Dual Eq 'soldano Slo'

Discussion in 'Building the Classics' started by Thiez, Oct 30, 2017.

  1. Thiez

    Thiez Well-Known Member

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    A question for the power supply part of the LEDS, hope someone can help me out here.
    I've added two LDR's for the dual equaliser (LDR 5 and LDR 6) and two leds for channelindication on the front panel of the amp.

    For one side i think i've got it correct now (18R resistor for the LDR's and a 220R for the channelindication). But now for the other side, if i switch the footswich, the upper 'bar' will become earth and you will get the situation in the lower schematic. So i understand that i can regulate the current with R64. But i cant seem to find the correct way how to calculate correct value of R64. And i think the signal led will need a separate resistor because of an other forward voltage then the LDR's.

    can someone help me out here?



    [​IMG]
     
  2. Thiez

    Thiez Well-Known Member

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    nobody?
     
  3. tschrama

    tschrama Well-Known Member

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    I can have a look... need a moment
     
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  4. RickyLee

    RickyLee Well-Known Member VIP Member

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    Dam sweet. You are the man!

    You are making me miss my days of working in the machine shop. If only I knew back then what I know now about amps, electronics and amp building . . . .
     
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  5. tschrama

    tschrama Well-Known Member

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    Try 18 Ohm for R63 (!) .. should provide about 9mA to the LDR1,4 and 5
     
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  6. Thiez

    Thiez Well-Known Member

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    Build is going slow but i had some time again to build on it. Installed the 18R resistor and installed a 33R on R64, the LDR's are working, Channel switching leds are working but the green led of the clean is very weak.

    I measure 3,18V on the plus side of the LDR 1, LDR4,...etc. Forward voltage of the green led is 1,77v. So 3,18v-1,77v=1,41v. 1,41*0,02A=70R (68R) resistor in line with the led to get 20mA. But like i said the LED is verry weak. The red led of the lead channel is working fine.
    Am i missing something?
     
    Last edited: Apr 29, 2018
  7. Thiez

    Thiez Well-Known Member

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    Been awhile... was busy building a 5e3 for a friend of mine and also building myself an sg guitar at the moment. So have to split my free time haha.

    But slowly the amount of loose wires decreases.

    [​IMG]
     
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  8. Geeze

    Geeze Well-Known Member

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    Looking great - from the viewpoint of a non amp builder!

    Russ
     
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  9. DeathAdder

    DeathAdder Active Member

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    Looking Great. I've been away for a while. What's the daughter board up on top?
     
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  10. Thiez

    Thiez Well-Known Member

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    I've used the standard SLOclone boards, the board on top is the separate EQ for the clean channel. Put it above the standaard EQ thats on the main board.
     
  11. royslead

    royslead Well-Known Member

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    I am not an amp builder by any measure of the words; but this build has really piqued my interest (the Soldano SLO, in general has always been interesting to me, though I have never played through one).
     
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  12. Thiez

    Thiez Well-Known Member

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    Fired my amp up today. There is sound but it kinda dissapoints me.. sounds quiet muddy in the low end, is that typical for SLO, or is there something wrong with my build?

    It also has quiet a bit of hum, without anything connected, with scope it seems to be introduced allready at the gain knobs. Can it be the led lights right underneed the gainpots that are introducing this? On the scope it isnt a constant hum, the line of scope is really 'crackled'.
     
  13. jensvonbustenskjol

    jensvonbustenskjol Active Member

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    Hi

    Regarding the hum: your heater layout looks really clean. I did some googleing and that specific layout had been discussed a bit.
    Looks like the overall recommendation is twisted pairs. The none twisted solution has high requirements for distance between parallel lines and crossing wires.

    Just a comment. I don't know.

    I had the same problem in my built. I verified it by hooking up a DC-supply to the heaters. Used a simple wallmart adapter for the test. Built a simple dc circuit later. Yes yes I know the love for ac in this forum, but dc is quite, and I'm a amateur ;)
     
  14. tschrama

    tschrama Well-Known Member

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    more likely induced by the current spikes through the diodes, charging the caps. Most likely induce due to the positive and negative wires being seperated in space, creating a inductance loop.

    If you keep ! all ! high AC current wires close to each other, you will have a super quite amp. Tiewraps are great for this. E. g. look at some Roccaforte builds.

    Filament hum is low freq, no sharp spikes on the scoop. No candidate here.

    The small DC current through the LEDs cannt induce interference.
     
  15. Thiez

    Thiez Well-Known Member

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    I dont think its heater hum, still there when pulling v4.
     
  16. Thiez

    Thiez Well-Known Member

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    Found the biggest part of the hum. Didn't ground the footswitch schematic separately. Soldano grounds this via the jack to the chassis, but i got isolated jacks.

    Now only a little heater hum left, gonna try to make it a bit quieter, but we're almost there.

    Also gonna lower the coupling cap of the drive channel to lose some muddy low end. gonna try a 4n7 first, maybe later 2n2 if it is still to much.
     
  17. FourT6and2

    FourT6and2 Active Member

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    If the chassis is powder coated, make sure you remove the powder coating on the appropriate pots/jacks that need it, and isolate the appropriate jacks/pots that require it. Make sure your chassis ground connections actually touch bare metal. The paint needs to be scraped/sanded away.

    You might also want to elevate the heaters. I did both of these things in my build and it's super quite.
     
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  18. Thiez

    Thiez Well-Known Member

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    All jacks are isolated. Are there any other jacks beside the footswitch jack that are chassis grounded on an SLO?

    I've used elevated heaters. But i am gonne twist my wires instead of parallel wiring (currently in my build).
     
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