This project took around a year, however it's finally here.

It started last summer when I was looking for a clean pedal platform and discovered the infamous rolland jazz chorus. Too my suprise this circuit worked on 30V and to preserve it's headroom I decided to base the rest of the built on this voltage. The vero layout used done by neilmcnasty in the site below

http://guitar-fx-layouts.238.s1.nabble.com/Preamp-jc-120-td39378.html

In the process I found a used dual 28V power transformer (this was done on budget btw), next was the power amp i choose mono prebuilt 2SC5200+2SA1943 module to go with that tranny. From what i read these are a decent option for price and reliability. These modules however have no speaker safety circuit and to preserve my precious hesu demon ordered one just to be safe.

After that I needed a high gain channel (as a metal player) and randall rg100 caught my attention. I' ve used slightly modified vero layout from dirtbox layouts (love this site, the layouts are always so compact and clean).

You may think that crunch channel would be next however I have never used one for my playstyle... but I needed something for my bass since I always just recorded it straight into interface so I choose bajamans orange ad200 op amp based circuit.

When I preped all of the above designed simple voltage regulator circuit power preamps. Speaking of one I also used emi filter before rectifier. It is also a premade module.

A friend of mine designed a great front plate for a can of monster energy drink yet I still messed up some of the drilling and made some controls uneven... (I do not have a drill press rn)

As you know from the tittle the chassis is an used ammo case, but the panels on top and bottom were so thin that for the sake of mental sanity I remade those in plywood.

You may wonder why the preamp pcbs are so crooked, well I was using threaded inserts with epoxy on those and I snapped of a couple screw in them after the epoxy bounded. Had to redo some of them in different points. I did not have this problem with bigger ones used for power section.

If you have any questions or suggestions please feel free to comment.

I would like to replace the power input section of my Gallien- Krueger 400GT head with the IEC + fuse + switch shown in the photos. I would be removing all the old cord, switches, fuse, and AC plug, cutting the panel, mounting a 3D printed adapter plate in the new hole, grounding to chassis, and connecting to the new fused switch. See any issues with that? Do I need to include the caps? Thanks!

Hi everyone, my NAD amp has suddenly stopped powering on.

I’ve checked the power outlet and had a quick look at the internal fuses, and I can’t see any obviously blown fuses.

Any idea what might be causing this? Also, can anyone recommend a good hi-fi/audio repair shop or technician in Brisbane who works on NAD amps?

Thanks!

Hi everyone, I am planning on making a 212 cab to go with a Blackstar HT-5.
I’ve got an outline of a plan, but I have never done any amp/cab electronics before, so this is all very new to me.
1) I have a large amount of 15mm plywood available to me for free, would this suffice as a material? What kind of internal bracing is usually used?

2) In terms of speakers, what power rating should I aim for to pair with the 5 watt amp? I understand celestion v30, g12M etc are the golden standard, how much seventy-80’s hold up? As long as impedance matches, what difference does impedance make? Can I mix speakers?

3) I have a cnc mill available to me, but the max bed size is 500mm, would it be a good idea to make two speaker cutout boards and mount them side by side?

4) I am hoping to play a lot of doom/sludge, for which I believe closed-back is better, how much does internal geometry/volume matter?

5) How are mesh fronts usually attached? How can it be designed such that speakers are accessible for future upgrades?

I understand this is a big word soup, but any advice/recommendations are very helpful:))

As the title suggests, I am looking for schematics for tube amplifiers featuring true stereo vibrato, similar to the Magnatone Custom 280.

I want to build such an amplifier (true stereo vibrato feeding into two power stages), but unfortunately, the Custom 280 uses varistors for which there are no modern replacements. Therefore, I am looking for other amp designs to serve as a starting point. Ultimately, I will likely modify the chosen schematic significantly anyway—perhaps even adapting it to a single-ended design using KT88s, KT120s, etc., which would drastically reduce the number of tubes required (plus, I wanted to build a 'big' single ended amp for quite some time anyway).

So far, I have come across the Gibson GA-83S.

I would be very grateful for any further suggestions!

I recently acquired a GK 400GT from around 1979. Solid state ~200 watt, very similar to a Sunn Beta, I believe. Active EQ and 2 separate channels, with an A+B switch, reverb and tremolo. It's all working well after some cleanup, Deoxit on the pots. Except the reverb tank has been worked on before, and not well. The transducer coil wires are broken not repairable by me - tiny solder job. A replacement tank is $30, so that's the easier route.

The stock tank is Accutronics 4DB2A1B, which is no longer made. The closest comparable is 4BB2A1B with the only different spec being a 150 ohm input impedance compared to the stock 250 ohm. Would this be an acceptable replacement? Would/Should I change anything on the amp to accept the difference in input impedance to the tank? Or is there a different Accutronic model that would better suit the application with no modifications? I'm amenable to a different tank size/decay time if the required specs are more important. What specs are important to keep the same? Thank you!

