Bottlehead Forum
Bottlehead Kits => Eros Phono => Topic started by: xcortes on March 10, 2012, 03:32:47 PM
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I switched the servo bias in my Eros to led bias and the 270 ohm resistor in the power supply to a triad C7x choke.
Sorry, I didn't follow good practice that dictates doing one mod at a time so I can't tell how much of the improvement to attribute to each mod. But boy did the sound improve! It took me like 10 seconds to detect a cleaner and more detailed sound.
Highly recommended. I guess I should start thinking about doing the chokes mode at the FP3. Hmmm, and how about a tube repro. Any resistors in the PS to replace with chokes? It would be a challenge mounting them!
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Interesting! I did the choke mod to my Paramounts and felt it too made a difference. I'll give it a try with the Eros.
I picked up Dan's Tube Phono demo and am excited to compare it to the Eros soon :)
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I have not done any power supply mods in the Eros, but I would never ever ever go back to the servo bias after making the mod to LED bias.
Where did you find room for the choke and where did you buy the Triad C7x choke? That choke was backordered everywhere I looked when I last tried to find it.
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Hello gents,
What tubes are you using with the led bias? I assume your not having problems getting them to bias. I am still waiting for the kit but I have a couple of Nos GEC CV4085s to sub for the ef86s. Curious to see if they would bias properly with the led bias mod.
Cheers,
Shawn
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I haven't done any mods to my Eros. So far I have been too busy listening.
I have the Eros Choke (bought from Allied Electronics). That is slated for the first mod.
Since most folks are going to tube roll, and since there are only 2 current production EF86 tubes most of us will end up with NOS tubes there. Therefore most of us can replace the servo bias circuit.
I bought a hand full of HLMP-6000 diodes and they don't look like what comes from Bottlehead. That makes me wonder about these being one for one replacements. I'll just order some from one of the big suppliers.
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What exactly is involved in replacing the servo boards? Its hard to imagine this amp sounding better but if people's experiences are good I might give it a try. Thanks
Robert Lees
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You can change the circuit by working on two places. The Os-Con can be replaced by the HLMP-6000, and the transistor "opened."
I just took a quick look at the schematic. You are not changing much. Like I said, the swap of the cap for the LED is the direct replacement. *** verify the LED orientation often!*** This should be pretty easy since the cap is at the edge of the board.
Then you can remove the 2N222 transistor. The easy way is to clip all three leads close to the board. You want to make certain that you don't short any of the leads together.
Edit: Since PJ didn't correct me below I am pretty sure the above method is going to do it. You don't want to leave any transistor lead in that cathode circuit because they act as antennae. Clip them right against the PCB.
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Where did you find room for the choke and where did you buy the Triad C7x choke? That choke was backordered everywhere I looked when I last tried to find it.
See this post for placement.
http://www.bottlehead.com/smf/index.php/topic,1695.msg12743.html#msg12743
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I have not done any power supply mods in the Eros, but I would never ever ever go back to the servo bias after making the mod to LED bias.
Where did you find room for the choke and where did you buy the Triad C7x choke? That choke was backordered everywhere I looked when I last tried to find it.
There's nothing magi about the Triad choke, at least not for the last several years. Anything of 5-15 henries, 200-350 ohms will do the job. I'm sure Hammond makes something close.
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Just did the LED bias mod. I had done the choke mod some time ago.
I too noticed an immediate increase in detail to the music.
Very easy mod to do and well worth it.
Debra
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GEC EV4085s in this Eros. Didn't measure voltages though!
I did the led change as described by Grainger. For placing the choke I followed Deb's pics although I used some standoffs too. Of course used shoulder washers and grounded the choke.
I had the choke in my stash.
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Before adding choke to Eros, make sure that output capacitors are connected outside foil to the plate of 6922.
That make caps less susceptible to hum.
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I have thought about this and have to agree with PJ, I can't see myself getting out the voltohmeter every time I try a new tube, especially when Doc says the difference is slight. OTOH installing the power choke may make a worthwhile difference.
Robert Lees
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Thanks, Grainger, for pointing to Allied Electronics for the Triad C7x choke. They have plenty in stock. It's the price vs. Hammond and all the others that makes the Triad choke attractive.
The LED bias mod is well worth taking out the DVM ... and then some! I did this mod 5 months ago now and my use of the Eros is still at about 4 times what it used to be before going to LED bias. The easiest way to describe the difference is probably in terms of money: the difference is more than $1,000.00 in retail value to me and that is being extremely conservative.
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You can change the circuit by working on two places. The Os-Con can be replaced by the HLMP-6000, and the transistor "opened."
I just took a quick look at the schematic. You are not changing much. Like I said, the swap of the cap for the LED is the direct replacement. *** verify the LED orientation often!*** This should be pretty easy since the cap is at the edge of the board.
Then you can remove the 2N222 transistor. The easy way is to clip all three leads close to the board. You want to make certain that you don't short any of the leads together.
Edit: Since PJ didn't correct me below I am pretty sure the above method is going to do it. You don't want to leave any transistor lead in that cathode circuit because they act as antennae. Clip them right against the PCB.
Grainger (or someone who knows better than I do),
When replacing the cap with the LED, is the cathode to ground (silver side) (-reg pad) or vis versa?
Thanks,
Aaron
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Aaron,
The silver band, cathode, goes to ground. Otherwise you end up with a reverse biased diode and no current will pass.
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Thank you sir! I'll have this mod along with the PS choke finished shortly.
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All right, guess I am going to have to bite and put a choke in the Eros. I put the triad choke in my Paramounts and liked the difference.
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Hello Xavier,
There are power supply dropping resistors in the Repro, but we have found with the quality of the shunt regulated power supply, the impact of using chokes in these positions is quite minimal.
As an experiment, you can remove the leads from the choke in your Eros and put the resistor back, the observe the changes.
Upgrading from the Repro involves a form factor change, hence the gigantic new Tube Phonos floating around (and maybe even a giant 300B preamp of similar ilk).
-PB
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As an experiment, you can remove the leads from the choke in your Eros and put the resistor back, the observe the changes.
I have done this twice now, I waited until I had a good grasp on the sound signature of the Eros. I used three different sources, and in the end I prefer it with the choke. The change was subtle so I don't think I can either quantify or qualify the difference, I just liked the sound better with the choke installed. I think I might have to give the led bias a try, though the amp sounds darn good as is.
Cheers,
Shawn