Preamp Connection To Power Amp

[BaltBass5]

Alright, so lately I'm in a phase of using Preamps into Power Amps as opposed to the traditional head setup. My reasoning for this is that my band also runs IEM's and I prefer the XLR on the Preamp into the IEM mix as it uses a Jensen Transformer. Additionally the Preamp has a 12AX7 Tubes.

Currently I'm using the Fender TBP-1 Preamp run into a Crown XLS 1502 Power Amp. The TBP-1 XLR out feeds our IEM rig then passes to FOH. As such I have to use the 1/4" Main out of the TBP-1 to feed the Crown.

As per the TBP-1 Manual, the 1/4" Main Out: "MAIN OUTPUT - Full-range output for connecting to a power amp input or to a bass amp Return jack."

As per the Crown manual, The XLS1502 Input allows for: "¼ Inch Input or Balanced XLR Input. 2 – ¼ Inch input connectors, Two 3-pin XLR input are provided."

What will yield the best results for connection?

1) 1/4" TS cable from TBP to 1/4" TS into the Crown
2) 1/4" TRS cable from TBP to 1/4" TRS into the Crown
3) 1/4" TRS cable from TBP to XLR into the Crown

 

[Old Garage-Bander]

These should all produce the same results.

The only caveat I see is in the length of the cable when using TS > TS.
This is an unbalanced signal and could be more prone to noise pickup as the cable length increases.
If the pre and the amp are co-located, the short cable shouldn't be a problem.

The other two schemes, using TRS and XLR are balanced signals. This is always preferred over unbalanced, especially as cable runs get longer.

Finally, if the XLR cable is the locking style it may be preferred over 1/4" just to help prevent getting pulled out.

Since you probably have both together in a rack. You ought to be good to go with any of these. That said, if it were me, I'd still prefer to use either of the balanced schemes. That way, if you get ground loop hum, it is easier to deal with.

 

[BaltBass5]

These should all produce the same results.

The only caveat I see is in the length of the cable when using TS > TS.
This is an unbalanced signal and could be more prone to noise pickup as the cable length increases.
If the pre and the amp are co-located, the short cable shouldn't be a problem.

The other two schemes, using TRS and XLR are balanced signals. This is always preferred over unbalanced, especially as cable runs get longer.

Finally, if the XLR cable is the locking style it may be preferred over 1/4" just to help prevent getting pulled out.

Since you probably have both together in a rack. You ought to be good to go with any of these. That said, if it were me, I'd still to use either of the balanced schemes. That way, if you get ground loop hum, it is easier to deal with.

That's what I thought as well....Thanks for the sanity check. Appreciate the Feedback!
They are racked together and only require a 12" interconnect cable.

 

[agedhorse]

I believe your preamp is unbalanced, so a TS cable should be used.

There are ways to use a TRS cable, but how it’s wired depends on how the output of the preamp is configured (ie. is the ring grounded or floating)

 

[Old Garage-Bander]

https://www.fmicassets.com/Damroot/Original/10001/OM_leg_bassamp_TBP1_Preamp.pdf

From the above link, it appears that your choices are TRS aka balanced (preferred), or TS aka unbalanced.
There are no XLR's on this pre.

They indicate that a standard TS instrument cable will work, but at the risk of increased noise.
Being this is a true transformer output you don't have some of the concerns that come with active balanced outputs.
We already discussed the merits of balanced vs unbalanced. Additionally, if you use TS, the output might be reduced vs TRS. Contributing to noise.

Again, this is based on the manual linked above. While it is from the Fender website, there may have been other versions that provided more limited output choices. Either TS or TRS should be safe, but TRS is preferred.

Rock on!

 

[BaltBass5]

https://www.fmicassets.com/Damroot/Original/10001/OM_leg_bassamp_TBP1_Preamp.pdf

From the above link, it appears that your choices are TRS aka balanced (preferred), or TS aka unbalanced.
There are no XLR's on this pre.

They indicate that a standard TS instrument cable will work, but at the risk of increased noise.
Being this is a true transformer output you don't have some of the concerns that come with active balanced outputs.
We already discussed the merits of balanced vs unbalanced. Additionally, if you use TS, the output might be reduced vs TRS. Contributing to noise.

Again, this is based on the manual linked above. While it is from the Fender website, there may have been other versions that provided more limited output choices. Either TS or TRS should be safe, but TRS is preferred.

Rock on!

