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SOLD OUT: PCE/Turbografx RGB THS7374 amps and cables

Started by mickcris, 04/01/2015, 10:16 AM

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mickcris


Keith Courage

I'm going to bump this and say that these are the best RGB amps I've ever used. I actually put these amps together myself now for my own use. However, before I started to do that mickris helped me out a lot and I could definitely see the quality in the design. Best picture quality I've seen from any r_g_b amp I've tried.

mickcris


mickcris


mickcris

bump.  at the request of leonk, have started the process of updating the amp board to viletim's suggested resistance at the output.  Will look the same as the previous version, but will be more correct.  The old design was not hurting anything, but might as well make it better.  Here is viletim's explanation:
http://nfggames.com/forum2/index.php?topic=4822.msg34061#msg34061

"Unfortunately the RGB signal the PC Engine is not 0.7 Vpp, it's actually 0.8 Vpp (I know because I bought a PC Engine a few months ago). To compensate for this I suggest attenuating the output slightly. Instead of a 75 ohm resistor in series with the output, you could use 86 ohms in series and 586 ohms to ground. This way it still looks like a 75 ohm output to the outside world. For E24 resistor values try 91 in series and 470 to ground. Not perfect but good enough - 0.67 Vpp is much better than 0.80 Vpp."

MNKyDeth

So this 0.8 is with the PCE but since all the other consoles use the same graphics chips this retains also for all consoles after the original PCE correct?

Because we pull the color directly from the chip itself it doesn't get processed through anything but the amp hence the brightness differences?

Just wanted to ask and maybe clarify a bit more. Also, bump :)

mickcris

I'm not a video engineer so not sure if i will explain it correctly but i will try.  But yes, this applies to all PC Engine and TurboGrafx systems.

The standard RGB signal is 0.7 volts.  After amplification on the THS7314 or NJM2267 (both are 6dB amps), this is what the output of the console should be sending to the monitor as it is what it is expecting.
http://www.syncblaster.com/RGBfaq.html

When you amplify the SNES or N64 with one of these amps it produces 0.7v, but when amplifying the signal from the pc engine it is 0.8v.  So the voltage being too high will make the picture too bright.  I have not actually measured it myself, but the output of the PC Engine RGB lines should measure around 0.4v before amplification and on an N64 measure around 0.35v.
http://www.sengpielaudio.com/calculator-amplification.htm
The reason the output resistance was changed from 75 ohms to 100 ohms was to compensate for this.  Doing it with the 91 ohm (with 470 ohm parallel to ground) makes it appear to be around 75 ohms to the monitor.  Before this amp was not taking into account that the monitor is also expecting 75 ohms along with 0.7v.  This new design corrects that.  Although the 100 ohm resistors on the output were not going to damage anything.

thesteve

it gets a bit more complicated then that
the 6260 uses a Vref-lo and Vref-hi to set the top and bottom of the RGB output, so it can differ between systems, but generally doesnt
also the output rigidity of the 6260 is quite low making its output differ depending on what amp its driving

mickcris

I got a sample batch of the new pcbs in the other day.  Have sent a couple out to get some feedback before I make an order for more boards.

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IMG

they are the same overall size as the old boards

MNKyDeth

I made a video installing the new RGB amp. it is a bit long for just an amp. I even cut out a lot of crap because I found out I ramble and apparently I very much like to ramble a lot. :)

So... Here is the link of me installing the new RGB amp from Mickcris.
Btw, its a bit fuzzy, blurry, but hopefully it is good enough. Let me know your thoughts on youtube and I will try to do more hardware stuff and hopefully, eventually get better cameras and stuff to make it better.

wildfruit

You sound different to what I imagined. I don't know why.

mickcris

OP updated.  There are a few new boards available and have the old ones discounted if you dont care about the resistors being soldered to the back (its the same circuit).

MNKyDeth

Quote from: wildfruit on 05/10/2016, 01:03 PMYou sound different to what I imagined. I don't know why.
Not sure if good or bad...  :D

mickcris

got my shipment of pcbs in. should have enough that i will never have to order anymore.  just need to start on building up some more.  I have 5 ready to go.  still also have about 10 "fixed" versions available also.

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mickcris

switched to tantalum caps on the output to lower the height of the board

mickcris


mickcris

bump.  still have a few "fixed" boards left and some new style ready to ship.

shugs81

Hi bud... Do you ship to the UK and if so how much???

