Hi there.
I want to build my self a RAT. I found this PCB: https://www.musikding.de/The-Rat-pcb-Distortion
Is this the same schematic as the original RAT ?
Thanks.
hey, yes that's a RAT clone
cheers
Quote from: rangermaster on March 02, 2021, 10:58:35 AM
Is this the same schematic as the original RAT ?
Strictly speakig, No..!! :icon_smile:
(neither from schematic nor from BOM (parts list) point of view..)
But yes, you can proceed building that kit which is close enough to "original"(*) Pro co RAT..
(*) there are more than a decade "original" versions designed by Pro Co..
Thnx for the replies.
Is a LM308M the same as the LM308 ? I can't find any info about these...
It's just the same..
Musikding kit declares LM308 and OP07 fully interchangable for particular schematic/layout but, IMHO, in case of using OP07, frequency compensation cap (C4, 33pF) should be left out.. :icon_wink:
I am using a LM308M then if it's the same as LM308. Isn't the 33pF in the original 30pF ?
I'm also using a 2N5458 instead of the 2N5457 that musikding uses in there schematic.
Ok i compared tye original schematic that i found on electrosmash with the one from musikding.
Almost everything is the same except a few components.. see photos in attachments. Is this a big deal or does this not affect sound ?
(https://i.postimg.cc/GT8MjQzm/20210303-071612.jpg) (https://postimg.cc/GT8MjQzm)
(https://i.postimg.cc/N9GSRmWK/20210303-071630.jpg) (https://postimg.cc/N9GSRmWK)
Hard to tell which components you are concerned about. There are sites that have lists of the (slightly) different values for every year/model of rat... they don't make big difference. Well, turbo rat is a bit different because LEDs...Check out here towards bottom of page:
https://www.coda-effects.com/2016/01/proco-rat-white-face-1985.html
30pf vs 33pf is no big deal. The tolerance on the parts means 10% difference is within margin of error or close. This part just shaves off the highest frequencies. Since the curve is gradual, beginning a "whole step" or so higher is trivial.
The FET is just a buffer and so adds little character of its own. 5458 will probably work. They are a little different, but if it works at all here it will be fine.
Well there is an extra 10k resistor before the output.. why?
And the 1K and 4,7uF are reversed in the musikding schematic.. why is this and does it affect sound ?
The power section is also different..
the extra 10k at the output is in parallel with the 100k volume pot. you have two choices - fit a 10k pot and no extra resistor instead, or just not fit the extra resistor. or, third option, fit the 100k pot and the 10k resistor.
series parts order makes no difference. the signal goes in one leg, and can go nowhere but out the other leg, so what happens inbetween is a mystery to us. cap first/resistor second [4u7/1k] or other way, makes no difference.
one important point you have missed relates to the difference in the supply section. electrosmash shows ground referenced gate for the out fet, whereas musicding takes the gate to a positive bias. this results in more clean swing for the fet - it is a point many rat builds [search] have problems with. the divider resistors and cap values will have little influence over the total sound.
also note that controls named "tone" and "filter" generally do the same thing, but in opposite rotational directions.
Ok thanks for the info!
So is it possible to adjust the IC +9v and ground issue you mentioned ? Just like the original rat ?
By "ground issue" maybe you mean the biasing of the FET. The pcb you are talking about has done that...they have chosen the "better" biasing arrangement for the FET already. That is the only issue that is likely to "bite" a beginning rat tamer.
Otherwise you should be fine with the PCB and parts listed. The chart I referenced is if you get more advanced and want to "collect them all." Although rat lovers tend to be satisfied with one (correct me if I'm wrong)...Big muff builders tend to be more into the many possible variations.
I think Gord (GGBB) is more suitable person for enlighten RAT variations..
(https://i.imgur.com/lXjW8Sv.png)
1. ok so it doesn't matter if i'm using the 10k resistor before the output or not.. i just don't understand why it's there :o what's the use of it..
