All posts by guitar poppa

About guitar poppa

Former product design teacher, now on retirement and still post war blues guitarist, i've been found of electronics since I was 14... The guitar poppa web site is the way to make known and spread my experience in transistor and tube vintage electronics


Project for this fall : An echo box that saturates like Little used to do…actuality : project to come
Get the joyful grit of the Chicago Southside harps !

Little Walter’s echo is like the reverb of punk-surf groups: it is as much a matter of timbre and sound texture as of pure delay. So I thought to add a SpanishMoss overdrive to the echo to get back that special sound… I’ll tell you what it’s going to be !…
Contact me for more information…

Bandeau fin gris moyen - L15

 Custom actuality : An old-fashioned amp head, with plenty of optionsguitar poppa's actuality : a project to come
A development of the Vox AC15…

Initially, a musician’s command based on the original AC15, with lots of options:
A 3-band tone, a booster, a line output with HP simulation, an attenuator …
And all built old-fashioned way on a turrets card (except for the effect loop).
My amps 10 to 25W

Bandeau fin gris moyen - L15

Project : a Di-Box that make your sound before injecting it into the PA.SimSymBox : boîte de direct qui met en valeur la couleur et le grain de l'instrument
To be sure of the sound quality you will send to the sound system of the bar …

Imagine an instrument preamp with adjustable tone and overdrive …
Add a speaker simulator, and a balanced output to the mixer …
You have everything you need to get your sound and send it directly to the sound system!
Contact me for more info and custom realization…

Bandeau fin gris moyen - L15

New : preamps for harp with solo Boost and balanced output to PA.preamps for harp with solo Boost and balanced output to PA
What it takes to be independent on small stages

Initially, an order from harmonica player Vincent Bucher … He wanted a CurvyMama preamp followed by a speaker simulator and a balanced output to the PA …
And also with a chorus push button, and an output for stage amp (if necessary) …
The “CurvyMama SimSym” product page

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New : a 3W microCombo with 13cm speaker
3W microCombo with 13cm speaker
The MicroCombo range now has a big brother

A greedy sound for the guitar or the harp in a beautiful solid walnut box.
The watts are real, as well in clean sound as in light crunch or in total saturation.
Speaker on your choice: Celestion, Sica or Jensen, depending on the desired sound color.
MicroCombo 3W product page

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News from the workshop: pedal modifications
pedal modifications by Guitar Poppa
Gain and roundness improved in a Fuzz Face Lift from Big Knob.

It is a Californian artisanal stompbox, which updates the Tone Bender II Professional with a silicon buffer and a fuzz circuit equipped with Russian germanium MP39A.
I bring more body, a better polarized buffer, progressive gain pot, adjustable bias …
Modifications and customizations by GuitarPoppa

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Custom : a 25W Silicium / Germanium hybrid amp head
25W Silicium / Germanium hybrid amp head
SweetGerm +25W

Association of the SweetGerm preamp and a 25W hybrid PowerAmp.
Germanium brings its color and the grain of overdrive, silicon improves reliability.
Customizable connections: lines, loop, phones etc …
Facebook review from the first client behind the project

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Custom : Pedal duos in a single box
Duos pédales - The Scream + VintageBoo
The [S]cream + VintageBoo

Initially, custom orders from friends … We have selected complementary pedal duos … With an additional economy of scale: a duo is less expensive than the two pedals that it brings together, because some circuits do not need to be repeated.
Contact us to discuss your desires and projects…

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First Germanium Micro-combos from 1W to 3W RMS
Germanium Micro-combos, from 1W to 3W RMS
On the workbench…

These will be two Micro-Combos for harmonica or guitar, respectively 1W and 3W…
The electronics are traditional, without integrated circuits. All germanium power amplifier and selected NOS speaker : The clear or overdriven sound will be lively, warm and rich!
MicroCombo1W product page MicroCombo3W product page

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A speaker attenuator with line output and bypassspeaker attenuator with line output and bypass
CoolCrunch fits in a box to be placed in the bottom of combos …

Realization on request of a harp friend for his Champ 57 reissue …
Two models, dedicated to 5W or 30W power amplifiers.
Continuous volume adjustment, byPass switch and line output always available…
CoolCrunch5 and CoolCrunch30 product page.

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Guitar Poppa likes to repair or update vintage ampsGuitar Poppa likes to repair or update vintage amps
Review and restoration of a french amp from 56/65 …

Renowned French brand: Stimer amplified the great Django, then the first french rockers …
I can repair or transform these old amps with all due respect.
But only small models, less than 25W: my workshop is very small!
(and international transport is so expensive!)

