If retro gaming in RGB is a hobby you enjoy you have probably experienced the problem of having fewer inputs available on your monitor or upscaler than RGB enabled consoles you want to have hooked up. The natural solution is to find some sort of switch box and many of us have turned to using RGB matrix switchers made by professional AV equipment manufacturer Extron. The Crosspoint series of switchers by Extron have become incredibly popular among retro gamers due to their high number of inputs and outputs and their relatively low cost when compared to other RGB switching solutions.
Lately, there has been a lot of discussion in the retro gaming community about c-sync and its potential to do harm to video equipment if not properly implemented into a retro gaming set-up. This is because there are actually two standards for c-sync with different acceptable peak to peak voltage ranges. The standard we as gamers should all be using is called 75 Ω c-sync which has a voltage spec of 300 mVp-p to 1.0 Vp-p. The other standard is called TTL c-sync which has a much higher voltage range of about 4.0 to 5.0 Vp-p. Some consoles output c-sync at TTL levels, like the SNES and Sega Genesis for example, and this is why your SCART cables need to have resistors and sometimes other components as well, on the sync lines in order to drop the voltage down to 75 Ω c-sync levels. If this isn't done and the TTL sync is fed into a device that is expecting 75 Ω c-sync, as most consumer grade video equipment does, then over time this will wear out the device's protection circuits and damage the device. One such device is the XRGB-Mini Compact Upscaler more popularly known as the Framemeister.
The Framemeister is a very expensive piece of equipment, so when I learned of the potential damage I could be causing it I decided to make sure everything in my retro gaming setup adheres to the proper c-sync standard. This lead me to discover that one of my SCART cables was missing the proper resistor. It also lead made me do a little more research on my Extron Crosspoint and discover that it has a feature called ADSP that is actually processing the sync signal.
When trying to figure out if my Extron Crosspoint was damaging my Framemeister my research made it clear that a lot of the retro gaming community was just as confused as I was. I could not find any definitive answer anywhere stating whether or not an Extron Crosspoint, a professional grade piece of equipment, was safe to use with consumer grade devices. What I did find was a lot of people disagreeing on two major factors, what ADSP actually is/does and what the DIP switches on the back of the unit do. The only way to clear this up once and for all is to clearly explain both, and to test the output on an oscilloscope. I decided to tackle this question so I borrow an oscilloscope from a retired electrical engineer friend of mine. His oscilloscope is old but it will get the job done and before we get to the actual testing, let's clear up those two major points of contention.
WHAT IS ADSP?
When I bought my initial Extron Crosspoint I wasn't paying any attention to which model I was getting beyond the number of available inputs and outputs. It wasn't until I learned of the different types of c-sync that I noticed the text on the lower right corner of the front panel indicating that the unit includes a feature called ADSP. Not knowing what this was I looked it up and found it defined in the manual for the 300 series of Crosspoints;
ADSP - Advanced Digital Sync Processing – An exclusive, all-digital process that regenerates the sync signal waveform and restores incoming sync level to 5.0 V p-p specifications. This ensures a sharp, stable image for improved signal compatibility with any LCD, DLP, plasma, or other digital display device.
For some reason, the meaning of this statement has been debated on forums but it seems clear to me that Extron Crosspoints with ADSP take all non TTL sync inputs and boost them back to 5.0 Vp-p, unterminated. Whether or not this is true is what I will be testing. If true, supplying this high voltage sync signal may be fine for professional equipment such as PVMs but could wreak havoc on the Framemeister.
SYNC TERMINATION SWITCHES
The other source of confusion is the DIP switches found on the back of most Extron Crosspoints. Extron calls these sync termination switches. They have two positions labelled 510 Ω and 75 Ω and indicate that they are for the first four inputs of the unit. Many people, including myself initially, have confused these as switches for toggling 75 Ω c-sync output but again, the manual makes its true function clear;
Sync termination switches — The CrossPoint 300 matrix switchers have sync termination switches on the rear panel for inputs 1 through 4 (figure 2-7). The switches provide a way to condition non-TTL sync levels greater than 5 Vp-p, enabling the sync to be properly passed from input to selected output(s). The matrix switchers have two sets of sync termination switches; one for horizontal or combined sync and a second set for vertical sync.
