2 Questions, Connecting Line Level only sub to Stereo, PC Audio Analyzer Software

rwgast

Member
2012-05-19 10:01 pm
Hi, I think this is my first post maybe second, apparently I signed up 5 years ago, hmmmm. WARNING LONG POST, if you just want to get to the point you can skip to the last two paragraphs.

Anyways I do alot of electronics and embedded systems contracting these days. When it come to my hobbys though I am really in to RF projects (a little HF, and a lot of Microwave sat stuff), and diy EE test equipment. I also enjoy building robots, and implementing self mapping and localization schemes using all types of sensors who's data has been filtered through DSP.

One day I ended up with a pair of infinty speakers from the 70s, the kind with the ribbon tweeters and a technics receiver and phono deck. Well I sold it all except the receiver which needs a bit of repair.

Well turns out the guy who bought my speakers commutes to LA every week and has worked in the music industry all his life from roadie with the beach boys and miss-e to dolby. Right now he is doing contract work for DTS. He is no EE but knows his **** about music, hes also been a vinyl snob since before records started being the only way the RIAA could make money.

Im no audiophile/phool, but I do enjoy decent sound when I choose music over a podcast and to me that means something like a cmoy and nice head phones (right now I have nice nice kingston's surprisingly? Some Audio Technica 50's, and a load of under %100 sets). Well I also have two other friends Ive known for a while, one is in a band called forever came calling and the other other basically has a home studio where he samples and writes the code for VST plug ins.

So my DTS friend asked me if I could do a good flat response consumer grade quality phono amp for under $50, the **** example with good reviews he let me listen to, then gave me two was this Bozak Maddison. He also hooked me up with a technics SL-D2 direct drive table with an ortofon omp10 cart, and a bunch of nice nice LPS like aftermath imports original imports and a lot of test records for sweeps, pink noise etc! He has enough contacts that if we can kick start a decent phono amp he can hopefully get it on to shelves of more boutique music and viynl stores.

Of course I said hell ya I want a product with my name on it! This should be a simple opamp circuit like a cmoy duh... Well I had no idea about the RIAA eq'ing on phono nor did I know that even just Moving Magnet Carts have no real standard impedance that is guaranteed which matching makes a bigger difference the the damn RIAA filtering tempco's! When he asked for an audio pre I thought well no **** I work in ghz sometimes I think I can manage a few KHz and stay away from audiofile BS, lol turns out I was a bit over optimistic! We plan to do a hi end one too, in what I consider the RIGHT way!! I will be using an AD impedance analyzation chip to help load the cart "almost" perfectly with a switchable cap network and digital pot. I will also be doing the RIAA curve in a PSoC which has a DSP block this way I will be able to hit exact values with ease and there will be no drift then out to a hi quality DAC! The entry one right now is taking a bit more creative thinking but I think I have it using 2 INA217 instrumentation amps set up in a clever way to eliminate any caps through the signal path.

In the process of creating these phono amps which I believe will be revolutionary (maybe not new ideas) in terms of performance per cost and no AF BS, I have somehow also been gotten myself in to making a two mic pre-amp's one for my friends studio and one for the band I know. In return they will use if they like and plug my gear, which will have are nice logo on it while FCC plays japan and the UK.

So here is my gear for testing, I have mid and low end consumer gear, but have access to studio monitors mics and sound padded room when needed. along with a boom box that has a built in turn table with speakers two feet apart. This way I can hear my gear on a range of what it might be used with from junk to studio.

technics sl-d2 Direct Drive turn table with ortofon omp10 cartridge

Sony PX300USB Belt Drive table bone stock ceramic cart not replaceable.

Polk Audio R30 floor standing speakers, acually on wooden end tables.

Yahmaha 45watt SW011 Active Sub with line level coax input ONLY

TOA BG-30 I got this on a trade for PC parts I am not sure what it is acually used for I was gonna scrap the heat sinks and transformer. In the end I used to amplify to different size crappy home theatre in a box subs, with a custom cross over on each. I always heard at least in car audio that different size subs would give you a better all frequency range of bass. It can mix up to 3 inputs and make a few 30w mono outputs. I had used a bunch of Y connectors to rig this and it would only work when through the TV.

Dayton DTA-100a mini 50w stereo amp with headphone amp. This was given to me working but I have to replace some of the cheap chinese power Electrolytics and beat RCA inputs, other than that the thing seems like a solid design! There is 50x more tech in it than my buddy 1000 dollar rack mount mic pre, which is 4 opamps on a single sided PCB all through hole parts. To give it credit it uses "AudioFile" caps and an "Audio Grade" shielded toroidal transformer (theres articles on why a shielded EI is better than a toroid transformer. To give him cedit he knew he would sell more samples if he upgraded to this pre because of the brand....

As far as recivers I have a

Early/Mid 90s Sony LBT D107 this is the one I use regularly it is stereo only 30 watts per channel and has CD, Video, and Phono in. Sorry about the e-bay link best I could find, I doubt its worth the $99 dollar asking price. It had a 5 disc CD changer I trashed, pawned all my CDs about 5 years ago, stopped buying CD's mostly in about 97-98.

