Custom Console System

[Johnsoir]

Hi all,

Amazing resource and community you have here!

I'm interested in building a custom console system. As has been discussed here before, I'm looking to copy the basic design of this;

Symbol Modern Record Console


The issue is I'm trying to do this on the cheap. (At least for now)

The cabinet itself will be made from 3/4" ply to keep the price down and add a bit of mass.

The electronic parts I figure I would need are;

A Turn Table
Pre-amp
2.1 Amp
2 x Full Range Speakers
Subwoofer
Power Supply

I'd like to use these speakers and this sub. I found this pre-amp. And thought about using this power amp. What type of power supple would I need to run all this?

I'd also like to split the input so I could also run an 1/8" TRS to a phone/mp3 player/ computer. A Spectrum Analyzer or simple L/R channel meters would be cool too.


I'm new to the DIY audio world and Though I have a basic understanding of circuits and their parts, I really must admit that I have no idea when what to do when it comes to amps.

I would love to build an amp and pre-amp that could do this, but cost and knowledge are working against me.

Has anyone done something like this? I have yet to see a DIY amp for a 2.1 system. Will the parts I've chosen even come close to what I want to do, or is this all just an impossible dream?

Any help would be great, I feel like I need someone to hold my hand through this, but I want to gain the knowledge of what I'm actually doing.

Thanks in advance!

 

[PetruV]

Lm1875t amplifier for mids and highs,and a tda7294 for sub

 

[chris661]

The subwoofer will be fine, though I'd advise you to reconsider your choice for the main left and right speakers.
Those Visatons are designed more toward PA use. While there are some examples of good quality PA drivers, I wouldn't expect these particular drivers to be much use. Here's the product page with the frequency response (which needs to be smoother in the treble) and dispersion characteristics.
BG 17 - 8 Ohm

Since you're using a subwoofer, you could go for smaller (3-4") units, and get a nicer high end, without compromising the low end performance.

I'd consider building your own amplifier and crossover. It might work out slightly more expensive than that amplifier, but the experience you'll gain will (IMO) be worth it.

For that particular amplifier, you'll need a transformer. Lets say 300VA, 22-0-22. A higher voltage will give more power, but I don't think you're gonna be short on that.
You'll also probably need to wire the voice coils of the subwoofer in series, as the sub amp operates in BTL, so I don't think it'll be too happy with a 4ohm reactive load.

I'd recommend getting yourself a switch for the audio input. I'd go for rotary, as that means you can put it inline with the other controls on the panel, and attach the same sort of control knob. Your choice on that one.

Wire the phono pre-amp and any other inputs you'd like to the switch, then go from the switch to the amplifier input.

HTH
Chris

PS - if you want to cheat a little on the speaker side of things, see if you can find a pair of Mission 760i speakers on the cheap. They're very good through the midrange and treble. Some prefer them with bass support, others find them okay. It'd mean you just need a stereo amplifier.

 

[Johnsoir]

Thanks for the very informative reply.

A few questions;

If I were to build my own amp, would I need to build one for the mains, and then a separate amp for the sub?

Could the rotary switch (say a four position) be used such that position 1 would be off, and position 2-4 would be different inputs?

Where would I get a transformer like that? Could I build one?

How do you wire a single subwoofer in series?



I guess I didn't look very hard at the mains speakers. I would like to keep it to a single speaker per side. I do understand the advantages of having mids, and tweeters; I just prefer the look.

I found an 8" full range driver that seems to be well regarded for DIY projects, though I can't say I really like stepping up another 1.5".

Would something like this speaker accomplish what I'm looking to do?


Thanks again, for the input!

 

[chris661]

Thanks for the very informative reply.

A few questions;

If I were to build my own amp, would I need to build one for the mains, and then a separate amp for the sub?

Ideally, yes.
When crossing over at around subwoofer frequencies (~100Hz), the required components to do a speaker level crossover become very very large, such that its often cheaper to build a second amplifier and add an op-amp based crossover.

Its your choice on whether to get the amplifier you mentioned earlier (which will work nicely), or building one of your own.
Both will work, but the latter will give you more experience.

Could the rotary switch (say a four position) be used such that position 1 would be off, and position 2-4 would be different inputs?

Generally, the rotary switches connect one thing to a variety of different positions. It'd be difficult to switch power supply and signal with the same switch (that's if you can find one that's rated for the current).
Short answer: not easily, it'd require a non-standard switch.

EDIT - it could be done using relays, but that adds another level of complication.

Where would I get a transformer like that? Could I build one?

If you fancy wrapping some bits of copper wire around a chunk of iron hundreds of times over, you could build one.
Alternatively, Google is your friend.

Note that when using a transformer, you'll be wiring up mains connections. This isn't something to be taken lightly - if you do it wrong, this stuff may well kill you. If you're ever in doubt, stop, unplug it, and either get an electrician around, or take lots of photos so we can check your work.