Each switch provides the option of selecting either 510 ohms or 75 ohms. The 75 ohms position is required only for an input with non-TTL sync, greater than 5 Vp-p. The normal position is 510 ohms.
Both of my Crosspoints have these DIP switches and they only apply to the input side of the Crosspoint. They are actually to reduce non TTL sync signals with peak to peak voltages higher than 5.0 Vp-p back down to a level that the Crosspoint can through successfully.
PUTTING IT TO THE TEST
These are the two Extron Crosspoint models I will be testing. The one I got initially is a newer model with ADSP, and the second one I purchased is older and doesn't have ADSP.
Top - Extron Crosspoint xi Series 12 x 4 RGB matrix switcher. I could not find any literature online specifically about the xi series of Crosspoints but the model number found on the side indicates that it is likely part of the 300 series. This model has ADSP.
Bottom - Extron Crosspoint Series 12 x 8 RGB matrix switcher. This model is older and does not have ADSP.
Both of my Extron Crosspoint's were tested under the same conditions. The sync signal was generated by my SNES mini that I modded myself for RGB output, running Super Mario World. To generate a load to test under RGB output was sent to my Sony PVM-8044Q RGB monitor. The signal was always pulled from the SCART head of the SCART to BNC cable connected to the PVM. Here is a shot of the test setup and the RGB mod I installed in my SNES mini.
In order to establish a baseline I tested the c-sync voltage directly from my SNES under load. The SCART cable I used for all tests was built by Retro Console Accessories and has a 330 Ω resistor on the sync line.
C-sync reading is approximately 830 mVp-p and falls with in 75 Ω c-sync spec as expected.
As I expected, the DIP switches had no impact on the sync output levels at all. To my surprise however, both Crosspoints performed identically. The older model that does not have ADSP also boosted the sync signal up to just shy of 2.5 Vp-p when under load. I had gone into this testing expecting the older model to not affect the sync signal at all and to be the better choice for use with my Framemeister but the oscilloscope doesn't lie. After seeing this in action I checked both manuals again and under the specifications for sync both manuals state;
Input level............................................... 0.5 V to 5.0 V p-p, 4.0 V p-p normal
Output level............................................ AGC to TTL: 4.0 V to 5.0 V p-p, unterminated
Both models of the Crosspoint output 4.0 to 5.0 Vp-p unterminated regardless of whether or not it has the ADSP function and when a load is applied this voltage gets reduced to approximately 2.4 Vp-p. According to the manual this output boost is done through use of AGC which stands for Automatic Gain Control. ADSP must merely clean up the input sync signal and not affect the output at all.
This leads me to believe that Extron Crosspoints will output 2.4 Vp-p for any console outputting c-sync. To test this theory I tested my RGB modded NES under the same conditions. Without the Extron the NESRGB generated a c-sync wave at 400 mVp-p. When passed through the Extron the output was again bumped back to 2.4 Vp-p. I also tested my N64 and Sega Genesis which had baseline voltage levels of 400 mVp-p and 500 mVp-p respectively and again, the voltage was boosted to 2.4 Vp-p by the Extrons. I now feel confident in stating that Extron Crosspoints should not be used directly with equipment expecting 75 Ω c-sync. 2.4 Vp-p is no problem at all for professional grade CRTs but if one of your Extron's outputs goes to a Framemeister's RGB input or something similar, you better add some resistance to the sync line to drop it back down to specification.
UPDATE - AUG. 30th 2017
Shortly after publishing my original findings I decided to add a 470 Ω resistor to my BNC to SCART cable to reduce the c-sync voltage coming out of either of my Extron Crosspoints back to 75 Ω specification. I was told by reddit user u/Typicalnervecell and Bob from retrorgb.com that this should do the job and I had also read that YouTube user neozeed1964 has had success with this as well.