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Pedal mods
GuitarPoppa, modifications, customisations, performances, ergonomie, usages spéciaux
Technical and ergonomic improvements; adaptation to personal uses.

Recently I adapted a [good] copy of TS9® for bass …
At the moment, I am modifying a Metal Zone® for the harmonica …
If your pedal is correctly designed and manufactured, we can customize it to your wishes!
Modifications and customizations by Guitar Poppa

CurvyMama + SimSym

CurvyMama is initially a preamp designed to process the flesh and grit of harmonicas sound. In this aim, It features a special tone circuit and a germanium overdrive stage.

This version + SimSym also features a boost stage.
Above all, it has an active speaker simulator, and a balanced output to the PA console.

CurvyMama SimSym Output, logo

CurvyMama SimSym Output, préampli spécial harmo avec simulateur de HP et sortie symétrique pour liaison directe avec la sono

The first CurvyMama SimSym, a custom order – March 2020.

Continue reading CurvyMama + SimSym

My Amps : 10 to 25 Watts

I make amplifiers for guitar or harmonica … Small, like my workbench !
Available as separate head … One can also order a combo, with a 10 or 12′ speaker.
The layout and the equipment are to be composed “custom” according to your project.

Transistor realizations feature a real power of 10 to 25W on 8 ohms.
They use a 60s germanium technology, which denies the bad reputation of transistors…
It brings especially a natural compression and a progressive transition to overdrive which have little to envy tubes, with a price also compressed!

I also realize high quality tube models, custom 5, 10 or 15W, with vintage or high-end components where it’s audible.

In both cases my aim is to offer amplifiers intended for home use or small concert venues, without technical weakness, and with a sound that will please the instruments.

Continue reading My Amps : 10 to 25 Watts

My stompboxes : DD size

I have designed some large format stompboxes (approximately 20 x 11 x 3.5cm), either because they have to contain a printed board of significant dimensions, or because they have to bring together several cards.

These configurations are often the result of custom orders by musicians with strong choices … Their requests have led me to design typical equipment, which are often associations of existing circuits.
Everyone can now benefit from these experiences, or imagine their own project!

Continue reading My stompboxes : DD size

Samples : LikeYourFace Fuzz

LikeYourFace - logo produit L15x300dpi

Classic smooth option

Big basic Fuzz and heavy riffs, in the manner of the sixties..
Strato-like guitar.
LikeYourFace with Fat preset ; Fuzz @ 15:00 (more is possible ; Tone @ 12:00 (neutral).
Wild thing (neck pickup) : then Shape of things (bridge pickup).

Fuzz used as a light overdrive : Bright Strato blues
Strato-like guitar.
Neck pickup and Bridge pickup mixed.
Fat Preset ; Fuzz @ 10:00 to get a smooth texture ; Tone @ 13h to get more harmonics.

Classic bright option

A scratching sound, with open strings and a bit boosted medium
Archtop Guild X160,bridge pickup at first, the  mixed pickups at the end.
LikeYourFace basic, Classic bright option. Fuzz @ 15:00. No preset nor tone.
In-A-Dadda etc. (micro manche)

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Recording conditions

Bandeau - Enregistrement - Samples-BirdMaster

2xEL84 amplifier from 1967, restored by me. Clean canal, tone control almost flat.
10″ speaker, Weber F10-150T (recommended for Fender Princeton) ; bass reflex cab.
Shure SM57, placed like in the pic above.
A bit of Holly Grail® reverberation, just for pleasure.

Strato-like guitar from the 80s, rather cheap but equiped with Rio Grande texan pickups.
Archtop Guild X160 from 1988.

Bandeau fin gris moyen - Samples


MicroCombo 3W is a portable and powerful micro-amp for guitar or harmonica.
The all Germanium power amp, the big brand speaker  give to it efficiency and musicality.
It will let you play at home or in small places, connected to an external cabinet or to the sound system of the bar.
Options are available when ordering.

MicroCombo 3W, ampli 3W pour guitare et harmonica - amplification au germanium

MicroCombo3W in its walnut enclosure.

Continue reading MicroCombo3W

My amps : MicroCombos

A MicroCombo prototype on the workbench …

MicroCombos are small 1W and 3W amplifiers. (I mean real watts on 8 ohms…)
They are made in old fashioned way, which gives them a special quality both from a technological point of view and according to their design :

Discrete components, 100% germanium transistors, AB class amplification.
Branded speakers, contemporary or NOS.
Solid wood enclosure (cherrywood or european walnut).

