Negative feedback amp mods. I also added a 50k linear mid pot with the 6.
Negative feedback amp mods Now I understand. Princeton Reverb Chassis By Marcus Albrecht Pay close attention to routing the tremolo's control and tube socket leads. Jan 8, 2012 · Re: Fender 'The Twin' Red Knob Version Mods and Repairs by Mark » Thu Apr 27, 2017 11:26 am Thanks for sharing your mods, do you have any clips of the amp after it was modded or a clip comparing the amp to a stock red knob Twin? List of Amp Mods 3-Way Negative Feedback Switch My favorite tube amp mod. The bias setup will not affect the tone as long as you are lucky and able to find a sweet bias spot with a set of tubes. Jun 6, 2019 · new Mod-4. 3-Way Negative Feedback Switch This is my favorite and most useful amp mod, a three-way SPDT ON/OFF/ON mini-switch gives you: Normal feedback / No Feedback / Heavy feedback. Adjustable Bias Adjust your power tube bias for max output and sweetest tone. This document discusses modifications that can be made to the Fender 5E3 Deluxe amplifier. this instuctable also regroup lots of information I will cover easy to hard mods, how to bias it properly, route wires to reduce, see re… Other types of feedback Some amplifiers, most notably the Marshall Valvestate transistor amps, use negative current feedback in lieu of negative voltage feedback, or a combination of the two. The 5E3 Deluxe is a notable example as well as many tweed models prior to the D series. 6k and stock). The amp must be sent to us. They take the DR from good to great. If I understand correctly, the first pot controls the amount negative feedback, and the second will decide how much of the frequency gets rolled off. If you eliminate it entirely, expect quite a bit more noise and possible oscillation problems, especially if there are other mods that increase gain MOD 4. While a few of the early smaller Fender amps did not feature global negative feedback, I'm unaware of the Princeton being among them. A common mod with these amps was to change the channels from parallel to series so the guitar signal went through both V1A and V1B before hitting the third V2A gain stage. You'll need to register to get there but it's definitely worth it. Adding a switchable negative feedback loop around the power amp makes some sense if you want to be Dec 24, 2019 · This is a cool mod on a lot of Fender amps, and on a Princeton Reverb my personal approach would be little different than the suggested three way switch. May 31, 2007 · 1. The Marshall JTM45 Oct 21, 2020 · Global & Local Negative Feedback Mods for ODS #102? by Greenback25 » Mon Nov 02, 2020 7:24 pm Does anybody have the schematics for the standard global and local negative feedback mods for Robben Ford style Dumbles? Jul 25, 2015 · Negative feedback is effectively removed from the circuit, giving approximately a 3dB voltage gain. Captain Amp Mods Fender Pro Junior The Fender Pro Jr. Aug 30, 2002 · The introduction of negative feedback results in a cleaner, some would say, more sterile, sound. That 50K adds A LOT of gain. I was watching one of Uncle Doug's vids, and would like to add a variable negative feedback control to the amplifier. Dec 9, 2015 · Hey all, just finished up a Princeton Reverb build! Sounds excellent and for once didn’t require a ton of troubleshooting to get it running. Normal / None / Heavy selectable feedback. Consider that the entire loop usually consists of just two pieces of wire going from point A to point B with a single resistor in between, and it’s incredible that this can be Jan 4, 2018 · This drawing illustrates all three wiring options Amp Man suggests for modifying a Fender’s negative feedback loop to create more control and alter tone. The depth mod (just a Without a Master Volume control, the power amplifier is more likely to be overdriven first, sometimes generating a type of distortion that is not always easy to ignore with a microphone. . A bypass capacitor is added to the cathode of the tube, giving another voltage gain of 3dB. The purpose of NFB is to eliminate distortion in the amplifier, reduce instability, and extend frequency response. Nov 3, 2025 · The negative feedback in this amp does seem to apply some negative feedback with low resistor values but it has to go so low that it alters the bias of the second triode as well. These modded amps are where Marshall got the idea for the 2203 Master Volume preamp described below. Of course, you can restore the high end with a presence control. The Marshall JTM45 was a direct copy of the 5F6A Bassman but the feedback signal was tapped from the 16 ohm output transformer secondary The Negative Feedback Mod on this page describes removing the driver tube's cathode bypass capacitor (C22) which will reduce the amp's overall output and reduce power tube overdrive distortion. AB763 Blackface Modifications Switched Negative Feedback This is my favorite mod for the 5E3. Test it out and as soon as I increase the depth control