i built an ambika with 6 SMR4 voice cards and one of them has significant difference in volume and is much louder (i dont have numbers in number of dB, but it is more than audible and disturbing). any idea where to start looking for problem on the voice card ?
Probe IC3 pin 8 ; IC2 pin 8 ; IC2 pin 9 ; IC3 pin 9.
And post photos of both a good one and the “bad” voicecard.
thanks ! i did not expected such a quick answer
i am travelling until next week. but i will check as soon as i have access to my ambika and tools and will do some checks and starting digging on my own with your advices and the schematics. i’ll post back my finding.
happy new year olivier and thanks a again for everything you do !
i did some probing. but my multimeter has a very low resolution on AC. (200v scale). so on all the pin i measured on, both on good and bad cards , all the pins you mentioned (i took pin 3 as ground reference) it oscillated between 0.03 and 0.04 v.
Is there a more precise or better way probe them ?
i recorded a sample of all the voice card. the number 2 is the faulty one and also attached pictures on both side of a good and bad card. as it is rather big i uploaded that to copy.com
Edit ! i think i have found the guilty one ! one 18k and 10k were swapped for eachother.
i will unsolder them, fix that and post back.
Why probing in AC though? It is my understanding that the Ambika only uses AC for the power section, and converts that to DC.
The voltage at the points to probe carry audio signals. Either you use a scope, or you “listen” to the sound on your voicecard / mixer. The idea would be to identify at which point the volume drop starts occurring by comparing a working voicecard with a bad one.
Sloved it was these two resistors swapped over.