Note that if you DIY your amp, you can pick a kit or something that'll run off 12v, which is rather handy as you can get laptop-style power supplies for those, which are nice and safe
You could also get a 12v (or any other voltage you can get a suitable power supply for) ready-made amplifier board, which is rather convenient.

How do you wire a single subwoofer in series?

The subwoofer you've chosen has two seperate voice coils, attached to the same cone.
The purpose of that is generally to give some flexibility in wiring and amplifier choice: a single one can be a 4ohm or 16ohm unit (for parallel and series coils respectively), or a pair could be 2ohm, 8ohm, or 32ohm.

For the bridged subwoofer output of the power amp you mentioned, it'd probably be best to series up the coils, giving a 16ohm load, as very few amplifiers can operate nicely when bridged into a 4ohm load.

If you're thinking of DIYing amplifiers, then make a 4 channel one (ie, a pair of stereo amps), and connect one amplifier to each voice coil of the subwoofer.

I guess I didn't look very hard at the mains speakers. I would like to keep it to a single speaker per side. I do understand the advantages of having mids, and tweeters; I just prefer the look.

I found an 8" full range driver that seems to be well regarded for DIY projects, though I can't say I really like stepping up another 1.5".

Would something like this speaker accomplish what I'm looking to do?


Thanks again, for the input!

I'd go with the 4" over the 8" for your application.

With full-range drivers, there's a lot of compromise around the size of the driver. A 3" driver will never produce much bass, but will do rather nicely for vocals and treble.
An 8" driver (even with a whizzer, they introduce their own set of problems) will put out a decent amount of low end, but the treble tends to get messy.
4" will do quite nicely, as its big enough to get to ~100Hz comfortably, while still keeping the treble qualities of smaller drivers.

The Tang Band 8" full-ranger does rather nicely across the board, but is also very very expensive...
.. and even so, it can't do what a good tweeter can.

Chris

 

[indianajo]

Where you buy a transformer has a lot to do with where you live. I usually recommend farnell.com as an electronics distributor worldwide, but their transformer prices are not competitive in the USA. Here many diy users like antekinc.com in NJ , but they just had a warehouse fire, so I don't know how compliant they are yet. You don't want to buy from their US warehouse in the EU, for example. The custome charge would be twice, ***** to US, then again US to Europe.
You can use the transformer and filter caps to run all three channels of amplifier, if you decide to go that way. For newbies I recommend LM3886 IC power amps, about 35 watts per channel. See the datasheet from datasheetcatalog.com. About $7.50 per IC (channel), plus a dozen other parts plus the power supply filter caps, and heatsink. See IC amp construction threads under IC amp forum, different than solid state forum. If you want more power, look at the honey badger sticky thread at the top of Solid state, and sold as a PWB by diyaudio store.
You don't want the AC power on the same switch as a selector involving magnetic phono cartridge input. The gain on phonograph circuits tends to be 50x. That can make it very sensitive to hum. Step one, IMHO, is putting the AC power stuff in a different steel box than the high gain stuff. Most manufacturers like Peavey and dynaco, have grounded steel bulkheads built into their equipment to separate AC from high gain.The transformer in both the dynaco and peavey amps I own, is wrapped in a steel (dynaco) or copper (peavey) magnetic flux shorter. You won't get that luxurious feature in a toroid transformer built in *****. So, AC power switch, transformer, pilot light if AC, on one side of the bulkhead. High gain stuff the other side of the buikhead.
If you're in the US, I suggest orphan speakers from the charity resale shop as the first trial. I frequently see speakers in there from big name receiver manufactures, orphaned by the death of the receiver due to 20 year old electrolytic caps and tired controls. Then if you don't like what you hear, you are out $20 and a couple of pieces of plywood. Watch out for the 20 year old electrolytic crossover cap in a used packaged speaker, it may need proactive replacement. I picked up a pair of nice looking 6 ohm 6" diameter whizzer cone ("full range") speakers from a Toshiba projection TV hulk out on the curb for the garbage, last month. Possibly better than what you are describing buying.
Look at speaker projects under speakers forum here, one of the sticky threads involves a full range speaker with a folded box using a 6" fostex driver with whizzer cone. I tend to buy packaged speakers with guarenteed time alignment and guarenteed frequency response, but they won't fit in a console wrapper.
Watch for the frequency response "production tolerance" curve on packaged speakers, my ear says some frequency response charts are a big lie. (A grand piano CD should sound like a real grand piano, IMHO).
Good luck. 1970's consoles go to the dump all the time, but 99.99% of the turntables had ceramic cartridges and tone arms that would rip the highs off a good LP in two plays. I know, my mother had a record ripper/player from RCA. That is how I got the dynakit stuff and an AR turntable as soon as I had a playing job. (1970). The college was using them in the library.

 

[Johnsoir]

I found this kit that seems to be a well regarded stereo power amp using LM3886TF's.

My major questions are; would each output then be run in series to a single voice coil of the sub?

And would the power supply be enough to also run a simple DIY Phono preamp?

Sorry for meandering all over the place but I swear some of this is setting in.

Thanks again!

