I made my own preamp...

[Bob's Mods]

...because the low end ones blow chunks. I've tried a number of lower cost preamps and they just ain't happenin. Funky distortions, phase problems, don't mix well, don't sound no where near pro.
It's a simple thing really but boy what a difference. I used a Lundahl transformer for input coupling and a Burr-Brown INA217 instrumentation amp. I used the PC board I stripped from a Bellari MP105 and it's housing.
It just goes to show the design doesn't have to be handed down from God, just use really, I mean really good components. These low end pre's use the cheapest ICs and caps money can buy. And they all do the same thing too. That's why none will ever work well. And low end tube mic pre's, give me a break. All these pres on the low end are just hopelessly crippeled.
Transformer coupling is the way to go when your dealing with 30 mV mic signals. Once the mic signal is boosted to near 1 volt you can get away with some high grade capacitor coupling, but not before.

 

[CanopuS]

Cool

a) How much did it cost you to make overall?
b) Any pictures?
c) Any sound clips?

Cheers

 

[Bob's Mods]

The mic input transformer cost 60 bucks and the instrumentation amp cost 5. There were some resistors, caps, a pot and a few connectors that cost in the range of 15 bucks. The power transformer module cost 12. The housing and stripped PC board came from a gutted Bellari MP105 that cost me 100 but bread board and a bud box should be cheaper than that.

I'll take a picture and post it for you as long as it's not too much of a pain to add a jpg to this newgroup site.

I have a sound clip but no place to load it so you can hear it. I'm expecting to have a my own web page later on in the year though.

The cost is low verses the performance you get from it. The lowest cost high grade preamps range from 500 and up. I believe it's performance is in the 500 buck and up range.

 

[Mark7]

There are places on line that will host sound files for you. Nowhere Radio and Soundclick, for example.

 

[Bob's Mods]

Thanks for the tip Mark but I only have a demo. I don't think it' worth setting myself up on one of those hosting services at this time.

Here is a picture of what I've made.

 

[TripleJ]

Whered you get the circuit diagrams?

Did you make the PCB yourself or order it?

 

[mshilarious]

Looks very nice, but c'mon, how could you leave that tube socket bare? At least wire up the heater for the glow!

Anyway, it would be interesting to do a comparison of your amp with a cheap pre using your transformer into the unbalanced input of the cheap pre with the opamp switched out for a better unit. It's not exactly fair to criticize a cheap pre when you spend the retail price of the unit just on your transformer. Let's say you spend $100 on parts, which seems about right, then you would probably have to set a wholesale price of about $300 (inclusive of labor), which would yield a retail price of $500 for a single channel.

The manufacturers don't set out to build a pre that sucks, they are just trying to hit a price point. There are dozens of posts on the Rack with people looking for $100 pres and $300 mixers. Somebody is gonna sell 'em something.

 

[protein]

It really impresses me when people make stuff like that. If I made it it would be 80% gaffa tape, 10% chewing gum and 10% solder.

 

[Bob's Mods]

I came up with the design from application notes and my own knowledge. I've attached my sketched out schematic. This design, I suspect is most likely similar to designs you would find in high end recording consoles. It is not something typically found as a stand alone unit. Manufactures are selling very cheap stuff on the low end that does not do recording justice. They are boxes that are designed to sell at "price point". You just can't make a "proper" preamp with CHEAP parts. You can make a respectable preamp for a low cost with high quality parts.
I was shocked at Mackie. I opened up my VLZ 1202 and found it loaded with cheap caps and op amps. It's no wonder why it records so funky when used as a recording console. They bragged about how it's "recording ready" but I say bull. It is a solidly built box with many features that make it handy and more useful for live than recording. Their advertising gives you the impression they are this entrepenuerul company with innovative designs but they do what many others are doing parts wise. A quality build is great but it has to be followed up with a sound equal to it's build and it just can't deliver the sound using JRC op amps and el cheapo electrolytics. Shame on Mackie. XDR op amps mean nothing, they are only a marketing ploy.
I've come to be very weary of claims. We have so many higher quality parts available today, more so than ever before, and yet the manufacutures are still using the same cheap stuff they have used for years. There is an additional cost to use better parts, but not so much so the price gets blown out of the water. The cost increase is reasonable for much improved performance. Great audio does not have to be mega buck expensive to sound good.
The PC board came out of a MP105 I had. I removed all the existing parts and used the bare board.

