My DIY Pre/phono Pre/Active XO/tube buffer

ben62670

Well I have been in design study mode for for the last year. I really want to step up in the Line stage department, and go 2 channel. There are a lot of smaller companies that make great gear, but it is way to cost prohibitive for a lot of us. I have been fallowing many of the great designers like Wat Jung, Nelson Pass, and Peter Daniels. These guys really put out some great stuff, and I have learned a lot from them, and watching what you guys like here(thanks Guys/Gals). I have been helped with a couple designers, and have came up with what should be a great flexible product. I just finally ordered custom PCBs made to my specs. They should be in Tuesday or so. For now I am going with a cleaned regulated 120v power supply(external). I am looking into battery power supply designs with a kick from madmax. I have been stuck in 12dc design mode(more complicated/noisier/lower performance), but after a doing some research, and again a kick from madmax I'll be working on a battery PS in the future:cool: The Pre is going to be selectable passive/active/tube line stages:cool::cool:. I have collected most of the parts, and have ditched the crappy rat shack proto boards. The XO parts are from Marchand Electric. You just can't beat the price performance that these things offer with a simple OpAmp upgrade. All OpAmps are going to be Burr Brown 2134 designs.

ben62670

Here is my PCB The green is the underside copper used for power only. The red is top copper, and the yellow is components.

I have three of these on their way:)
Ben

Face

I like the smiley.

ben62670

Face wrote: »

I like the smiley.

I was thinking about writing something on there like...
I like pie (bags favorite)
I like big ****, butts...
Made on Pluto
FU China
My X puts out
....
Good thing you can't insert images:eek:

BTW the phono section (on left) has eyes:D

madmax

If you are going through all the work to do a pcb why not go smt and make all the circuits nice and tight? 0805 component size is easy enough to work with by hand. A little ground plane would go a long way too. You can actually draw it in with pcb express. I'd stick a bypass .1mf ceramic caps right next to the + supply pin of each IC too. Its good to not have 90 degree bends on the supply lines, I see two of those. They lead to spurious noise. Its better to go 2 45's rather than 1 90. Most designers tend to never run weird angled lines unless absolutely necessary but that is only an aesthetic thing, doesn't matter functionally. Fun stuff!

Edit: You can lay out the through hole resistors vertically and keep the traces short. Two pads at .1" apart.

ben62670

madmax wrote: »

... why not go smt and make all the circuits nice and tight?.... A little ground plane would go a long way too. You can actually draw it in with pcb express. I'd stick a bypass .1mf ceramic caps right next to the + supply pin of each IC too.
Edit: You can lay out the through hole resistors vertically and keep the traces short. Two pads at .1" apart.

SMT for me... not yet!

Ground plane issues.... I'm listening

The caps you suggested are already in the plans. You can't see them because I am going to mount the directly to the components;)

Yes to the vertical resistors. I do this on smaller boards to keep things tight. I chose not to go that route on this run (3 board minimum with no silk screen)because it is harder to visualize the components on the PCB.

Do you drive a train?
Thanks for the suggestions. A wise man listens much, and talks little(please ignore my post count:o)

Thanks
Ben

Early B.

ben62670 wrote: »

The Pre is going to be selectable passive/active/tube line stages:cool::cool:.

This is very intriguing. I often wondered why I haven't seen more preamps with these options.

ben62670

Early B. wrote: »

This is very intriguing. I often wondered why I haven't seen more preamps with these options.

Thats why I am doing it. Nice Pre's with only one of the three options are $1000 easy This is going to be a three in one deal;) Don't like SS with particular albums go tube:) Have a great DAC run passive:) Running a piece of equipment with moderate outputs like a tape, tuner, or IPOD(I am not endorsing portable units into HiFi!) use the SS with the gain stage;)
Did I mention I'll have a remote:cool:

Systems

Looks like you have a two section line stage with an input buffer follwed by the volume control, then the output section.Will the first stage have gain or will it just strictly operate at unitygain?

Also if the electrolytic caps on the output side of your regulators are 100uf or more you might want to add a protection diode(1N4004) across the regs or they could be damaged when unit is turn off.

Jung recommends using a paralelled combination of 120uf low impedance electrolytic(Panasonic FC series)and a .1uf Panasonic stacked film for bypassing close to the supply pins on the opamps.

If you went the SMT route you would not be able to swap different op-amps easily.

The OPA 2134 has very low offset so you can most likely forgo using a coupling cap at the output.I have them in several of my projects and offset is never an issue.

ben62670

GV#27 wrote: »

Looks like you have a two section line stage with an input buffer follwed by the volume control, then the output section.Will the first stage have gain or will it just strictly operate at unitygain?

