Avalon - U5 DI Preamp

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Re: Avalon - U5 DI Preamp

Postby Phil Smith » 23 Jul 2015, 21:31

Just quick snap shots of current progress..
Almost all traces on the main board, all top layer traces on tone and boost boards and my vision ( :) ) of boost pcb bottom layer (the boost board is pretty simple)
The chip on the tone board (RN1) is just resistor network MDP16-03 10?G with 8 resistors (pin 1-9, 2-10, 3-11 ... 8-16). According to its datasheet ( http://www.vishay.com/docs/31511/31511.pdf ) "G" stands for 2% tolerance and 10? is resistance - but on the photos third digit/symbol is "4" as far I can see, but in the datasheet in should be R, K, M or 0.. BTW, for example, 104 makes sense - 10 to the power of 4 = 10 kOhm. Somebody please check me on this one out.

Regards,
Phil
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Re: Avalon - U5 DI Preamp

Postby okgb » 23 Aug 2015, 20:43

Bumpdate any progress ?
I've never used one but the people who I know that own them , Like them
[ and it seems to be more than " I paid allot so it's gotta be great " ]
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Re: Avalon - U5 DI Preamp

Postby 2weiund2wanzig » 12 Sep 2015, 09:02

Are photos of the tone board bottom still needed? I could try to take one, just have to ask a friend if i am allowed to open his U5 :-) Bottom is the side pointing to the back of the U5?
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Re: Avalon - U5 DI Preamp

Postby Phil Smith » 27 Jul 2016, 06:58

Hey everyone!
Sorry for delays.. what a busy year!.. :shock:

Unfortunately, current progress is still the same, cause there's all I can draw with these pics of the guts.. :slap:

2weiund2wanzig wrote:Are photos of the tone board bottom still needed? I could try to take one, just have to ask a friend if i am allowed to open his U5 :-) Bottom is the side pointing to the back of the U5?


Yes, indeed!
I hope your friend still has one))
I'll send you a PM.
Actually there are several "unseen" sectors:
1) Obviously, a bottom (soldering) side of the tone board;
2) Nice photo of the motherboard's component side / soldering side of the front panel area (switches, LEDs, etc).

Cheers!

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Re: Avalon - U5 DI Preamp

Postby ilcaccillo » 13 Sep 2016, 04:50

I've used this DI quite a few times, I was never really impressed by it's sound.
It's just too much circuitry for the goal it wants to achive, being a DI.

It sounds definitely worse than High quality DI's that cost less like the Aguilar Tube DI, Radial with Jensen transformer or the plain and simple EMO passive DI Box.
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Re: Avalon - U5 DI Preamp

Postby Arnostuck » 12 Apr 2018, 01:08

Hi,
Here's the list of the components seen (except resistors) on the pcb ASSY 5600-9520 produced in 2005 :

Capacitors :

-C1,2,3,4 : 2200uF 63v Nichicon CE 85° (LQ/M) LS=22mm
-C6,8,9,11,13,14,15,18,29,30,31,38,39,40,43,44,45,46 : 100uF 50v BC036 T8 LS=9mm
-C7,12 : 10uF 63v BC036 T8 LS=5mm
-C50,C51 : 10uF 63v BBC036 T4 LS=5mm (under pcb: C50 between R93 and Q24 // C51 between R90 and Q24)
-C52 : yellow tentale ? MEC 68J NPO

Can someone please help me to confirm the brand/model of the grey caps C43,44,45 100uF 50v ?
IMG_1848 cap.jpg


At first sight, I'd say Vishay Cap BC036 from 2005 :
-Rated RMS ripple current at 100 Hz, 85 °C = 250mA
-Max. leakage current after 2 min at 50v = 33uA
-Max. impedance at 10 kHz and 20 °C = 0,7 ohm
-Useful life: 3000 h at +85 °C

I will perform a full recap, what would you advice as replacement : long life, low ESR, high ripple current ?
Panasonic FM ? The same Vishay but newer ?


