Bottlehead Forum
Bottlehead Kits => Eros Phono => Topic started by: Brooklynbottle on April 02, 2024, 12:06:08 PM
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Just completed my Eros 2 build and ran through the resistance and voltage checks. Everything within spec except for 1A & 1B reading 100v.
I read through the forum and noted Paul's advice to look more closely at the regulator board (near Au7) and took the following readings:
OA/B 220v
AKREG 7.09
BKREG 7.06
A/B bregs 0
I examined my wiring and solders all look to be up to snuff.
Obviously something is up w/ the BREG voltage.
Many thanks in advance for guidance.
Addendum:
Is it possible that I fried my 431's? I accidentally installed the 220 ohm instead of the 220k ohm and powered up as recommended before I spotted the error and replaced w/ the correct resistor.
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Here are the images of the board/Au7 socket in question.
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One last symptom to report. My EF 86's were warm, but not glowing (when viewed in a dark room).
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Just completed my Eros 2 build and ran through the resistance and voltage checks. Everything within spec except for 1A & 1B reading 100v.
Is this IA and IB on the regulator board over the D socket or on the PC board up front?
OA/B 220v
AKREG 7.09
BKREG 7.06
A/B bregs 0
I accidentally installed the 220 ohm instead of the 220k ohm and powered up as recommended before I spotted the error and replaced w/ the correct resistor.
I'm super confused here. The manual says to test the board above the D socket and not to proceed if those voltage checks don't pass, but you say you've completed the build so they must have passed at some point?
On the D socket PC board, OA/OB each connect to the breg pads with wire and allow the regulator to work to pull down the incoming B+ to 220V regulated. You have an appropriate set of Kreg voltages and correct OA/OB voltages, so my suspicion would be that you should redo your Breg measurements.
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Oh boy.
The reason you're confused is because I'm confused more!
I was checking
A1 and B1 at the A & B sockets! (Not on the board).
Everything checks out to spec as per the manual.
The only thing that's a bit odd is IA & IB read 259.8V (on two different meters).
Is this a cause for concern?
Thanks for the assist.
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The only thing that's a bit odd is IA & IB read 259.8V (on two different meters).
On the front board or the board above the D socket?
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The board above the d socket.
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Front board reads within spec for voltage
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My suspicion is that you just have AC powerline voltage that's slightly below nominal, but 5V of difference there isn't anything to stress over.
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Got it. I'll connect the Eros and see how it goes!
Thanks much. Will report the results.
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So close!
My left channel is maybe 20% lower in level than the right.
Here are my readings:
1a 221.1
1b 219.5
OA 166
OB 163.3
OC 95.5
OD 96.6
OKa 96.6
OKb 97.5
OKc 1.53
OKd 1.32
Breg b 221
Kreg b 7.11
Breg a 219
Kreg a 7.11
Seems everything is within spec. Both sides of the Au7 are glowing.
Any ideas?
Thanks again!!!
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PS swapped cables with R channel remaining the same.
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I would let the Eros cook overnight to see if that changes anything. If nothing changes, also try swapping the EF86s to see if the low level follows a tube.
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Tube swap early on did not affect signal variation. However I suspect suspect "settling in" might be the key. Signal improved a bit with longer play. Thanks again! Will report results.
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The proverbial rabbit hole!
Conducted the following diagnostics:
Dropped to one interconnect to a/b compare Left & Right Eros OP channels.
Hooked up my old Mojo phono pre-amp to r/o channel imbalance from the phono cartridge (was OK)
Swapped a/b position tubes
Finally installed a rudimentary dB meter app which indicated an approximate 10dB deficit in the R channel. Confirming what I'm experiencing.
Seems the Fidelity is fine right channel just quieter.
Any ideas?
Thank you.
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I would be sure that the 10,000uF caps up front and the 100uF caps on the front PC board are well soldered, as a loose joint on one of those will leave you with perfect DC voltages but a large difference in gain.
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Thank you.
I can't imagine what it must be like diagnosing the myriad difficulties created by an army of amateur assemblers of the Bottlehead line of products!
I'll fire up the iron.
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I hate our diagnostic session has hit the second page.
I re-flowed the 100uF caps and removed, swapped sides and re-soldered the 10,000uF caps. No improvement on the R side gain.
Full fidelity, just an annoying deficit in comparative volume.
Any other suspicions?
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Reading through @caderette, perhaps my 6922 is the source the channel imbalance? Switching the 86's didn't change the discrepancy.
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Ten dB is about 70% less voltage, not 20%. The gain of the two triodes in a 6922 might possibly vary by as much as 20%, but not 70%!
I see two choices - either gather more data (measure gain at several frequencies), or just try refreshing all the solder joints. Personally I'd start with those on the eq network tag strip.
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Fair enough. I'm sure there has to be fault in my soldering somewhere!
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Quick clarification. Is there a concern that solder flow from an upper terminal strip position to lower position may cause problems? I figure they occupy the same terminal, but I want to make sure excess flow isn't contributing to my channel imbalance in the EQ circuit.
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Quick clarification. Is there a concern that solder flow from an upper terminal strip position to lower position may cause problems?
No, no concerns with that.
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Well I took the C4 board off. Re-soldered the whole thing again, touched up my t strips on the R side. Checked voltage, fired it up and same diminished signal on the R.
Took the C4 board off again l, touched up the pad and wanted to share the current situation before I put everything back together for another test. Perhaps there's something I missed?
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I'd be a little suspicious of either lead free solder or a bit of a cool iron on that one.
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Reflowed C4s board. Touched up the t strips. Re-assembled, checked resistance and voltage. Everything in spec. I also checked continuity of all the wiring to the board which was also normal.
Plugged the Eros in and I'm closer. I've got a 7-10dB deficit in the R channel based on my crude sound meter app. This is an "improvement" from the 20dB difference as measured by the same phone/app.
I'm apprehensive about burning up my board at this point.
I'm planning on leaving the Eros powered up for a while in hopes I can get things evened up.
I hate to admit defeat, but I think fully correcting this imbalance may be beyond my capabilities.
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Update on an update. Soaked the Eros for 24 hours.
I used the averaging function on my sound level meter and we're at a 4dB deficit on the R channel.
I haven't re-touched the front, A/B board. Is that a potential source for imbalance?
BTW using standard Kester solder w/ the iron at max.
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Normally there is a large variation to acoustic measurements, due to room acoustics. So I have to ask, how exactly are you measuring this 4dB difference?
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Fair question. Just trying to quantify what my ears tell me when listening.
I'm just using my phone app while capturing a dB average reading at approximately 12" from the face of the speaker.
I know it's far from precise, but I was hoping the information would aid in the diagnostic process.
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Final dispatch. My Eros is functioning as intended! Channels are balanced (as confirmed by my crude app based sound metering) My vinyl has never sounded better. I can only postulate that I just needed to sit down and spend an evening using the Eros for everything to even up. Thank you for the support and urging to double check my work. Consider the case "resolved".
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What ended up being the solution?
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It must've been a combination of a maxed out iron reflowing my work and soaking/using the Eros? I wish I had a definitive "smoking gun". So it goes with amateur assembling.