Modding GK 1001RB-II head with stereo input

deadsled · #1 08-07-2011, 10:19 PM

I play upright bass through a standard gk 1001rb-II head. My upright uses a stereo piezo pickup which has to pass through a 2 channel preamp to balance, eq and blend the two channels into a mono signal to go into the amp.

The GK head has a 1 mega ohm input so I can go directly in and the bass sounds fine but the problem is if I bypass the preamp and plug my TRS cable straight into the amp I only get the tip signal. My question is, if I put a stereo input jack in the amp and use the ring portion of the input to carry the second pickup what can I connect it to in the amp? I was thinking the crossover circuit but someone at GK suggested sending it to the send portion of the effects loop.

I have tried this and I got a very low signal then I got a lot of noise then the signal changed into a lot of noise and the clip light went on and stayed on. What am I doing wrong? Does anyone have a suggestion?

**B-string** · #2 08-07-2011, 10:38 PM

Quote:

Originally Posted by deadsled

I play upright bass through a standard gk 1001rb-II head. My upright uses a stereo piezo pickup which has to pass through a 2 channel preamp to balance, eq and blend the two channels into a mono signal to go into the amp.

The GK head has a 1 mega ohm input so I can go directly in and the bass sounds fine but the problem is if I bypass the preamp and plug my TRS cable straight into the amp I only get the tip signal. My question is, if I put a stereo input jack in the amp and use the ring portion of the input to carry the second pickup what can I connect it to in the amp? I was thinking the crossover circuit but someone at GK suggested sending it to the send portion of the effects loop.

I have tried this and I got a very low signal then I got a lot of noise then the signal changed into a lot of noise and the clip light went on and stayed on. What am I doing wrong? Does anyone have a suggestion?

The only thing that might work is to connect to the tuner out jack. You would be bypassing the first stage JFET but???
The way they had you try probably caused a feedback loop. Don't think they understood you wanted to connect both pickups at once without any mixer?

deadsled · #3 08-08-2011, 02:41 AM

I think I screwed up by connecting the grounds of each jack together. I should ground them both individually right?

I think I was on drugs when I did the soldering! I could just use a jumper wire to the ground of the tip portion correct?

AwkwardLoudness · #4 08-08-2011, 03:01 AM

Either purchase another GK 1001RB-II and run the two amps in stereo or use a different amp that has two blended channels.

WingKL · #5 08-08-2011, 05:23 AM

The latest issue (6) of Bass Gear Magazine has an article on the Headway EDB-1 preamp that seems like a much better solution than hacking into your GK amp.

chadds · #6 08-08-2011, 05:41 AM

Raven Labs Mdb-1. Find one used. Has TRS & two TS to be used simultaneously. Three level controls one for each.
Side chain effects all in a third rack size.
Don't hack your amp!!

deadsled · #7 08-08-2011, 01:17 PM

I already have plenty of stereo preamps and don't want to carry two amps!

I asked for help modding the circuit, that's what I want to do. I want to lighten the load. I don't want advice on how many amps to carry and what preamp to buy. I want help from someone that knows how to mod a circuit.

4Mal · #8 08-08-2011, 01:54 PM

hacking the Gk sounds like a terrible idea ... that jack is very likely to be hard soldered to a PCB. The combo cable idea might work with a piezo. Never tried it... Tie the ring & tip together, connect both grounds to the sleeve. Sonically, a buffered blend of the two is going to be the winner.

Rack the thing up with one of you stereo pre's and save yourself some potentially expensive headaches ... Something small like little K&K stereo gizmo that blends 2 into mono. Is what I've been looking at... Velcro the thing on top of the Gk and you're still basically just carrying the head.

FWIW I used to front end my 1001 RB II with an Alembic F2B so I could get two channels - I dug that setup a lot... worlds loudest Fender Showman :-)

**B-string** · #9 08-08-2011, 01:56 PM

Quote:

Originally Posted by deadsled

I already have plenty of stereo preamps and don't want to carry two amps!

I asked for help modding the circuit, that's what I want to do. I want to lighten the load. I don't want advice on how many amps to carry and what preamp to buy. I want help from someone that knows how to mod a circuit.

No need to be so rough on these guys their points are valid and in your best interest. No guarantee this mod will work as you have no "mixer" circuit to attach to. You could wind up with oscillation (feedback squeals, any number of troubles).
The sleeve on both jacks should be grounded, the tip is one pickup and the ring is the other pickup.

deadsled · #10 08-08-2011, 11:27 PM

Not trying to be rough but I have all the pre amps and solutions to make it work. I just want to experiment with a mod that might help all my fellow upright slappers that play Gk heads. Finding a good preamp is a never ending ordeal and I would like to find a built in solution that needs no external box to solve the problem.

