Bottlehead Kits > Eros Tape

Finally assembled, but not sounding great

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vakman:
Hi All,

I've measured the voltages and they all seem in line with normal expectations

Left
1A = 228
0B = 93.3
bA = 0
0A = 173.2
Breg = 95
Kreg = 1.469

Right
1A = 224.5
0B = 96.8
bA = 0
0A = 166.7
Breg = 97.9
Kreg = 1.696

Also sharing a close up view of the circuit board for review

vakman:
Here is the photo. Finding it hard to post the photo. Keeps timing out

vakman:
Some additional images of the Technics, with the new tiny board and mechanism to allow the new pre-amp to be connected to the heads with the original wiring.

vakman:

--- Quote from: Doc B. on November 04, 2019, 04:17:23 AM ---Typically if this is a dramatic difference it could be due to an error in the wiring of the eq components, or possibly something in the switching setup could be causing a problem. Does the switch completely switch out the internal preamp when switching to the Eros? If the head is being loaded by both preamps at the same time that could cause a problem. If the difference is subtle it can be something as simple as cable capacitance from the deck to the Eros input, or from the Eros output to the equipment downstream of it impacting the sound. I have been to more than one trade show where we needed to change the cables from deck to Eros or Eros to preamp because of a cable mismatch.

Are the voltages all correct in the Eros? Have you run a tone tape to see what the frequency response of the deck is like when using the Eros?

--- End quote ---

Yes, switching is completely independent and not coupled together. eg. Internal is completely separate from External, as can be shown in the photos and connected to the main Technics board using an identical plug

Not sure how I can measure the cable capacitance from the deck to the Eros input

Doc B.:
It's not super clear from the images but I am guessing that you pull the gray repro head cable plug from where it is plugged in to the internal preamp as shown in the photos, and re-plug it into the little header on the RCA jack board, which feeds the RCA jacks closest to the header to create a direct head output. Is that correct?

That looks like it should work. I would suggest running a tone tape and determining what the frequency response is like. You can use a Y adapter at the output of the Eros and feed the signal from the extra output of the y adapter back to the line input of the deck. That way you can monitor the line in signal on the Technics meters. This would help determine of the issue is between the head and the Eros or the Eros and the rest of the system.

Do you know the input impedance of the preamp that the Eros output is connected to? It is best if it is above 15K ohms, and short cables, like 1M or less are best. Interconnect cable capacitance is usually spec'd by the manufacturer or if you have something DIY you can usually look up the spec of the cable used. It is spec'd by the foot, ideally something low like under 20pF/ft. You want the lowest capacitance possible from head to Eros, and low capacitance from Eros to preamp as well. If you DIY cables, there are several foamed teflon coax cables that are around 17pF/ft that work well.

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