2. if i understand correctly.... the IC LM308 is wired better/wiser then a typical rat ? And what did you mean exactly by this results in a more clean swing for the fet ?
3. i understand now that reversing the 4.7uF and the 1k doesn't change the sound.. either way the end has the same value and results.
sorry maybe stupid questions but i'm kinda new to all this and trying to learn.
2) Not sure what you meant by "IC +9 and ground issue." The other fella mentioned:
"one important point you have missed relates to the difference in the supply section. electrosmash shows ground referenced gate for the out fet,...."
...and that was what I was talking about. The transistor, the FET, has its gate "biased" by a resistor to ground in some versions of the Rat, and in others by a pair of resistors, one to +9 and one to ground, that are called a "voltage divider." Here the resistors are equal (2.2M), so the voltage is 1/2. This arrangement is better, your musikding schematic includes it.
The simple explanation of bias and "swing;"
Your signal may be traveling along a wire swinging up and down from 0v, say from +1 to -1, "2 volts peak to peak." When it goes to minus, a transistor will turn off, causing nasty noise. If you bias the wire by adding a DC voltage to it, say 4.5v, your signal swings between 3.5 and 5.5. Same size signal, but now the transistor stays on the whole time, and what comes out is still sweet music. Opamps also require bias, in the big Rat comparison Antonis posted above it is R4 connecting the input to the voltage divider...
You can read more about biasing buffer stages here: http://www.muzique.com/lab/buffers.htm
What I can't explain is why it would sometimes be OK to have a FET biased to ground only, like in some RATs.
Quote from: idy on March 04, 2021, 01:25:20 AM....What I can't explain is why it would sometimes be OK to have a FET biased to ground only, like in some RATs.
What's the worst that can happen? Distortion?
I mean, the most it can swing in the "wrong" direction going into that buffer is about 0.6V anyway, and don't we want this point to be more negative than the junction of the transistor and R9 anyway in order to keep the body diode reversed biased?
Quote from: rangermaster on March 03, 2021, 02:14:05 AM
Well there is an extra 10k resistor before the output.. why?
And the 1K and 4,7uF are reversed in the musikding schematic.. why is this and does it affect sound ?
The power section is also different..
The "extra" 10k (musikding R10) comes from the "RAT-bypass" status LED circuit (similar to the millennium bypass) introduced in the original RAT2 (no longer used in true-bypass RAT2s). It is meant to be paired with 10µ for the output cap C10 instead of 1µ so that the low-pass filter formed by the cap and the volume pot in parallel with the resistor doesn't change from the original setup with just the cap and the 100k volume pot. LEAVE IT OUT (unless you are building a RAT2 clone complete with RAT-bypass status LED). See R15, C13 and notes in the Multi-RAT schematic below.
(https://i.postimg.cc/DW82FcFQ/Multi-RAT.png) (https://postimg.cc/DW82FcFQ)
The electrosmash schematic is wrong - but the 1k-4.7µ order is unimportant.
The power section ... The change to the biasing of the output FET (musikding R11, R12, C14, R9) is as already mentioned designed to bias the gate at ~3V. It is similar to the biasing used in the Turbo RAT (Multi-RAT R16, R10) which was a necessary modification of the original biasing because the Turbo RAT op-amp output voltage swing was greater than the RAT because of the higher forward voltage of the Turbo RAT's LED clipping diodes. The musicding setup is potentially less noisy than the Turbo RAT and is helpful most of the time even in RATs where a common problem is having the FET go into cutoff. KEEP THIS BIASING. I use something similar in my clones.
Note also that musikding's R3 is not original - but is helpful.
Thanks. Yes, that signal is pretty small after the clipping, and no, distortion at that point wouldn't mess up a pretty hi-fi sound. And the gate should be more negative than the source... making sense.
So the extra resistor was there to help the LED switching find a good path to ground if the volume was all the way up? And then you need a bigger output cap to keep the same response... OK.
