Boss GE-7 HiFi mod for you :D

[MartyMart]

I bought one just last week and thought it was OK !
"Pushtone" in another thread said " Plug in, powerup and REDUCE the level on the lower 2 bands -100/200Hz and listen through your amp "

Result = HISS !!  - and LOTS of it ... shock horror ... why ?

So I searched through various GE-7 threads, but could only find the "opamp" change suggestions.
I found a schematic in my collection, drawn by Jon Halveson, which looked "good" but the component numbering
didn't quite match my "2006" GE-7 , so I had to do lots of looking, tracing and writing stuff down !

Here's what I found from a combination of Jon's schem and my actual unit :

There's three 8pin DIL opamps which are TL022's
Two further opamps are SIL types, which I dont have any of
There seems to be three 1uf electro caps in the signal path
There are five tantalum caps used as part of the tone stack, one to each of the bands ( the other two smallest ones are poly caps )

I guess that the tantalums were used in the larger values because of size, but Poly caps DO fit, if you're careful about placement
around the central "screw" that holds the top board down.

Here's the changes that I made, with board numbering from the 2006 unit NOT the schem, though some did match up :

            --Boss GE-7 HiFi Mod--

Remove the three TL022's, install sockets and fit NE5532 opamps ( other low noise versions are fine, such as TL072 )
( watch the pinout as you do this, all three opamps have pin 1 facing the top "open" end of the board)

Remove the three 1uf electro caps , C21 C22 C32 and replace with 1uf poly caps ( they are available, mine were 10mm high )
If they are hard to find, then perhaps 680n or 470n would be fine ..

Tone caps:
Remove C10 ( 1u5 tantalum ) and replace with a 1uf poly cap ( closest value but may effect the 100Hz band a little, pushing it up to 150hz ?)
Remove C9 ( 0.68uf tantalum) and replace with a 0.68uf poly cap
Remove C8 (0.33uf tantalum) and replace with a 0.33uf poly cap
Remove C7 (0.15uf tantalum) and replace with a 0.15uf poly cap
Remove C6 (0.1uf tantalum) and replace with a 0.1uf poly cap

DONE !
Result :
No noise increase when same test as above done, pedal seems silent when engaged and the bands
seems much smoother sounding to me.
Well worth the couple of bucks and the 25 minutes to do the mod
If anyone can add anything to this - please do !
Enjoy,
Marty.

[Pushtone]

Excellent work Marty!

This GE-7 hiss has been bugging me since the first day.
I asked a couple of other players about theirs and they had the same HISS results.
The stock GE-7 is just plain noisy.
I was fairly confident that yours would do the same.

I'm going to open mine up this weekend.

I wonder how long until we see some website offering commercial mods for the GE7 based on your work?

[MartyMart]

Thanks Push !  I dont give a sh** who uses it, I've had my fair share of info here and just
hope it helps some people ditch the "hiss" 
If it's for sale somewhere .... what the heck should I do about it ! It's a Boss anyway's 

Just one other thing, the final output cap is a 10uf tantalum (C11) this could probably work
as another 1uf poly cap and be a bit cleaner sounding ...
To keep the 100Hz band the same, a 1uf poly with a 470n in parallel would work, however
there's just not room for them between the two boards .... I may try and squeeze it in (  ooh eer ! )
( there's not much 100Hz in a gtr low E anyway huh ?  just makes your amp turn to mud )

MM.

[Nuts]

oops

[MartyMart]

Jeez - 150 views and one reply !!
Anyone got any comments/additions to this ?

[lowstar]

sure i got a comment on this.

way cool 

i just wish i could find a used ge-7b to perform those mods on (i´m sure the bass version is not that much different except cap values for the eq), been searching for 2 years now.
then all that would be left for me to find would be pq-3b 

cheers,
lowstar

[toneman]

i wonder if these mods will work for the Behringer EQ700 
My EQ700s will arrive in a few days 
Probably all surface mount(?)   
Will check for hiss............... 
thanx for the tutorial!!   

lowstar- U can make your own 7b from the 7...it's just a few caps   

[Dai H.]

I've done some swapping like that which usually makes a difference in noise, but sometimes subbing films for alu electros makes it sound too clear or have too much low end, which I suppose is the difference in freq. characteristics. Is there some general rule such as "halve the value when you sub a film for a alu electro" to doing that (say, for coupling caps)? Anyone have a hard time finding big films, try surplus places, sometimes you can find bigger ones cheap or relatively inexpensively.

[MartyMart]

I've done some swapping like that which usually makes a difference in noise, but sometimes subbing films for alu electros makes it sound too clear or have too much low end, which I suppose is the difference in freq. characteristics. Is there some general rule such as "halve the value when you sub a film for a alu electro" to doing that (say, for coupling caps)? Anyone have a hard time finding big films, try surplus places, sometimes you can find bigger ones cheap or relatively inexpensively.

I'm not aware of a "rule" like that Dai, however, before I got hold of my 1uf poly's, I often used .47uf poly's
when replacing 1uf electro couplingcaps, actually anything around .22uf and above should work fine.
Also several Fuzz's which call for 10uf electro's work great with 1uf poly's !!
Where possible, I alway's replace electro's and tantalum caps from the signal path, unless the "grainy" sound
is something that you're after.  ( this could be a good thing in many "fuzzy" FX pedals )

MM.