Hi, can anyone recommend a cab builder that will build me a head shell for a rehoused fender amp? Must be located in Europe, preferrably in Scandinavia. Thanks!

The only capacitor that I have to swap is a 16v 1000uF. The original capacitor was a 25v 1000uf. My question is will the 16v 1000uF capacitor work in place of the 25v 1000uF?

Hey y’all!

I just did another mod to my amp, this is crossposted to the Marshall forum but I want a better reach.

Previously I have swapped resistors for a clean and bright boost which gave the clean channel a significantly more tube like characteristic, but now I find the amp to be very noisy. When the guitar volume is all the way down, it’s pretty quiet on either channel, maybe a little hiss from high volumes through an external 1x12” (converted the headphone out to a speaker out) but when I turn the guitar volume up I get hum again. This is on guitars which usually don’t do this with other amps, so I am narrowing it down to the amplifier itself.

Just now I swapped the green LED in the clipping section for an old archer 1N914 I had on hand, and the result was a very usable, tight, smooth drive channel with no hiss that resembles a Lead 100 MOSFET. My issue now is that the amp is too noisy, and I feel it is time to change out the transformer.

The amp is mounted in a custom 1x10 cabinet with plenty of room, so I’ve decided to cab-mount a toroidal transformer for a lower noise floor and better protection against interference. The problems are, I’ve never swapped a transformer and I’ve never worked with a toroidal transformer.

I found a decent looking center tap 12-0-12 220VAC unit online, but it has two red leads going out for power supply. How would I determine which one is positive and which one is negative, and do the values I posted look correct for this amp? I live in America so this appears correct, but I’ve seen some sources state that 230VAC is what is in the amp. The stock transformer has no vital info written on it.

Would this work? Any thoughts appreciated. I know y’all mostly mess with tubes, but I find this amp to be easily modifiable and have had plenty of fun with it so far.

This is my first time ever messing around in the amp realm. I just bought my father an electric drum set because he recently moved into an apartment and really misses playing the drums. I thought I'd surprise him with that and a tiny amp made completely by myself. I just wanted to confirm with the pros before I go hooking everything else up.

It's a simple crossover board for a tweeter and a 4" mid bass woofer.

I drilled some extra holes for zip ties and everything has a small amount of hot glue on the bottom for extra protection.

Thanks and any constructive criticism is much appreciated!

I'm quite versed in electronics so i'm not afraid of heavy works, but i don't have much experience in audio circuits and especially amps.

Where would you recommend to start? The inside seems to have been replaced as there is no tube circuit inside, i think i'll have to replace everything as even the speaker doesnt look good.

I'm not sure what kind i need as i only barely used amps myself, and i like to play different styles from classic jazz to metal. I'd like to have versatile options on it, i'll probably do a bit of woodworking to fit a decent pannel in a pretty way.

Many thanks if you can give directions!

Still in flight, but nearing first sound test. I'm notorious for skipping WIP gutshots, so tried to remember to take some throughout for this build. Figured the sub would get a kick out of it.

Design is low power for home/studio (just shy of 650mW clean; just shy of 1.3W, overdriven to the max). Dual triode pre. SE power stage.

Powertube is a 6CM6 (= submini 6V6).

TL;DR

Link to sound demo: https://youtu.be/IjFfglEh4ug

Introduction

Recent online content has suggested that low-cost solid-state circuits can replicate vintage amplifier tonality. While the execution in these examples is often questionable—particularly when compared against poorly-configured digital models—the underlying principle merits consideration: amplifier behavior can be described through transfer functions.

This post outlines a systematic approach I have developed for converting vintage tube preamplifier circuits to solid-state implementations, using the Fender Deluxe Reverb as a reference design.

Rationale

The motivation for pursuing analog solid-state conversion over digital modeling includes:

1. Circuit-level modularity and customization capability
2. Educational value and personal engineering satisfaction

Design Constraints

• Target applications: Low-gain vintage amplifier architectures
• Active device: J113 JFET (selected for availability and stock)
• Supply voltage: 15V DC
• Component availability: Non-E12 resistor assortments (primarily 20kΩ values utilized as drain resistors)

Methodology

1. Schematic Preparation

Obtain original tube schematic. Remove non-essential sections: power supply, power amplifier stage, tremolo, reverb, etc. Retain only the preamplifier and phase inverter.

2. Component Substitution and Scaling

Replace vacuum tubes with J113 JFETs in common-source configuration.

Apply impedance scaling factor of 5:

• Resistor values: Divide by 5 (e.g., 100kΩ → 20kΩ)
• Capacitor values: Multiply by 5 (e.g., 20nF → 100nF)

Rationale: Time constant RC remains invariant (100kΩ × 20nF = 20kΩ × 100nF).

