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


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 …
Thanks 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 — nr 1, 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?

Bandeau medium rouge - L15 - Tonalité

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.

Bandeau medium rouge - L15 - Tonalité

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 the order of 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.

Bandeau fin gris moyen - L15

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.

My products

My products, produits, composants, components - Tropical Fish - 56n

My main activity is to design and manufacture stompboxes, preamps …
• Some of my products are deeply rooted in the history of vintage gear : they develop traditionnal models that are still referential and deserve to be updated or improved.
My aim is to be attractive on this double challenge : vintage & contemporary quality.
• Other products are original models. Designed for themselves, or in response to an individual order… It is then my double experience of musician & technician that I propose to you …

Continue reading My products

Samples : The (S)cream overdrive

Samples.The (S)cream - Bandeau de titre L15

The 3 presets : classic (=TS9®) ; clear ; deep

3 bluesy improvisations , using each of the 3 presets…
Low drive @ 9:00 — Consecutive presets : classiccleardeep.
Strat-like guitar, neck pickup.

Samples. The Scream. Bandeau fin gris moyen - L15

Texture according to the drive setting

Two different drive settings, harmonies in D …
Classic preset — Consecuting settings : low drive @ 9:00 / mid drive @12:00 / low drive @ 9:00
Strat-like guitar, bridge pickup.

Two different drive settings, on Next time you see me…
Deep preset — Consecuting settings : low drive @ 9:00 / mid drive @12:00
Strat-like guitar, neck pickup.

Two different drive settings, playing rhythm patterns in F sharp minor …
Deep preset — Consecuting settings : low drive @ 9:00 / mid drive up to 12:00
Strat-like guitar, bridge pickup.

Samples. The Scream. Bandeau fin gris moyen - L15

Texture according to the diode mixing

4 different mixings, silicon diodes + LEDs, playing a slow theme …
Successively :  1 : Leds 100%  /  2 : Leds 50% + silicon   /  3 : Leds 25% + silicon  /  4 : Silicon 100%.
Deep preset — Drive up to 1h:00.
SG-type guitar, mixed pickups.

Samples. The Scream. Bandeau fin gris moyen - L15
Recording the samples

Samples : The Scream. Bandeau - Enregistrement avec Stato

• The (S)cream is JTC4558 equipped.
• Diodes :  100% silicon on the first four samples ; leds + silicon on the last.

• 2xEL84 amp from1967, fixed by me. Clean canal, light mid notch @ 500Hz
10″ Weber F10-150T speaker, bass reflex boxed.
Recorded with a SM57 close to the speaker, between dome and edge.
A bit of Holly Grail® reverb…


The (S)cream

The (S)cream is an advanced diode overdrive that develops the sonic potential of the classic small green box :
Its sound comes from the TS9, but not exclusively centered on midrange: The (S)cream can as well recover the sound of 1975-85, recall the nervous grain of the first Black Face amps, or generate a contemporary overdrive …

The (S)cream

The (S)cream basic - Boîtier - 1- les deux versions

The (S)cream —  Basic version and  *** version.

Continue reading The (S)cream

Samples – SweetGerm

Produits - SweetGerm _logo produit L15x300dpi

Chubby option, with its caressing tone

Cool blues playing  : Reconsider
Guild Archtop, mixed pickups.
SweetGerm on Jazzy preset.
Body @11:00, to get bottom without orvedrive. Présence @10:00 for clear harmonics.

Brownie option, with its old school grind

Rythm guitar with lows and treble  : Soft latin overdrive
Guild Archtop, neck pickup.
SweetGerm on Jazzy preset.
Body @12:00, to get textured lowrange. Présence @11h, to get treble above.

Approximate and filthy picking : Dirty country
Guild Archtop, bridge pickup.
SweetGerm on Mighty preset.
Body @12:00 to put dirt. Présence @9:00 to avoid a scratchy sound and get warmth…

Bandeau medium rouge - L15
Samples recording

2xEL84 amp from1967, fixed by me. Clean canal, Baxandall in virtually flat position.
Celestion 12″ Seventy-80 speaker, bass reflex boxed.
Recorded with a 565 Shure placed close to the spaker between dome and suspension.
A bit of reverb.