[MartyMart]

i wonder if these mods will work for the Behringer EQ700 
My EQ700s will arrive in a few days 
Probably all surface mount(?)   
Will check for hiss............... 
thanx for the tutorial!!   

lowstar- U can make your own 7b from the 7...it's just a few caps   

The EQ700 doesn't seem to suffer with a "hiss" problem, the crappy parts/sockets etc are more
to worry about !
MM.

[Dai H.]

I've done some swapping like that which usually makes a difference in noise, but sometimes subbing films for alu electros makes it sound too clear or have too much low end, which I suppose is the difference in freq. characteristics. Is there some general rule such as "halve the value when you sub a film for a alu electro" to doing that (say, for coupling caps)? Anyone have a hard time finding big films, try surplus places, sometimes you can find bigger ones cheap or relatively inexpensively.

I'm not aware of a "rule" like that Dai, however, before I got hold of my 1uf poly's, I often used .47uf poly's
when replacing 1uf electro couplingcaps, actually anything around .22uf and above should work fine.
Also several Fuzz's which call for 10uf electro's work great with 1uf poly's !!
Where possible, I alway's replace electro's and tantalum caps from the signal path, unless the "grainy" sound
is something that you're after.  ( this could be a good thing in many "fuzzy" FX pedals )

MM.

thanks Marty,

another type to look into might be the "audio use" alu electros such as Nichicon MUSE, Rubycon  Black gates, etc. They can sound clearer than regular alu electros and have the same sort of size advantage being electros compared to films. I scrounged up some used/removed ones for the mixer section headphones area in a casette Portastudio, and there did seem to be a slight improvement (seems there is usually a 100 to 470uF or so to ea. side of the phones output, maybe there are more noticable since directly connected?). Ordinary ones seem to have a bit less definition which is probably good sometimes. Also, I don't know if you can get them in your locale, but there are SIP versions of 5532s, NJM makes a 5532S (9 pin SIP) and 5532L (8 pin). I have some some 5532S which I bought maybe ten years or so ago.

[lowstar]

lowstar- U can make your own 7b from the 7...it's just a few caps   Lips Sealed

i don´t even have a ge-7 to start with. 

[Dirk_Hendrik]

May I put some attention to this post I did a while ago:
http://www.diystompboxes.com/smfforum/index.php?topic=47296.0

(get the schemmo of a GE-7 to see which components are mentioned as RA, RB etc.)

Although the component values of a GE-7 are well chosen for the frequencies they have to filter (as in, pretty accurate) recalculation of the component values for for instance the Bore-ringer mentioned above coud give good results im making the thing sounding more musical.

[MartyMart]

May I put some attention to this post I did a while ago:
http://www.diystompboxes.com/smfforum/index.php?topic=47296.0

(get the schemmo of a GE-7 to see which components are mentioned as RA, RB etc.)

Although the component values of a GE-7 are well chosen for the frequencies they have to filter (as in, pretty accurate) recalculation of the component values for for instance the Bore-ringer mentioned above coud give good results im making the thing sounding more musical.

Good stuff, thanks Dirk
I didn't really change much with this mod, just got rid of the Hiss, but might have a look at my EQ700 now !

MM.

[birt]

so basicly the GE-7 design isn't noisy but the components are? that's good to know since i wanted to use the design for another effect... thanks for this thread

[kismet78]

So, modding a GE-7B should be pretty much the same?

[trevize]

ehm...   twenty bucks per auction for your work

http://cgi.ebay.it/Boss-GE7-GE-7-Equalizer-Mod-Kit-Clean-Boost_W0QQitemZ270087174271QQihZ017QQcategoryZ101973QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

[MartyMart]

Well, he does have a long list of satisfied customers  !!
Doesn't sound unreasonable for a complete instruction kit 

[R.G.]

Is there some general rule such as "halve the value when you sub a film for a alu electro" to doing that (say, for coupling caps)?

Cap Substitution:
1. Never use an aluminum electro in an application where the exact frequency matters, as in filters. Never. Use aluminum only where you only need enough.
2. Never use tantalum unless you have no other choice.
3. For coupling capacitors, doubling the cap extends frequency response down by one octave; halving the cap increases the lower cutoff frequency by one octave upwards.
4. For simple one-L, one-C filters, the frequency is proportional to the square root of either component. Changing the cap by 2 changes the frequency by 1.414.

The doubling/halving/square root things are gross overgeneralizations based on the simplest possible cases.

There is no real substitute for knowing the circuit and doing the math.

[amz-fx]

When doing mods like this, you need to consider at least 3 specs:  noise performance, current draw and input impedance.  Here are some comparisons for the TL022 vs. the 5532.

Noise Performance (at 1kHz)
NE5532 = 5 nV/√Hz
TL022 = 50 nV/√Hz

Current Use (per amplifier)
NE5532 = 8.000ma
TL022 = 0.130ma

The noise is definitely lower but the current consumption is WAY up!  Multiply that by the 6 amplifiers in the chips you are subbing and battery life is drastically shortened...

Input impedance on the chips is another matter...  the TL022 is very high since it has a jfet input but the 5532 is quite low, even for a bipolar input.  The change in input impedances may cause the pedal to perform differently than how it was designed...  the RC4559 is a better choice than the 5532 as a sub...  noise is not quite as low but input Z is higher and current use is only about 1.6ma per amplifier.  Even the TL072 would be a decent sub:  TL072 = 18 nV/√Hz and 1.4ma per amp.

Just about anything is better than the 50nV noise on the TL022 but most dual chips will draw more current since the 022 was designed for low current consumption...

regards, Jack