Recent Posts

1

Kaiju Stereo 300B amp / Re: Painting Suggestions Concerns for PC-5's

« Last post by Doc B. on Today at 06:19:12 PM »

As long as the oven temp is down where you suggest this is fine. We learned the hard way several years ago that higher temps can cause pretty bad embrittlement of the hammered paint and it can crack and chip off the part.

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Technical topics / Re: Fixed attenuator for balance control?

« Last post by 2wo on Today at 05:43:38 PM »

How about adding a pot in place of L-pad to the desired channel and dial it in.

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Technical topics / Re: Fixed attenuator for balance control?

« Last post by phatfish on Today at 03:52:20 PM »

I'm good with rolling my own.  It sounds like an LPad would be more appropriate than a single resistor?

I did find a calculator, but it seems geared towards speakers:
https://sengpielaudio.com/calculator-Lpad.htm

Using 50,000 Ohm and 1.5 db came up with pretty different numbers than hmbscott.
R1 = 7930.24
R2 = 265248.86

How would I go about calculating this for the EROS2 > Mainline?  Sounds like the mainline impedance is variable due to the attenuators I assume "25Kohms minimum" from the product page.  Is 50K more typical or was that just an example?

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Kaiju Stereo 300B amp / Re: Painting Suggestions Concerns for PC-5's

« Last post by hmbscott on Today at 01:21:55 PM »

I've been painting chassis plates and end bells with Rust-oleum Hammered, which takes forever to harden so I use a little trick that should work well with any similar gloss enamel. Note that I specifically recommend against doing this with a choke or transformer or anything else with circuitry in it. This is strictly for metal parts.

After spraying I give the part 24-48 hours to dry then I place it in our kitchen oven set at 180F and leave it there to bake for 30-45 minutes. After which I give it another 24 hours before using. This does two things. It greatly speeds up the curing and making it hard enough for assembly without fear of marking it up soft paint, a huge benefit because without this step I have had to wait 2-3 weeks for a thick Hammered paint coat to harden sufficiently. Secondly, it really enhances the gloss. It gives it much higher gloss than as-sprayed.

After using (abusing?) the oven this way I run a self-clean cycle on it to blast out the fumes that had off-gassed from the paint. Oh, by the way, I haven't shared with my better half that I have abused our oven in this manner, and I have made sure she would not be home until several hours after completing the paint bake/oven clean cycle to ensure the kitchen no longer smelled of paint fumes.

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Kaiju Stereo 300B amp / Re: Painting Suggestions Concerns for PC-5's

« Last post by Emoreigns on Today at 08:45:10 AM »

Thanks Doc-

Painting the bell of the transformer is always the first thing I do on these builds, so the paint can dry- All good there!

I liked the look of the PC5's the way they are, so I am glad I don't have to paint them and can use them as is!

As always thanks for the help!

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Kaiju Stereo 300B amp / Re: Painting Suggestions Concerns for PC-5's

« Last post by Doc B. on Today at 07:39:37 AM »

The PC-5s and OT-5s are covered with a clear varnish that is impregnated throughout the laminations, coils and all over the outside. You can paint over it to change the look, but it is not necessary for protection.

The bell end of the power transformer does not have a protective varnish. It only has a waxy coating that is a temporary finish intended only to last through shipping. I do recommend stripping that wax coating and painting or clear coating to prevent rust.

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Kaiju Stereo 300B amp / Re: Painting Suggestions Concerns for PC-5's

« Last post by Emoreigns on Today at 06:02:52 AM »

Is it necessary to paint the PC-5's to prevent rust like the transformer bell/ caps?

I'm right at the point of installing these in my Kaiju build right now, and figure it will be easier to paint them before they are attached haha-

I'm not sure if it is proper protocol to reply to an old thread like this for a similar topic, or if it is correct just to start a new thread!

Thanks for the help everyone!

8

Technical topics / Re: Fixed attenuator for balance control?

« Last post by Paul Joppa on Today at 04:04:55 AM »

The problem with that kind of attenuator is that the impedances are important but never provided by the maker. (I think that's because the explanation it thought to be too complicated for the average customer.)

I have some 12dB Harrison Labs units with 10K input impedance, which is pretty low for Eros. One person, somewhere on the Web, has measured a Rothwell - I think it was a 10dB unit - at 100K which is good for Eros, but it's output impedance would be around 30K, which means it would likely change the attenuation of the switched controls.

Technically, you are better off rolling your own.

9

Technical topics / Re: Fixed attenuator for balance control?

« Last post by hmbscott on Yesterday at 08:30:33 PM »

It contains a very simple circuit called an LPad, that consists of two resistors. One connects signal to ground (R2) and the other connects inline in the signal path (R1).

The trick is to figure out what two resistor values to use, which is complicated by the fact that the LPad R values depend to a degree on the impedances of both the source and driven components (driven impedance typically is the most important).

It's possible to buy the RCA shell and add your own R1 & R2 resistors wired as described to make your own LPad attenuator with the attenuation you want.

Assuming the impedance your driving is 50kOhm. A pair of resistors that will preserve that 50KOhm impedance while introducing approximately 1.5dB of attenuation is R1 = 23.2kOhm and R2 = 124kOhm. I believe both values should be available as 1% tolerance resistors. If anyone would care to double check my numbers, I'd appreciate it. However, I think if you build one using close to those values, it should be about the right attenuation.

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Technical topics / Fixed attenuator for balance control?

« Last post by phatfish on Yesterday at 06:29:56 PM »

I have a bit weaker hearing in my left ear and was happy to add a balance control to my crack.
https://forum.bottlehead.com/index.php?topic=15470.0

Well, I've got the upgrade bug and I'm planning on a mainline.  I'm looking for the best way to attenuate the right channel a fixed 1 - 1.5db between my EROS2 and future mainline.  I'd prefer not to add a balance pot to the mix with the assumption that'll defeat the benefits of the stepped attenuators.  My thought was that I could add a bit of fixed attenuation via an RCA adaptor.  Something like this:
https://www.parts-express.com/RCA-Line-Level-Attenuator-1-dB-266-230?quantity=1

I haven't been able to find something like this in stock anywhere (only much larger values).  I assume it's just a resistor in there and is something I could create myself, but I have no idea what value I would need.  Any advice on the best way to accomplish this?  I'm also curious the ideal place in the audio stream for something like this: Turntable > Phono Preamp > Amp > Headphones?

Thanks for reading.