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PLX-1804 Parallel

#42
So i quess i will hook it up as i did my last poweramp.That was....
Sansamp 1/4` ( 1Kohm) output to the Balanced Input on the back of the amp.
It should be fine after i jumper the inputs.I cant wait to get it !
So i will be back to inform after ive bought the amp & gave it a good testing.
Thanks everybody that has helped with the thread.
Growly.
 
#43
This has been an interesting and informative thread. I have a Sansamp RBI, currently driving the power section of an older GK 800RB. I am interested in acquiring a dedicated power amp (along with a Sansamp RPM!). Now I know to look for things like input sensitivity, existence or value-settings of a HPF, etc. Someone with serious knowledge and experience with these sorts of things should submit a Sticky to the TB Amps forum to assist us less-experienced folks....
 
#44
RockDoc said:
This has been an interesting and informative thread. I have a Sansamp RBI, currently driving the power section of an older GK 800RB. I am interested in acquiring a dedicated power amp (along with a Sansamp RPM!). Now I know to look for things like input sensitivity, existence or value-settings of a HPF, etc. Someone with serious knowledge and experience with these sorts of things should submit a Sticky to the TB Amps forum to assist us less-experienced folks....
Click to expand...
Yeah man, the chances of just picking any Poweramp off the shelf without info is a mistake i have learnt.So im very lucky that TB is here to help.Without it the best bet is to try before you buy but that cant be sometimes & you must know the knowlegde first before you get it.I suppose there is bass players that have gone for power without taking into account the sensitivity of the Poweramp or its features !
I think I should be o.k. from here on in...:eyebrow:
Growly
 
#46
Any grown-up equipment can drive any any pro power amp. A lot of it can come close to doubling as an arc welder. It's just that some bass preamps didn't get the memo about 50 years ago. And the manufacturers of the bass preamps? Good luck on getting grown-up "nominal output" specs from them either. Some of them don't even know what this means.
 
#48
zombywoof5050 said:
Right.
Years later when I wanted more power, I did my homework when searching for a new poweramp. On top of that, as soon as I received it I internally switched the input sensitivity from 1.5V to 0.775V. And since I like to run in parallel mode, jumpering two 10K ohm unbalanced inputs is like connecting to a 5K ohm input (I hope I have this right) which is not going to work well at all with the F-2B.
Sorry, Growly Lytes, if I took your thread off track and caused you any alarm.
Click to expand...
Can you please tell me how its possible to internally switch the input Sensitivity & can it be done with most amps ?
Saying i want to bring the QSC PLX-1804 from 1.2vrms down to 0.775vrms or 1.0vrms can i do it or tech do it for me ?
This would mean you can drive the amp with no worries at all.If your Preamp has a hard time pushing it bring the Sensitivity of the amp down to 1.0v or 0.7v to drive it better seeing theres no sensitivity switch ???
 
#49
Bob Lee (QSC) said:
I'm saying that parallel inputs each get the same voltage--i.e., "half" doesn't go to each one. Please don't advise people that.

Alembic preamps have low output signal capability and extremely high output impedances (perhaps they're still anticipating that the pres are used as extended front ends to regular heads for passive instruments?), so reducing the input impedance causes more loss in the output impedance.

That is not the same as "half goes to each input."
Probably not, but amps with higher input impedances will not cause as much loss in the preamp's output impedance.
Click to expand...

Another way to put it is that the inputs of each side, regardless of which way you configure the jumper, become the same point electronically. They each feel the same voltage.
 
#50
Geez I wish I understood half the conversation on this thread.:confused:
Can anyone break it down for me and explain what exactly needs to "match up" when selecting a preamp and power amp? What does all this input/output sensitivity/impedence, vrms stuff mean?
Basically, I'm reading that if the input sensitivity on the power amp is too high and the output sensitivity on the preamp is to low than you'll have trouble "pushing" the poweramp. Correct? When choosing a setup, do I just read the specs of each and consider the difference in sensitivity?

Whats vrms?

I didnt necessarily "choose" my current rig. I had some of it given to me and some of it purchased. I just assumed or hoped it would all work good together. I know, NOOB mistake!! I do notice that I really have to crank (@2'oclock) my gain on the SVT IIP preamp to achieve the volume I need when playing with drummer and guitardists.