A Technics SA-R177 this guy goes for about 40 on e-bay and has 4 speaker outputs that can be switched off or on by buttons labeled Speakers A and Speakers B. That manual says stereo but so Im not sure why four speaker outs. It also has needed inputs but no sub out and I need to open it up and work on it a bit, the volume knob is really scratchy and the left channels turn on and off when turning it up. This is also a good time to look at the technics phono pre-amp.




In his scurry for a mic-pre more accepted my gear now also contains a a rack mount ART DTS II Tube Mic-Pre

I also ended up with a SURE SM58 dynamic mic. I have pleny of condenser capsules and peizos for test runs.

A Line 6 15 Watt Spide III DSP amp which was bought for an ephinone accoustic wich I have added DIY piezo and condinser mics to along with a telecaster set of pick ups, but is fairly usefull for some quick testing of things!

And finally a few PC's/Laptops.... the laptops sound is worthless and the main PC has an X-FI that's not that great. I ran some software and found out just how unflat sound cards are... I am thinking of buying this Asus Xonar u5, 196khz sound card. I need the 196khz stereo in for some RF stuff but I am afraid it wont be as flat as a true audio interface! I have all kinds of electronic test tools that can aid me including a desktop scope with fft, quality DMMs, a 1pf through 10uF cap meter for cables... but what I really need is a Scalar or Vector network analyzer to characterize equipment and filters, and how it affects frequency response and THD. I have the parts here to put together a 1-40mhz SNA, but that was for some RF stuff at this point I just need to get something for free or cheap that works and quick. All a network analyzer does is do a frequency sweep then plot an FFT response curve on the device under test. I tried a program called TrueRTA but unfourtantely to get the features I need it is 90 bucks, which I cant afford a long with a new sound card. Even if I could it does not measure THD! We have parteners with really hi end specialized equipment for box specs but I need something to give me a rough idea of some commercial amps and see if tweaks I make to my amp make it any better. Basically in my first phono amp I need to test the drift patterns of the RIAA network to publish max DB the filter will be off when stuck in a freezer or hit with a heat gun vs room temperature. I also need to make sure I have as FLAT of a response as possible! I do not want any color in my pre's! I think my truly flat Audio Technica headphones sound AWFULL with the receiver set at 0db on every eq bar, but the point is if you are doing Vinyl rips to a PC or using a mic-pre you want a flat clear transparency, if your mic adds "color" so be it but you don't want the pre adding more "color". So if any of you guys know what a network analyzer is and can recommend some software, free open source is the best windows/linux is fine, but any software pay or not is better than nothing, since I am not thinking in terms of audio engineering but in EE maybe that is why I can not find what I need. Also please let me know if the Xonar USB card should be good, like I said I need 192khz stereo input I am willing to step down to a 96khz model if it has a flat response and low noise as long as it isn't over $100 bucks, seems like most "Audio Interfaces" are kind of hit and miss.

Ok Lastly I need to get this active sub working in my stereo system and I do not know what the best approach is, as I said it only has a single line level RCA input no speaker inputs and I have no sub out on either receiver, nor does either one have a pre-amp out. I have two ideas and I am not sure which is the best solution. So for right now well say im using the sony 30 watts out on L and 30 watts out on R. I am powering my 50 watt polks with it (down the road I will most likely use the Dayton 50 watt to power it). My room is small 30 watts is plenty for me! So the first idea is to add two sets of stereo wire to the back of the sony outputs then one set one each line goes to polks, the other two are tied together, grounds parallel with each other, hots parallel with each other. Then soldier those unconnected paralleled (briged) speakers to a PCB which contains something like a HiZ BUFF634T or a J-Fet, this way the PCB is no drawing any power away from the actual Polk speakers, next I would maybe need an opamp with a little gain? After that a female jack the the active sub gets plugged in too? Second Idea would be to just run extra R/L wires that run in to an opamps based mixer to get a mono signal and the opamps output feeds the subs RCA?
 

rwgast

Member
2012-05-19 10:01 pm
Im sorry that post was so long :/

your link isnt what I am looking for though. First I want to build, but secondly what I am after is the best way to tap speaker level outputs mix them to mono and buffer them to a very High impedance. The sub has its own amp volume and cross over system. I wasnt sure if the manufacturer listed the frequency response or if that was a cross over point so I ran a sine sweep on it with my function gen.

I guess where I am a bit mixed up is #1 what would be the difference between building a mixing circuit to get mono, and just bridging the L-R channels, will one way perform better than another, and secondly how to I make sure the mono signal is never above line level, The speaker to line level converters I have seen are just speaker taps to RCA jacks with resistors in between them.
 

rwgast

Member
2012-05-19 10:01 pm
You know thinking about this maybe the proper most proper way to achieve this goal is to open the stereo and tap L+R right before the power amp and then mix them to mono at unity gain then add a single RCA jack on the back panel.

Im thinking this would be the best way to use my dayton 50w amp too, I figured originally I would just run coax with the center conductor hot and the sheild ground then screw with the volume until it was line level. But in reality that would mean that I would be running any of the sonys power amp non transparencies through the dayton amp.... I guess this idea could even be adopted all the to before the preamp and home made preamps could be made to if the sonys suck
 
use an inverting opamp to sum the two inputs to a single signal.

The summed output is the "SUM" of the two inputs and for equal signals will be double the level of each input signal.
If all the crossover function is in the bass channel, then you don't need to add any filtering.
But I suspect the bass channel only has the low pass filter and that means you still need to add in the two high pass filters for the stereo channels.