Diodes :

-D1,2,3,4 : 1N4004
-D5,6,7,8,9,10,11,12,13,14,15,16,17,18 : 1N4148
-ZD1,3 : unreadable
-ZD2,4 : unreadable
-ZD5,6 : unreadable

OPAMPs & Tansistors :

-U1,2 : National LF412CN (code JR56RD)
-Q1 : O.N. TIP31CG + large heat sink
-Q2,3,9,13,17,21,24 : C546B
-Q4 : O.N. TIP32C + large heat sink
-Q5,6,7,8,12,16,20,25 : C556B
-Q10,14,18,22 : ST BD139
-Q11,15,19,23 : ST BD140

Special resistors :

-VR1 : trim Bourns W203 545C (Bourns part 3296)
-RN1 : Dale Resistors Network 104G MDP1603 (Dale part 0418)
-R100 : added under pcb 475R 1% 1/4w

Enjoy
Arno
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Re: Avalon - U5 DI Preamp

Postby Arnostuck » 12 Apr 2018, 17:16

Hi, small add-on about diodes and Opamp (ground is the reference point for measuring voltages) :

ZD1 and ZD3 are small size, same as 1N4148 but first branding is 1N7..., the next letters are on the dark side of the pcb.
ZD2,4,5,6 are 1N4744A and looks like Vishay diodes.

-ZD1 : 1N7.?.. (anode= gnd cathode=+6,22v)
-ZD3 : 1N7.?.. (anode= -6,30v cathode=gnd)
-ZD2 : 1N4744A 15v (anode=gnd cathode=+14,4v)
-ZD4 : 1N4744A 15v (anode=-14,88v cathode=gnd)
-ZD5 : 1N4744A 15v (anode=+17,3v cathode=+32,3v)
-ZD6 : 1N4744A 15v (anode=-32,3v cathode=-17,5v)

OPAMPs & Tansistors :

-U1 : National LF412CN (code JR56RD) alim +15v/-15v // polar. pin1=+7,5v pin7=+7,5v
-U2 : National LF412CN (code JR56RD) alim +15v/-15v // polar. pin1=-9,5v pin7=-8,8v

Enjoy

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Re: Avalon - U5 DI Preamp

Postby Alco34 » 04 May 2018, 19:50

Hello,

Beautiful topic !!!
The Avalon U5 is a best seller DI for Bass, very expansive, and there are no schematics on internet.
This topic is the only one on the subject of the inside box.

To undestand why the U5 is a good product, i decided to make reverse engineering on this unit, but I haven't any U5.
I use all the informations on this topic (very nice pictures of PCB and list of components).

I began to establish a schematic to try a DIY U5 DI and the principle is following:
The U5 uses 4 amplifier stages:
1st stage is the head amplifier with gain and HF limitation.
The passive tone shaping folows 1st stage.
2nd stage is to bufferize tone control and deliver headphone signal
3rd and 4th stages are the symetrical outputs (one for each polarity output with cross coupled feedback gain like DRV134 chip).
The input signal of 3rd and 4th stages is the headphone signal.
The microphone level is made from line output by resistor pad.

All the circuits on the right side is for power supply. The heatsinks are on power supply regulation made by discrete components.

Each amplifier stage is designed a like a power amplifier with a class A output stage, a voltage amplifier, a singleton input stage and a DC servo control by AOP (LF421) to perform DC coupling by removing any DC capacitors.

But there are 2 capacitors at the input of 1st and 2nd amplifier stage: this is not a real DC coupling amplifier (DC coupling only on symetrical drivers).

To finish the job,I need some help : anyone have the values of resistors? the values are sensitive and I can't find this from pictures because the color code is not easy for me (color vision mismatch).

Once validated by Spice simulation, I plain to post the scheme of the U5 to validate the design and help to explain the functions.

The Spice simulation will complete the PCB work, that is incomplete.

Regards

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