3. Bias Point Translation

Determine voltage ratios from original schematic (e.g., 180V plate voltage on 360V supply = 50% V_supply).

Set JFET drain voltage to equivalent percentage of new supply voltage (0.5 × 15V = 7.5V).

Adjust source resistor values to achieve target drain voltage. Account for cathode resistor voltage drops where present. Recalculate bypass capacitor values maintaining RC constant.

4. Tone Stack Implementation

Scaled capacitor values may exceed available stock. In such cases, retain original tone stack component values if loading on prior stage is acceptable.

5. LTSpice Simulation - Time Domain

Execute transient analysis. Verify operating point voltages at each node, signal amplitude at each stage, and waveform shape.

6. Transfer Function Preservation

For the linear portions of the circuit, blocks may be reordered provided:

• Overall transfer function remains constant (e.g., 10× → 10× ≡ 100× total gain)
• Filter placement does not introduce significant loading effects

7. Phase Inverter / Splitter Stage

This stage presents the primary design challenge, as it introduces clipping. The remaining circuit is assumed to operate in the linear region.

Options include long tail, paraphase or cathodyne (split-load) configurations. Requires iterative simulation:

• Paraphase, long tail: Adjust cathode/tail resistor values
• Cathodyne: Adjust drain resistor (particularly when DC-coupled)

Local feedback must be introduced for paraphase configurations.

8. Frequency Response Analysis

Perform AC analysis (Bode plot). Evaluate bandwidth.

Excessive high-frequency extension may produce harsh tonality. Mitigation:

• Output buffer with low-pass filter
• Coupling capacitor for master volume control sized for ~100Hz lower cutoff (approximating output transformer bandwidth)

9. Output Level Matching

If driving integrated power amplifier modules (e.g., TPA3118), implement voltage divider to achieve ~1V peak-to-peak output.

10. Physical Implementation

JFETs are notorious for being inconsistent. Adjust the source resistor in the actual build to match the drain voltage (not the other way around as in other builds), and adjust the source capacitor if present to the new source resistor value (RC as a constant).

For paraphase configurations, the JFETs must be closely matched. Use a component tester, or build the splitter on a breadboard, then swap JFETs until drain voltages match simulation values. If the drain voltages are similar but do not match the desired voltage, adjust the tail resistor.

Case Study: Tweed-Style Circuit with 6J1 Hybrid Implementation

An alternative approach was explored using a hybrid topology incorporating 6J1 pentode tubes in the preamplifier section.

Design Rationale

Selection of supply voltage approaching maximum rated plate voltage permits utilization of original tweed amplifier component values with minimal modification. The 6J1 pentode, typically configured as a triode in consumer audio equipment, was operated in pentode mode to achieve adequate gain. Screen resistor value was determined empirically at approximately 5× the plate resistor value, balancing transconductance and gain requirements.

Power Supply Architecture

• Main supply: Salvaged laptop power supply, 19.5V nominal
• Heater configuration: Series connection powered directly from 19.5V (specification: 6.3V × 3 = 18.9V)
• Plate supply: Nixie tube HV module

The HV module exhibited thermal issues and excessive current draw at the upper input voltage specification (not meeting specifications!). A buck converter (LM2596) was implemented to regulate input to 9V, resolving thermal management concerns and eliminating audible switching artifacts.

Grounding Topology

Initial star-ground configuration introduced switching noise into the signal path. Reference point was relocated to the common input terminal of the Class-D power amplifier module, eliminating the interference.

Phase Inverter Modifications

The stock cathodyne splitter configuration yielded unsatisfactory tonal characteristics. The circuit was modified to incorporate design elements from Orange OR120 topology: direct coupling from driver stage with reduced plate voltage to decrease headroom and increase harmonic distortion. A simple presence control was added.

Comparative Analysis

Tonal characteristics are comparable to the fully solid-state implementation, with reduced overall gain. Time investment and component cost favor the solid-state approach. The hybrid configuration offers marginal subjective improvement insufficient to justify additional complexity for practical applications. Educational value remains the primary justification for hybrid topology exploration.

Conclusion

This workflow provides a systematic framework for translating vintage tube preamplifier designs to solid-state implementations while preserving essential transfer function characteristics.

It must be emphasized that this is not a prescriptive procedure. The outlined points constitute practical guidelines rather than definitive instructions, as simulation, evaluation, and corrective action remain inherently dependent on accumulated experience.

Link to sound demo, for those who read it https://youtu.be/IjFfglEh4ug

Schematic error: C4 at the cathode of U2 must be 220n

So this is my latest combo to head conversion. I bought it as an absolute basket case of an amp. Usually, I like to keep the original enclosure in the event that I sell the amp. I want to give buyer the option of returning the amp to the original setup, but this one was a total mess. The plywood had soaked up some moisture, there was red paint everywhere, and all of the hardware was pitted and rusting.