If I can't then it's no big deal but if I can then i will be king of the world, King Kong won't have **** on me!

johnk_10 · #11 08-09-2011, 12:05 AM

IMO, modding a GK 1001RBII is not a good idea. it's a single channel amp with the input jack soldered to a pcb. at best you'd just be tying the two output signals of your bass together in mono with no blending/mixing option, so you might as well use an adpater like this one and leave the amp alone:

Hosa GPP 290 Audio Adapter, Stereo 1/4" Female to Mono 1/4" Male | Full Compass

i know you don't want to add external pieces for simplicity, but IMO, a tiny external active mixer (in a very small box) velcro'd to the amp would be a better option.

something like this:

Amazon.com: Five Channel Mini-mixer: Software

deadsled · #12 08-09-2011, 10:57 AM

I appreciate all your kind words and not so helpful advice.

I understand all the terrible reasons why this should not be done but that's not helping the situation at all! I have removed the mono input, yes I have mad soldering skills and work on circuit boards quite often. I replaced it with a stereo input of the same model with the legs of the ring portion bent upward as to attach point to point wiring to.

I was a moron when I wired it and used a shielded cable and wired the ground portion of the wire to the ground side of the input jack to the ground portion of the other (effects send) jack.....d'oh! Looking back I should just jumper the ground side of the ring segment to the ground portion of the tip of the input. Then run the signal portion of the ring segment to the tip portion of the effects send.

In theory I was hoping I could tie into the crossover and use the 1001RB-II woofer/tweeter control to mix it. If there are any electrical engineers out there that could help me figure it out or the closest to what I want I would appreciate it. I don't really want to know what you all think I should do so if you can't help me figure this out keep your opinion to yourself, sorry to sound harsh.

johnk_10 · #13 08-09-2011, 11:03 AM

Quote:

Originally Posted by deadsled

.....................yes I have mad soldering skills and work on circuit boards quite often. I replaced it with a stereo input of the same model with the legs of the ring portion bent upward as to attach point to point wiring to.

I was a moron when I wired it and used a shielded cable and wired the ground portion of the wire to the ground side of the input jack to the ground portion of the other (effects send) jack.....d'oh!

well then, so much for your "mad soldering skills' and experience with pcbs.

.............unsubscribed........................

Passinwind · #14 08-09-2011, 11:35 AM

Quote:

Originally Posted by deadsled

In theory I was hoping I could tie into the crossover and use the 1001RB-II woofer/tweeter control to mix it. If there are any electrical engineers out there that could help me figure it out or the closest to what I want I would appreciate it. I don't really want to know what you all think I should do so if you can't help me figure this out keep your opinion to yourself, sorry to sound harsh.

Please post a schematic of your amp.

BassmanPaul · #15 08-09-2011, 12:53 PM

Quote:

Originally Posted by deadsled

In theory I was hoping I could tie into the crossover and use the 1001RB-II woofer/tweeter control to mix it.

in order to do what you envisage you would have to totally redesign and duplicate quite a fair amount of the pre-amp circuitry. Even if completely successful you would reduce the resale value of your amp to zero. All this to reduce your carry in load by one tiny micro mixer. Sorry sir but your plan makes no sense to this engineer!!!

deadsled · #16 08-09-2011, 02:50 PM

Quote:

Originally Posted by johnk_10

well then, so much for your "mad soldering skills' and experience with pcbs.

.............unsubscribed........................

I said I had mad soldering skills not circuit design skills

deadsled · #17 08-09-2011, 02:53 PM

Quote:

Originally Posted by Passinwind

Please post a schematic of your amp.

Here you go....

johnk_10 · #18 08-09-2011, 02:56 PM

[quote=deadsled;11311045]I said I had mad soldering skills not circuit design skills/QUOTE]

then you obviously have no business being in there.
IMO, asking for someone on talkbass to completely redesign your amp's preamp is ridiculous.

love your avatar, but can't handle your attitude. good luck with that.

unsubscribed.........again............

deadsled · #19 08-09-2011, 02:59 PM

Quote:

Originally Posted by BassmanPaul

in order to do what you envisage you would have to totally redesign and duplicate quite a fair amount of the pre-amp circuitry. Even if completely successful you would reduce the resale value of your amp to zero. All this to reduce your carry in load by one tiny micro mixer. Sorry sir but your plan makes no sense to this engineer!!!

Not interested in resale value or totally redesigning the preamp. Why can't I just feed the ring signal into the crossover? It doesn't need to be balanced or eq'd just send it into the mix and maybe adjust it in or out. What may be valuable to someone else may not be valuable to you but it's still important to me.

I am really starting to understand why so many people say there are nothing but pretentious a-holes on this site.

deadsled · #20 08-09-2011, 03:07 PM

Quote:

Originally Posted by johnk_10

then you obviously have no business being in there.
IMO, asking for someone on talkbass to completely redesign your amp's preamp is ridiculous.

love your avatar, but can't handle your attitude. good luck with that.

unsubscribed.........again............

Why don't I belong in there?, because I'm trying to learn something? I can repair things and am learning more about circuits as I go. You've never heard of a chef starting at washing dishes before he learns to cook?

Again, if you have nothing to contribute to the conversation then mind your own business! I don't need discouragement, no offense.