Thanks fo rall the replies! helps me a lot.
So correct me if i'm wrong..
1. I can leave the R10 10k resistor out of the PCB.. no need to jumper the connection ? (not really useful in this schematic i understand)
2. reversing 4n7 and 1k doesn't matter or change the sound and value on the end of the line.
3. Opamp IC is in this PCB wired correctly to get the best bias/values
thanks again.
trying to learn that's all.
Quote from: idy on March 04, 2021, 10:46:28 PM
So the extra resistor was there to help the LED switching find a good path to ground if the volume was all the way up?
Sort of yes - the switching circuit not the LED itself. Look the green section. Q2 operates as a power switch for the diodes-resistor-LED string between Q2 source and ground. When pedal is engaged (FS2b flipped right as shown), Q2 gate is biased high via R13 to +9V - JFET is therefore "on" so +9V supply at drain flows through drain-gate to LED. When bypassed (FS2b flipped left), gate is now connected via 10k R15 to ground and therefore biased low. 100k volume pot alone wouldn't bring bias low enough. With gate biased low, JFET turns off and supply to LED is stopped.
Quote from: rangermaster on March 05, 2021, 12:09:32 AM
Thanks fo rall the replies! helps me a lot.
So correct me if i'm wrong..
1. I can leave the R10 10k resistor out of the PCB.. no need to jumper the connection ? (not really useful in this schematic i understand)
2. reversing 4n7 and 1k doesn't matter or change the sound and value on the end of the line.
3. Opamp IC is in this PCB wired correctly to get the best bias/values
thanks again.
trying to learn that's all.
Yes. Leave R10 out - not jumpered - that would ground the output signal.
So i got it working but there is a lot of squealing/oscillating noise when the gain pot is turned up...
I checked every part and every wire(short wires) but it all looks fine. I also tries replacing the opamp but that doesnt work either.
Does anyone know how to fix this ?
Here are some pics
(https://i.postimg.cc/mP8m5NY1/20210311-103355.jpg) (https://postimg.cc/mP8m5NY1)
(https://i.postimg.cc/wR82mWpZ/20210311-103402.jpg) (https://postimg.cc/wR82mWpZ)
(https://i.postimg.cc/2bBTysPn/20210311-103421.jpg) (https://postimg.cc/2bBTysPn)
Keep some distance between the circuit input and output wires. Clean up their solder joints. Shielded wiring for the input specifically might help.
(https://i.postimg.cc/hXg85YTK/image.png) (https://postimg.cc/hXg85YTK)
Special attention to the foot switch; wires close together there can do it. Some folks wire the 3pdt so the "in" and "out" side are on the outsides and the LED is in between...
Thanks guys. I will creat some distance between the wires.
I did wire the switch this way.. like i always do with these switches.
(https://1.bp.blogspot.com/-my24V2ib658/W1AOFKhkyJI/AAAAAAAAEVM/8hmEAVc9x08AFavpGKLEVHG9VHhpE4fOQCLcBGAs/s1600/3pdtSwitchWiring.gif)
Also the gain pot does not really do what it should do.. it tapers a little from 0 to 2 and then the gain stays the same....
Quote from: rangermaster on March 11, 2021, 02:39:48 PM
Also the gain pot does not really do what it should do.. it tapers a little from 0 to 2 and then the gain stays the same....
What kind of pot did you use? Linear taper or log?
I have build some rats and they all works great, even oce I changed a bit the last bufer to use a npn transistor insted the Jfet.
I have the pcb design just to print and etch.. ...the regular rat and the mod rat for NPN or Jfet use.
2N5457/2N5458/BF245 works perfect
BC547/2N2222/2N3409/2N4401/2N5088... ...any pnp.
Saludos
The pots are B100k. Linear
Quote from: rangermaster on March 11, 2021, 03:22:52 PM
The pots are B100k. Linear
Only for Asian & American suppliers..