Also if the electrolytic caps on the output side of your reguators are 100uf or more you might want to add a protection diode(1N4004) across the regs or they could be damaged when unit is turn off.

Jung recommends using a parralelled combination of 120uf low impedance electrolytic(Panasonic FC series)and a .1uf Panasonic stacked film for for bypassing close to the supply pins on the opamps.

If you went the SMT route you would not be able to swap different op-amps easily.

The OPA 2134 has very low offset so you can most likely for go using a coupling cap at the output.I have them in several of my projects and offset is never an issue.

First stage has no gain. 1st, and 2nd are going to be between the volume control. 2nd may have gain. This can easily be adjusted, but seeing the active filter is going to be in this configuration 2nd stage may not be used at all. Output coupling caps may be bypassed for the same reason;) Good eye:)

.1uf's are going to be implemented on the pins of the regs.

I am not a big fan of IC sockets, but I am going to use them on the trial board for reasons you have mentioned.

Caps on the output side of the regs are probably going to be 220uf pieces. A link to the diode protection would be appreciated.

I designed the boards to be fairly universal so I am not stuck with three boards for one project;)
Thanks
Ben

Systems

ben62670 wrote: »

A link to the diode protection would be appreciated.

I assume you are using LM7815,7915 regs.I will try and find the info online,if not I will scan it and then post it when I get a chance.

madmax

ben62670 wrote: »

Do you drive a train?

Yes, and I get to blow the whistle too! Every now and then I even toot the horn. I did the last 3 products sold by my old company and one so far for the new company. Concept, electrical design, schematic, pcb layout, documentation you name it. Normally a different person takes care of each area but I always just want it done before other people can get to it.

SMT is no problem. After you solder your first op amp you think "that wasn't too bad". Sometimes its hard to find a particular part without buying a ton of them but you can usually get around that by choosing parts carefully.
madmax

Systems

madmax wrote: »

SMT is no problem. After you solder your first op amp you think "that wasn't too bad".

It is the desoldering thats the problem:DSo if you want to try different op amps your in for a challenge and risk damaging parts and traces.

ben62670

For OpAmps I am pretty hard set on using just the 2134's. I have gone over this with a fine tooth comb, but one misplaced trace can do bad things.
A couple things that I would change on future design would be to get rid of the big copper pads under the main caps, remove the couple dog legs on the phono PS supply traces to the OpAmp's -15vdc side. Run the signal ground on the underside of the PCB, and a little more to the left(I did not realize that the boards were double sided when I started). I really don't believe these are going to affect performance, but nearly everything can use improvement.
I appreciate the input. This is my first real attempt on a real PCB, and not a project board.
Also if you guys could give a little advice on where to get good signal caps, IC's, resistors that would be greatly appreciated. I would like to use Wilma caps, but your suggestions will not go unheard.
Thanks again
Ben

ben62670

GV#27 wrote: »

I assume you are using LM7815,7915 regs.I will try and find the info online,if not I will scan it and then post it when I get a chance.

Yes, and yes:D
Thanks
Ben

Systems

If you don't have one yet get the Digi Key catalog.They sell Ti/Burr Brown and some excellent passive parts.http://www.digikey.com/

They stock the Panasonic ECQ series of polester caps that work great for coupling and they are reasonably priced(but they are butt ugly brown:eek:)Pass has recommended these and the YAGEO metal film resistors for use in some of his popular DIY projects.

The Panasonic P series or EPCOS polypropylenes are the bomb for use in active filters.

ben62670

I need the DigiKey catalog for sure. The online cat kills ya!
Thanks for the suggestions.
Ben

Systems

ben62670 wrote: »

I need the DigiKey catalog for sure.

The print one is over 2200 pages.

Thanks for the suggestions.

Your welcome,These are the resistors and caps I usually use in my active crossovers and other projects.


btw. I will scan that regulator data sheet for you tomorow.

madmax

www.newark.com is good too and they will accept credit card orders like digikey does. I order almost all my components for work projects from digikey.

Systems

Well can't find my National Semi data book ,the kids must have used it for Hamster bedding.:(
Anyhow adding the protection diodes is easy,just use rectifier diodes such as the 1N4004.
On the LM7815 you connect the cathode(white stripe) of the diode to the input( pin 1) and the anode to the output(pin3).

On the LM7915 connect the cathode of the diode to the output (pin3) and the anode to the input (pin2).

