Adding a Pre-Out to an integrated tube amp


I've got two sub amps with line level only inputs and a Melody I880 integrated amp with no pre-out. So I want to add a pre-out for the sub amps. Two amps so need L/R not summed to mono. Being a tube amp everything is easily accessible and first thought was take right off from the volume. But then doing some research saw people recommend using an op-amp or resistor, and some others saying you need a schematic to take the signal after the pre-amp stage but before the amp. Seems to me line level should be enough, ie right off the volume will be okay, but will it? Anyone done this and know what will work?
millercarbon
Um, is this some cheapie you don't mind using for an experiment??

E
Are you aware that the voltages in a tube pre are lethal? Just letting you know.
Nothing cheap about it.
I was planning on unplugging it.
If this is a high quality integrated leave it alone. Sell it and get something that works for you.

Leave first time electronics hacking to cheap gear you don't mind ruining.

Best,
E
millercarbon,

     Please simplify your life and buy 2 Dayton Audio SA1000 sub amps.  You'll save yourself hours of aggravation and possibly electrocution.

     The best new price I found is $409 each on Amazon.

     However, I came across this shop in St. Louis selling 2 used for $600.

https://reverb.com/item/6598543-2-dayton-sa1000-home-theater-subwoofer-amplifiers

     It's on the Reverb site and the ad states the seller is temporarily away.  But this looks like a very good deal worth waiting for and you can message the seller.

Tim
     
That's exactly what I have. The Dayton accepts line level inputs only. My options are add a pre out or use a Line Out Converter to drop speaker level down to line level. That's what I've been doing with my current sub which has a plate amp that accepts speaker level. The Dayton's don't and I thought adding a pre-out might be easier/better but maybe not. Checking around it seems the right LOC might be the way to go. They look kinda tacky but if it works I could hard wire it inside using existing unused RCAs which would be an improvement on the cheap ones on the LOC and look a lot better too. 
millercarbon,

     I may be mistaken, but I thought the main benefit of speaker level connections was for powered subs, that accept speaker level inputs, with the sub's input coming from the speaker level outputs of your main speakers' amp or amps.  The idea being the matching or blending of the sound and characteristics of your subs and mains more seamlessly.
     Of course, it's your system but I just wanted you to know, imho, that if there are any sq benefits they will be very subtle and likely not worth the effort. 
     Prior to the Swarm, a local dealer here in Indy let me borrow a couple of smaller REL powered subs for 2 weeks that had both line and speaker level inputs.  I experimented with many different locations for these subs in my room and I compared using line vs speaker level inputs at each new positioning of the subs. Both methods sounded very good to me but I honestly couldn't convince myself I heard a benefit to either method.  I switched to just line level inputs rather quickly, mainly to save time but I honestly could not distinguish between the two.  You may be able to but I'd still suggest not setting your expectations too high.
     I run all my subs via line level and the bass response quality and integration with my mains is exceptionally good.  The hookup is simple and easy.  Just thinking of what you're planning on doing is hurting my head.

Best wishes,
    Tim
     I may be mistaken, but I thought the main benefit of speaker level connections was for powered subs, that accept speaker level inputs, with the sub's input coming from the speaker level outputs of your main speakers' amp or amps

I think of it more of a convenience feature. They don't implement a high pass filter since that would be expensive and prone to error due to variable nature of speaker impedance from model to model.

Line level crossovers can implement low and high pass filtering more consistently.

This is by far the simplest, clearest explanation of why and what and how to do it as I have been able to find. http://www.epanorama.net/circuits/speaker_to_line.html

There's also tons of LOCs I could buy, but they are all the same inside and so you are paying mostly for a box and some connections with hardly any of the budget going to the parts inside. Which, come to think of it, just described the majority of high end components! lol! But seriously, look at it- two 10k and two 1k resistors. Grand total $2 with tax, and I can pick em up at Vetco tomorrow.

The Melody has 4 inputs. I'm only using 2. So here's what I do:

Disconnect the internal wiring from one pair of input RCAs. Solder a wire from the hot leads of the speakers to the hot pin of the RCAs, with one 10k resistor in series. (See circuit diagram link above.)  Solder one 1k resistor across each RCA. Done.

Now the Melody amp sees a 10k load, which is insignificant, and the Dayton sees a 1k impedance, which is fine. The line voltage the Dayton will see at the max output of my amp is about 2v, maybe 3v, which again is fine. Well within the Dayton's level adjustment range.

This by the way is exactly what I've been doing the last 10 years running my Talon sub off the speaker outputs. Which I know. Because some guys posted the plate amp circuit diagram. The only difference is the location of the circuit- inside my amp vs inside the plate amp.

Solder two wires, and four resistors, slap a PRE-OUT label on the back, hook er up she's ready to go!

Thanks, guys!


Well I went to Vetco and bought two 10k and two 1k resistors, soldered the 10k in series with the speaker out, soldered the 1k across the RCA to ground, and guess what? Nothing blew. Works just fine.

The hardest part turned out to be getting enough heat into the speaker binding post to get a good connection. Cost me a grand total of $1.54 for parts. So even cheaper than the cheapest LOC, not to mention it looks a lot better (looks completely stock from the outside) and trick as hell because, mod!

And oh yeah- the Swarm is AWESOME!!!!