Lab Rat build!
- Thread starter drgonzo1969
- Start date
vigilante398
Authorized Vendor
Yup, definitely check for stuff like that. In normal operating conditions the MOSFET shouldn't be getting very hot, nor should any of the components really. I mean the tubes will get warm, but you know what I mean.
I have the power section of the Lab Rat running and will get things back in the enclosure before checking the audio. Replacing the UF4007 solved the problem. Of course I only got there after replacing several other parts that did not fix the problem. The diode I took out looked OK on the board and seems OK with my meter after I pulled it, but it was the weak link.
That is two boards where I had defective parts that were a pain to troubleshoot -- the diode here and a bad inductor in a recent Black Eye build. The saving grace is that the parts count on these boards is pretty low so it makes it easier to sort things out.
That is two boards where I had defective parts that were a pain to troubleshoot -- the diode here and a bad inductor in a recent Black Eye build. The saving grace is that the parts count on these boards is pretty low so it makes it easier to sort things out.
drgonzo1969
Well-known member
Glad you got it sorted out. hope the audio is all set too. I tried all the different IC's (Motorola LM308H, LM308N, OP07, NE5534 and AS301AH) I had on hand last night in my regular rat. After testing them all, I decided to go with the AS301AH for the lab rat. All the ICs sounded almost identical. But the AS301AH sounded a little better to me.
Erik S
Well-known member
But... But... LM308...
Betty Wont
Well-known member
THAT's what I'm talkin about!!! Team 301 all the way baby!
drgonzo1969
Well-known member
hahaha I know. I wanted to like the motorola more but..... my ears heard something
drgonzo1969
Well-known member
As for the clipping diodes, I am going to test out them in the lab rat since I have sockets installed in the 4148 and LED spots. If I wanted to try assymetrical clipping in the lab rat, would it work I put two 4148s in series in one of the sockets and then an LED in the other? Im not quite sure how to implement the assymetrical clipping from schematics. here is the schematic for Proco Rat Solo.
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vigilante398
Authorized Vendor
Yup, exactly that.
drgonzo1969
Well-known member
Nice! I am starting to understand these things!
vigilante398
Authorized Vendor
drgonzo1969
Well-known member
I've got some germanium diodes I am going to try as well. I could do the same assymetrical thing with germaniums right? two in series in one socket and LED in the other. Are there any other silicon options besides 1n4148 worth trying out?
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derevaun
Well-known member
Somebody correct me, but isn't the asymmetry in asymmetrical diodes just about the total Vf in each direction? Ge diodes will have their distinctive character of course. I would expect that 2 series germaniums would add up to around a third the Vf of a red LED. It would be interesting to look at the waveform after that kind of clipping stage 
drgonzo1969
Well-known member
I have never heard of anyone doing asymmetrical germanium clipping in a rat before. I got the idea from the build docs of the Aionfx Titan (OCD). But I cant really tell how they are doing it from the schematic (too many dip switches). It might not be possible with the lab rat. Im just spit balling ideas and thought this might be a cool option try while trying out clipping options. here is the build doc for aionfx titan. he mentions it under the "Other Version Changes" section. version 1.4
derevaun
Well-known member
Only one way to find out! If Ge Vf is around .3v, and a red LED is around 1.8V, it's still pretty asymmetrical with .6V against 1.8V.
If you haven't seen this video from Arito Suzuki, it does a nice job of demonstrating it in soft clipping mode. I would expect the differences to be more noticeable with hard clipping like in the Rat?
If you haven't seen this video from Arito Suzuki, it does a nice job of demonstrating it in soft clipping mode. I would expect the differences to be more noticeable with hard clipping like in the Rat?
drgonzo1969
Well-known member
NICE! I had not seen this video but this is great stuff. very interesting!
drgonzo1969
Well-known member
This guy has some other great videos too. thanks for posting!
No issues with the audio working properly. I went through my IC inventory and settled for now on using an OP07 just because it was the quietest one in the bunch. I think my LM308 (not metal can) was the runner up. I may try a couple of the "standard" mods to take C5 and R8 out out of the circuit and try a different cap value for C8.
I don't hear a lot of difference between the two different pairs of clipping diodes but I haven't had time to play with it a lot yet. I also used an on/off/on SPDT switch for the clipping diodes so I can add one diode connecting to the center lug of the switch that is always on (when the switch is off) so the other two positions will add different diodes to mix.
Do you have a Picture of your Lab Rat Build?