Their clear sound is mild, and they crunch at low level without sounding harsh, with a roundness that has nothing to regret from tubes.
They are well suited for home rehearsals, and even for small parties !
They were originally designed for the guitar, but I quickly grasped the interest of working just as much for the harmonica, taking advantage of the grit of old transistors …

Continue reading My amps : MicroCombos

Germanium transistors for Fuzz – 4

Switching transistors
ex : 2N404 (the american classic)

The first transistorized circuits for automation and computing required specific components that were straightforward in their response but without extreme bandwidth. Rather close to radio frequency transistors, they are distinguished by their reliability and deliberately moderate maximum frequency. Some models may produce a vintage sound grain, suitable for Fuzz Face. They could make as much reference as the ubiquitous small power audio transistors : American do-it-yourselfers have not been mistaken, and have since a long time embraced the classic 2N404 …

Continue reading Germanium transistors for Fuzz – 4


CoolCrunch is made to attenuate the volume on the speakers without lowering the master volume of the amp …
One keep then the crunch without breaking the ears …
Due to its small size and simplicity, it fits inside the combos and in your budget.

CoolCrunch 5 & 30. Logo

CoolCrunch5. Speaker attenuator in a Fender Champ 57 reissue

A CoolCrunch5 prototype installed on the back of a Champ 57 reissue.

Continue reading CoolCrunch


LowVoltTube is an original pedal that combines two fundamentals of the guitar sound :
— A preamp-overdrive, TS9 type, with its tone control …
— A tube stage included to generate a vintage grain.

The tube is a 50s NOS model, specially designed to work directly with 9V or 12V.
Boutique quality, but for a moderate price !

LowVoltTube preamp/overdrive - Logo

LowVoltTube. Préamp/overdrive with JRC4558 and NOS tube 6ET6 (EF98)

LowVoltTube — First issue, 2018.

Continue reading LowVoltTube

Mama’s tone controls

General principle

CurvyMama’s tone controls are original circuits, working in the frequency ranges that cause the roundness and clarity of the sound : Low mids between 150 and 250Hz, and the medium / trebles articulation between 1 and 3 kHz …
Traditional circuits seldom operate on these specific frequencies, but rather on bands that are easy to spot but not so substantial on  the musical wise.

So, setting the tone of CurvyMama may seem less obvious than keeping bound to the broad categories Low / Medium / Treble. This is much like adjusting sound colors, more subtle nuances. It can be very intuitive. Musicians have ears, right?

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CurvyMama, a preamp/overdrive for harp. Special Tone controls.

The controls of CurvyMama, Harp version.

The tone controls


• Sets the level of upper bass and low mids. (100 to 250Hz). This setting gives the thigh to the harps and somme curves to the guitars, without bringing unnecessary bass.
• Almost neutral effect in 12 o’clock position.


• Balances the overall balance of the mid-high range (500-2000Hz).
• Almost neutral effect in 12 o’clock position.
Turned left : filters to a darker, softer tone.
Turned right : filters to a clearer and more biting tone …
• Very interactive with the Contour setting.


• Contour sculpts the medium / high frequencies that Biting has globally set.
• It treats together and symmetrically the medium to 600Hz and treble to 3000Hz.
Turned left : attenuate the treble AND draws a slight medium hump.
Turned right : hollows the medium AND boosts the treble.
• Almost neutral effect in 12 o’clock position.

Specific switches of the Harp version

The Less Mids switch straightens the bandwidth in case of excessive mid frequencies.
It notches the tone to 1.5kHz. It’s good for the ear, especially in the case of crystal bullet mikes that sound often harsh. Just as useful, it reduces the risk of feedback.

The Invert Phase switch don’t change the tone, but reverses the phase of the output signal.
This can be very useful to minimize feedback. For a given position of the musician on stage, there is always one of the two positions that alleviates the problem.

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Useful benchmarks

The Bottom, Biting and Contour settings are neutral when they are set at 12 o’clock.
It is convenient to quickly recover a sound reference and then work its color.

• Knobs all turned in the same way give a sound of low interest, and sometimes just an increased volume.
One get richer sounds with controls set on different positions.

What setting order ?

It is better to start with the most general settings, then go to the most special settings, and finally set the nuances …

1. Bottom. Starting with bass and low medium, one gets immediately the roots of the sound, where the fundamentals are … The general level and the grain will depend on this first setting

2. Biting. One can then set the sweet / biting balance. This is important because guitar and harp are instruments that can be easily aggressive to the ear.

3. Contour. Finally we specify the mid / high zone:
denser and hot on the left, more hollowed out and pointed on the right …
This leads to differentiate and carve into the sound.