PS I love the way my rig sounds now and Im hoping I just got lucky matching them up. I was just always curious as to why the preamp gain had to be up so high? So long as nothing is in danger of being "blown up" I guess it dont matter.:hmm:
 
#51
monroe55 said:
PS I love the way my rig sounds now and Im hoping I just got lucky matching them up. I was just always curious as to why the preamp gain had to be up so high? So long as nothing is in danger of being "blown up" I guess it dont matter.:hmm:
Click to expand...

If it sounds good it is good. Ignore where the knobs are pointing unless you see shiny red lights all the time.

Vrms = RMS volts. Please read the Talkbass Amps FAQ thoroughly. Bongomania has written extensively about these types of issues as well. I won't tell you to do a search, but...:cool:

Growly: There is a mod for the1804 to change input sensitivity. You can have it done at the factory or by a capable tech. IIRC it's just a switch of one resistor value, but Bob can undoubtedly elaborate. None of my preamps have any trouble with the stock configuration at all.
 
#52
Passinwind said:
Vrms = RMS volts. Please read the Talkbass Amps FAQ thoroughly. Bongomania has written extensively about these types of issues as well. I won't tell you to do a search, but...:cool:

Growly: There is a mod for the1804 to change input sensitivity. You can have it done at the factory or by a capable tech. IIRC it's just a switch of one resistor value, but Bob can undoubtedly elaborate. None of my preamps have any trouble with the stock configuration at all.
Click to expand...
Cool thanks bud, im going to enquire about doing this.I suppose the Sansamps wont have trouble but it would be better if the sensitivity was around 1.0v or even lower for me anyways. It would help me push the amp all the way to the top !!
I know its sounds mad :hmm:
Your right about sensitivity, if the Preamp sensitivity is lower than the amp your going to have to crank more gain to get the same level.If it were at 0.7v it would take less gain to do the same.
So im going to try to bring the sensitivity down via the factory before i get it then i will not have any worries about driving the amp.
I wanna thank everybody that helped & you have helped.
Cheers With Beers !!:bassist:
Growly
 
#54
Hello Bob,
I just rang the whole sales for QSC AU & im waiting for a call back from them.
I wish people could have told me about the sensitivity before.It was the main reason for the question`Will the Sansamp RBI & RPM push the PLX-1804 properly to its full output ?
If i can bring it down to at least 1.0v i will be sure that it will work & work good at that !
Il be back to let you know if they can do it here in Australia.
 
#57
I think he means the gain knobs.
O.k Bob the guy from QSC Wholesale just rang me & said he doesnt know about this & if you could give me a name so he can chase this up for me.He said he cant imagine that QSC would do this just for one 1804 ?
Anyway he said to ask you Bob if you can let us know how to go about getting this done. His name is Ian Woodhouse.
Can you please tell me how i can get this done via the factory or another way ?
 
#58
Growly Lytes said:
I think he means the gain knobs.
O.k Bob the guy from QSC Wholesale just rang me & said he doesnt know about this & if you could give me a name so he can chase this up for me.He said he cant imagine that QSC would do this just for one 1804 ?
Anyway he said to ask you Bob if you can let us know how to go about getting this done. His name is Ian Woodhouse.
Can you please tell me how i can get this done via the factory or another way ?
Click to expand...

Yes.

I was just waxing poetic.

:D

Joe.
 
#59
We'll do any factory mod that the customer wants to pay for, as long as it's not illegal or unsafe. A gain mod via factory special order would add about $45 USD to the wholesale price, and I don't know what the retailer would then pass along to the customer.
 
#60
Growly Lytes said:
I think he means the gain knobs.
O.k Bob the guy from QSC Wholesale just rang me & said he doesnt know about this & if you could give me a name so he can chase this up for me.He said he cant imagine that QSC would do this just for one 1804 ?
Anyway he said to ask you Bob if you can let us know how to go about getting this done. His name is Ian Woodhouse.
Can you please tell me how i can get this done via the factory or another way ?
Click to expand...

If you can talk Bob into telling you which resistor to change, you can just bring it up here to Groom Lake and I'll do it for free.
 

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