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Post subject: Need help for the elect theory knowing guys re DRRI
Posted: Fri Dec 23, 2011 9:03 am
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So i did a couple mods a couple days ago on a DRRI i picked up.The first was the "fritz" mod, that allows you to use the reverb and vibrato (tremolo for real) in the Normal channel. That channel is the best of the two for overdrive, the Vibrato is too shrill because of the bright cap, but i didnt want to take the bright cap out, because i like the clean sound. I also changed C25 from a .001 to a .01, to lower the headroom, so with my low output PAF equipped PRS, I start getting breakup at 4 instead of 7 or 8. These 2 mods made the amp perfect, i couldnt imagine going back to stock, well maybe the lower headroom mod at some point, but not the channel reverb one.
Another HUGE plus to doing that mod, is my two channels are now in phase with each other, and I can jumper them so i plug into input 1 of channel 1, and jump to channel 2, and i can access both without unplugging plugging cables.
Ive jumped them sever different ways to find what I like,what I'd llike to know is; I know what im hearing, but i dont know why. Ive repaired, modified, built amps and pedals, but my knowledge is all working knowledge i picked up. First by fixing things doing a step by step instructions, moving on to build kits, the breadbaord point to point. Over time, i have knowledge for what Im doing.

A lot of you have a good working knowledge of electronics theory that I dont, Im more of "lets do it and see what happens' as opposed to theorizing, wish i had more working theory. anyway
Ive done the jump in the following ways; the normal, plug guitar into channel 1 input 1, using a patch cable to jump from input 2 to channel 2's input 1.

-another way is using a Y cable, plugging both male ends into input 1 on both channels.

- the other way gets a bit more confusing; I have an adapter that is a male jack, with two female jacks in the back, just like the Y cable, but its not a cable, just a jack. On this one, ive plugged the male end into input 1 of channel 1, and my guitar into the female input, and the patch cable that goes into channel 2 input 1 in the input right next to it.

-another option was using the Y cable, with both ends going into channel 1's input 1 & 2.

Most of these give me a differnt tone, but can i get the explanation of what's going on when i do this?


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Post subject: Re: Need help for the elect theory knowing guys re DRRI
Posted: Fri Dec 23, 2011 10:04 am
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Forget theory and learn to read a simple schematic. All that is involved are simple resistor circuits on the amp inputs, very clear on the schematic. Anyone that wants to work on amps should learn to follow a schematic.

Looking at the schematic will reveal the magic. You have two 68K resistors on each channel's inputs to the amp, one resistance when input one is used, and a different value when input two is used. The jacks select which resistance. Using input one on either channel by itself, puts both resistors in parallel, giving 34K, while using input two by itself selects only one of the 68K resistors. So input two on each channel is attenuated 6 db when used alone. Both inputs for each channel become equal when both are used simultaneously.

Jumping the channels with a cable from normal input two to "vibrato" input one, puts some of the resistance in the signal path between normal channel and "vibrato" channel input one. So guitar into normal channel input one, and out of normal channel input two into "vibrato" channel input one, the guitar signal goes through one 68K resistor (to V1), and then back out through the other 68K resistor on normal channel, and then through another 34 K of resistance on the input of the "vibrato" channel. When you use the "Y" cable plugged into inputs one of each channel, you are only going through 34K on each channel then straight to the preamp tube circuit on each.

In other words, the different ways to jump the channels, will each have a different resistance selected. A third option (different resistance/different sound) would be to put the jumper cable from input two of normal channel, to input two of "vibrato" channel, changing the attenuation a little more compared to using input one of "vibrato" channel.

Yes, I wish they would get the terminology straight myself. Easy as pie, tremolo is varying the volume, and vibrato is varying the pitch. The amps don't have vibrato and the Strats don't have tremolo. It has been screwed-up at least since Leo misnamed the vibrato on a Strat, calling it "tremolo". Did no one have the guts to bring this to Leo's attention? :roll:

http://support.fender.com/schematics/guitar_amplifiers/65_Deluxe_Reverb_schematic.pdf

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Post subject: Re: Need help for the elect theory knowing guys re DRRI
Posted: Fri Dec 23, 2011 10:36 am
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That answers my questions. Iwould read the schematic, but alas, my laptop doesnt work. I dontknow if you've every tried to read a schematic on a 4" cellphone screen, not the easiset thing to do. SO running the Y into both inputs on 1 channel will yield the same as just plugging into input 1?


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Post subject: Re: Need help for the elect theory knowing guys re DRRI
Posted: Fri Dec 23, 2011 11:48 am
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:lol: I can barely read them on a computer screen.

You are correct, a "Y" wouldn't really do anything if used on only one channel, as doing this will connect the two resistors in parallel just the same as plugging into input one only. If you wanted to be picky about it, the use of the "Y" for only one channel will add a very small, negligible amount of resistance to the total. So as long as a good cable is used, no difference in sound, so no point.

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Post subject: Re: Need help for the elect theory knowing guys re DRRI
Posted: Fri Dec 23, 2011 12:29 pm
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I wonder if plugging the Y cable into input 1, then plugging nothing into the other Y connector would do anything at all. The wire connecting. R12 w/ r25 allowing channel 1 to use Tremolo and reverb as well as putting the channels in phase is by far the most useful mod on these amps. Putting a 10;trimpot go adjust the midrange will be good. I've. Heard them with 8K and 10k. The 10k sounds better, but I wonder if later down the road id want less mids, hence the use of trimpot. The 10k was what was used in 1965, and 8 was with silverfaces. They use like a 6.8; now. Also changing C25 to lower the headroom is great if you don't need loads of headroom. I want to change the reverb pot to one with a better taper, annd change the tube for the tremolo to 12au7 is supposed to tame. The reverb a bit, though the reverb played through the normal channel is pretty tame. If I didnnt use the tremolo as much as I did, id probaly just render it deactive to free up some gain.


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