My DIY phono pre

ben62670

Well I have started this too. I am losing my pre with phono input, and decided to build a phono pre with a tube stage(later it will be added). Well I have been looking at phono pres for a bit, and of coarse decided to build one. The standard pre's you get are typically feed only DC+, and ground. Also typical pre's are not complete dual mono till you start spending. Well I am building a dual mono RIAA compensated pre with an external +15 0 -15 regulated power supply. The boards are completely independant of each other sharing just the PS. Should be fun.

Edit: Burr Brown OPA134 OpAmps;)

ben62670

http://www.geocities.com/rjm003.geo/rjmaudio/diy_pho5.html
I went one step further, and made mine dual mono. Real nice, and tight to RIAA curves.

DollarDave

Are you marketing these? I would sure might like to try one.

ben62670

I might be making these for Polkies. I have to try it out first and make sure it doesn't sound like A$$:D I feel pretty confident though. I am working on the Pre right now. The big plan is to have the PS, Pre, active XO, and tube buffer in one chassis that is pretty large so I can keep noise to a minimum. There is going to be an XLR jack on the back of the Pre that is going to feed the phono Pre amp the unregulated AC. On the phone Pre I am going to rectify it, and do noise suppression there via snubbers, and PF caps. I am waiting on the regulators to come in. They should be here soon. I may hook it up unregulated if the PS is stable. I want to run one channel through Chucks Outlaw 990, and one through mine. I will just use an axillary input for my Pre.This way I can switch back, and forth.

ben62670

Well here is the line stage for the Pre-Amp(not the phono Pre). This will be installed prior to the active XO. This is also a Burr Brown OpAmp, and dual mono. Nothing is shared , but the power.

ben62670

6000uf, and 19.6vdc rails. This is unregulated. I am going to do the regulation near each circuit. I have decided with the rails that high I can rectify it at the transformer, and step it down on the phono Pre, and in the case. I may just build the PS completely separate just to be cool:cool::p BTW I love all these little boards. Kinda modular.

Face

Go to bed you kook!

ben62670

Why its almost time to get up! Just ordered more parts!

madmax

Why not go with batteries? Cheap and quiet. D cells should last a long time. You could even seperate the supplies, go with twice the amount of batteries and get twice the life.
madmax

ben62670

A good power supply is plenty quiet. I know batteries are quit the rage with some higher up gear, but a small hand full of 1uf caps in the right spots, and regulated is plenty good and quiet. Also more circuitry is required to get the +- rails with a battery system, or you have to design with +12vdc + ground. Tubes are going into this project also, and the heaters plus the modules would draw too much for a battery system IMHO. I may do a battery system if someone wanted a clean Pre only with the phono stage, but for me I am going to stick with a nice PS.

ShinAce

The only time I'll use batteries is if the device needs to be portable.

Regulators are plenty good. Not to mention the amps themselves are designed to reject power supply noise.

ben62670

If anyone can hear any hum I promise to give them ear plugs:D

ben62670

Ok I have a torid for the tube heaters, but it is 7.34 volts AC. What should I do?

madmax

ben62670 wrote: »

A good power supply is plenty quiet. I know batteries are quit the rage with some higher up gear, but a small hand full of 1uf caps in the right spots, and regulated is plenty good and quiet. Also more circuitry is required to get the +- rails with a battery system, or you have to design with +12vdc + ground. Tubes are going into this project also, and the heaters plus the modules would draw too much for a battery system IMHO. I may do a battery system if someone wanted a clean Pre only with the phono stage, but for me I am going to stick with a nice PS.

There is a reason its the rage. Don't understand the rail thing, you should be good with a pretty wide voltage range. Remember what we are looking at here, a slightly better preamp can cost you 100 times more in the market. Just an opinion. BTW, tube radios were made for a lot of years with batteries.
madmax

ben62670

When you go with batteries you have only positive, and ground. When you go with a PS you have positive, negative, and ground. This gives you push pull. You can make a PS with batteries that will do the positive, negative, and ground, but the problem is is that you induce switching noise with needs to be attended to. If you are going battery with the swing voltage you might as well build a proper PS. I don't feel like fiddling with batteries, and a charger. Some guys do. I have been studying a lot of designs over the last year. Lots of them are incredibly over priced fancy cases with a hand full of good components. Look at the latest gain-clones out there. People are paying through the nose for them. I have meet the designers online, and these guys are some really good guys who do very neat work, but when it comes down to the nitty gritty you need to buy good parts, design your case so that you do not have stray RFI, or MFI interference. Not rocket science. Just involves a lot of research;)

madmax

ben62670 wrote: »

When you go with batteries you have only positive, and ground.

