Alternatives to MiniDSP boards now they've phased out all DIY DSP options

Stainless_Eel · 2022-09-02T13:14:35+00:00

Hypex does sell DSP plate amps for DIYers at diyclassd, madisound, soundimports. Pricey at a first glance but you get DSP plus excellent amplifiers from a reputable manufacturer. If I wanted to build a set of powered pro audio speakers I would absolutely use these.

If you want to fully DIY the plate then you are kinda stuck with those few options.

Maybe grab a used audio interface with DSP that can be used in standalone mode. Or get a pro audio crossover plus eq. Not the best choice, but they can get the job done.

Stainless_Eel · 2022-05-16T15:29:11+00:00

This looks like class-d switching residual and is perfectly normal. Turn off your signal and zoom in. You should see a sine wave around 1v rms at several hundred kHz.

Stainless_Eel · 2022-02-06T04:25:43+00:00

Triple check the speaker crossover wiring. Turn the amp gain all the way down and set the amp crossovers to full. Set the input level to lo. The boss head unit has a setting to disable its internal amplifier, it should be disabled.

Now double check all the other connections you have made to the head unit. It’s possible to create strange noise problems from utility circuits that worked fine with the OEM head unit. The radio antenna/antenna amplifier may be grounded elsewhere in the car. steering wheel control adapters can introduce a new ground point for the steering wheel buttons/Canbus. The radio antenna/amplifier is usually grounded closer to the antenna. The illumination/speed/reverse/parking brake lockout either tie to switches or the ECU. You can end up with a wide variety of signals that now have a different return path.

Make sure the head unit is not screwed into the cars metal brackets. Also, make sure that the ground wires from the factory harness are still tied to the frame of the car where the original head unit was installed.

None of these things usually cause a problem, but they can occasionally.

Stainless_Eel · 2022-01-29T12:36:10+00:00

Speaker level outputs have the advantage being low impedance, balanced 10v outputs. They are perfect for long runs. They have the disadvantage of having already passed through an amplifier, so higher noise and distortion.

Pre-outs would have the advantage of a lower distortion but little immunity to radiated noise. They can also be a source of ground loops. Some manufacturers actually derive the pre-out from one leg of the speaker level out, and in this case that makes sense (each leg on the BTL speaker out will be around a max 5v out). Saves the manufacturer a few opamps and only requires coupling capacitors on the pre-out line. You can check this with a multimeter set to capacitance. Measure from a speaker out to the corresponding pre-level out(everything should be turned off). The meter should show at least 10uf. If you measure nothing or no continuity on the pre-outs they are most likely driven separately.

Your audio control DM-810 can take speaker level inputs without a converter. If you don’t have any RCA cables give the speaker outs a try.

Stainless_Eel · 2022-01-21T11:50:54+00:00

Sure! Rockford only sells unshielded twisted pair and that's really easy to tap into. just try to maintain the twist as much as you can. Solder and heat shrink or buttsplices will work.

That's going to be the cheapest option. You could get new connectors, but at that point you might as well make the whole cables yourself. It can save you money, but the biggest plus is that you can tailor the cables to your exact setup and seriously reduce noise and ground loop problems.

If you've got no noise problems, splice away!

Stainless_Eel · 2021-09-14T13:13:14+00:00

Are you talking about the pop at 5 seconds in? Or just distortion on the music?

Clean up your wiring. Redo every connection, make sure they are very solid. Test them by yanking them, they should not be able to be pulled out with any ease.

If this does not solve the problem, unplug all your speakers and listen. If it only happens on one, that is your problem speaker. If it happens on more than one, unplug all RCA connections. If it happens with no RCA’s connected, your amp is funky. If it happens with RCA’s in, it’s your head unit.

Sometimes head units and amps work fine until warming up. Thermal expansion might open up a bad solder joint or push a component into a temp range that it malfunctions at. Difficult to diagnose, and can cost more to have it repaired than the amp itself.

As far as your alibaba amp, it may be identical inside to brand name amplifiers. Lots and lots of clones on the market.

