Ibanez GSR200 Onboard Bass Preamp  [schematic]

Pickups, wiring schemes, switch techniques and onboard active electronics for guitars and basses
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Kyosanshugi
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Post by Kyosanshugi »

Hello all,

So a while back I picked up an Ibanez Gio GSR200 bass off of craigslist for cheap, and though it sounded kinda like crap with everything on it stock, I got infatuated with the onboard preamp it came with, especially after opening it up and seeing that it was a relatively simple circuit. Well, I've been working on tracing it for a while, and after a good amount of trial and error, I finally built a working copy and drawn up a schematic. The circuit is compact and fits comfortably in the body cavity of many basses. I'm about to build like three more of these things and put them in other basses and also my Dano baritone, for kicks. Enjoy!

ibanez new_s1.png
(original image: https://img.photobucket.com/albums/v11/ ... new_s1.png)

ibanez new_layout.png
(original image: https://img.photobucket.com/albums/v11/ ... layout.png)

ibanez new.png
(original image: https://img.photobucket.com/albums/v11/ ... %20new.png)

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davidmochen
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Post by davidmochen »

Hi, anyone care to describe the role of IC1B in this circuit?

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george giblet
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Post by george giblet »

It's part of a gyrator (IC1B, R6, R9, C8). It looks like a 1.0H inductor in series with 1k (R9) and in parallel with 2.2M (R6)

For this circuit you can ignore the 2.2M part. What you have is a 1H inductor in series with 1k and that's in series with C7 (4.7uF)
and the three elements form a series resonant circuit. The resonant frequency is 72Hz. The way it's wired gives a peaking bass boost
at 72Hz.

R10 and C5 give a shelving type treble boost.

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Post by vangelismetheny »

Kyosanshugi wrote: 18 Jul 2017, 07:48 Hello all,

So a while back I picked up an Ibanez Gio GSR200 bass off of craigslist for cheap, and though it sounded kinda like crap with everything on it stock, I got infatuated with the onboard preamp it came with, especially after opening it up and seeing that it was a relatively simple circuit. Well, I've been working on tracing it for a while, and after a good amount of trial and error, I finally built a working copy and drawn up a schematic. The circuit is compact and fits comfortably in the body cavity of many basses. I'm about to build like three more of these things and put them in other basses and also my Dano baritone, for kicks. Enjoy!

ibanez new_s1.png(original image: https://img.photobucket.com/albums/v11/ ... new_s1.png)

ibanez new_layout.png(original image: https://img.photobucket.com/albums/v11/ ... layout.png)

ibanez new.png(original image: https://img.photobucket.com/albums/v11/ ... %20new.png)
Thank you my brother so much! You save my life with this post and documentation.. :applause: :applause: :applause:

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Renegadrian
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Post by Renegadrian »

Sorry to resurrect such an old topic, I saw some pics of the phat II and it has some differences...b20k pot, different ic, some component values, etc - I'd like to see the phat II traced.

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Post by george giblet »

Renegadrian wrote: 16 May 2024, 22:18 Sorry to resurrect such an old topic, I saw some pics of the phat II and it has some differences...b20k pot, different ic, some component values, etc - I'd like to see the phat II traced.
I'm pretty sure I saw at least one variation as well. I started to trace it but I couldn't get enough from the pics to make it worthwhile. At some point Ibanez produced response curves for these things and I have a feeling the circuit in the thread didn't match up. I just left it for a rainy day. It's been a while since I looked at it.
Ibanez Phat II - Frequency Response (Ibanez GSR180-BS Gio 4 String).png
Ibanez Phat II - Frequency Response (BTB EDB GSR).png
PHAT2R PCB
Phat 2R - rough schematic V10 (no cap values).png
There was talk of one of the Phat circuits being the same as an EMG board.

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Post by george giblet »

Since we cracked open the thread: There's at least four PHAT/PHAT II boards.
Also I believe there is a PHAT response which is different to the PHAT II.

Here's the dilemma:
- The circuit at the top of the thread, or my retrace, appears to be PHAT II.
Typically found on GSR200, GSR205, GSR206 basses, from say 2006 to 2017/2018.
- It seems the response from that board doesn't match the PHAT II plots from
Ibanez. In fact with the resistor values it cannot match the PHAT II plots.
- The later circuit 2018/2019, PCB PHAT2R, can match the PHAT II plots.

1) Through hole

SR300DX
https://www.talkbass.com/threads/ibanez ... q.1192848/

I can see 2M2 resistors which makes me think it is similar circuit to the one at the top
of the thread.