I ordered some resistors from Digikey and once I had the resistors in hand I got right to work adding a 470 Ω resistor to my BNC to SCART cable originally built by Wookiewin on ebay. Here is a photo of the installed resistor shortly before covering it with the heat shrink tubing.
I retested both Crosspoints with my RGB modded SNES mini under the same conditions as my initial testing. The only difference is the added 470 Ω resistor on the sync line of the BNC to SCART cable.
Extron Crosspoint with ADSP. BNC to SCART cable with 470 Ω resistor on the c-sync line.
C-sync reading is approximately 600 mVp-p.
The 470 Ω resistor did the trick. It reduced the sync voltage to 600 mVp-p which falls nicely into the 75 Ω c-sync specification range. Adding this to your own cable is very simple and anyone with a soldering iron can do it. If you are currently using an Extron Crosspoint with a Framemeister, OSSC or similar device this is a necessary bit of work that will only cost you a few bucks. This solution will allow you to continue to enjoy the convenience and functionality of an Extron Crosspoint while ensuring a long life for your more expensive gear. If you want to purchase a 470 Ω resistor or two for your own cables they can be found here. Thanks to retrorgb.com for the link.
This is a great article; thanks for posting.
Regarding potentially unsafe sync levels, am I right in thinking that an Extron Crosspoint could potentially take a component (YPbPr) input and output via a SCART cable, but not a SCART (RGBs) input and output via BNC/component cables?
Obviously assuming the device receiving those unusual signals on the other end are able to still process what’s given (for example, in the past I’ve sent YPbPr through a gcompsw into a gscartsw and then into a PVM, which was able to determine it was getting YPbPr despite having gone through a SCART cable at one point).
Hello, Thanks for your article its really helpful and informative.(now i know to use 470ohm resistor when i make a bnc to scart cable)
I’m waiting to my crosspoint to arrive. Its one of the older model ( 8 inputs 4 outputs, no ADSP).
I have a question regarding the audio side on the switcher. Does it boosted? The audio level that it’s outpoting is safe to use on ossc or any other consumer device?
As per the manuals linked, All extron crosspoint 300 have ADSP, I think some models are not labeled “ADSP” on the front, so… ADSP is just signal conditioning for the sync lines, In the manual they use an example of a sync signal degrading over a long cable, and the ADSP restoring the signal to appropriate levels. Not much use for the feature in retro gaming, unless you have problems on your sync signal.
I’ve only ever used my crosspoints with component cables, but I assume that with SCART that you’re plugging something into either the H or V ports on the crosspoint for sync? Do these TTL sync characteristics also apply to composite or component video with sync on luma?
I’m so sorry, I’ve been panicking and googling and ended up with a ton of tabs open looking for info on this question and for some reason didn’t think to CTRL + F this page for “component”. I see now your response to Wolf where you provide the answer to my question.
Thanks for your service and have a nice day 🙂
Hi Trevor, thanks for the awesome article. It’s very helpful to see that someone else had already done the legwork to see what exactly ADSP does to the signal.
I was wondering if you might want to run an experiment with your Extron and oscope. Most retro consoles only use RGBS (not RGBHV), so this leaves the Vertical sync line unused. I’m curious if the non-ADSP Extron units do any sort of processing on the Vertical (or horizontal for that matter) sync line, or if you could be sneaky and pipe composite through it – allowing for a possible extra 12 composite consoles in it, even more if using component and have both H and V free.
I’m also curious if ASDP models would just strip sync off if a composite video.
Of course, this would produce a TTL level signal that would need to be dropped down if it’s not just hooked to an oscope.
Let me know if you might be interested in this little science experiment 🙂
Hello, i appreciate very much this article which is very clear. I’ve got some questions if anyone can help me to learn and understand more. If my extron outputs to an UMSA (http://arcadeforge.net/UMSA/UMSA-Ultimate-SCART-Adapter::57.html) using a bnc to vga adapter, my sync level will be attenuated to respect scart standard or not? Because if UMSA attenuates TTL to 75ohm standard is just perfect for my needs. Thanks again.
