[Paladin79]

LOL the word meter comes from the Greek word metron meaning to measure. It is hard to use a meter and not measure something.

Anyway the meters measure current and I believe the Crack puts out around 333 mw at 300 ohms with clipping at around 10v rms. Since current equals power divided by voltage the meter would show about .03 amp, safely within the range of the meter. Impedance does vary with frequency and you can probably use headphones down to about 100 ohms with this amp so I figured a .5 amp current range would be a good place to start. I can adjust the meters down to a .1 amp range if need be. YMMV but this is what I considered when looking around for VU meters.

 

[CarlosUnchained]

I'm new to DIY world so I'd like to start with a kit, the Crack caught my eye.
Since is an OTL amp It does not pair well with my LCD-X.

I'm looking for advice on what parts change/add/remove to make it more powerful on the 20 ohm region.

Also I'd like to add a second pair of RCA variable output to use it as preamp.

Is something like that possible having the Crack as a base?

 

[Allanmarcus]

I'm new to DIY world so I'd like to start with a kit, the Crack caught my eye.
Since is an OTL amp It does not pair well with my LCD-X.

I'm looking for advice on what parts change/add/remove to make it more powerful on the 20 ohm region.

Also I'd like to add a second pair of RCA variable output to use it as preamp.

Is something like that possible having the Crack as a base?

It will not pair well. There is some discussion on some mods you can try on the Bottlehead forum <http://bottlehead.com/smf/index.php?board=24.0>, but from my reading, it's just not recommended for low impedance headphones.

 

[Paladin79]

I'm new to DIY world so I'd like to start with a kit, the Crack caught my eye.
Since is an OTL amp It does not pair well with my LCD-X.

I'm looking for advice on what parts change/add/remove to make it more powerful on the 20 ohm region.

Also I'd like to add a second pair of RCA variable output to use it as preamp.

Is something like that possible having the Crack as a base?

Unless someone else gives a good answer on the RCA out as preamp, I was going to experiment with that in the next few weeks and I can get back to you. I have a lot of other things I am doing first but I definitely have room for another set of RCA jacks on the back plate of the amps I am building. (I went with front and back plates as well as a standard size top plate all in copper.)

If it works and you want to use the original plate, you should be able to drill two more holes for said preamp out.

As far as the headphone impedance, I personally looked at it as a reason to buy more headphones. I modified one pair of Colorado Headphone Company cans by adding 250 ohm drivers and by turning them from closed to open.

 

[i luvmusic 2]

IMO you have two options regarding preamp out.

1. TRS to RCA adapter.

2.The headphone jack is switch so you can attach a RCA jack to the other side of that jack.

I personally like the option 1.

 

[Paladin79]

IMO you have two options regarding preamp out.

1. TRS to RCA adapter.

2.The headphone jack is switch so you can attach a RCA jack to the other side of that jack.

I personally like the option 1.

Personally, I would go with something more permanent like the second option. You would definitely have the volume controls in the circuit so the sound output would be variable. I will have to check and see how they did it on my Valhalla 2, I have only used such circuitry on existing amps and had not given it a lot of thought yet.

 

[i luvmusic 2]

Or you can connect the RCA from the POT's output or where the HP jack's connection from the pot's output any of these connections will work.I like it on the other side of the jack so if a HP jack is inserted the connections to RCA will be off(HP jack is switch type).
I've never done the option 2 but i did with the option 1.

 

[Paladin79]

I will have to think about it some, at least trying out the cable should be similar to hooking up the circuit at the same point so I will see how well I like it with amplified speakers. I also have a NAD amp in circuit with standard speakers I could hook up pretty quickly. It would be nice to get some tube sound going through that amp.

This may be a great weekend to put on season five of House of Cards and do more work on the Crack amps.

 

[Allanmarcus]

wow, I just tried the Crack as a preamp. I'm impressed. Listening through my Koss ESP950, and A/B comparing between the Crack and a Mjolnir 2 as preamps (DAC is Bimby). I'm hard pressed to tell the difference. Now I have to pull out the Taurus Mk 2 and try the set up with that amp.

If it works well, I may tap out of the headphone jack and put in a set of RCA females on the crack for preamp out like @i luvmusic 2 suggests.

I also posted on a crack preamp thread to see if the crack experts have better ideas.

