Build a Preamp

[FuzzBoxVoodoo]

I have a LowEnd Hand wired preamp that sounds great but it does have one thing that bugs me and that isthe volume control must have the wrong Impedance pot as it goes from min to max in the first 10% of its throw.
I also have a SAMamp coming that if I like it as much as I am hoping I would want to make it in to a Rackable unit.
On these hand wired units it looks like there can be 1 or 2 transformers caps,resistors,tube sockets,various pots and jacks etc also there is a ss headphone amp in the LE pre.
If I have the tools and the ability to put one together then how hard would it be to get the parts needed could I get them all from some place like Mouser?
I have been dabbaling in Vintage Stereo repair and have done some basic repairs from just Recapping to blown power supplies,Outputs etc so while Im no technician I do have some hands on expierence.
Thanks for your help.

 

[BassmanPaul]

In all seriousness, a pre-amp is one of the easiest things for a neophyte to build. Whether tube or SS just takes a couple of handfuls of components. There ARE things that you have to consider when deciding what you need.

Are you going to drive a tube power amp or, like most of us, stereo SS amp. A tube power amp tends to have a fairly high input impedance while SS much lower. How much voltage does the chosen amp need to deliver its maximum output.

If a tube power amp. a simple twin triode circuit such as the Bassman or the B15 would most likely drive the amp fully.

If SS then a pre using op-amps is very simple to implement.

If you chose tubes to drive SS then you have to ensure that the pre-amps output stage can drive something like 10KΩ impedance. That means the pre will need an output impedance an order of magnitude lower, say 1KΩ or 600Ω even better. The one I'm using currently has two transformer isolated outputs at 300Ω each. One I use for DI the other drives my Carvin or Mackie power amps.

Paul

 

[FuzzBoxVoodoo]

Do you happen to have any schematics for a Tube/DI Preamp to feed a SS Carvin?
Even something to give me a visual idea of the circuit.
Thanks Steve

In all seriousness, a pre-amp is one of the easiest things for a neophyte to build. Whether tube or SS just takes a couple of handfuls of components. There ARE things that you have to consider when deciding what you need.

Are you going to drive a tube power amp or, like most of us, stereo SS amp. A tube power amp tends to have a fairly high input impedance while SS much lower. How much voltage does the chosen amp need to deliver its maximum output.

If a tube power amp. a simple twin triode circuit such as the Bassman or the B15 would most likely drive the amp fully.

If SS then a pre using op-amps is very simple to implement.

If you chose tubes to drive SS then you have to ensure that the pre-amps output stage can drive something like 10KΩ impedance. That means the pre will need an output impedance an order of magnitude lower, say 1KΩ or 600Ω even better. The one I'm using currently has two transformer isolated outputs at 300Ω each. One I use for DI the other drives my Carvin or Mackie power amps.

Paul

 

[rpsands]

For your first time you might want to start with a kit. I believe there's a bass preamp kit by london power out there that's quite cheap (150ish). You'd have to buy a box, but those are not ridiculously expensive IIRC.

 

[FuzzBoxVoodoo]

I am looking for a certain sound more than the project side of it.
I was thinking that I could use a cheap M8 Furman power strip 1U because the front panel is a open slate pretty much and it already has the power and switch and see if I could get some ideas from both of the hand wired units I already have,I just dont know if I can get the transfomers inside of a 1U.
I do really like the idea of having the tube sockets on the back panel facing outwards like my LowEnd does but I think that they did it that way because the 6SN7 tube socket is just slightly larger than the inside space on the 1U chassis.
The LowEnd has 2 transformers inside and the SAMamp appears to have 1 small and 1 large transformer that wouldnt fit in the 1U.

With a schematic I would be able to flow both of these hand wired pre's and get a idea how they work and go from there,I didnt want to re-invent the wheel maybe just copy it a little for my own personal use and learn a few things about them so I could do my own tweeks.
Thanks Again for any help.
Steve

For your first time you might want to start with a kit. I believe there's a bass preamp kit by london power out there that's quite cheap (150ish). You'd have to buy a box, but those are not ridiculously expensive IIRC.

 

[Jim C]

For your first time you might want to start with a kit. I believe there's a bass preamp kit by london power out there that's quite cheap (150ish). You'd have to buy a box, but those are not ridiculously expensive IIRC.

Here's the link; pre-amp is $150 and power supply is another $150.

http://www.londonpower.com/catalog/product_info.php?cPath=15&products_id=76

 

[fdeck]

With a schematic I would be able to flow both of these hand wired pre's and get a idea how they work and go from there,I didnt want to re-invent the wheel maybe just copy it a little for my own personal use and learn a few things about them so I could do my own tweeks.
Thanks Again for any help.
Steve

Well... a time honored way to get your feet wet in electronics is to "trace" a circuit, i.e., draw a schematic from inspection of the circuit. This might also tell you what you need to know, in order to simply mod one or the other preamp.

 

[rpsands]

Here's the link; pre-amp is $150 and power supply is another $150.

http://www.londonpower.com/catalog/product_info.php?cPath=15&products_id=76

Do you know of anyone who's built one of those and reviewed it? Color me curious

It looks like with chassis, power supply and kit would set you back around 385, which seems pretty reasonable although not amazing.

 

[FuzzBoxVoodoo]

The LondonPower kit looks really cool and would be a great way to start to learn what is needed.
I still wonder if the power supplies could be had elsewhere for less.
Thanks for the great info so far and I will draw a schematic of the pre's that I have and then fiqure out what does what and why.
EDIT:
I was just looking at London Powers 1U rack mount for $85 and that is steep for that assembled looking thing,I think that I will use the Furman Power supply that I mentioned as they are ony $25 and look better and appear to be better built.
I was talking to a tech friend who told me to check with Antique Electronics for very reasonably priced Transformers.
I want to build a hand wired no circuit board preamp because those have been the ones that have impressed me much more than the circuit board style like my SVP-Pro.
Steve

 

[BassmanPaul]

First, don't get tied up with cost for the power supply. Finding parts that will fit into the about 1.5" of internal height is a search and a half. It's also the most important section of a pre-amp.

Antique Electronics is a great resource, I use them myself, as is Parts Express or MCM. The Mouser catalog is a mine of useful parts.

There is nothing wrong in using a properly designed PCB in a pre=amp. It supports the individual components well and is easy to mount. True point to point is good too. It depends on what the builder is going after.

Paul