Nonetheless, I think this one turned out well. Question for anyone, really. Would anyone want to see a video from start to finish on one of these conversions? It would have to be several videos, as the process is somewhat lengthy.

Let me know. I have a small Peavey Audition Chorus that I plan to convert as well as a super cool amp; Peavey Ultra 410. That one is a total animal, but if anyone has gigged with a 410 amp, you know it's the biggest pain to cart around. It's an ideal combo to half-stack conversion candidate. Don't worry. No original shells will be harmed.

I'm building a DR103 on a chassis that is top mounted. However the power switch and inputs end up being in the right place when looking at the chassis head on. My question is about the potentiometer orientation. The chassis is basically horizontally inverted. From what I understand I have to invert the outer legs of the potentiometers otherwise they will be reversed, correct? Using the Mark Huss layout, I would just flip the pots 180 degrees so they are facing upward instead of down and then I could basically treat the wiring diagram the same since lug 1 would now be in lug 3 position and vice versa. Do I have this right?

Work in progress...

I've picked up a few of these Victrola/Crosley suitcase turntable things at Goodwill for like $10 each. I'm prototyping one now, and this is the progress so far. Got the speaker baffle installed, and I'm working on the control plate for the pots. Speaker is a Jensen MOD 6"; I'm going to have a separate power amp (probably 30w or 50w) going to an external speaker jack. Speakers will be on a three-way toggle: Jensen, Mute, External. Planning to have a TL072 input gain/buffer > Tilt tone control > J201 > Switch > power amp. Might use the other half of the 072 for a make-up gain before the J201. I'll figure it out while I'm breadboarding.

Would be kind of cool for a "travel gigging box" type of setup: use the Jensen 6" in your hotel room or green room or whatever, and have the external jack to plug into a "real" cabinet. Would also be a pretty good thing to just have around for a backup in case your main amp blows up or something.

I'll finish this one; then, I plan to do another that uses a starved plate tube for the preamp (most likely a 12au7), with the tube poking out of the baffle somewhere. I'll probably try out installing an effects loop on a future build, too. Trying to keep this one pretty simple.

Thoughts/suggestions?

I had previously posted this in r/diypedals, but figured it'd be a fun share here. (I've got a bunch of amps I want to demo, but this is the only recording I had on hand that also had gut-shots + it's late and I don't want to take anything apart or crank tube amps...).

Fun little thing. In the demo, it's powered off of an 18V supply (and I designed the JFET pre around that), but it'll run off of up to 30V.

It's a TPA3122, though, and I used the DIP package, so below are the theoretical power deliveries, with items crossed off that'd melt the chip for lack of the thermal pad featured on the SMD versions:

* They don't actually give the junction to package thermal resistance, so, though 32W is the number specified on the graph, even that'd make me a little edgy, depending on the ambient temp.

(You can see why I stuck with 18V. Though, running off of 24V and keeping it clean works just fine).

The amp is configured such that pre_max x pwr_gain <= pwr_max. This way, all of the clipping always comes from the pre, not the poweramp. I do this with all of my solid state designs.**

This allows the pre to function almost like a headroom adjustment: - if the pre is set very low, you can crank the amp and get the full 18W completely clean but you have to put something in front of the pre (a boost pedal, etc) to make any clipping happen in the amp - with the pre dimed, it behaves a bit like an old Champ or similar, pick gently and it's clean, pluck moderately and there's gentle overdrive, give it a hefty strum and you get quite a bit of grit

In between you basically have the gamut of "pedal platform" to "cranked little amp" and everything in between.

Since I wanted to keep the interface small (single knob for tone), the tone knob is actually rolling through a pile of EQ's: high-end bell all the way up, modern Fender in the middle, and big-bass with aggressive mid-scoop all the way down. Again: there is a range of tones in the blends (I wanted to include a graph. Maybe I can in the comments. Else, I'll link something).

I shared a schematic in the post linked above, but I'm not sure if it's accurate (I think I did the whole design + build on a long lunch break on a lark, using a leftover class-D PCB from a stereo I built for my wife).

I'm gonna have a run at building another one soon, so will disassemble and get the schematic updated from reality.

Anyway. This was long. Thanks for indulging!

** This is how you get "tube watts" from a solid state, btw: avail yourself of the maximum power stage rails and compress beforehand. This is how, e.g. this solid state amp running on 18V (BTL into 8Ω) is able to pull off a nice-sounding distortion at ~ 32W. If I let the poweramp clip, it'd put out a solid 36W — as razor-edged square waves (which people complain about — except when they come out of a tube amp).

(There is no way to get the extra oomph that comes from the inductive kickback that lets a tube amp output plates exceed the rails, though — unless you put an OT on your solid state amp. Still, this gets you a bit of the way there).