HiFi Haven Group Project - Building The "World's Best Tube Phono Preamp"

[Salectric]

The value is 80 ohms. That particular resistor (unlike the other two) is not a critical value. It functions as a stopper resistor for the eq compensation.

I checked my notes about the LEDs. The ones I used are HLMP-6000 and I bought them from Allied Electronics. They are red LEDs and each one drops between 1.5 and 1.7 volts depending on current. The red color is important because other colors will have different voltage drops.

 

[jmathers]

Couldn't find the LEDs at Allied but Mouser had some. Would you recommend getting extras since I suspect they vary a bit?

 

[gable]

Pretty certain 80 is correct. I got mine from Texas Components.

 

[gable]

Couldn't find the LEDs at Allied but Mouser had some. Would you recommend getting extras since I suspect they vary a bit?

In similar situations I've usually ordered a bunch, then measured them for voltage drop, as that's the parameter that matters in this situation.

 

[Salectric]

In similar situations I've usually ordered a bunch, then measured them for voltage drop, as that's the parameter that matters in this situation.

That sounds like a good idea. Also, the leads of the LEDs are somewhat delicate so you should order some spares in case of a mishap. I try to use the bare minimum of heat when soldering them. No problems to date but I can see how a spare could come in handy.

 

[Wntrmute2]

Are the 5687's LEDs wired in series or parallel? I know, I have a long way to go before needing that information.

 

[paul_b]

Also be careful to buy the HLMP-6000 with leads. There are surface mount ones available that won't work well for this purpose.

 

[Salectric]

Are the 5687's LEDs wired in series or parallel? I know, I have a long way to go before needing that information.

Series. The whole idea is to get a voltage drop between the cathode and ground (bias voltage), and the 5687 needs a higher voltage drop than the D3a. When the LEDs are in series their voltage drops add.

 

[Wntrmute2]

This is what I bought for the umbilicals. Three and 5 pin to keep from plugging the heaters into the B+ and vice versa. Rated at 500V 25A from Amazon. Should be here tomorrow.

 

[Salectric]

This is what I bought for the umbilicals. Three and 5 pin to keep from plugging the heaters into the B+ and vice versa. Rated at 500V 25A from Amazon. Should be here tomorrow.

Nice!

 

[Wntrmute2]

Michael Percy has these values in stock of the nude foil Vishays.
75
82.5
3.01K
3.32K
21.5K

I'm thinking I should order the exact values shown in the schematic.

 

[Salectric]

The critical resistor values are the 21.5K and 3.18K. You want those to be exact 1% tolerance values. Michael has the 21.5K but he will need to special order the 3.18K. It usually takes a couple weeks. No big deal.

The 80 ohm resistor is not a critical value. Either the 75 or 82.5 ohm will do just fine.

 

[jmathers]

Any preference on the Vishay TX2352s or the pricier ultra low TCR TX2575 Z-foils?

 

[gable]

FWIW, I bought the 2352's in the specified values.

 

[Salectric]

Any preference on the Vishay TX2352s or the pricier ultra low TCR TX2575 Z-foils?

I have never compared them. Mine are 2352.

 

[gable]

The output coupling cap doesn’t have to be 2uf. If I were building it today I would probably try a 0.47uf Copper Vcap instead.

Does the value of this cap affect frequency response? I would love to be able to use a 0.47uF cap in this position.

 

[gable]

This is what I bought for the umbilicals. Three and 5 pin to keep from plugging the heaters into the B+ and vice versa. Rated at 500V 25A from Amazon. Should be here tomorrow.

Do you have a link to these? They look quite nice.

 

[paul_b]

Does the value of this cap affect frequency response? I would love to be able to use a 0.47uF cap in this position.

Yes, and it can be fairly significant depending on what you're driving with the output of the phono pre!

 

[gable]

Yes, and it can be fairly significant depending on what you're driving with the output of the phono pre!

Well it will be going into my Slagle AVC, then on to my JE Labs Simple 45 amp. 100k input impedance, iirc.

is there a formula I can use to calculate?

 

[Wntrmute2]

Do you have a link to these? They look quite nice.

I can't seem to get to Amazon here at work today but search Amazon for WF28 connectors. A bunch should come up.