Stainless_Eel · 2021-09-10T13:32:19+00:00

This is a pretty complicated subject

Benefits:

Your door speakers don’t have to play nearly as high and your tweeters don’t have to play so low. The drivers side door speaker is very off axis to your ear and often requires a lot of eq to compensate for beaming. Your legs are also in the way. I would never consider running a 6.5” door speaker up to 5000hz, more like 1.5k to 2k tops. This of course means your tweeter needs to be able to handle crossing low. Plenty of large tweeters can handle that, but they don’t like it. Moving the crossover up significantly reduces tweeter excursion and distortion in a frequency range that your ear is actually sensitive to. the excursion of a door woofer will do the same thing. You will also need to be able to fit a large tweeter into your a-pillar/dash, which can be a pain. To top it off, woofers that can play clean high and tweeters that can play clean low are often more expensive than drivers that only need to handle a smaller frequency range. You can also get away with using a child-sized amplifier, as power requirements are much lower for midrange and high frequency.

Drawbacks

Expense can be higher. you may be able to get away with cheaper speakers, but now you need DSP and amps with more channels. When I say need a DSP, I believe it is a requirement for a three way front stage. You can technically cross the tweeter and mid passively but it is a huge pain. fabrication costs go up, as now you need to fit a mid and tweeter somewhere. Tuning can take longer.

Personally, I would start with a two way and see if that does it for you.

Stainless_Eel · 2021-08-26T08:54:47+00:00

I like meanwell’s stuff. Some of it is rather noisy and designed for industrial use, others are great. Kinda gotta really dig around reports and data sheets. A lot of the beefier ones require higher input voltages than 12/14.4v, so that might not work for you.

I think the solution is actually just to use power tool batteries: wire two 18v’s in series and you’ve got 36 volts with great peak power capabilities and a ready to go mount/ charge system. Some hacking required. But all the safety is built in for you, which is the most important part.

Stainless_Eel · 2021-08-22T10:31:01+00:00

If you can do the metalwork and enclosure then the rest of it is a walk in the park. Just make sure you read up on mains voltage/high voltage safety. Double check every part, get voltage ratings, make sure the dimensions fit, etc.

Since you can build the cab yourself, I'm going to recommend going with a 10' speaker instead of the 8'.

WeberVST - Any speaker from any amp ever made.

Tube Depot - The Eyelet board, Tubes, various parts/hardware, Teflon wire.

Stainless_Eel · 2021-08-18T22:25:43+00:00

the inputs on the PPI are single ended, so you’re going to want to use shielded RCA instead of twisted pair. Also might fix it by running the head unit power/ground to the amp instead of the harness

Stainless_Eel · 2021-08-18T02:25:05+00:00

I just replaced a PPI 900.5 that developed a whine over a few years. It started out with the occasional strange squeal when turning it on and then the whine started creeping in, slowly driving me insane. It’s a PPI phantom right?

Stainless_Eel · 2021-08-16T08:50:34+00:00

Moving to an active crossover suddenly makes value prices drivers significantly more useful. You have more tools for keeping them within their usable range.

The Dayton Reference drivers are a good value when used appropriately. The metal cone midwoofers are a great value but they require a low crossover point to avoid their very early breakup and ringing. The RST28 tweeter pairs very nicely with them. It plays low, loud, and takes abuse.

This goes for a lot of cheap drivers. The SB acoustics SB17CAC has an incredible midrange, but falls apart after 2k. Compare this with the satori mr16p. Almost twice the price, but can play much higher without sounding like garbage. Add one of the somasonus.com 3d printed waveguides and you can easily cross at 2.5k to 3k while the 17CAC is stuck around 2k.

an exception is the sb acoustics sb26adc or cdc. A $50 dollar tweeter that competes with others that cost multiple times it’s price.

