Page 1 of 2 12 LastLast
Results 1 to 35 of 53

Thread: Ampeg V4 wierd channel 1 & 2 interacting

  1. #1
    Member
    Join Date
    Jul 2019
    Location
    boro
    Posts
    66
    Thumbs Up/Down
    Received: 11/0
    Given: 36/0
    Rep Power
    0

    Question Ampeg V4 wierd channel 1 & 2 interacting

    I have on my workbench '74 Ampeg V4 non-master volume model which acts weird... This amp has two completely separate channels, each one is driven by its own 12AX7.

    It's something I can't understand. When I plug into CH#2 everything is fine, but when I plug into CH#1 sound is quiet and distorted, gets louder and better when... channel 2 volume is turned up. I have resoldered connections on the pcb of both channels but nothing changed.

    In basic words

    1. When I plug into CH#1 - both CH#1 and CH#2 volume pots are working and interacting with each other
    2. When I plug into CH#2 only CH#2 volume works (so as it should).

    Any ideas?
    Click image for larger version. 

Name:	Zdj?cie 07.12.2019, 17 45 53.jpg 
Views:	24 
Size:	5.58 MB 
ID:	56268
    Click image for larger version. 

Name:	Zdj?cie 07.12.2019, 17 41 32.jpg 
Views:	21 
Size:	6.67 MB 
ID:	56269
    Click image for larger version. 

Name:	Zdj?cie 07.12.2019, 17 40 37.jpg 
Views:	20 
Size:	5.84 MB 
ID:	56270
    Click image for larger version. 

Name:	V4.jpg 
Views:	38 
Size:	2.58 MB 
ID:	56271

    0 Not allowed! Not allowed!

  2. #2
    Supporting Member
    Join Date
    Mar 2018
    Location
    Germany
    Posts
    2,542
    Thumbs Up/Down
    Received: 1,899/1
    Given: 1,097/2
    Rep Power
    5
    Check cathode voltages (pin 3) of V1 and V2. Do these change with vol settings?

    1 Not allowed! Not allowed!
    - Own Opinions Only -

  3. #3
    Member
    Join Date
    Jul 2019
    Location
    boro
    Posts
    66
    Thumbs Up/Down
    Received: 11/0
    Given: 36/0
    Rep Power
    0
    Quote Originally Posted by Helmholtz View Post
    Check cathode voltages (pin 3) of V1 and V2. Do these change with vol settings?
    No, I have constant 1,9V on V1 and 2,1V on V2

    0 Not allowed! Not allowed!

  4. #4
    Supporting Member
    Join Date
    Mar 2018
    Location
    Germany
    Posts
    2,542
    Thumbs Up/Down
    Received: 1,899/1
    Given: 1,097/2
    Rep Power
    5
    Is the amp in original condition (no mods)?

    What is the common plate voltage at V1/V2 pins 1? (This is the point where both channels are mixed and could possibly interact.)

    What happens/changes if you swap V1 and V2?

    0 Not allowed! Not allowed!
    Last edited by Helmholtz; 12-07-2019 at 09:15 PM.
    - Own Opinions Only -

  5. #5
    Supporting Member
    Join Date
    Dec 2009
    Location
    UK
    Posts
    3,556
    Thumbs Up/Down
    Received: 290/0
    Given: 39/0
    Rep Power
    14
    I'd pull V2 and see if channel 2 volume still interacts when plugged into channel 1.

    Also, check the grounding on the input sockets. I can't see it with this amp, but i had a similar situation with an amp where there was a grounding problem at the input where there was a lot of corrosion. The shorting contact on channel 2 was high resistance and channel 1 grounded through the input circuit of channel 2 and neither socket made proper contact with the chassis.

    2 Not allowed! Not allowed!

  6. #6
    Member
    Join Date
    Jul 2019
    Location
    boro
    Posts
    66
    Thumbs Up/Down
    Received: 11/0
    Given: 36/0
    Rep Power
    0
    Channels are independent, so you can remove V1 (CH1) or V2 (CH2) tube and run the amp only on one that you like

    In this case,
    If I pull out V1 tube then Ch#1 does not work at all CH#2 works good (so, up to specs)
    If I pull out V2 both channels does not work.
    Of course I have checked/changed those tubes (including later V3 12DW7 and V4 12AU7)

    After jack-input inspections:
    The 5,6Mohm resistor on CH1 input jack gives me strange readings, but I'll unsolder it from the circuit and check again. The CH2 jack does not properly "close ground" when cable is removed but I think this only leads to hum when volume put is up without an instrument plugged.

