I built a Rat clone kit, and hmmmm...

Yes, very nice, now I definitely want one. Rather than keep waiting on the Aussie distributor to get them in (& pay their high price) I think I'll do a Vero board one with switchable assymetrical clipping. Cheers
 
Thanks for that. There's a few different variations of the rat on that site, I was planning on using one of them. He does a very good job of the Vero layouts. Cheers
 
The first RAT's used a TO-99 cased Motorola LM308H like thisC__Data_Users_DefApps_AppData_INTERNETEXPLORER_Temp_Saved Images_s-l225.jpg (these are the ones I just scored).
They then changed to a DIP (dual inline pins) Motorola LM308AN like thisC__Data_Users_DefApps_AppData_INTERNETEXPLORER_Temp_Saved Images_XHSNQ.jpg
The Chinese ones use an OP07DP chip that is also a DIP format. Latest US Rats's use a LM308A, but so long as its the LM308 you're golden (at least, that's what they say). Cheers
 
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I have a "Rat2" and a "You Dirty Rat" and dig them both. The YDR is perfect, it is my favorite of the two since I got it. The Rat2 is also pretty awesome. I put a socket in it (Rat2) and tried both the LM308N opamp and the Texas Instruments OPO7DP opamp. I wound up putting back the TI opamp. The germanium diodes in the YDR bring it up a few tonal notches to my old ears. To the OP of this thread, welcome back to the Rat race!
 
As I'm putting one together, I've done a bit of research into on stompbox forums. General consensus on the LM308 vs OP07DP chips seems to be that the OP07DP is more aggressive but thinner sounding with the LM308 also sounding a bit tighter. The OP07DP equipped units use a 27pf compensating cap where as the LM308 equipped units used a 33pf cap originally, later units a 30pf which some think has a bit to do with the OP07DP's thinner sound, along with this chip also having a faster slew rate than the LM308. Suggested fix is to increase the value of the OP07DP's compensating cap (ceramic disk cap) from 27pf to up around 100 - 150pf to get them sounding the same as the original chip, though how it sounds is a personal preference thing & opinion seems equally divided as to what sounds best. Germanium diodes have a much lower forward voltage drop than silicon so clip the wave form more (hence lower volume) but clip with rounded off edges kinda thing, rather than the abrupt, sharp edges clipping of silicon devices so the clipping is "softer" somewhat, even though they are set up as hard clippers in the rat. A popular mod (like the BYOC mouse) is to add switchable (soft) clippers into the feedback circiut (tube screamer style), the hard clippers being switch out when these are in use. This gives "overdrive" rather than distortion, making for a versatile pedal. Another thing I picked up on stompbox forums is that some people experience squealing at extreme settings with Vero board builds so I'll do mine "point to point" on prototype board to avoid this problem. Cheers
 
ivan H said:
As I'm putting one together, I've done a bit of research into on stompbox forums. General consensus on the LM308 vs OP07DP chips seems to be that the OP07DP is more aggressive but thinner sounding with the LM308 also sounding a bit tighter. The OP07DP equipped units use a 27pf compensating cap where as the LM308 equipped units used a 33pf cap originally, later units a 30pf which some think has a bit to do with the OP07DP's thinner sound, along with this chip also having a faster slew rate than the LM308. Suggested fix is to increase the value of the OP07DP's compensating cap (ceramic disk cap) from 27pf to up around 100 - 150pf to get them sounding the same as the original chip, though how it sounds is a personal preference thing & opinion seems equally divided as to what sounds best. Germanium diodes have a much lower forward voltage drop than silicon so clip the wave form more (hence lower volume) but clip with rounded off edges kinda thing, rather than the abrupt, sharp edges clipping of silicon devices so the clipping is "softer" somewhat, even though they are set up as hard clippers in the rat. A popular mod (like the BYOC mouse) is to add switchable (soft) clippers into the feedback circiut (tube screamer style), the hard clippers being switch out when these are in use. This gives "overdrive" rather than distortion, making for a versatile pedal. Another thing I picked up on stompbox forums is that some people experience squealing at extreme settings with Vero board builds so I'll do mine "point to point" on prototype board to avoid this problem. Cheers
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Wow, that is a dense synopsis. There is a lot more to pedals than meets the eye!!
 
Yes, in many cases there is a lot more than meets the eye. Some very talented designers out there, as well as some very talented tinkerers' who spend a lot of time & effort to improve pedals, Fred Briggs comes to mind. The Super OCD I built to his spec is a very good overdrive/distortion. There's also some very knowledgeable people who analyze the circuit functions of fx & give the knowledge to the masses, like RG Keen & Jack Orman. A few "booteeker's" also contrived to stompbox forums. Analogman is a regular contributor, amongst others. Cheers
 
RVA said:
Wow, that is a dense synopsis. There is a lot more to pedals than meets the eye!!
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Heck yeah man! Personally I can't hear a great deal of difference between the LM308 and the TI chip. Maybe I'm crazy but I feel the TI sounds cleaner.
 
ivan H said:
Yes, in many cases there is a lot more than meets the eye. Some very talented designers out there, as well as some very talented tinkerers' who spend a lot of time & effort to improve pedals, Fred Briggs comes to mind. The Super OCD I built to his spec is a very good overdrive/distortion. There's also some very knowledgeable people who analyze the circuit functions of fx & give the knowledge to the masses, like RG Keen & Jack Orman. A few "booteeker's" also contrived to stompbox forums. Analogman is a regular contributor, amongst others. Cheers
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The gent from Fulltone now has a new version 2 OCD he has come out with which is suppose to have some kind of new fancy buffering to it. It suppose to have a new internal switch for the buffer.
 
Catmandue said:
Heck yeah man! Personally I can't hear a great deal of difference between the LM308 and the TI chip. Maybe I'm crazy but I feel the TI sounds cleaner.
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No, not crazy, apparently the differences are "subtle"& as many prefer the OP07DP as do the LM308. Of note, the YDR has only ever used the OP07DP & later variants with the LM308 use a Texas Instruments unit instead of Motorola. I've never owned one but according to people that have owned several, its hard to find two that sound exactly alike (though all have the "rat" sound) due mostly to the less than ideal filter design. They use low value resistors (47r & 560r) & high value electrolytic caps (2u2 & 4u7) for the high & low frequency dumps. Electrolytics can have as much as 20% tolerance. A better approach would be high value resistor's & low value film caps to get the same frequency response & tighter tolerances. Electrolytics are also used in two points of the audio path. I plan to use close tolerance tantalum's in place of the electrolytics. These will be the only changes I make. I like to research pedals before building, just so I know what makes it tick. Cheers
 
Ivan I want to do the Led Zep Presence album thing and have the teacher transfer knowledge from your brain to mine. But I'm also a bit leary about what else might be in there. (LOL)
led_zeppelin_presence_inside_the_object.jpg
 
Haha, yes, you have good reason to be Leary. I've probably done quiet a bit of "damage" over the years that you might cop too. But any time I can help with anything, you're welcome. Cheers
 
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