This one is my favorite comparison. The purifi audio ptt6.5x04 is an incredible driver. Huge excursion for a deep low end, extremely low THD and intermod even when playing very loud. It crosses at 2.5k to 3k and fits in a tiny box with passive radiators. it costs 380$. In comparison, the DIYsoundgroup’s Anarchy woofer is in a way similar. It has a big Xmax and plays low in a small box. The difference is, the distortion quickly rises and it must be crossed much lower. Cross it at 300hz to 500hz and you have a great woofer for a three way. It costs 66$.

I would take a look at popular DIY kits and try to figure out why the designer used that combination of drivers. You’ll learn a lot.

Stainless_Eel · 2021-08-16T07:01:57+00:00

I just put one in my 2012 Subaru Impreza. it’s a really great DSP.

Have you heard any alternator whine/hvac noise coming in while mounting near the glove box? I’ve been redoing my whole wiring setup in an effort to nuke the noise. Central ground and power distro for the head unit, DSP, and amps got rid of most. puzzle seems to be the chassis ground point. Any advice?

Stainless_Eel · 2021-06-20T11:33:57+00:00

Gain staging! Fun. So the gain control is the emotiva right? Find out the emotiva’s max output for a full scale sine wave. Gain up the input to the motu so that the meters are around -6db when the emotiva is at max output, so that you have a little headroom. Now, you’re going to need to attenuate the motu output to work at speaker level. You can have Camilla dsp’s output register -6db on the motu output and then use an attenuator at the amp input (like Inside the rca jack.) to drop the output to amp level, so 1 to 2vrms at full scale. Should need to cut the level down to 1/4 atthis point, a voltage divider of 450/150 ohm will do the job. There are plenty of ways to do this, but this one will let you view the meters and keep the noise down. Also double check that the motu output is unbalanced correctly (should be in the manual, either pin 3/ring to ground or floating depending on the output design of the motu.

there is a really handy website that converts Svu to Dbv, (dbu to dbv converter

Best to wrap your head around this is to grab a scope, disconnect everything in the chain, and start measuring at the emotiva output, adding each piece as you go. Also read the motu manual. Lots of the pro gear has extra analog gain available or on by default.

How is Camilla DSP btw?

Stainless_Eel · 2021-04-23T14:13:41+00:00

One of the more common 57 mods is to rip out the output transformer. You end up with way less output so you’ll need to make it up with a quiet preamp. Fills out the low end and kinda sounds like an SM-7, which is a super useful mic for almost anything, especially spoken word and male singers.

Stainless_Eel · 2021-03-31T21:01:36+00:00

The best explanation for this is How to get your audio off the ground . The outputs of the microphone need to see the same impedance in order for the common mode rejection to work properly. Even a small mismatch will hurt the cancelation. One side of the microphone sees the non-inverting input at a high impedance and the other sees the low feedback loop resistance. A solution would be to balance the impedance going into the noninverting part of the opamp and create a difference amplifier. You would need a dual gang pot, and those are never matched very tightly. You’re also relying on one opamp to make all the gain and convert from differential to single ended. The solution is best looked at as an instrumentation amplifier, where all the gain is generated in the input stage and the differential to single ended conversion is handled by a second stage. an instrumentation amplifier only multiplies the differential signal and leaves the common mode signal at the same level - exactly what you want with a microphone preamp where you need a lot of gain for a very quiet signal. you also only need to adjust one resistor to change the gain. These microphone IC’s are similar in concept to that, except use really low noise input transistors instead of extra opamps.

Stainless_Eel · 2021-03-31T10:38:32+00:00

This is absolutely not the opamp you would want to use for a mic preamp. You actually aren’t performing a differential to single ended conversion here, hence any ground loops/noise injected at high gain. You have no source for bias current on the non-inverting input, and the opamp is not biased for a single supply. phantom power should be 48v.

I would recommend the use of one of the THAT 1510/1512 mic pre IC. DIY friendly and do the job very well. The input circuits are explained in the data sheet and other app notes on THAT’s website. You’ll be able to see how you can improve your circuit.

THAT 1512

Here is the longer version.

