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

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

Overdrive The [S]cream by

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.


Preamp-overdrive with NOS* germanium transistors.
Made to give voice to guitars, electric or acoustic bass.
2 knobs set simultaneously tone and drive.
It nourishes the tone of amps that sounds too flat, and facilitates your musical expression :
Good for jazz, blues and elegant rock…

* NOS: New Old Stock… New transistors from the sisties to eighties.



SweetGerm, basic version .

Continue reading SweetGerm

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…
In the USA, there are larger JEDEC standard cases (TO5 box) or smaller (TO18 box) as the european TO1.
Transistors manufactured in Eastern Europe used an elongated version of the TO1 case : some ACs, SFTs manufactured under license, and the national productions in the East.

The TO1 dimensions were not strictly followed by all manufacturers, which can seem surprising nowadays. 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

Germanium transistors : Black Glass models

 They were thus nicknamed in allusion of their very particular black glass case. Glass technology had been selected because at that time plastics were still unable to ensure a perfect seal between case and terminals. They have been the first transistors widely available, and the aged electronic techs have fond memories of them. It must be said they are found in the earliest fuzz, the first solid state professional audio systems and computers.

This is an opportunity to discuss the properties of the main types and identify their ability to be used in circuits devolved to guitars .
NB: I will only talk about transistors that I actually had in hand.

Continue reading Germanium transistors : Black Glass models

My first transistors

In the early 1960s, tubes still ruled consumer electronics. Family equipment was dark, and smelled of hot Bakelite or grilled dust. It hummed with a sound which we do not yet know that he was well on guitars. We began to listen sounds from elsewhere. Funny little flashy devices went invading our teenager bedrooms and participated in their clutter. They diffused sharp sounds that slammed well with rock and Roll or Brit Pop. It was a completely different sound than family equipment. We spent our sixties adolescence between these two sensations: muffled brown old receivers and bright orange pocket transistors, such as between blues and pop.

When we opened our pocket radios to replace the battery, we finded out these tiny stuffs that would become essential components of the twentieth century : transistors.

Continue reading My first transistors

Germanium comeback

The long era of synthesizers provoked a return sometimes offensive, sometimes conservative to guitars. This brought back into fashion both vintage instruments and equipment. Guitars, amps, stompboxes, all the electric guitar chain turned back to its roots. That did not stop the digital mutation, which is a hugh scale phenomenon, but brought back to light the technical aspects that built the culture of the electric guitar. The return to grace of tube amps represented a major phenomenon. On his humble level, the rediscovery of Germanium seems to be another signifying axis.

Continue reading Germanium comeback

Stompbox power supply : An overview

Stompboxes power supply is both a trivial issue and a relevant subject. There are some basic points behind banality that can help make a good choice — and avoid troubles — when organizing a pedalboard. This overview on the current situation will bring some classic issues, such as polarity of old pedals, consumption orders of magnitude according to types of stompboxes. The big issue remains choosing between traditional transformer power supplies and switching power supplies, that nowadays begin to impose their technology, but are not always appropriate to analog circuits…

A second article will expose points on which ensure personal choices … A third will be devoted to the system that equips my Guitar Poppa pedals, in order to power them silently through any types of DC power supply respecting the negative to ground standard.

Continue reading Stompbox power supply : An overview

Stompbox Power Supply : Poppa’s tricks

Early stompboxes were exclusively powered by batteries. Their low consumption made it possible. When most demanding stompboxes came around 1978, external power supplies, less or more stabilized, were necessary. Today, current switching power supplies are widespread because they are cheap for the manufacturer and reliable for the user. The problem is they are often noisy when used on analog equipment.

So I had to integrate the issue of power supply in my Guitar Poppa project : My products had to operate as silently as possible with any negative grounded DC power supply, and providing 7 to 12V in charge. As I moreover use both silicon NPN and germanium PNP transistors, the question of polarity was added to the problem.

From these objectives came a specific supply circuit that is in all my effects pedals. It uses an active noise filtering and decoupling cells.

Continue reading Stompbox Power Supply : Poppa’s tricks

Look at them caps !

Components are as humans: their look and reputation are superimposed on reality.
When I started in electronics, there were hardy components that were not afraid to show their machining traces. Then I saw industrial series colored like pop art paintings, pretty miniature pearls but of poor sounding, or conversely cheap looking stuff sought for their performances, and military components with an astounding sound sensitivity under their shielded shell .

I would like to tell you two adventures that catched my eyes or my ears, or both.

Continue reading Look at them caps !

Biasing a fuzzbox

In electronics, bias usually refers to a fixed DC voltage or current applied to a terminal of an electronic component such as a diode, transistor or vacuum tube in a circuit in which AC signals are also present, in order to establish proper operating conditions for the component.

This issue is evident in HiFi or PA equipment. It is the same in an Overdrive or a Fuzz : even if their output signal is saturated, it has a specific shape that must not be damaged.

This article aims to take stock, being precise both from a technical point of view and from a musical point of view… It is a bit long, but I think it is useful.

Continue reading Biasing a fuzzbox

Stompboxes : True Bypass

This article is devoted to one of the best known switching system : the True Bypass, which is generaly said to be the best, although it has some not so known limits … We shall see that the big question is that TrueBypass keeps a high impedance bypass routing, which makes this circuit not so efficient as usually said when many pedals are chained.

This introduces to a classical quarrel among guitarists : Pro and cons buffering…
Input buffering will be the subject of a second article.

Continue reading Stompboxes : True Bypass

Input buffers

Buffers are devices that are interposed between a signal source and an active circuit. The most simple ones do not provide signal amplification but operate impedance matching. This prevents from signal losses, espacially concerning the level and the bandwith.
They are technically very useful but little known, and sometimes badly regarded by vintage electronics purists under the pretext that historical circuits do not have any of them — and that Japanese equipment is stuffed with.

Guitar Poppa could not stay indifferent to this electronico-aesthetic quarrel…

Continue reading Input buffers