Yes, I would think that the UMSA would do the attenuation for you. Most of the time RGBS over VGA is equipped to handle TTL sync, like on the OSSC for example. In the case of RGBHV I think it is always at TTL level, but don’t quote me on that. The UMSA advertises that it converts RGBHV to RGBS and outputs over SCART so I would hope that it is attenuated to SCART standards. I would still check it though, if it were me. I don’t personally have any experience with that particular device.
I hope that helps! Let me know if you need anything else.
I am not a retro gamer.. But Many of my friends are facing the same confusion. I’ll share this to them.. Hope it helps
Thanks a lot!
I’m building a Dreamcast cable and unfortunately I don’t have access to an oscilloscope. If my TTL section is outputting 5Vp-p then would I use a 470 ohm resistor to bring it down to 75 ohm termination under 1Vp-p, or would I require a 940 ohm resistor since my voltage is approximately double the voltage seen in your tests?
I know almost nothing about the dreamcast so take everything I say here with a big grain of salt. When not under load (ie not connected to anything) the Extron outputs 5 Vp-p if my memory serves me correctly. Its not until it is under load that the voltage drops to 2.4 Vp-p and I would guess that this is also the case for you. If your TTL output is 5Vp-p unterminated, it will drop when under load and you will likely only need the 470 ohm resistor to drop the voltage to a safe level but I can’t know for sure without actually testing it, obviously. It also may be that you need other components on the sync line as well, like the Genesis for example. I’m sorry I can’t give you a concrete answer.
Thank you so much for getting back to me.
I own an Extron Crosspoint 88HVA, though I only use it for my YPbPr connections. I’m actually creating the 5Vp-p condition by pulling up the HSync and Vsync lines from +5V with limiting resistors and running everything through a 74LS86. From there I have TTL CSync at 5Vp-p, though I need to bring things down below 1Vp-p, ideally around 600mV, so I don’t blow the multiplexers on my GSCART. This is outside the scope of your testing but I really do appreciate your thoughts. I may have to connect it directly to my PVM until I get my hands on an oscilloscope to be sure of what I’m dealing with.
Oh I see. It does sound to me like the 5 Vp-p you have there is not under load and will drop when connected, so you likely will only need to add a 470 ohm resistor to the line.
Thanks so much for this. Been fiddling around with my recently-purchased Extron—I didn’t realize it had ADSP before I bought it and was freaking out about possible damage, so your article is a great relief!
I’m going to put a resistor in my BNC-SCART that goes to my OSSC. But I also have a Shinybow RGB to component converter that ultimately connects to a consumer CRT. I should also add a resistor to the SCART cable that goes from the Extron to the Shinybow, right? The voltage would probably place additional strain on it, just like the OSSC.
My 3rd display Is a PVM which I *believe* can handle TTL just fine. But correct me if I’m wrong about that.
I’m glad I could help. Yes, you should also protect your Shinybow RGB to component converter as well. You should really protect any consumer level RGBs equipment. I am pretty sure that specific device is rated for 1Vp-p/75 ohm input only and even if it can handle TTL levels of sync dropping it to 75 ohm levels won’t hinder anything. Your PVM should be fine. I haven’t run across a model of PVM yet that isn’t rated for TTL sync but if you tell me your PVM model number I will double check for you just to be sure. Thanks for reading!
In your updated test results you say that adding the resistor is necessary for going from a crosspoint to an ossc but I thought the ossc could accept higher voltages on its inputs? Maybe it is because I am outputting my scart signal via a bnc to vga cable and the vga input on the ossc is rated higher? Also have you tested how the crosspoint handles if you use bnc male to rca female adapters so you can run component video through it? I’m curious if it adds more juice to the component signal and if the component input on the ossc is rated to handle that.
Lastly if the dip switches don’t do anything does that mean I never have to change them no matter what I put into the crosspoint or does it mean that if I have it set to 510 and it is getting 75 (or vice versa) I could be damaging the crosspoint or image quality in some way?