4. Play with the Biting / Contour interaction :
Biting and Contour each operate in their own way in the same medium-high range.
• General principle: Biting ensures a global balance while Contour carves détails…
• They are cumulative if they are turned in the same direction :
dark on the left, sharp on the right.
• They draw nuanced sound profiles when they are operated in opposite directions :
for example, one is turned to 10:00 am when the other is turned to 14:00, and vice versa …

5. Think of adjusting the texture by setting the Drive (Gain) :
Drive allows you to dose the grain of the sound, from a smooth texture to the appearance of a grain, then to the overdrive on loud passages or in the entire musical game.
• The overdrive is very related to the tone controls settings because they work upstream of the saturating stage, like on vintage amps.
• In particular, Drive and Bottom are almost always jointly settled.

Good finds!

Guitar Poppa

Germanium transistors for fuzz -3

High Frequency Transistors
ex : OC44 (Rangemaster, 1966)

High frequency germanium transistors have appeared as a second generation. Their elaborate technology made it possible to obtain a consequent gain even at radio frequencies : 30MHz, then 100MHz or more.
More expensive, and fragile at the beginnings, they have not been much used by pedal manufacturers, before all concerned by economy and robustness.

The OC44 was however exploited by Arbiter in the first Treble Booster, the Rangemaster, where its gain and bandwidth yet modest worked perfectly.
With the contemporary recoil, we rediscover the quality of these transistors, the fineness of their sonic grain, and their real interest in designing modern boosters and fuzz …

Continue reading Germanium transistors for fuzz -3

Germanium transistors for Fuzz -2

Audio preamplification transistors
ex : NKT275 (Fuzz Face, 1966-67)

These are the most common germanium transistors. They were designed for audio pre-amplification circuits in consumer and mid-range equipment, where they quickly replaced the tubes. They are distinguished by a gain which can reach 200, and a maximum frequency of about 1MHz.

Pedals made in 1966-68 first operated with black glass models like OC75 and then encapsulated glass like OC76 and OC81 … As the AC125 and AC126 by Philips / Mullard were a bit expensive, cheap versions like the NKT275, and some SFTxxx had their hour of glory before being forgotten, then rediscovered around 1990 …

Continue reading Germanium transistors for Fuzz -2

Germanium transistors for fuzz -1

Output audio transistors
ex : AC128 (Fuzz Face, 1966-69)

These transistors were at first designed to drive the loudspeakers of radios and consumer audio products. They are distinct from other families by their dissipable power and their maximum collector current.
In 1967, some models have been known as bringing a so called “creamy” sound texture to Fuzzboxes. Therefore, they gained a reputation that made this family of components enter the guitar effects culture.

Continue reading Germanium transistors for fuzz -1

Hi-GeFuzz samples

Hi-GeFuzz - bandeau L15


Basic Fuzz. (soft but more grainy than 2 transistors fuzz boxes)
Speedy Sunshine of your love.
Archtop guitare , neckpick up.
Hi-GeFuzz ***,  Classic Ge  option — Preset : Soft ; Fuzz : 12:00 ; Tone : 12:00.

Fuzz like in 69.
An old minor stuff.
Strato-like guitar , Neck pickup.
Hi-GeFuzz *** , Classic Smooth option — Preset : Deep ; Fuzz : 14:00 ; Tone : 12:00.

*** Bee&Wasp model : notched or boosted mids, like in today’s feeling
Hairy bottom.
Strato-like Guitar.
Hi-GeFuzz *** , Bee&Wasp option. — Fuzz : 14:00 ; Tone : 12:30.
Neck pickup and Deep preset — Bridge pickup and bite preset.

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Recording conditions

Samples, enregistrement.

2x6BQ5 amp from 1967, restored by me. Clean canal, Baxandall tone control almost flat.
Weber F10-150T (10″) (recommanded for Fender Princeton amps), bass reflex boxed.
SM57 Shure mike, placed as on the picture.
A bit of Holly Grail® reverb, just for the pleasure.

Strato-like guitar from the 80s, rather cheap but fixed with texans Rio Grande pickups
Archtop Guild F160T frpm1989, genuine pickups.

Stompboxes : BB and B size

Guitarpoppa : pédales

My activity is to design and handcraft stompboxes, preamps or small amps.
It feeds on my experience as a musician and technician trained in the 60s.

Some of my pedals perpetuate the tradition, with updated means.
Others have an original design.

They are usually manufactured in autonomous boxes, most often in the 1590BB american format, approximately 12 x 9 x 3cm, or its narrow version 1590B, 12 x 6 x 3cm …
I also combine two circuits as a duo in a single larger box.

Continue reading Stompboxes : BB and B size