    When those channels meet in the circuit? on the half of the 12DW7? Am I reading the schematic well?

    0 Not allowed! Not allowed!

  7. #7
    Member
    Join Date
    Jul 2019
    Location
    boro
    Posts
    66
    Thumbs Up/Down
    Received: 11/0
    Given: 36/0
    Rep Power
    0
    What's ever more weird, I removed Ch2 wiring (input->PCB) from the PCB to get only I channel connected and its still the same. Both controls of 1/2 channels affect volume. I don't see any modifications on the PCB and components, the rest look stock

    V1 plate voltage is 230VDC, V2 is a bit higher (280)

    Update: I don't have any wire connected to the R15 (I see on other amp guts that its there) But I also dont have any loose wires inside...

    0 Not allowed! Not allowed!
    Last edited by boroman; 12-08-2019 at 11:07 AM.

  8. #8
    Supporting Member
    Join Date
    Mar 2018
    Location
    Germany
    Posts
    2,542
    Thumbs Up/Down
    Received: 1,899/1
    Given: 1,097/2
    Rep Power
    5
    Channels are independent
    No, channels are not completely independent. In fact the plates (pins 1) of the respective second triodes of V1 and V2 are connected and share a common plate resistor (R13). Consequently these plate voltages must be the same. If you pull either V1 or V2, the voltage across R13 must drop as total current is halved.

    Please post all V1 and V2 plate and cathode voltages.

    2 Not allowed! Not allowed!
    - Own Opinions Only -

  9. #9
    Member
    Join Date
    Jul 2019
    Location
    boro
    Posts
    66
    Thumbs Up/Down
    Received: 11/0
    Given: 36/0
    Rep Power
    0
    Yes, you're completely right.
    I meant, they are independent to some point, they do join onto one EQ.

    V1 12ax7 228v
    V2 12ax7 228v
    V3 12dw7 319v
    V4 12au7 209v

    when V1 tube removed: V1 & V2 are 266v
    when V2 tube removed: the same (266v)
    when both V1 and V2 tubes are removed: 325v on both V1 and V2...

    V3 & V4 voltages stay about the same value with or without pulling those tubes.

    0 Not allowed! Not allowed!

  10. #10
    Supporting Member
    Join Date
    Mar 2018
    Location
    Germany
    Posts
    2,542
    Thumbs Up/Down
    Received: 1,899/1
    Given: 1,097/2
    Rep Power
    5
    At the moment I am only interested in V1/V2 voltages.

    I assume these:
    V1 12ax7 228v
    V2 12ax7 228v
    are pin 1 voltages? Please always specify pin numbers as each tube has 2 plates and 2 cathodes. Are cathode voltages (pins 3) always close to 2V?
    What are the voltages at pin 6 and pin 8 of V1/V2?

    To verify cathode resistor values, pull V1 and V2 and measure resistances between pins 3 and ground.

    Do you have a scope and signal generator?


    V1 plate voltage is 230VDC, V2 is a bit higher (280)
    If these are pin 6 values, they are off. Check pin 8 cathode voltages and measure R5,6,11,12.

    1 Not allowed! Not allowed!
    Last edited by Helmholtz; 12-08-2019 at 06:27 PM.
    - Own Opinions Only -

  11. #11
    Member
    Join Date
    Jul 2019
    Location
    boro
    Posts
    66
    Thumbs Up/Down
    Received: 11/0
    Given: 36/0
    Rep Power
    0
    Quote Originally Posted by Helmholtz View Post
    At the moment I am only interested in V1/V2 voltages.

    I assume these:
    V1 12ax7 228v
    V2 12ax7 228v
    are pin 1 voltages? Please always specify pin numbers as each tube has 2 plates and 2 cathodes. Are cathode voltages (pins 3) always close to 2V?
    I'm amazed by your knowledge, Helmholtz!
    Anyway, yes, those in the last post were from PIN1 to ground..