Taper String Asia (common) Europe America Vishay
Linear LIN B A B A
Log / Audio LOG A C A L
Anti-log - - F C F
Quote from: antonis on March 11, 2021, 04:09:37 PM
Quote from: rangermaster on March 11, 2021, 03:22:52 PM
The pots are B100k. Linear
Only for Asian & American suppliers..
Taper String Asia (common) Europe America Vishay
Linear LIN B A B A
Log / Audio LOG A C A L
Anti-log - - F C F
I've lived the majority of my life in various places in Europe, and I've never seen a Log "C" pot or an Anti-log "F" pot. Basically everything I've seen follows the Asian/US pattern: A=Log, B=Lin, and if you can find it C=AntiLog. That's the standard, and Vishay are just having a laugh. Dunno what they were thinking.
Quote from: rangermaster on March 11, 2021, 03:22:52 PM
The pots are B100k. Linear
That's the problem - they need to be log especially the gain pot.
Quote from: ElectricDruid on March 11, 2021, 05:49:38 PM
I've lived the majority of my life in various places in Europe, and I've never seen a Log "C" pot or an Anti-log "F" pot.
I'm away from my junkbox but I promise you some revealing photos tomorrow Tom.. :icon_wink:
Quote from: antonis on March 11, 2021, 06:07:49 PM
Quote from: ElectricDruid on March 11, 2021, 05:49:38 PM
I've lived the majority of my life in various places in Europe, and I've never seen a Log "C" pot or an Anti-log "F" pot.
I'm away from my junkbox but I promise you some revealing photos tomorrow Tom.. :icon_wink:
.... popcorn ......
Ok.. so after isolating the wires and put them away from each other no change.
I have read that changing the 30pf cap can solve this. It should tame the opamp ?
What value should be best? And does it effect sound?
30pF cap is considered as "compensation capacitor" and it affects op-amp's Slew Rate..
(the smaller the cap the faster then slew rate and vice-versa..)
By raising its value you'll make op-amp respond "slower" for high frequency harmonics..
For 9V supply, 30pF cap and Slew Rate 300000 (taken from dadatasheet) the frequency limit is at about 5.3kHz so I don't think your squealing issue is comensation cap value..
Ok now i'm really confused.
Dunno what else it could be
I changed the pots to 100k log.
Quote from: rangermaster on March 31, 2021, 05:54:58 AM
Dunno what else it could be
Try to use a much bigger value cap (470pF say) instead of 100pF feedback cap..
(the one in parallel with Gain pot)
You might lose some high frequency gain so proceed to lowering its value untill squealing point just appears.. :icon_wink:
Try using shielded wire for the input connections.
Ok i replaced the 100pf with a 470pf... still there....doesn't change a bit
I removed c3 and c4 (30 and 100pf cap) and the noise was still there..
If so, it's more wiring/shielding interference than "inherent" circuit issue..
Ok i'll replace the wiring today with some thicker sheath wire and will solder them on the volume pot out and C1 cap instead of next to each other on the pcb.
Maybe this will help.
I know this is a zombie thread by now but...
There's a 1nF to ground (C2 on Musikding schem).
Leave your ceramic caps alone and increase C2 to 10nf. That should kill the squealing.
I spoke with someone at Musikding a while ago about the extra R10 to ground before the vol pot and they said it affects the volume. I can't recall which option made it louder though, keeping or removing it.
Quote from: Widows on December 17, 2021, 08:03:30 PM
I spoke with someone at Musikding a while ago about the extra R10 to ground before the vol pot and they said it affects the volume. I can't recall which option made it louder though, keeping or removing it.
It does not affect overall volume, but it does affect the taper of the volume pot. so the comparative volumes at mid-way up will be different, but 10 is always 10 and zero is always zero whether the 10k is in or out. See explanation about what it is actually for earlier in this topic: https://www.diystompboxes.com/smfforum/index.php?topic=126585.msg1211126#msg1211126.