the amp got *way* louder. first hit the market in late 1993, or at least the first release was released in September 1993. negative feedback loop mod - clipping the purple wire from the speaker out to the circuit board. new Mod-6. Switchable negative feedback loop. The Marshall JTM45 was a direct copy of the 5F6A Bassman but the feedback signal was tapped from the 16 ohm output transformer secondary Oct 13, 2021 · An extremely simple network that can have a tremendous effect on any guitar amplifier’s ultimate sound, the negative-feedback loop remains a rather mysterious thing to many new and novice amp builders and modders. One simple mod is removing the negative feedback. I added a negative feedback switch at the back (2. Improved heater wiring . It’s a really cool effect that I can’t wait to use in a band setting. An extremely simple network that can have a tremendous effect on any guitar amplifier’s ultimate sound, the negative-feedback loop remains a rather mysterious thing to many new and novice amp builders and modders. However, I'd like to add a switch so I have both flavors available, but don't really know where to start The power amp section of the AB165 got a couple of bad tweaks. 8k grounded to the pot so when the pot of set to 1 it’s effectively stock. This is often due to using negative feedback around the power amp, which the second of two mods in this excursion. The mod involves removing the reverb from the Normal channel, lowering the gain of the pre-amp, increasing the caps on the reverb to make it fuller, replacing the tone stack capacitors with higher quality caps, removing the protection diodes on the 6L6s, adding negative feedback, and changing the ground reference resistors on the heater lines. 3-Way Negative Feedback Switch This is my favorite and most useful amp mod, a three-way SPDT ON/OFF/ON mini-switch gives you: Normal feedback / No Feedback / Heavy feedback. Mod Your Fender Pro-Jr!: Hi, in this instructable i will show you ways to mod your pro-jr to change the sound in pretty much every ways. I’ve got a ampmaker wf55 I made ages ago. Simple mods like these make the 5E3 more versatile while preserving its original tone. This mod involves repurposing the ground reversal switch and employing it in the negative feedback circuit. Makes a subtle difference. 68uf cap Used a 10W 25Ohm power tube cathode resistor Switching the NFB circuit in and out of the amp gives some interesting tonal varieties. Rock 'n Roll! All that said, tweaking the 5E3 circuit so that it can use a 12AX7 up front is a reasonable adventure. I mean with the depth control at minimum it sounded just like it always does and by 9:00 on the pot the amp was just roaring loud. I put a standby switch in everything I've got a little hotter PT where I can use a 6L6 I recently took out my triode switch and converted it to another preamp cathode bypas cap option. Feb 20, 2022 · I would like to go from the normal 5E3 gritty goodness to the Negative Feedback Mod (NFB) with a footswitch. (R7 - 22k) Jvm Mods Great news!!! The JVM Forum is back in action thanks to the efforts of the moderator Andy. You know, all the buzz terms you see in ad copy on the subject of negative feedback. If you reduce or remove the negative feedback, you wind up with a hairier, more overdriven sound. I also got a plug in SS rectifier. Variable negative feedback new Mod-5. Mar 24, 2011 · One of the mods (the Attitude Mod) affects both channels. First, let’s have a very broad look at what negative feedback actually is. Here, the resistor ringed with gray, red, brown, and silver value marks is being desoldered, one lead at a time, to make way for another. Negative feedback can leave you and your amp feeling a bit flat and somewhat lifeless. I tried to add a negative feedback switch by using the 8ohm tap from the OT, and had no change whatsoever to the sound of the amp. --------------- Well it’s been some months since the Col Thread Apr 1, 2018 afd100 mod anti stiffness mod c83 mod choke mod compression Jan 11, 2010 · From what I understand this has to do with adding the negative feedback loop to the CVR per the "Moyer Mods". They carry a powerful signal that can interact with nearby leads and components Oct 13, 2021 · negative feedback mod is a big one, that's in negative feedback knob. One is the stupid, unbalanced bias circuit and a strange implementation of the strange negative feedback loop which was never seen in any Fender amp before or after. Without the extra switches and knobs on Mar 18, 2021 · Removed the standby switch Added the following Rob Rob mods - Switched Negative Feedback mounted by the speaker jack ( removed second speaker jack to make room) - a pre-PI master volume between the V1 and V2 - lead channel using the two normal input jacks - V1A uses a 2. I checked all connections with a DMM, everything checked out. once you have negative feedback you can use depth and presence, or change where depth freq and presence freq