Oh no, not at all. Its all about references. Lets say you have two batteries, 1.5 volts each in series for 3 volts. If ground is attached in the middle you have +1.5 on one side and -1.5 on the other.
madmax

ben62670

madmax wrote: »

Oh no, not at all. Its all about references. Lets say you have two batteries, 1.5 volts each in series for 3 volts. If ground is attached in the middle you have +1.5 on one side and -1.5 on the other.
madmax

Not true. I have no idea where you heard that. If you connect a wire between two 1.5 volt batteries you still have 1.5volts and ground not -1.5 volts. There is no -1.5 volts there. Basically you might as well toss the second battery. Think 24v starters in diesel trucks.

Systems

madmax wrote: »

Its all about references. Lets say you have two batteries, 1.5 volts each in series for 3 volts. If ground is attached in the middle you have +1.5 on one side and -1.5 on the other.
madmax

I believe you are correct.You can also use a single battery and achieve a ground reference or virtual ground by using a pair of resistors.

Although they will operate at +-5volts keep in mind most hi performance op amps perform best with voltages in the +-12-15 V range the OPA134 included.

ben62670

GV#27 wrote: »

I believe you are correct.You can also use a single battery and achieve a ground reference or virtual ground by using a pair of resistors.

Although they will operate at +-5volts keep in mind most hi performance op amps perform best with voltages in the +-12-15 V range the OPA134 included.

I did do some research on using straight VDC, and with some mods the 134 runs nicely with 24vdc, and ground.
Ben

Systems

ben62670 wrote: »

I did do some research on using straight VDC, and with some mods the 134 runs nicely with 24vdc, and ground.
Ben

You mean a single supply of 24 volts?:eek:I thought it was only rated for 18 volts max.

ben62670

GV#27 wrote: »

You mean a single supply of 24 volts?:eek:I thought it was only rated for 18 volts max.

18 +-, or upto 36vdc ground. I would never push that kinda voltage though. Too bad you are so far we could have some fun with this stuff. Not to many guys like to dive in.
Ben

ben62670

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=OPA134PA-ND

Systems

ben62670 wrote: »

18 +-, or upto 36vdc ground.

Ah OK ,FWIW besides higher voltages to get the best results from it requires the use of A bipolar(+-) supply.Using a single supply comprimises its noise rejection(see PSRR in data sheet).

Too bad you are so far we could have some fun with this stuff.

Yes that would be fun.You are certainly digging in deep and thats what I like to do as well.Its very satisfying building your own component and having it work (and maybe even sound good )for a fraction of the cost of a commercial piece.

ben62670

My XO boards just came in! Shweet!!!

ShinAce

Just to reiterate what GV is saying.

Yes, you can create negative voltage with batteries. Just like how you can get a negative temperature, 0 volts is not actually 0 power. So if you center tap 2 batteries, you have +x/0/-x . You can also create a virtual ground(not so good). I tend to use 2 12 volt batteries during prototyping and then switch it up to dual regulated supplies in the end(sometimes +/- 12v, sometimes 15)

Dual supplies are better for most op amps.

I think I missed another point though.

Systems

ShinAce wrote: »

I think I missed another point though.

which one?

ben62670

Well this went quick. I don't have the screw terminals actually soldered to the board I just put them on one board so you can see what they look like. I prefer to solder all connections;)

Systems

Well do you think you have enough projects on the go yet?:D


Those X1 kits are a steal,I see you wisely installed some Burr Browns in them instead of the stock ancient op-amps.
Agreed a solder connection is the way to go.

ben62670

Just got 10 each of the 15vdc-, and 15vdc+ regulators! Its going to be another late night. Some time next week I think I'll work some sleep into my schedule:)

ben62670

GV#27 wrote: »

Well do you think you have enough projects on the go yet?:D


Those X1 kits are a steal,I see you wisely installed some Burr Browns in them instead of the stock ancient op-amps.
Agreed a solder connection is the way to go.

Yes they are a steal! No hunting parts. Toss the original opamps, and run them!

madmax

ben62670 wrote: »

Not true. I have no idea where you heard that. If you connect a wire between two 1.5 volt batteries you still have 1.5volts and ground not -1.5 volts. There is no -1.5 volts there. Basically you might as well toss the second battery. Think 24v starters in diesel trucks.

You gotta be kidding me. Thats all I can think. You have to connect a third wire you goof.
madmax

-1.5+ gnd -1.5+
-<<<<<0>>>>>+
-1.5___G___+1.5
Batt1_____Batt2
-_____3V____+