 

[indianajo]

You need a separate LM3886 amp for each 8 ohm or 4 ohm speaker package. If your "speaker" has a midrange and tweeter separated by a "crossover" so that it is that many ohms at each frequency, then it counts as one speaker. However, on your woofer, I would put the two coils in series so it was an 8 ohm woofer. LM3886 don't produce a lot of current, so you get better power transfer @ 8 ohms, IMHO. Read the datasheet for the subwoofer & LM3886 for more detail. So with 2 treble/mid speakers, and a subwoofer, you need three LM3886 channels. There are some 3 channel amps out there, but they are assembled overseas. Personally I'd buy a pair of Peavey PR10's and hide them behind a grill. Light on bass, but it is a 2 channel solution. I've got Peavey SP2's on poles each side of my piano, and that is a real 2 channel solution because those speakers go down to 54 hz. But at 94 lb each, you don't want to package that in a console. PA speakers, also, project the highs down; they are meant to be mounted high on poles above the audience.
Your power supply needs 55 to 70 vdc for the LM3886, and +-15v for a preamp. Most of the transformers at antekinc for example, have both 37v windings and two 18 v windings. You tie the two 37 v windings together at the CT to make a 74 v winding and lose 1.2 v in the diode bridge. You run each 18 v winding to a diode bridge to make two separate 15 v supplies, and tie the plus of one to the minus of the other, to make +-15v. A voltage regulator like a LM317 smooths the 18v down to 15 v. Preamps require very smooth power supplies, usually. +-15 is a standard voltage to run op amps; for a preamp or mixer. Depends on what preamp circuit you buy or build, what voltage you need for the preamp.
The wattage transformer you buy would be enough wattage for three 35 watt LM3886 amps, or maybe 200 VA (watts). You want about double the wattage from the transformer than you need as music.
Or you could buy a switcher power supply from connexelectronic.com (in the diyaudio vendor forums below) that has a 200 VA 70 v output and a +- 15 V outputs. The switcher power supply definitely has to be in a separate compartment of the enclosure because they howl, and you need a choke RF filter on the supplies going through the wall to keep the howl out of the amplifier part. Then you need more filter caps on the amp side of the wall, after the choke filters.
Power supply design of transformer/bridge/capacitor supplies is covered very well in Thomas Floyd Electronic Devices, the Electron Flow Version , a surplus community college text I found at Goodwill charity resale. I've learned the stuff the hard way over the years, but it is much more organized in a text like that. It also tells you how to use a DVM to check supplies and amps, and shows some of the common assembly errors people make on hand built prototypes. ( I make a few myself). Or you can learn about power supplies under the Power Supply forum of the diyaudio amp section, but it is much less organized that way.
Good luck. We all start somewhere. I learned some things out of the 1959 Ford Car manual, some out of the Sears Roebuck "wire your house in hours", pamphlet, and had special coaching by a WWII veteran radio repairman (Navy) who was my 10th grade chemistry teacher.

 

[chris661]

However, on your woofer, I would put the two coils in series so it was an 8 ohm woofer. LM3886 don't produce a lot of current, so you get better power transfer @ 8 ohms, IMHO.

Sorry sir, the subwoofer has a pair of 8ohm coils, with the datasheet giving T/S values for both coils in parallel.


Bearing in mind that budget is a factor here, I think it might be worth recommending some switch-mode amplifiers, as their higher efficiencies mean a smaller transformer can be used.

That LM3886 kit would do nicely, but you'll probably end up needing 4 channels, so there'll be two channels feeding the sub, each seeing an 8ohm load.

Chris

 

[Johnsoir]

All great info, thank you very much.

The Chip Amp Kits I linked to earlier seem to be missing a transformer? So I would need to source this correct?

Would seem to be more cost effective to go with my original assembled board and then source a transformer for that. This would at least give me the three channels I am looking for.

If I could find a stereo LM3886 kit with power and transformer for a decent price I think I might be able to just get a powered sub used and work that in.

The transformers don't seem to be included in any kits I can find though, and also seem to be difficult or expensive to source on their own.


My hunt continues, but I can at least say that I am learning a lot just from the research.

Thanks again for all the help!

 

[chris661]

You'll need either a transformer, or a DC power supply.

I've had a look around on some Canadian websites, and I'm struggling to find a suitable source for transformers. eBay isn't too useful either - they're all very expensive.

Thing is, a transformer converts one AC (what comes out the wall) voltage to another, then a circuit on the board makes that into DC (same as batteries) for the amplifier to use.
You could effectively bypass that circuit and use a different DC power supply, which are actually nice and easy to find...
New AGT 36V DC 10A 350W Regulated Switching Power Supply Shipped from California | eBay

Edit - you'll need two of those or a 72v version, should be do-able either way though.

HTH

Chris

 

[Johnsoir]

Thanks for all the help chris.

I'm on the hunt for a transformer though it may be some time before I can gather all the parts. Every turn I have taken so far has bumped the price up higher and higher, but I think the quality will speak for itself in the end.

I'll keep you posted as I progress!

Cheers