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Keeley - Germanium Amplifier [traced]
Posted: 11 Mar 2018, 17:55
by apollomusicservice
Thanks to mirosol photos
viewtopic.php?f=7&t=28913 and some others from the internet, I drew my first version of this schematic. Some values missing.
Re: Keeley Germanium Amplifier
Posted: 11 Mar 2018, 23:12
by Manfred
With regard to these both schematics:
https://robertkeeley.com/woo/wp-content ... -FUZZ1.png
https://i.pinimg.com/originals/e4/5e/41 ... 2e5789.jpg
is my guess for following Values:
R8 = 4.7 Kiloohms
C5 = 10 Microfarads
C6 = 47 Microfarads
R1 = 51 Ohms.
Re: Keeley Germanium Amplifier
Posted: 12 Mar 2018, 22:44
by Manfred
The schematic is right according the PCP trace, but there is something not right here.
The base of the AC128 has no DC connection, therefore the biasing cannot work.
A base potential divider or a base resistor connected to ground is missing on the PCB is missing.
Re: Keeley Germanium Amplifier
Posted: 13 Mar 2018, 12:13
by apollomusicservice
Manfred, if you look at the photo, there is nothing else connect to base of the transistor.
Re: Keeley Germanium Amplifier
Posted: 13 Mar 2018, 14:31
by deltafred
It must be relying upon leakage to bias it.
Re: Keeley Germanium Amplifier
Posted: 13 Mar 2018, 19:07
by Chugs
Temperature stability will be an issue.
Re: Keeley Germanium Amplifier
Posted: 13 Mar 2018, 21:39
by deltafred
Chugs wrote:Temperature stability will be an issue.
Just call it mojo.
Re: Keeley Germanium Amplifier
Posted: 14 Mar 2018, 05:39
by Manfred
deltafred wrote:It must be relying upon leakage to bias it.
I see, an unusual ciruit, so that I trial is needed to find out the truth.
Re: Keeley Germanium Amplifier
Posted: 20 Mar 2018, 18:05
by Manfred
I ran a trail of a reduced circuit today.
I applied the collector and emitter resistor of the EQD Crimson Drive schematic.
I was really very surprised, the circuits works indeed without base resistor.
The input signal level varied from 100 Millivolts to 1 Volt RMS.
The clipping started at a input level of about 300 Millivolts.
Re: Keeley Germanium Amplifier
Posted: 21 Mar 2018, 01:19
by Manfred
I made a further trial adding the bypass capacitor.
The clipping started at much lower input levels.
Unfortunately, 70 Millivolts is the lowest output level of the integrated oscillator in my digital oscilloscop.