diggy fresh
Well-known member
Hi peeps, here's a cool little germanium line amp i want to clone for historical reasons.
It is a McCurdy AT-218. from the datasheet ( thanks Byron!), it says it is a "mixer amplifier" intended to be after a 600 Ohm fader. It has 35db of gain. also stated is "active impedance matching input", low output impedance and may be used with input/output transformers.
It is a common emitter amplifier followed by a emitter follower.
I am still learning and would like to know if it is possible to mod it for variable gain? and how? without affecting the circuit too much (impedance etc.) It says the R2 1k trimmer will " alter the gain +/- 1db without seriously altering the input impedance.
If i changed it for a bigger trimmer, or a pot, could i vary the gain more? any adverse effect?
i'd like idealy to be able to change the sound and add distortion etc, kinda like the Chandler Germanium.
If not possible i could always use an attenuator before or after but a way to vary the gain directly would be cool, no idea how Chandler does it.
some specs:
frequency response : 30hz to 20k
input noise : -120 dbm
source impedance : 600 ohm, unbalanced
input impedance : 600 ohm
load impedance: 600 ohm, unbalanced
output impedance : 75 ohm
input level : -40 dbm
power requirement : -36v, 10 ma
Any help would be appreciated
John
It is a McCurdy AT-218. from the datasheet ( thanks Byron!), it says it is a "mixer amplifier" intended to be after a 600 Ohm fader. It has 35db of gain. also stated is "active impedance matching input", low output impedance and may be used with input/output transformers.
It is a common emitter amplifier followed by a emitter follower.
I am still learning and would like to know if it is possible to mod it for variable gain? and how? without affecting the circuit too much (impedance etc.) It says the R2 1k trimmer will " alter the gain +/- 1db without seriously altering the input impedance.
If i changed it for a bigger trimmer, or a pot, could i vary the gain more? any adverse effect?
i'd like idealy to be able to change the sound and add distortion etc, kinda like the Chandler Germanium.
If not possible i could always use an attenuator before or after but a way to vary the gain directly would be cool, no idea how Chandler does it.
some specs:
frequency response : 30hz to 20k
input noise : -120 dbm
source impedance : 600 ohm, unbalanced
input impedance : 600 ohm
load impedance: 600 ohm, unbalanced
output impedance : 75 ohm
input level : -40 dbm
power requirement : -36v, 10 ma
Any help would be appreciated
John