Hi all,
I just finished to build the Wallin's mic preamp but it doesn't work. I don't have a PCB so I lined up the components on a plywood board using the layout presented in the Wallin page, and connected them through wires or directly using the component's lead.
I connected also the switch and battery and tried to power the preamp, but the led didn't illuminate. So I tried to find the error and checked all the connections and component values.
The connections seem OK, the resistors also, but I found a strange behavior on the small capacitors (C2, C5 and C10 on the schematic), because they measured in the 5-10 nF range, i.e. a lot more than they should.
I subsequently found that the resistors have a capacitance in that range and since C5 and C10 are wired in parallel to a resistor this could explain my measure. Probably also the C2 measure has a similar explaination since it is wired in parallel to the mic.
Anyway I'm asking to someone that has successfully built the preamp to measure those caps and confirm that **on board** they don't measure as specs.
Sorry for the long post and thanks in advance for your help.
Ralf
I just finished to build the Wallin's mic preamp but it doesn't work. I don't have a PCB so I lined up the components on a plywood board using the layout presented in the Wallin page, and connected them through wires or directly using the component's lead.
I connected also the switch and battery and tried to power the preamp, but the led didn't illuminate. So I tried to find the error and checked all the connections and component values.
The connections seem OK, the resistors also, but I found a strange behavior on the small capacitors (C2, C5 and C10 on the schematic), because they measured in the 5-10 nF range, i.e. a lot more than they should.
I subsequently found that the resistors have a capacitance in that range and since C5 and C10 are wired in parallel to a resistor this could explain my measure. Probably also the C2 measure has a similar explaination since it is wired in parallel to the mic.
Anyway I'm asking to someone that has successfully built the preamp to measure those caps and confirm that **on board** they don't measure as specs.
Sorry for the long post and thanks in advance for your help.
Ralf
Hi Ralf, I'm just about to head off to work so can't measure now, but a quick question, did you use the same voltage reference as Eric did, or a different one? I used a different one and mine didn't work, I had to add in an extra resistor to get it started. I can dig up what I had to do later if you have used a different one 🙂
Tony.
Tony.
Hi Ralf, from memory I used a completely different part to Eric it was a zy something I think... same specs but different manufacturer. I'll have a look tonight 🙂
Tony.
Tony.
Hi Ralf, I haven't had a look at the circuit yet (I'm not sure if I will be able to get accurate capacitance readings with my meter but I can give it a go), but I did find what I had to do to get the circuit to work properly.
Put a 100K resistor from +9v to the non ground side of the LM4040 (ie between R1 and the LM4040. I actually used a LT1009CZ instead of the LM4040 because at the time that was what I could get hold of, but Jason Neils original version of this preamp had the 100K resistor (and was using an LM4040).
I don't have what the symptoms were except that it didn't work, everything looked fine and "the voltage reference was out" by how much I didn't record.
Tony.
OK I found the original circuit I did, I can't get any meaningful measurement at all with my DMM. But looking at some of the big caps in close proximity to the ones you are trying to measure, separated by a few resistors, I don't think you are going to be able to work out anything meaningful from in circuit measurements. Hopefully the suggestion I have made will help, if not, taking voltage measurements at various points in the circuit for comparison would be much better 🙂
Put a 100K resistor from +9v to the non ground side of the LM4040 (ie between R1 and the LM4040. I actually used a LT1009CZ instead of the LM4040 because at the time that was what I could get hold of, but Jason Neils original version of this preamp had the 100K resistor (and was using an LM4040).
I don't have what the symptoms were except that it didn't work, everything looked fine and "the voltage reference was out" by how much I didn't record.
Tony.
OK I found the original circuit I did, I can't get any meaningful measurement at all with my DMM. But looking at some of the big caps in close proximity to the ones you are trying to measure, separated by a few resistors, I don't think you are going to be able to work out anything meaningful from in circuit measurements. Hopefully the suggestion I have made will help, if not, taking voltage measurements at various points in the circuit for comparison would be much better 🙂
Last edited:
Hi Tony, I will try your suggestion.
Re. the voltage measurements, unfortunately my volt meter is very basic and not accurate enough. I will try though.
And the caps can be measured better from the other side of the PCB 😉 - I was simply trying to understand if my measures were normal, I don't need a precise one.
Thanks, Ralf
Re. the voltage measurements, unfortunately my volt meter is very basic and not accurate enough. I will try though.
And the caps can be measured better from the other side of the PCB 😉 - I was simply trying to understand if my measures were normal, I don't need a precise one.
Thanks, Ralf
- Status
- Not open for further replies.