2) SMD

PCB is marked: PHAT EQ (not PHAT II)

Reported to be Phat II from 2006 GSR205
https://www.talkbass.com/threads/ibanez ... eq.848511/


This is also appears to be the same as the circuit at the top of the thread.
However, when I traced the board there seems to be errors in the part values.
Also different part designations in a few spots.
Also the pot is 20kB
Phat Phat II (PCB PHAT EQ) (GSR205 2006) - schematic.png
This is too close to the schematic at the top of the thread, so I'm think there's errors in that
schematic. The problem with my trace is I don't know the ceramic capacitor values and
I don't have a PHAT frequency response (It won't match the PHAT II plot since the larger resistors
mean less boost than PHAT II - that's why I think there's PHAT and PHAT II.)

After reviewing some boards/basses I think it *is* PHAT II but does not match the
Ibanez's PHAT II plot. So that's where things get stuck.

3) SMD

PCB marked: PHAT EQ II

I have no info on this one.

Image:
https://i.ytimg.com/vi/YWO5V7QA0Nw/maxr ... 43gpR_eeag
Video:


4) SMD 2018

PCB Marked PHAT2R

The one I traced in the previous post.

https://www.talkbass.com/threads/ibanez ... 511/page-2

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Kyosanshugi
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Post by Kyosanshugi »

Funny that this topic should be resurrected now that I'm trying to bring my bass back to life after years. Tried building my schematic as posted originally, albeit with a different layout. Didn't work. I wired it up externally and tried my bass through it. Didn't get signal at all with a 4558, got a little signal with the pot dimed with a TL052. Something's not right. Going to try some of the other component values posted here on a breadboard and see what I discover.

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Post by Kyosanshugi »



Breadboarded it up mostly according to my original values, changing only C4 (C5 in george's schematic above) to 470nF. It works, I think. Don't have a bass amp available for testing right now, but I do get a significant bass boost when turning the pot. Can anyone explain in relatively simple terms how to calculate the frequency response of the circuit, or is there a calculator out there?

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Post by george giblet »

Hi Kyosanshugi, I actually spent quite a few hours piecing together what's going on with these preamp. However, because I didn't resolve everything I didn't post the info. There's so many points it's hard to summarize them in an intelligible way but I'll give it a go:

For your schematic, which I believe is for a through hole PHAT-II board, I'm convinced the 4u7 (C4) should be 470nF. The other part value which is uncertain is the resistor R9 (1k). I suspect this could be 10k. From my research the pot should be 20kB. I have not seen any units with 25kA.
Phat II ibanez new_s1 (2007) - corrected.png
I found this pic which shows the part values on the overlay and the has visible through-hole parts values, which are different to the overlay. Annoying, the only value which is hard to be certain of from the pic is R9 (your schematic).

From GSR200 2005 left handed
ibanez GSR200 2005 left hand (through hole) 1.png
ibanez GSR200 2005 left hand (through hole) 1.png (596.13 KiB) Viewed 608 times
ibanez GSR200 2005 left hand (through hole) 2.png
ibanez GSR200 2005 left hand (through hole) 2.png (234.58 KiB) Viewed 608 times
What else is clear is the silkscreen does not match the loaded parts. What I suspect happened here is the values on the silk screen are PHAT whereas the actual parts loaded are for PHAT II.

The GSR200's were released around 2005 with PHAT II but before that there were some other basses with PHAT controls. Around 2005 the older basses were phased out over a year or two then the newer bases with PHAT II arrive, that included the GSR200s.

If we look at the *resistor* values from the smd PCB labelled "PHAT EQ" we can see the resistor values match the silk screen on the through-hole PCB. So I do believe those resistor values are for PHAT (I). What's confusing is the GSR200's supposed to be PHAT II but the smd "PHAT EQ" PCB I posted earlier was from a GSR205 (2006). It's possible the 5 and 6 strings used PHAT and the 4-string used PHAT II, at least for a period. The GSR200 series basses were made in different countries and may have different builds, especially early on. That might also explain why there are both through-hole and SMD boards from the same period. These aspects of the preamp are very confusing!

It's also possible at some point the SMD "PHAT EQ" PCBs were loaded with "PHAT II" values, as what is done with the through-hole. However the example I posted doesn't do this.

I think the SMD boards marked "PHAT II EQ" use values like your board. These came out roughly 2010 and were used upto about 2018/2019 where *newer" basses get updated with the smd PHAT2R preamp. Models starting earlier than 2018/2019 which were still sold used smd "PHAT II EQ". Then in 2023 or so yet another PCB came out which is different again but seems to follow the smd "PHAT II EQ" board to some degree. Considering how many basses have been sold there's very little detailed info on the PCB's.

