic, the RMS control is a variable cathode resistor on the power tubes. I.e. the amp uses combined fixed and cathode bias. To get rid of it, set the RMS control to whatever setting you like and then measure the resistance. Replace it with a 5W fixed resistor with that value. That is th...
by d95err
Wed Oct 22, 2014 6:23 am
Forum: Technical Discussion
Topic: Taking an RMS control out of a circuit
Replies: 15
Views: 2301

Re: Taking an RMS control out of a circuit

On the schematic, the RMS control is a variable cathode resistor on the power tubes. I.e. the amp uses combined fixed and cathode bias.

To get rid of it, set the RMS control to whatever setting you like and then measure the resistance. Replace it with a 5W fixed resistor with that value.
by d95err
Mon Jun 09, 2014 6:23 am
Forum: Technical Discussion
Topic: Elementary questions on gain.
Replies: 36
Views: 3913

Re: Elementary questions on gain.

1. The "gain" value you're talking about is basically the theoretical max gain of the tube. The design of the gain stage will limit the actual gain. I.e. substituting for a higher/lower gain tube does not necessarily mean higher/lower actual gain. 2. It would depend on circuit design and and input s...