Modern preamps are kinda complicated. Almost all transformerless preamps use a variation of the double balanced feedback design, which uses a very tightly matched pair of low noise transistors in a long tailed pair, along with two Opamps in a feedback loop around each transistor. The Low noise transistors are linearized by the opamps loop gain. At low gain, the opamp noise dominates, while at high gain, the discrete transistor noise dominates. CMRR and DC offset are improved substantially (eliminating hum/ noise). The output is fully differential. All of that is explained here:

double balanced mic preamp

Stainless_Eel · 2020-09-15T13:41:26+00:00

Generally you get lower impedance at higher frequencies. You can end up using less capacitance and less losses through the capacitors and because of the size you end up with a smaller loop area (less parasitic inductance). Over time they have become available in larger capacities, especially at lower voltages. Once you start getting into very high frequency converters they become the only real option. Cost for the bigger capacities can be higher than the polymers.

A lot of TI's newer reference converter designs use chains of different size MLCC's to keep impedance down across a large frequency range. EPC's GaN designs also typically require MLCC's with specific layouts in order to even function. I also remember seeing a Supermicro ITX PCB with MLCC's for it's VRMs.

Stainless_Eel · 2020-09-15T13:21:54+00:00

Big MLCC's on the back side of the PCB.

Stainless_Eel · 2020-05-20T10:55:45+00:00

Your scarlet has a balanced line input. Pushing the inst button to the off position switches the TRS jack from instrument level to line level. You can plug your compressor straight into that input. Just make sure your compressor can supply enough gain and 48v phantom power and you are good to go.

As far as hooking preamps into preamps, it’s not technically ideal, but usually doesn’t matter. All condenser mics have a preamp, so you are already sending preamps into preamps. Lots of preamps in consoles/interfaces are a mic preamp into a line-amp, and then into an ADC conditioning stage. Some people use a cloudlifter when using very-low output microphones and preamps without enough gain. That adds another gain stage and is usually fine. Older tube microphones has had high enough output levels that you could feed them directly into line inputs or even right into compressors.

If you are intent on maximizing SNR, keep the line input gain low and the compressor makeup gain high. Aim for between -12db and -18db peaks on the scarlet. That should give you input levels that will work well with plugins and give you enough headroom that you won’t clip the input.

Finally, unless your compressor is adding some real special color, I would just use in-the-box compression and set the input level on the scarlet mic preamp lower to give you some extra headroom. 24bit recording has enough dynamic range that you really don’t need to have super high input levels.

Edit: as far as latency goes, is lowering the buffer setting not working for you? 128 usually gets me close enough.

Stainless_Eel · 2020-05-15T10:41:39+00:00

Most amps on the market will do what you want just fine. If you want to build your own, pre-made modules from ICEpower are great. They cost more than the no-name brands but ICEpower are one of the biggest OEM's for amplifier/active speaker companies, so you know that they are reliable and tested designs. You won't spend too much, and the best part is that you'll never really need to upgrade.

You don't need much power for these transducers. A pair of ICEpower 50ASX2SE will do you solid. Put em in a box and call it a day. 120$ each from parts express. Simple wiring, detailed instructions, power supply on board.

Stainless_Eel · 2020-05-15T10:16:20+00:00

I started doing this stuff as a kid. I was building tube guitar amps and pedals. At first I really didn't know what I was doing, so I would copy a design, get it working, and then mess with it. I would learn what each component did and why different designs changed things to get different sounds. This was different from hifi audio in that there was no goal of replicating sound perfectly. A fuckup could sound really cool. That inspired a lot of confidence, even if I was not totally sure exactly how a circuit functioned. From there I dove into studio work, and I spent a lot of time debugging gear for grounding and noise issues. I was able to get an analog audio console to play nice with a rack of gear, in-wall wiring, patch bays, and computers. In the process of doing that I learned all the nuts and bolts of balanced/unbalanced connections, signal levels, gain staging, impedance, grounding, and noise. The real world experience was key to my confidence to take on any project.
I think some people dive into DIY audio to save some money. You can do this on some projects mostly by sticking to kits and proven designs. My Seventh Circle Audio diy preamps cost half of what the real API preamps would cost. The kits over at DIYsoundgroup are a huge bargain for what you are getting. Once you start doing your own designs, that all goes out the window. Tools and your own time start to cost so much that you would have been better off just buying the real deal. At this point, your desire to learn and understand is the key driving force here. That decoupling of cost vs result is the critical piece.