Ibanez started to produce frequency response curves for PHAT II around 2008. However neither the resistor values on the silk screen (PHAT) or the actual part values (PHAT II) can match this response. Only the smd PHAT2R preamp can match Ibanez's PHAT II, and only if I set the cap values - we still don't know if the actual PHAT2R PCB uses my cap values.

I've left out a lot of details but that's what I know. Some things are consistent but there are many holes. The main point is there's different versions of this preamp out there.
Last edited by george giblet on 07 Jun 2024, 22:49, edited 6 times in total.

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Post by george giblet »

Here's a few pics of the 2023 version:

5)
05 Ibanez phat II 2022_2023 back.png
05 Ibanez phat II 2022_2023 back.png (361.12 KiB) Viewed 601 times
05 Ibanez phat II 2022_2023 front.png
05 Ibanez phat II 2022_2023 front.png (292.49 KiB) Viewed 601 times
Notice the 2M2 resistors and Tantalum caps ie. it doesn't continue on from the PHAT2R but
reverts back to something like the earlier boards. It looks like the 1k input resistor
has been changed to 7.5k. I cannot see any other values from these pics to confirm
Ibanez went back to the earlier "PHAT II" values.

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Post by george giblet »

Kyosanshugi wrote: 07 Jun 2024, 17:23 Breadboarded it up mostly according to my original values, changing only C4 (C5 in george's schematic above) to 470nF. It works, I think. Don't have a bass amp available for testing right now, but I do get a significant bass boost when turning the pot. Can anyone explain in relatively simple terms how to calculate the frequency response of the circuit, or is there a calculator out there?
There's a calculator here which will work for single bands:
https://www.muzique.com/lab/gyrator.htm

Here's what the responses are like from the circuits proposed so far. There is a very significant difference in the uncertain resistor R9 being 1k or 10k.
phat phatII phat2r response V10 (speculative).png

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Post by Kyosanshugi »

George, you are coming through with the info, I appreciate what you're doing!
george giblet wrote: 07 Jun 2024, 19:57 For your schematic, which I believe is for a through hole PHAT-II board, I'm convinced the 4u7 (C4) should be 470nF. The other part value which is uncertain is the resistor R9 (1k). I suspect this could be 10k. From my research the pot should be 20kB. I have not seen any units with 25kA.
Indeed, I used a 470nF on the breadboard and it sounds right. As for R9, I have a 1k inserted atm. I'll try some different values between 1k and 10k and report back. I also think I put the A25k pot in there because that was what I had on hand at the time. The second revision prototype I built (that didn't work) used an A20k. Using a B20k on the breadboard now. Honestly, when I did this trace I was doing a lot of drugs and I'm not surprised that I mixed up things like that. lol
george giblet wrote: 07 Jun 2024, 19:57 Phat II ibanez new_s1 (2007) - corrected.png

I found this pic which shows the part values on the overlay and the has visible through-hole parts values, which are different to the overlay. Annoying, the only value which is hard to be certain of from the pic is R9 (your schematic).

From GSR200 2005 left handed
ibanez GSR200 2005 left hand (through hole) 1.png

ibanez GSR200 2005 left hand (through hole) 2.png

What else is clear is the silkscreen does not match the loaded parts. What I suspect happened here is the values on the silk screen are PHAT whereas the actual parts loaded are for PHAT II.
These boards look very familiar, and the parts arrangement matches up with my layout in the OP. I do remember taking detailed pictures of both sides of the board while tracing, but those are on a hard drive that is long gone. The original bass was also stolen, sadly.
george giblet wrote: 07 Jun 2024, 19:57 If we look at the *resistor* values from the smd PCB labelled "PHAT EQ" we can see the resistor values match the silk screen on the through-hole PCB. So I do believe those resistor values are for PHAT (I). What's confusing is the GSR200's supposed to be PHAT II but the smd "PHAT EQ" PCB I posted earlier was from a GSR205 (2006). It's possible the 5 and 6 strings used PHAT and the 4-string used PHAT II, at least for a period. The GSR200 series basses were made in different countries and may have different builds, especially early on. That might also explain why there are both through-hole and SMD boards from the same period. These aspects of the preamp are very confusing!
As noted on my schematic, mine was an Indonesian model. Board/parts availability may well have varied by country, and manufacturers could have had different BOMs that they simply chose according to what parts they had. This, of course, is pure speculation on my part.
george giblet wrote: 07 Jun 2024, 19:57 Ibanez started to produce frequency response curves for PHAT II around 2008. However neither the resistor values on the silk screen (PHAT) or the actual part values (PHAT II) can match this response. Only the smd PHAT2R preamp can match Ibanez's PHAT II, and only if I set the cap values - we still don't know if the actual PHAT2R PCB uses my cap values.
Questions and mysteries abound! Again, though, I appreciate what you've brought to the table.