Adding these diodes will protect the regulators by allowing any voltage stored within the output caps to bypass the reg,otherwise when power is shut off this potential would be fedback and discharged through the reg potenially damaging it.

Cheers

mhardy6647

but... wh... where do the tubes go?

ben62670

I have not decided where to put the tube stages. I want to get the Pre going first. I could do a single tube at the volume control for all channels driven, or another idea I had was to have 3 tubes 1 for full out, 1 for low out, and 1 for high out. The tube setup is going to be modular also so it is no big deal to move it around.
Ben

ben62670

mhardy6647 wrote: »

but... wh... where do the tubes go?

Here is the pre setup. I am too tired to add voltage now. Its almost time to get up.
I am waiting for a quote on a nice chassis. I don't know if I want gold, silver, or black. Black would match my gear, gold is... well its gold, and the silver looks real sharp, but doesn't scream look at me like gold does. I don't know.

ben62670

I missed a note the PO had placed on my door Friday. My remote control is in!!! I just have to pick it up at the PO! Alps pot, 5 source selector, and a mute button;)
I am a happy boy! Other shipments should be in today. This thing is coming together.
Ben

ben62670

Its here! Well another piece:)
Alps motorized pot, and remote source selector;)

Edit: The thing comes requiring 9-12vac. Easy fix though the rectifier will be omitted, and I will feed it 15vdc just the the rectified voltage would have been with their design. I don't need any extra transformers, or ac in my box!

ben62670

HeHe I got my tubes on:D I have my tube stage implemented, and what a huge difference in the mids, and highs. This thing really brings them to life. The heater is running a little hot at 7.2vac instead of 6.3, but a resistor in line will cure that. This thing is real cool. I am using the same design that Fredv used in the accurian setup(thanks Fred). I purposely left out the filter caps on the heaters, did not use any shielding except from the toroidal tranny to the heaters. I really expected at least some noise I am running one channel unbuffered, and the other with the tube. Slightly more gain with the tube. In the black box I have a switch to engage, or disengage the DC blocking via a Dayton .1uf poly cap. Without the cap I do get DC, but none with it (of coarse). I am very pleased. Test chassis is an old gutted JVC tuner;) If the resistor to the heater makes a difference I might as well make that adjustable too:)
Ben

ben62670

My PCB's are on the way! The tube Pre has been running a few days. Too much gain for what I am doing. No biggie It shouldn't be too hard to change. The DC blocking caps are rather large, and slowing coming into there own. This is my first experience with tubes so I don't know how long it should take to burn in. Sound stage is very sweet, mids, and highs are sweet. The bass is the only thing that hasn't fully come in yet, but it is a little early to tell anything. They are running monitor 4.6's with the Morel tweeters being driven by the accurian amp. This weekend it is going into my main system. Also I have a ton of 1% yageo resistors, and nice caps on the way. I am very interested in the SQ is going to be with the better pieces. I did some modding on the remote boards. Stock it gives you a choice of 4 unbalanced inputs, or 1 balanced. A couple jumpers in the right spot, and I have 5 inputs now. One neat thing about the source selection is it turns itself down between sources, and returns to the volume it was before the source change. The remote itself has great range, works great, but it is kinda flimsy.
Well you guys sparked my curiosity with vinyl, and tubes. All I can say I am glad I listened.

Thanks
Ben

Frank840

So when are you going to start making amps ? and i will need a price on crossovers as i am going to try building my own speakers

ShinAce

He is making amps as well(another thread), gainclone amps.

ben62670

Frank840 wrote: »

So when are you going to start making amps ? and i will need a price on crossovers as i am going to try building my own speakers

Nothing is going to be sold for a little while. I am actually going to build a couple units that I want to send out to Polkies to get some feedback on first. Similar to the cable swap program we had here. I'll put you on the top of the list of Polkies to check out my work. What I want to do is see if I can build something real nice at a real good price. The Pre is actually something I want to sell. I know that I can build a real nice unit much less expensive than what is being offered out there, and much more flexible;)
Thanks
Ben

Frank840

ben62670 wrote: »

Nothing is going to be sold for a little while. I am actually going to build a couple units that I want to send out to Polkies to get some feedback on first. Similar to the cable swap program we had here. I'll put you on the top of the list of Polkies to check out my work. What I want to do is see if I can build something real nice at a real good price. The Pre is actually something I want to sell. I know that I can build a real nice unit much less expensive than what is being offered out there, and much more flexible;)
Thanks
Ben

that be Cool, cant wait to see the turnout all i here is great work from you.Keep it up :cool: