Howlin's Pre build Blog

[Howlindawg]

As per the title I've started work on a new pre to match my >power amp<.
The purpose of the thread is threefold
1] To keep a record of the project.
2] To perhaps encourage others to have a bash at an easy DIY project (*)
3] To perhaps get some input as the project progresses

(*) I was only motivated to get into DIYing my own kit after reading threads in this section.

Progress will be steady if not downright slow at times as I have other demands on my time at the moment in the form of some ongoing renovations around the house and a GoldWing based Cafe Racer project bike.

[Howlindawg]

So first up is the casework, drilled and ready to go.
The chassis is from HiFi2000 in Italy to match the poweramp.
The flush fitting illuminated power switch is from Onpow.

Those vents in the casing will be needed later.


And a shot of the rear.
RCAs are silver plated CMC.
I've used these previously on my Power Amp and DAC builds and really like them.
note: 3/4" (19mm) is the industry standard spacing between RCAs

[speedysteve]

Wow looks nice - as you say perfect match for the power amp...
Can't wait to see what you put in it.

[gthang]

Cool, good luck with the project.

[meridian man]

If its like the power amp it will be cool, I'm amazed at peoples "diy" skills.

Well done!

[Howlindawg]

I'm amazed at peoples "diy" skills.

I'm hoping this thread will show that pretty much anyone could have a go at this.
The only tools used so far have been a Screwdriver, Spanner, Square, Electric Drill, Dremel.
All that's required is a little care and patience.

[sq225917]

What's going in it?

[Howlindawg]

What's going in it?

Short answer: A pair of DCB1 buffers and a phono stage. Nothing complicated.

Longer answer: This is going to be a sort of ongoing testbed. An opportunity for me to compare the performance of various components for myself and evaluate their sonic performance. The aim is to gain some first hand knowledge that I can carry forward into more complex projects in the future.

This is the second step in the process for me. Prior to this I've compared Passive vs Pass B1 vs DCB1 built up with el cheapo components. Having settled on the DCB1 the next step is to build it up using some quality components. Then I'll turn up the heat...

[i_should_coco]

[sq225917]

Hypnotize or Mezmerize?

[Howlindawg]

Hypnotize or Mezmerize?

Hypnotize HotRod (hence the vented enclosure).
At least, that's current the plan.

[Howlindawg]

Made a little progress last night and got the selector switch installed and wired up.



Selector switch is an Elma 2 pole 6 way switch.
I'm only using 5 inputs so to restrict the movement of the switch to just 5 positions a stop pin was also required (you need to ask for one when you order).

All signal wiring is solid core silver with PTFE insulation and I'm using WBT silver solder which is lovely to work with.
Need to be careful when working with this stuff not to burn the PTFE with the soldering iron as the fumes from burning PTFE are really nasty.

It's worth spending a bit of time to get the connector rod between the knob on the front panel and the switch alligned properly as this has a pronounced effect on the feel of the switch in operation. Get it right and there's a really smooth action to the switch with a solid click as each source is selected.

[snip]

Looking very good there,

Once you get to putting boards in there, are you going to use self adhesive vinyl standoffs? Otherwise I would suggest you install a large board sat on 5 standoffs that you can then attach circuit boards to, rather than end up with a whole lot of M3 taps in the bottom plate from various circuit boards you have had in there over time (like my own preamp, hehe)

//Jan

[Howlindawg]

Sadly not much progress on this project recently due to other demands on my time.
However I did find time to sort out the volume pot.

The pot is an Alps Blue Beauty, chosen as it's good value for money and sees service in some excellent commercial pres.
I found it much easier to solder the wires to the switch before installing it into the case.
I also added some heatshrink around the joints to provide some strain relief to the rather fragile solid core silver wires.
Connections are from left to right; Signal in, Signal out, Ground.



Once the pot was mounted in the case I decided to wire it up as a passive for the moment and see how it sounded.
Nothing exciting here but so far so good, no pops when changing source and total silence when no source is playing.
Pretty much what you'd expect from a passive built with decent components.
Once again, spending a bit of time to get the extension lined up correctly for the volume control is worthwhile for that silky smooth quality feel.




And this is what it looks like so far as a fully functional passive pre...
Cost so far is approximately €220



The power supply is next but I'm still awaiting some parts and have just been informed that the caps I had on back order don't look like they'll be arriving any time soon.

In the mean time there are a few niggles with the casework that I'd like to get sorted.

• I'm not happy with the front panel.
  I'll be trying to blag some time with a milling machine to recess the knobs into the faceplate by a few mills and will add some brass bushings to support the control extensions.
• The steel casework isn't solid enough for my liking, particularly the base.
  Will want this sorted before the heatsinks and transformers start going in.
• The hard plastic feet supplied with the case are a joke.
  They'll need replacing.

[Howlindawg]

I would suggest you install a large board sat on 5 standoffs that you can then attach circuit boards to

Hi Jan.

There will be a large 5mm plate of Alu or Copper bolted to the base and the PCBs will mount directly to that.
This will be needed to dissipate the heat from the components to the Heatsink which will be mounted to the rear of the case where the vents are.

[snip]

Hi Jan.

There will be a large 5mm plate of Alu or Copper bolted to the base and the PCBs will mount directly to that.
This will be needed to dissipate the heat from the components to the Heatsink which will be mounted to the rear of the case where the vents are.

Grand idea, this will also alleviate your problem with the bottom plate, I have a few of these chassis and they are pretty good, but as you say the bottom plate is a bit floppy, I have used a similar approach in bracing it.
When you get around to installing the power supply you would probably be well off considering shielding off that volume potentiometer, I am sure however that you have already thought of this.

//Jan

[zebra100]

How does the volume control perform? Do you get a big increase in volume for a small turn on the pot?

I had this issue with my Apls Blue based pre for my LM3875 GC power amp. I used a 50k dual log pot. To solve the issue, I employed a resistor shunt (47k).

[Howlindawg]

Do you get a big increase in volume for a small turn on the pot?

No, quite the opposite, it's very gradual.
I'm using a 10K pot though.

So far very happy with the sound quality of the Alps but will be trying it shunted just so that I can judge the effect for myself.

[Howlindawg]

Well I eventually got around to ordering up the remaining parts and boxes have started to arrive.

Nuvotem encapsulated transformer and PRP metal films for the PSU.


Z-foils and Caddocks for the signal path


Mills wirewounds, Elna Cerafines, Takman Carbon films


Unless I've missed something that should eb all the remaining parts I needed.
Better get on with it so!

[RichG]

Martin,
The DCB1 is a very good circuit, especially if you can closely match the FETs (this makes a big difference). With the quality of components you've opted for it should turn out very sweet indeed, although personally I'd have gone for a switched attenuator over the Alps. I look forward to seeing this come together.
BTW I've got a bundle of 2SK170s here - if you get stuck let me know.