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Post by Kyosanshugi »

george giblet wrote: 07 Jun 2024, 21:33 There's a calculator here which will work for single bands:
https://www.muzique.com/lab/gyrator.htm

Here's what the responses are like from the circuits proposed so far. There is a very significant difference in the uncertain resistor R9 being 1k or 10k.
Thank you so much for this! Quite interesting, those plots. I think I need to up my equipment game a bit and analyze this circuit in a little more detail. I know a little more now than I did back then, after all. :D

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Post by Kyosanshugi »

Looking at your pics of the THT boards, I see that there is a 0.47u electrolytic. That's probably the mistake I made with C4(C5), I associate electrolytics with values of 1u and up. With an electrolytic in the circuit, would the negative point towards the gyrator?

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Post by george giblet »

Kyosanshugi wrote: 08 Jun 2024, 00:57 Honestly, when I did this trace I was doing a lot of drugs and I'm not surprised that I mixed up things like that. lol
It's hard enough getting these things right with a straight head :mrgreen: .
These boards look very familiar, and the parts arrangement matches up with my layout in the OP. I do remember taking detailed pictures of both sides of the board while tracing, but those are on a hard drive that is long gone.
I've found quite a few pics of the solder side of the board and all the through-hole PCBs have a similar circuit. (Values unknown.)
The original bass was also stolen, sadly.
Not good!
As noted on my schematic, mine was an Indonesian model. Board/parts availability may well have varied by country, and manufacturers could have had different BOMs that they simply chose according to what parts they had. This, of course, is pure speculation on my part.
Yes it's has to be put down as possible.
Questions and mysteries abound! Again, though, I appreciate what you've brought to the table.
Yes, nuts.
Looking at your pics of the THT boards, I see that there is a 0.47u electrolytic. That's probably the mistake I made with C4(C5), I associate electrolytics with values of 1u and up. With an electrolytic in the circuit, would the negative point towards the gyrator?
To me it looks like a *non-polar* electrolytic. You could use an electrolytic. The polarity isn't too important since the voltage across the cap is nearly zero. You might need to check the voltage on some bipolar opamps.


FWIW, I dug up this video,

Ibanez Soundgear GSR205SM Bass - Review, Restring, Setup, Demonstration - YouTube


The video is Dec 20, 2020 but the board is one of those 2023 models. So maybe my I still haven't got the dates lined up yet. Maybe the 2023 boards are similar to the "PHAT EQ II" smd boards.

In the video the guy does some samples with the PHAT control at 0%, 50% and 100%. I ran his 0% samples through the circuit then compared the outputs with the 100% samples. The circuit configuration which sounds the closest is the PHAT II circuit with the resistor set to 10k (basically my corrections to your schematic with the resistor set to 10k). The other circuits give too much gain boost. It's possible he is running some compression on his recording and when he kicks in the PHAT control the sound gets more compressed. I might try knocking the gain down on the other circuits to match the level to see if *tone* of those is any closer. It's not going to be a 100% accurate experiment because the guy might not hit the strings as hard when he turns on PHAT. To get around that I used the segment where he pops on the back pickup.

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Post by george giblet »

I played around a bit more matching the sound samples. Also tried another video. I came to the conclusion the recordings seem to have a lot of compression.

Without compression only the PHAT II + 10k values produce the correct level when the PHAT control is full. The tone produced is quite a bit crisper than the sound samples.

In order to make the tone less crisp we need more bass boost. However, the extra bass boost increases the level. If I apply some post attenuation to emulate level compression then I can correct the level. If I do that the PHAT(1) circuit sounds closer in tone. The PHAT II + 1k circuit seems to lose too much of the very low frequencies.

So it seems reality is somewhere between PHAT II + 10k and PHAT(1), perhaps more towards PHAT(1). There's too many confounding factors to split the difference using this matching method.

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Post by Kyosanshugi »

So I've been playing with the disputed component values using that calculator you linked and vibes and I came up with a combination I liked. Fat low end boost with little mid-range clipping.

https://imgur.com/gallery/preamp-phat-schematic-GIA2e3k

Using the numbering scheme in this schematic, change R6 to 4M7, C4 to 560nF, and R9 to 10k. I was looking to have the bandwidth focused on the open low strings, and this gave the best results to my ear, as far as my crap Squier practice amp allows it. Wonder what you'll think of it.

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