The XLR is the DI output.
I have XLR input on the amp so I could go TRS 1/4 to XLR input on the amp but don’t see an advantage to that over TRS 1/4’ out of the pre to TRS 1/4” in on the amp. Unless I am missing something.

 

[agedhorse]

I had to go back to the service manual on this because it's been years since I saw one.

The main out is unbalanced line level, and IF using a TRS cable will impedance balance the ring for use with balanced TRS or XLR inputs with the TRS-XLR wired pin 1 to sleeve, ring to pin 3 and tip to pin 2.

The DI output is selectable pre-post and has enough gain to drive the 1:1 transformer to full line level, but the post eq take-off point is pre master volume so it's not an ideal output to use as a main output to drive a power amp.

 

[BaltBass5]

Cool…so at this point I’m using the XLR post EQ as an output to feed our IEM rig (Soundcraft) and then it’s passed from IEM to FOH.

I’m currently using a TS cable (12”) from the TBP-1 main out to the Crown Channel input 1/4”.

Works great but didn’t know if running a TRS vs TS between the TBP and the Crown would yield any benefit.

Thx for all of the replies.

BTW I’m using the Crown to feed a Mesa Subway 212 cab which is an absolute beast of a cab!

 

[agedhorse]

If the TS cable works ok, you are good to go.

 

[BaltBass5]

If the TS cable works ok, you are good to go.

Thx!!

 

[Old Garage-Bander]

The XLR is the DI output.
I have XLR input on the amp so I could go TRS 1/4 to XLR input on the amp but don’t see an advantage to that over TRS 1/4’ out of the pre to TRS 1/4” in on the amp. Unless I am missing something.

Oh yes. There's the XLR connector. Missed it on the first go-round. Just started my caffein infusion.

As long as you are using balanced cables, there is no advantage to one style of connector over the other. Some XLR's can lock into the mating connector, while TRS 1/4" does not, though TRS tends to hold better than a TS, all else being equal. But that's just a mechanical situation where a cable might accidentally get pulled on. In back of a rack, short cable between the two pieces of gear isn't likely to have that happen. TRS to TRS 1/4" will be every bit as "sound" (bad pun intended) as using XLR.

 

[Old Garage-Bander]

I had to go back to the service manual on this because it's been years since I saw one.

The main out is unbalanced line level, and IF using a TRS cable will impedance balance the ring for use with balanced TRS or XLR inputs with the TRS-XLR wired pin 1 to sleeve, ring to pin 3 and tip to pin 2.

The DI output is selectable pre-post and has enough gain to drive the 1:1 transformer to full line level, but the post eq take-off point is pre master volume so it's not an ideal output to use as a main output to drive a power amp.

Good bit of sleuthing there.
When in doubt (about the operator manual) RTFSM.

 

[agedhorse]

These are all old enough to need to go back to the docs, memory is no longer reliable enough.

 

[mrperkolator]

The DI output is selectable pre-post and has enough gain to drive the 1:1 transformer to full line level, but the post eq take-off point is pre master volume so it's not an ideal output to use as a main output to drive a power amp.

Is this a common issue? I was starting to figure out a setup that used preamp floor pedals and then a power amp head. Is that an uphill battle? Is it better just to buy a bass head that's both preamp/power amp?

 

[agedhorse]

Is this a common issue? I was starting to figure out a setup that used preamp floor pedals and then a power amp head. Is that an uphill battle? Is it better just to buy a bass head that's both preamp/power amp?

Yes it's common, but it's not an issue. You can use the main out to drive a preamp, just as the manufacture intended.

Note that many pedals are unable to drive power amps to rated output because they do not have sufficient drive capability. You will want to do your homework on this before going down that road.

 

[mrperkolator]

Yes it's common, but it's not an issue. You can use the main out to drive a preamp, just as the manufacture intended.

Note that many pedals are unable to drive power amps to rated output because they do not have sufficient drive capability. You will want to do your homework on this before going down that road.

well if I still need a pre after the pedals... then it doesn't seem efficient $$ wise. Seems I'd be better off buying a rackmount-able head and skip preamp pedal as long as head can be used like a DI box if speakers aren't needed

 

[agedhorse]

well if I still need a pre after the pedals... then it doesn't seem efficient $$ wise. Seems I'd be better off buying a rackmount-able head and skip preamp pedal as long as head can be used like a DI box if speakers aren't needed

Yes, one solution is to buy a rack mount head that fits your tone goals, the other choice is to choose a pedal that's capable of driving a power amp to rated output.