Archtop Guild F160 guitar from 1989. Original pickups.

Samples : GeAmp1W micro-amp

GeAmp1W - Bandeau - visuel pour samples

Geamp1W, 1W on 4 ohm. All germanium power amp.

Tone and drive

Effects of the tone control : 4 settings to play a white soul riff.
Weber 10-inch speaker, bass reflex boxed.
Level is set near crunch level…
Archtop guitar, neck pick up, almost full volume.
Tone @ 09:00 (vintage) ; Tone @ 12:00 (flat) ; Tone @ 13:00 ; Tone @ 15:00 (Fenderish).

Effects of the tone control : an old picking style tune. (3 samples)
Weber 8-inch speaker, semi-open cabinet.
Level is set just just under crunch level, unless heavy played notes…
Strato-like guitar, center + bridge pick-ups.
Tone @ 09:00 (vintage) ; Tone @ 13:00 (slight bright) ; Tone @ 14:00 (classic bright).

Overdrive by power chords : a boogie woogie in the style of the 40s
Weber 8-inch speaker, semi-open cabinet.
Level is set to get a generous and meaty saturation. Tone @ 12:00 (flat).
Archtop guitar, neck pickup. Downed  treble and full volume.
(In case of low output level guitars, you’ll get an analog drive using the “brown”preset ) …

Bandeau fin gris moyen - L15

Tone and style

Little bluesy improvisation
Weber 8-inch speaker, semi-open cabinet.
Level is set near crunch level… Tone @ 14:00 (classic bright)
Archtop guitar, neck and bridge pickups together, withheld and contrasted playing.

Picking country blues guitar
Weber 8-inch speaker, semi-open cabinet.
Level is set just under crunch level, unless heavy played notes. Tone @ 13:00 (slight bright)
Archtop guitar, neck and bridge pickups together.

An heavy stuff in B
Weber 10-inch speaker, bass reflex boxed.
Level set to get crunch without jamming the sound. Tone @ 12:00 (flat).
Archtop guitar, neck pickup, almost full volume.

Bandeau medium rouge - L15

Technical datas

GeAmp1W Mk2.1 - Enregistrement - Bandeau combiné

GeAmp1W , creamy option, 9V powered, 0,8W RMS output power.
Would overdrive easier with 7,5V, would have more headroom with 12V.

Speakers :
Weber CVC8, 8″. Boxed in a small semi-open cabinet (from an old Danelectro®).
Weber F10-150T, 10″. Bass reflex boxed (the cabinet I use when playing in clubs).
SM58 Shure mike,  closely placed and almost towards the center.
A bit or more of Holly Grail® reverb, just for pleasure.

Strato-like guitar, cheap model, but re-equipped with texan Rio Grande® pickups.
Archtop Guild F160. Original pickups.

Germanium transistors : Sonic properties

There is a “germanium sound”. It is especially suitable for guitar amplification, and can apply to harp and some keyboards. The sound of germanium has a warmth and a granulity as pleasant to the ear as the tube sound, without being the same : The sensation of warmth is about equivalent (for analog reasons, in particular the Miller effect that dynamically attenuates the high frequencies). The sonic  grain of germanium is generally a bit rougher than the tube grain, and especially less flat and plain than silicon …
In all domains of audio, germanium transistors and their “good defects” are opposed to the cold pharmaceutical perfection of integrated circuits.

After years spent in tests and development, I feel able to specify some characteristic parameters… And happy to share this knowledge that I apply in the products shown on this site ; stuffs just to please the guitars.

Continue reading Germanium transistors : Sonic properties

Germanium transistors : TO1 case models

The TO1 standard was the first all-metal case used for germanium transistors when the black glass models were abandoned around 1964. This concerns European series like ACs, industrial series ACYs, ASYs, ASZs, the british NKTs and the japanese 2SAs…
Transistors manufactured in Eastern Europe used an elongated version of the TO1 case : some ACs, SFTs manufactured under license, and the national productions of these countries.

The TO1 standard was not strictly followed by all manufacturers, which can nowadays seem surprising. From another point of view, this can help identify the origin and sometimes the quality of the transistors. This article is here to share some pointers and background information.

Continue reading Germanium transistors : TO1 case models