Eros-2 few questions

[georgeged]

Hi.

Few days ago I bought Eros 2, downloaded manual and read it this weekend. I find out, that resistor 90R9 resistor, connected to EF86 anode is not on schematics (page 7). Instead, acc. to schematics, there should be just piece of wire. Where is mistake - in schematics or further in manual?

Another question: in Eros-1 C4S board Q1 was 2N2907, in Eros-2 - PN2907. I might have few 2N2907. Can I use them at this position?

And the last question: bending the leads of  HLMP 6000 LEDs  "up" - I guess reason is just to see band that identifies the cathode and check orientation of LED in case of any fault? Or if oriented "as they should", LED’s are lighting too bright and are visible from the open bottom of preamp?

Giorgi

[Paul Birkeland]

Yes, I put a plate stopper on the EF86.  I would recommend following the instructions in the manual.

You can use 2N2907s on the shunt regulator board if you want to, just be sure they don't touch the PC board.

The band on the LEDs should be visible so you can be 100% certain that they are installed properly.  We used to provide instructions to place them the other way, and it's far more difficult to know if they are installed properly in that orientation.  If you put them with the band facing the board and you end up needing some help with your build, it's entirely possible that we will need to have you remove and replace them so we can see the bands and check that off the list.

[georgeged]

Thank you Paul!

[georgeged]

Paul,

I found your old post regarding parts upgrade:

The coupling caps in the stock kit are 1.0uF Solens (though we may have shipped you 1.5uF's in their place).  This would be the most significant upgrade, and you could easily go much lower than 1.0uF, .47uF is a decent choice.

There's also a 0.1uf cap in the shunt regulator circuit that's potentially worth upgrading.  A 400V cap is OK here.

The 75K 1/2W and and 47K 2W resistors are also very much in the signal path, those could be upgraded, but be sure to use 1% parts or buy enough to match.

The 10.5k resistor, 0.030uF, and 0.010uF caps make up the RIAA network, you can find decent upgrades for those at Parts Connexion, but again, keep the resistors as 1% parts, caps at no more than 3% unless you can find a pair that measures closely.  For the 0.030uf cap, paralleling two 0.015uf caps tends to be easier to implement than finding a 0.030uf.

- 47K 2W: can I use 1.75W resistor? I'm thinking about Dale RN / CMF70. BTW: which type is better here - metal film or carbon film?

- 10.5K RIAA resistor: acc. to manual/parts list value is 10.7K. Which one is correct?

[Paul Joppa]

The 47K resistor carries significant DC and should be metal; film is more practical than bulk metal or non-inductive wirewound. But no carbon, it's more likely to be noisy. A 1.75-watt rating is acceptable. It can be 5%.

You did not mention the 75K, but I'll note here that the ideal value is 76.8K; we used 75K because 76.8K was not readily available in the Dale RN series. It should be metal film for the same reason as the 47K. Minimum 0.5 watt rating, 1% preferred.

The original calculation says that 10.5K is ideal. If I recall correctly, switching to 10.7K was to compensate for the change to 75K instead of 76.8K.

[georgeged]

Thanks for the comprehensive answer.

I am an idealist by nature, so I will change 75K for 76.8K and 10.7K for 10.5K...  I'm also ordering additional Panasonic ECW-F 0.01uf and 0.03uf caps (10pcs of each) to match as close to design values as possible.
Hope my kit will be shipped soon 

[Paul Joppa]

The Dale RN series has a particularly good reputation for being quiet; that's one reason we went to 75K rather than using a lower quality resistor in the "right" value. So be sure you get a high-quality metal film - it may take a little hunting!

Science is all about the exact value; engineering is all about the best compromise.  :^) 

[Thermioniclife]

Hey PJ, Truer words have never been spoken between science and engineering!

[georgeged]

Mouser has both values available in RN55 / CMF55 series