That’s correct. I was only referring to the SCART input of the OSSC. TTL is unsafe for that input, but the VGA input CAN take TTL sync so you are fine there. Sorry, I should have been more clear about that. As far as running component through the Crosspoint, everything I was testing here only applies to RGB with C-Sync. Componenent is fortunately a much simpler situation. Crosspoints do not do any processing on any of the RGB video lines on the unit, only the sync lines. Whatever you plug into the RGB lines, be it RGB, component or even composite, you get the same coming out the other side of the Crosspoint. Apparently you can even run audio through those lines if you want, but I haven’t actually tested that myself. So the answer is no, the Crosspoint will not boost anything when it comes to component video and it is completely safe to use component through a Crosspoint with the OSSC, Framemeister or any other piece of equipment that accepts component video.
As for the DIP switches, they are only for conditioning really high sync levels on the input side of the Crosspoint so the Crosspoint can actually handle process it. Regardless of what position that switch is in, you get the same sync out of the Crosspoint. To answer your question, it does not effect the picture quality or damage the Crosspoint itself. You should just leave them all set to 510 ohm because that is the default and if you are using it only for retro gaming there is never a need for toggling it to 75 ohm because you likely won’t ever have a sync signal high enough for that to matter. I know it seems weird that the 75 ohm setting is for sync that is not 75 ohm, but that’s what the manual says. Just leave them all set to 510 and know that whatever console you are putting into it, it is not damaging the Crosspoint or degrading your video quality.
Thanks very much for your article and reply. You cleared up every question I had.
My pleasure, I am glad I could help!
It doesn’t seem to be on mine…the RGB line seem to be roughly doubling the vpp from what I can tell on my crosspoint 1616 series.
Did you add the 470 ohm resistor to your cable on the input side or the output side? I’m asking because I’m going from my Crosspoint output (Bnc to Bnc) straight into a pvm. But you said you added it to a Bnc to scart cable. I guess I would just put the resistor on the sync output line then. Thanks for this write up, really pulling my hair out as to why I can’t sync to my pvm thru the Crosspoint, when scart to Bnc straight into the pvm syncs fine.
I added the resistor to the SCART head of my BNC to Scart cable, so on the output side of the cable itself and on the output side of the Crosspoint. As for the location of the resistor on the cable, it doesn’t matter where in the sync line it goes. All that matters is the total resistance and adding it anywhere on the sync line of your output cable will have the same effect. In your case however, you shouldn’t need to add resistance if you are going straight to a PVM. PVMs, like Crosspoints are professional equipment and are designed to handle 75 ohm and TTL sync. The 2.4 p-p should work just fine with your PVM, but maybe you have a model of PVM where this is not the case. It would help if I knew what model of PVM and Crosspoint you have. Also, what console are you using? You’re right though that if it syncs fine without the Crosspoint, and doesn’t sync with the Crosspoint, the Crosspoint must be causing the issue.
PVM 14N6U and a Crosspoint Ultra 128 w/ADSP. Saturn (model 2) works fine straight into the PVM but refuses to sync with the Crosspoint. I have a model 1 I can test and also a Genesis model 1 I can test but they arent readily available without hassle atm (in the middle of a move). I was just doing preliminary testing because I am about to build my game room in the new house. I’ve had the Crosspoint for several months and had only tested it with composite and s-video until now (of course it works great with those). I had no idea about the sync boosting causing issues but I know now. Thanks a lot for this write-up, I didn’t see anything about this on retrorgb.com and I can’t imagine I’m the only one with this issue so this is very helpful. Hopefully others will find their way here as well. I ordered a pile of those resistors and will try that out and report back my findings (may be a couple weeks though).
Interesting. That should work, so I am confused as to why it isn’t. The 14N6U is rated for sync right up to 4Vp-p just like most other PVMs so you shouldn’t need to add any resistance between the Crosspoint and the PVM. I will be interested to hear if you are able to get your Genesis or model 1 Saturn to work with the Crosspoint. They should all work fine… Let me know what you find when you get a chance to test them. Bob from retrorgb did mention my findings on his podcast and he has told me he will eventually link to it on his site but I guess he hasn’t gotten around to it yet. Thanks a lot for reading and if you have any other questions I am more than happy to help if I can.