are centered with depth/presence freq (advanced) Jul 3, 2016 · Here was the plan First off I reduced the amount of negative feedback on this lil amp by increasing the resistor value to what I had in the drawer for my carbon comps 47k it is. In almost 20 years of production the curcuit was altered somewhat. Adjustable Balanced Bias Using a Balance Pot Adjustable bias with a balance pot to evenly bias unmatched power tubes. This is something like a presence control, but it affects the gain levels on the Soak channel AND it brings a bit of "hair" to the clean channel for those times when you're running mostly clean but want a bit more bite when you're really Dec 8, 2016 · Click to expand I did the same on a 5f2a based amp that I own similar results being brighter and more breakup. Nov 9, 2017 · Decreasing or eliminating negative feedback results in a quicker (but not necessarily at a lower volume) onset of overdrive, slightly more extended treble & bass, slightly more dynamic pick attack, and a slightly higher noise floor. I tried using the 16ohm Trying to get my head round negative feedback. Negative feedback can make an amp sound more "solid-state" by reducing the interaction between the speakers and the amplifier. Jul 9, 2012 · Amp headroom can also be adjusted by swapping the resistor in a negative-feedback circuit for a different value. Unleash the tone of your Pro Jr with the Supreme Mod Kit from Fromel Electronics! The Fender Pro Jr is a great value and a good sounding little amp, and with a little help can be a GREAT little amp. Try lifting the negative feedback,raw control is great,try NOS tubes,different speaker,change bias cap to 1k from the stock 470 ohm to get the bias a little cooler. For any modding information please go to the Modding Bible section of the forum. I never realized what an impact negative feedback can have on a high gain amp until today. Flip the switch back and you have your unaltered beloved 5E3 tone. I hadn’t see a presence control in a 5E3 (with a bypassed cathode) so I went about figuring out how to add one. Add Negative Feedback Loop (NFB): WHY: To further reduce the hiss found on the Lux and increase your headroom you must add a NFB loop to the ‘Lux. Both mods really add a lot of new tone options - the negative feedback allows you to go from stock JVM feedback all the way through 2203 JCM800 territory, to 5150 and VOX type negative feedback. Presence control. However, Rob Robinette's footswitch mod actually only toggles between no 22uf bypass cap and NFB. Combine this position with the Gain Boost Switch and you have a virtual 5E3. No---not all tweeds had negative feedback. That is less negative feedback right outta the gate so we have a little more drive and crunch already. I do believe this will change the negative feedback voicing to not match any existing Fenders. Jul 18, 2023 · I'm a total newbie, only built one amp so far (it worked first time and sounds great), so please be kind! I built a 5F1 based kit from AmpMaker in the UK, please see the attached schematic below. 2k, 5. Consider that the entire loop usually consists of just two pieces of wire going from point A to point B with a single resistor in between, and it’s incredible that this can be The negative feedback loop can easily be tweaked to alter the treble cut and distortion in your amp. Since then, much has changed. I put a 22k resistor in series with a 50k pot (tested the range with DMM beforehand), and at no point along the pot sweep did it sound any different than when it was switched out. If you want a total tonal transformation Negative feedback switch I've got a 5E3 tone stack that switchable/off to the original Champ raw sound. Without a Master Volume control, the power amplifier is more likely to be overdriven first, sometimes generating a type of distortion that is not always easy to ignore with a microphone. The 'No Feedback' position makes the amp break up early kind of like a 5E3 Deluxe. Dec 31, 2017 · Greetings! I have two questions regarding an NFB mod that I made to my Fender Hot Rod Deville 212 based on lots of info I found online. I chose to use a 500k B pot to introduce and do away with the negative feedback. It describes several popular mods including adding a master volume, switched negative feedback, and creating a lead channel. Adding Negative Feedback (NFB) 'civilizes' the 5E3 amp by decreasing Fender Silverface Amp Modifications There are many ways to tweak the tone or "voice" of a guitar tube amplifier. I also added a 50k linear mid pot with the 6. The negative feedback loop can easily be tweaked to alter the treble cut and distortion in your amp. However Dec 5, 2019 · Most amps deal with this sort of issue with negative feedback that handles the low end but it will also dull the high end. Apr 19, 2010 · I'm testing this negative feedback mod for a Carvin Nomad (see attached, called Attitude Control by author Hasse). HOW: Solder a 10k resistor in the empty space marked