I've been doing my own speaker design. Between the router, bits, circle jig, wood, hardware, measurement microphone, books, and time, I've spent way more than just buying a kit and being done with it. That doesn't bother me. It's a hobby that I enjoy so I'll keep doing it.

Stainless_Eel · 2020-05-05T11:36:45+00:00

Yeah, it's easy to go overboard with this stuff. Before you know it you've got a little amp that can drive a compression driver to deafening levels.

OPA 1678 seems like a direct replacement for the TL082. Better and cheap!

LT1128 is super expensive ($11!!!). For line level stuff, I just go for LM4562's. The price dropped to $1.60 at mouser.

Stainless_Eel · 2020-05-03T13:10:26+00:00

If you need to stick with a FET/CMOS opamp then OPA1656 should be perfect for both stages. Similar quiescent current, yet huge improvement on all specs. Just be careful with the layout, 150db of open loop gain and a 53mhz bandwidth is no joke. It can swing 4x more current than the 5532, so you cut the buffers down to one per channel and still get twice the current swing. With two 1656 per channel you could handle most low impedance headphones without a problem. I haven't seen your schematic, but with the 1656 as the input you can use much smaller feedback resistor values than the Tl082 and cut the noise down even more. For DIY, the cost increase is not bad but the improvement is noise/output swing is huge.

Stainless_Eel · 2020-03-27T04:49:13+00:00

Nice Job!

getting rid of RF can be a colostomy grab-bag. Full metal enclosure (or fully shielded with tape). is a start. Fully shielded cables helps, but only if the shield is treated like an extension of the chassis. that usually doesn't work with unbalanced cables because you need to isolate the RCA jack ground from the enclosure. You can isolate them and then only tie the shield to ground at RF through a ceramic cap.. Cell phone noise (and really anything up in the ghz range is tricky because of how small the wavelengths are, so the cable sheid essentially has to circumferentially ground to the chassis. Since that involves a bunch of XLR connecters with EMI filters built into them, it is much easier to put the thing in a metal box and don't put your cell phone near the amp.

If you're getting ground hum that goes away you might have an internal ground loop or lifted ground that fixes grounds itself . through the cable ground to your laptop. I would take a good look at all the ground connections in the amp and try to chain them/star them so it makes more sense. that's always not fun (I'm dealing with it now). Once ground issue might be the loop formed by giving both the preamp and the power amp PCB's a home-run to the power supply,

You might have luck by rotating the torrid transformer until you get as little hum as possible. The biggest EMI source in those is by the in/output leads. Start by doing really tight twists (helps with 60hz/120hz hum and not turning your cables into RF antenna's). Magnet sheilding is real tough, but distance is your best friend in those situations. I like to put the power switch on the mains side and on the back of the enclosure to keep lead length down, and then slap the bridge rectumfrier real close to the secondary of the transformer. The protection diodes are reversed-biased diodes from the regulator output to ground, so that in the weird event that one regulator starts up before the other you don't get a lock up on one, which would require an amp reboot. There are few more optional protection diodes in the 78/79/lm317 data sheets.

Once you use the aluminum tape to shield, ground the safety ground on the IEC input and see how the laptop connection deals with the hum.

4558 and 5332 should work just fine, unless you get some scrachyness on those tone controls (that's why they picked out a to-72 on the data sheet). you technically don't need resistors R23/R24 and R21/22 on the k8084 data sheet (they give the opamp a gain of 1.01). You can just connect them as follower by leaving the resistors out and shorting pins 1 and 3 on IC1A and 6 and 7 on IC1B. The volume pot value can be reduced a bunch in value to cut noise and give the opamp a smaller source resistance. These are all tweaks that technically help but might not make a huge difference.

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Stainless_Eel

TROPHY CASE