 

[Bob's Mods]

msh....I agree with you completely. Companies will sell whats selling whether it does the job or not. If there are people out there who would buy a hammer with a hollow plastic handle, someone would sell it. It wouldn't be worth a damn but someone would sell it. For me, I would not be interested in doing something unless I could do it right. These companies are just selling sub standard stuff just to make a buck and thats ok for them. I come from the view that a proper low cost quality solution does not exist and that all manufactures are doing the same thing to make a buck and this does not benefit the newby or extremely cost conscience user who discovers this later in his learning curve. I do believe a quality low cost solution can be done when done on a mass production scale.

 

[turnitdown]

Bob,
I agree with your views on preamp cost/consumerism etc....

But, I'd like to throw a question out there...

How much would you retail your new preamp for, if you were to distribute it? Would it be in the low-end price range of $100-$200?

If not, you prove a point for the low end stuff. It fills a need. Not everyone has the $$ for a higher price unit, and retailers can't really afford to sell a "Better" unit (like yours) for that lower price point. Some folks only feel like spending $100-$200 for pres, as it's just a hobby.

Me?? I went with used Symetrix sx202's.... I thought it was a reasonable compromise of price/performance...

Can't wait to hear some clips though.... should sound great!

 

[NL5]

Hey,

I can host a clip if you want. You have got me intrigued. Do you have any links to other schematics - maybe for a true tube pre. I think I wanna try building one.

Thanks,

NL5

 

[Bob's Mods]

In reply to turnitdown, I'm guessing the unit would sell in the 200 to 300 range. It's hard to know for sure. This unit is not a toy, it is for someone who has a serious level of interest in the recording arts but on the lower end of the cost curve.

NL5, if you want to host the demo I made Saturday, that's fine by me. I'll need your email addr and you can post it for all to hear.

 

[NL5]

Email it to -

blowfish@attbi.com

 

[Flatpicker]

Cool mod, Bob! I love the way you hacked up that Bellari!

If you have some "pro-studio" friends, you should take it to them and ask something like "Hey guys, you mind comparing this "toob" Bellari to your high-end stuff just so I can see how bad it really is?" and then watch their jaws drop.

I totally agree about transformer coupled inputs vs. capacitor coupled inputs. Caps are ok for output coupling, but for inputs, the transformer is the best way to go, IMHO. I'm currently working on a few mic pre designs myself, one being similar to this one.

As far as retail price goes, a single channel pre of this caliber would street price for around $500 easily. Heck, the low-end Grace (forgot model #) is basically the same thing without the Lundahl, and it's $500.

 

[Bob's Mods]

I've sent my demo to NL5 so he'll point you to it.

This was just a quick put together short one track at a time demo. It was recorded and mastered by me using Voxengo plugins, a Behringer DEQ2496 that was modified by me and a CAD M177 that was also modded by me.

Bob

 

[bleyrad]

Hang on Bob, let's talk about the Mackie VLZ again.

You said it uses cheap JRC opamps and cheap caps.

That sounds like a VERY easy upgrade. What if we just stuck some AD825's in there and nicer caps? If not, any recommendations as to what would probably work as drop-in upgrades?

Even OP2134's would probably be a significant upgrade.

 

[krimson]

Good luck in modding a Mackie VLZ mixer. When I had my 1642, I had opened it up numorous time to repair it. Anyway most of the components are surface mount, so soldering would be very, very tough. You could probably get away with replacing the cap it it with something better but thats about it.

 

[Bob's Mods]

I've been using the Burr-Brown 2134s in my upgrades. As far as modding the VLZ is concerned, forget it. It's a nightmare. Could it be done? It's not really do-able. You might be able to upgrade one mic channel but it's a lot of work and skill. Do you have the tools and skill to rework surface mount? Most people don't. This unit is very tightly packed.

Well I gotta disappear for a number of hours but I'll be back.

Happy trackin'

 

[NL5]

Here ya go -