Thanks!

mickcris

Quote from: shugs81 on 08/04/2016, 01:18 AMHi bud... Do you ship to the UK and if so how much???

Thanks!
I do.  Depends on how much it weighs.  I just charge whatever it costs to ship.

mickcris


mickcris

I tied out a new install location on the duo now that the amps are pretty low profile.  Replaced a different amp with mine:

https://imgur.com/a/gXniJ
Ignore that hole the wires are going through.  The previous modder drilled that and I just used it cause it was there.  You can just bring the wires up on the back of the PCB, directly behind that hole.  I also put some kapton tape on the shield below the amp just in case it would ever fall (which isnt very likely).  There is still plenty of clearance between the caps on the amp pcb and shielding.

I will probably take some more pics when I do another one that doesn't have extra holes in it.

blueraven

 :shock: Looks awesome! Those last install photos were incredibly clean.

...and that is one huge bag of chips  :mrgreen:

mickcris

Quote from: blueraven on 10/15/2016, 12:42 AM:shock: Looks awesome! Those last install photos were incredibly clean.

...and that is one huge bag of chips  :mrgreen:
Thanks.  Would be nice if all those pcbs already had the components soldered to them.  :)

mickcris

Did another one, but this one was from scratch so no extra holes all over the place.

https://imgur.com/a/DazFG

everything fits nicely

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mickcris


mickcris

bump.  amp has been updated and now uses a THS734 instead of a THS7314.

xcrement5x

Ever put one of these in a Laseractive?  Just wondering how the output from there will look. 

mickcris

Quote from: guest on 01/21/2017, 10:17 PMEver put one of these in a Laseractive?  Just wondering how the output from there will look.
I have not.  I'm sure it can be done though.  I think I've seen somewhere about doing it, but it only works in the pce/tg16 module and not laser active specific games iirc

xcrement5x

Quote from: mickcris on 01/22/2017, 01:28 AM
Quote from: guest on 01/21/2017, 10:17 PMEver put one of these in a Laseractive?  Just wondering how the output from there will look.
I have not.  I'm sure it can be done though.  I think I've seen somewhere about doing it, but it only works in the pce/tg16 module and not laser active specific games iirc
Oh yeah, I know about the limitations of the RGB, basically it can only take the RGB from the PAC not the LD since the video is natively in composite.  Other implementations I've seen for RGB on the LA make it so that you basically have RGB for both the Genesis and PCE PACs.

I guess I'm basically just wondering if the tweaks that have been done for this chip to make it optimal for the PCE would impact the stronger RGB signal that is sent by default from the Genesis PAC. 

mickcris

i never really looked into how it was done before.  but yes, it should make the output for the gensis a little darker, but it would make the output for the tg16 look right.  if you use an amp that has the 75 ohm resistors, the opposite would happen.  this is assuming that the PAC is just a tg16 consoles shoved inside of it as i have never really looked into this before. 
you could maybe rig up some sort of switch for the output resistors to swap between different ones.

mickcris


mickcris

I have 4 of the previous rev amp with the ths7314 for a discounted price is anyone is interested.

IMG

price is $12 a piece shipped if you are in the USA.  if you are outside of the USA, there might be a small shipping charge also.

all gone

MobiusStripTech

Installed one of mickcris boards in my personal Duo R this weekend. Can't recommend it enough. That and I hear he is a rather handsome fellow as well as a gentleman.

mickcris

Quote from: MobiusStripTech on 02/26/2017, 08:19 PMInstalled one of mickcris boards in my personal Duo R this weekend. Can't recommend it enough. That and I hear he is a rather handsome fellow as well as a gentleman.
haha.  thanks. :oops:

mickcris

have replaced the sync strip scart cable with a small add on board to be installed in the console.  It could also be installed in the scart head if you really wanted to, but better to do it inside the console.  Board outputs 75 ohm sync, but could be easily modified to output TTL sync if one required it.

com4


mickcris

regular sized 8 pin din euro scart cables now have a pcb

IMG

I was thinking this would make building them quicker but that's not really the case.  Still, they look a bit nicer than my previous cables with the all the ground jumpers.

mario64

Quote from: mickcris on 05/28/2017, 07:18 AMregular sized 8 pin din euro scart cables now have a pcb

IMG

I was thinking this would make building them quicker but that's not really the case.  Still, they look a bit nicer than my previous cables with the all the ground jumpers.
How can I go about ordering one of these? I'm hoping it will address the audio hum from my Duo R

mickcris

Quote from: mario64 on 07/24/2017, 09:23 PM
Quote from: mickcris on 05/28/2017, 07:18 AMregular sized 8 pin din euro scart cables now have a pcb

IMG

I was thinking this would make building them quicker but that's not really the case.  Still, they look a bit nicer than my previous cables with the all the ground jumpers.
How can I go about ordering one of these? I'm hoping it will address the audio hum from my Duo R
Sent you a pm

mickcris


mickcris


mickcris

#91
I have updated the amp with output resistor values closer to the ideal values of 86 ohm with a 586 ohm to ground.  The ideal values can only be done with 4 resistors so have changed to the closest I could get it with 2.  Now using an 86.6 ohm resistor with a 604 ohm resistor to ground.  Both resistors are 0.1% tolerance.  See the math below:

IMG
https://i.imgur.com/M22k3bg.jpeg

mickcris

since im no longer selling these, i shared the files if anyone wants to build there own
https://oshpark.com/profiles/mickcris

NightWolve

IMG

Nice looking amp, so how did it compare to turbokon's (http://www.tg16pcemods.com/) ? Just curious, even with discontinuing it.

mickcris

see the 1st post.  that amp uses 75 ohm resistors which make the output too bright.

xcrement5x

Are you going to make more eventually? I think they are great amps and used them in my laseractive.

mickcris

#96
Quote from: guest on 05/25/2018, 01:41 PMAre you going to make more eventually? I think they are great amps and used them in my laseractive.
I dont plan on it.  I got sick of soldering them.  I was doing every one by hand so not the most efficient method.

console5 still has some kits if you are interested in soldering one together
https://console5.com/store/ths7374-rgb-pcb-kit-for-nec-turbo-grafx-turbo-duo-pc-engine.html

or if someone on here wants to get some boards made from the link above and sell them pre built that's fine too.  I just got tired of doing it.

also, mobiusstriptech informed me of this earlier today
they should be selling what is the same thing soon (not that im really supporting these guys, but that might be the only option to get on pre-soldered since i'm no longer selling them).

the v1.0 circuit was an update to micro's original with viletim's brightness fix added.  then the newest version just swapped out the ths7314 for the ths7374 and made the parts smaller.  Its still basically the same circuit from the data sheet.
https://nfggames.com/forum2/index.php?topic=4822.msg34061#msg34061

xcrement5x

Man, that assembly line makes me appreciate even more what you were doing. 

I'm glad they are doing a bit of QA on them at the end but still, that video has some interesting comments going on. 

mickcris

#98
It has come to my attention that there is a mistake on the 7374 PCB.  The 4th output is unused and is tied to ground while it should be floating.  This is causing the IC to run hotter than normal.  I would think the risk is fairly low as some of these have been in use for almost 2 years now.  My guess would be that it running a bit hotter will cause the amp to wear out faster.  Its also a possibility that the 4th channel could just go out and the chip return to normal temps.  The temp its running at is still below the continuous operation long term reliability max temp.  Having said that,  I have not had any reports of any of them failing yet but you may want to either modify the board or discontinue using it.

I tested one and after running for an hour, I measured it with my Fluke 87 meter and its running at 65 °C.  With the 4th output floating the temp is 30°C.  Per the data sheet:
Maximum junction temperature, continuous operation, long-term reliability is +125 °C

You can fix this by lifting that leg.  Here is pic with an arrow pointing to the pin that needs lifted
https://imgur.com/a/cMeWI3l
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I found it easiest to just de-solder that side of the IC, lift/break off the leg, then re solder that side down.

If you purchased one of these and would like me to lift the pin for you or give you a refund, send me a message and I will get back to you.  I may need proof that you purchased it from me.  I will only refund ones that I sold that I had soldered. If you bought one from console5 though i will lift the pin on it.

If you want me to lift the pin, send me the pcb(s) along with a piece of paper with a return address and you email.  I will lift the pin and then send it back.

If you want a refund, send me the pcb(s) along with a piece of paper with your paypal email address.  I will then send $20 to your paypal account per amp.

Ergot_Cholera

I am the one who noticed this :-". Maybe I should have contacted you directly but I wanted to make sure that I was correct in my findings. I didn't post here because its mostly dead  :-({|=