R41. Mar 22, 2017 · The negative feedback that your boss might give you during your annual appraisal and negative feedback in an amplifier are different things, but the results can be similar. WITH the NFB in place its great and I like the clean - also like how much it reduces the inherent hiss of the original design. Switchable Solid Hoffman Amplifiers Tube Amp Forum, Modified a 5E3I'm certain that Neil Young loves it when the power tubes of his 5E3s get the snot beaten out of them 'coz they're biased so hot. It can also make the transition from clean to distortion more abrupt, as the negative feedback loop fails when there is insufficient forward loop gain to maintain the loop, which occurs when the output hits clipping. I combined the two. I added SPST switch between OT secondary and 22K resistor which breaks that connection. Make sure the amp is up to snuff everywhere else. I’d personally like a variable resistor (a potentiometer) to vary the amount of feedback to my liking depending on what sound I am going for. Channel voicing vintage-style mod switchable clean/crunch green boost anti gain mods with gain switch and bite control controllable negative-feedback-mod choke mod master mod JVM 410 Captains Favorite Mod package price: 397,- € If all the extra knobs are too much for you, you can get all the modifications with our favorite pre selected sounds as well. NOTE: This is a service, not a DIY product. Given that the amp now has a twin reverb output transformer, it is now running at 8 ohms. The author's favorite mods include switched feedback, a lead channel, and master volume. I installed a Soldano style depth mod in my Mig60. The mod is useful to me to brighten up the amp when using humbucker based guitars, though too bright for single coils. Dec 8, 2016 · The first several variants of the Princeton were single ended amps & all featured global negative feedback. It changes the amp from a one trick pony to a very versatile amp by giving you much more clean headroom at the flip of a switch so higher volume 'clean jazz' can be added to the 5E3's repertoire. It's a pot that allows you to change the negative feedback from the stock amount right down to zero. I'm pretty sure that Fender has released ltd edition versions with these mods, in the past. Examples of Quiet Modern Princeton Reverb Build Lead dress in amps with reverb and tremolo is very important to prevent hum, oscillation and instability. These mods will make your amp more reliable, have less noise and better tone. 3-Position Negative Feedback Switch with: Normal 5E3 / No Bypass Cap / NFB for three levels of preamp gain. This was suggested by @mhammer and by watching Uncle Doug: NFB and Presence. To reduce noise caused by AC powered heaters I employed two techniques: virtual center tap and DC heater reference. Amp designers and modders can alter the clean and overdrive tone by changing component values, adding components, removing components, adding gain stages or even adding complete circuits like negative feedback. Mar 17, 2018 · My goal is to build this amp into the ultimate AB763 head unit, and have size correct 1x15 Vibroverb, 2x12 Twin Reverb and 4x10 Super Reverb cabinets. This amp is a solid build and very quiet. The purpose of the NBF loop is to clean up the tone and cancel out the mid/higher frequencies and upper harmonics (distortion) at the entry point of the phase inverter which is placed in front of the power tubes. The second modification involves re-purposing the ground-reversal switch so that you can either play the amp stock or remove some or all of the negative feedback that was part of the stock design. A pretty standard set of mods is master vol, Bassman tone stack, and a negative feedback adjustment. The bypass on mine is wired to a toggle switch so I can turn bypass on and off. We have to remember, Leo & his team (along with many amp producers of the day) did not so much "design" these amps, rather, they lifted the designs what mods to fender 135 watt twin? - The Steel Guitar Forum Strings & instruction for lap steel, Hawaiian & pedal steel guitars The RobRob Deluxe amplifier incorporates the following modifications: Lead Channel Mod Higher gain channel designed for cleaner, leaner, modern overdrive tone. This channel is very pedal friendly and really responds to boost pedals. The idea is to add variable resistance at R71, which feeds the negative feedback loop. Also Takes the Foglifter a step further with adjustable negative feedback. Edit to add that a 12AY7 in the V1 spot can do some nice things, and is a cheap easy mod. I've read that this is supposed to make the amp sound less stiff and more "tweedy". 7K cathode resistor a . 3-Way Negative Feedback Switch This is my favorite and most useful 5F6A mod, a three-way SPDT ON/OFF/ON mini-switch gives you: Normal 27k (2 ohm tap) feedback resistor / No Feedback / JTM45 equivalent 10k feedback. gkqjmbombfgsrcmxksbvnnxporhizcesbleaixmgfaialfcijrpnzcebwxyruynexu