Or you can connect the RCA from the POT's output or where the HP jack's connection from the pot's output any of these connections will work.I like it on the other side of the jack so if a HP jack is inserted the connections to RCA will be off(HP jack is switch type).
I've never done the option 2 but i did with the option 1.

i tried option 1 and it worked well; very well, with my ESP 950. I think it sounds as good as my Mjolnir 2 as a preamp. I also tried with my Taurus mk 2, and was impressed. I will do more listening this weekend, and if I like it, I will look into option 2. I confirmed with doc on the actual bottlehead crack forum (which I highly recommend), and he recommended coming off the jack rather than anywhere else for preamp out jacks.

 

[Paladin79]

The headphone jack is indeed the most logical place and as I said earlier, method 2 is the one I would prefer to use other than for test purposes.

I will take the output into powered Martin Logan speakers as well as through a NAD amp I refurbished that has dual volume controls (my preference).

Very good question Carlos and excellent answers Luv!

 

[CarlosUnchained]

Thanks @Paladin79 ,

I see that the preouts can be achieved somehow, but not the issue for low impedance cans. Since I'm not willing (for now) to buy another pair of headphones, I'll skip the Crack.

I found this interesting build that fits my needs much better. I'll add preouts and try to upgrade power out. Lower price but full responsibility on getting the right parts.

https://wtfamps.wordpress.com/papa-rusa-headphone-amplifier/

What do you think of it?

If I get too scared I might save enough money for S.E.X.

 

[Allanmarcus]

Thanks @Paladin79 ,

I see that the preouts can be achieved somehow, but not the issue for low impedance cans. Since I'm not willing (for now) to buy another pair of headphones, I'll skip the Crack.

I found this interesting build that fits my needs much better. I'll add preouts and try to upgrade power out. Lower price but full responsibility on getting the right parts.

https://wtfamps.wordpress.com/papa-rusa-headphone-amplifier/

What do you think of it?

If I get too scared I might save enough money for S.E.X.

Very interesting. You also might consider a Garage 1217 amp. Many people lover their (easy to build) amps.

 

[Paladin79]

I may have time to look at it in more depth later today but are these folks basically telling you which parts to buy or selling a kit? It has been ages since I studied cathode follower amps but personally I prefer things that have been out there a long time such as the Crack, where there is a proven history and upgrades have been made. I have looked at other such kits where the sellers were solving hum issues long after kits were sold and completed and such things bother me. Bottlehead has a great support structure in place and the amps have been around a while. That is my opinion and probably not the answer you were seeking.

I also think what I saw skimming that site is that those amps would be for more seasoned builders. I would not have any issues but if you do not have a background in electronics, Bottlehead takes you step by step through soldering and safety and is an excellent first choice. You can look around on this site and see if anyone here talks of building that amp and the results they achieved.

If you can be patient, my son insists on being able to hook up some 32 ohm headphones to an amp I will build for him, I may well be building a SEX or Mainline soon if they can handle said impedance. (I have done little research on them thus far so perhaps Doc B can jump in here and enlighten me.)

Tom

 

[DavidA]

Thanks @Paladin79 ,

I see that the preouts can be achieved somehow, but not the issue for low impedance cans. Since I'm not willing (for now) to buy another pair of headphones, I'll skip the Crack.

I found this interesting build that fits my needs much better. I'll add preouts and try to upgrade power out. Lower price but full responsibility on getting the right parts.

https://wtfamps.wordpress.com/papa-rusa-headphone-amplifier/

What do you think of it?

If I get too scared I might save enough money for S.E.X.

Agree with @Allanmarcus about the Garage 1217 amps but like you said in the Lyr2 thread the looks are not great IYO.

One thing that I love about all BH amps like the Crack and SEX is the great instructions and support structure of users and the manufacture as @Paladin79 noted.

 

[CarlosUnchained]

@Paladin79 , patience is one of my virtues.

This guy (Mr. @Sodacose) doesn't sell anything, he just explains his designs and which parts you should use to build your own and a few possible upgrades. Btw, he's answering a lot of noob questions and he's willing to help me get what I need to start.

As I said previously, I'd rather start with a kit, the problem is that I can't find many options out there, and even less that fits my needs and taste. I need power for low impedance, preouts (some load would be nice but not needed) and chasis is also a important part for me.
He recommended me to go with a small speaker amp as I use the LCD-X (4 W @ 8 Ohm for speakers and 1 W @ 32 Ohm for HP) as his project: https://wtfamps.wordpress.com/la-luciernaga-part-2-the-amp/

I read that both S.E.X. and Mainline handle low impedance pretty good, but we are getting to another range of price.