    V1 PIN3 = 2.0v
    V2 PIN3 = 1.8v
    V3 PIN3 = 60.5v
    V4 PIN3 = 8.5v

    What are the voltages at pin 6 and pin 8 of V1/V2?
    V1 PIN6 = 151v, PIN8 = 2.7v
    V2 PIN6 = 193v, PIN8 = 1.9v


    To verify cathode resistor values, pull V1 and V2 and measure resistances between pins 3 and ground.
    Resistance between PIN3 to ground with both tubes pulled is 3.3kOhm


    Do you have a scope and signal generator?
    If these are pin 6 values, they are off. Check pin 8 cathode voltages and measure R5,6,11,12.
    Infortunately I don't have a scope, as well as signal gen. too, but I may feed some signals from computer. The amp sounds very good on CH2 (on CH1 too when CH2 is turned up as well). No hum, noise, loud output. I have changed the bias resistor and some caps too.

    R5 = 6.8k
    R6 = 391k
    R11 = 6.7k
    R12 = 390k

    What confuses me, I don't have anything put in the C22 and some other (like R7) slots - the solder joints on the back look like factory ones (?) I think they might be from V4B ("B" version) or something that shares the same PCB...
    pic:
    Click image for larger version. 

Name:	Zdj?cie 09.12.2019, 08 59 21.jpg 
Views:	12 
Size:	5.57 MB 
ID:	56285

    0 Not allowed! Not allowed!
    Last edited by boroman; 12-09-2019 at 10:01 AM.

  12. #12
    Member
    Join Date
    Mar 2018
    Location
    Sweden
    Posts
    35
    Thumbs Up/Down
    Received: 6/0
    Given: 1/0
    Rep Power
    0
    Quote Originally Posted by boroman View Post
    What confuses me, I don't have anything put in the C22 and some other (like R7) slots - the solder joints on the back look like factory ones (?) I think they might be from V4B ("B" version) or something that shares the same PCB...
    pic:
    Click image for larger version. 

Name:	Zdj?cie 09.12.2019, 08 59 21.jpg 
Views:	12 
Size:	5.57 MB 
ID:	56285
    Notes in schematics says: "R1, R7, C1, C4 will not appear in some units"

    0 Not allowed! Not allowed!

  13. #13
    Supporting Member
    Join Date
    Mar 2018
    Location
    Germany
    Posts
    2,542
    Thumbs Up/Down
    Received: 1,899/1
    Given: 1,097/2
    Rep Power
    5
    So finally we have all relevant V1/V2 voltages. They look good except for the first triode of V1, which has 30% increased plate current. Is R2 (5.6M) ok and correctly connected?

    Update: I don't have any wire connected to the R15 (I see on other amp guts that its there) But I also dont have any loose wires inside...
    What does this mean? R15 (3.3k) is the cathode resistor of the second triode of V2 and needs to be connected between V2, PIN3 and ground.


    From your symptoms I am convinced that the problem is in the V1/V2 circuitry. I suspect something wrong (something shorting or bad connection) on the vol pots board ("64-60-071") or its outer wiring.

    0 Not allowed! Not allowed!
    Last edited by Helmholtz; 12-09-2019 at 06:30 PM.
    - Own Opinions Only -

  14. #14
    Member
    Join Date
    Jul 2019
    Location
    boro
    Posts
    66
    Thumbs Up/Down
    Received: 11/0
    Given: 36/0
    Rep Power
    0
    Quote Originally Posted by Helmholtz View Post
    So finally we have all relevant V1/V2 voltages. They look good except for the first triode of V1, which has 30% increased plate current. Is R2 (5.6M) ok and correctly connected?



    What does this mean? R15 (3.3k) is the cathode resistor of the second triode of V2 and needs to be connected between V2, PIN3 and ground.


    From your symptoms I am convinced that the problem is in the V1/V2 circuitry. I suspect something wrong (something shorting or bad connection) on the vol pots board ("64-60-071") or its outer wiring.
    There's a hole near R15 that is not connected to anything. Will try to show tomorrow. I have pics of guts fro manother V4 and there's a wire that does down somehwere from that point. I don't know it may be other revision of the circuit or something. The bad voltage on the 1st tube may be due to that I unsoldered one of the jacks from the PCB (it was unsoldered when I did the measurements).

    I will try to resolder it back again, check once again + check the potentiometer board

    0 Not allowed! Not allowed!

  15. #15
    Don't forget the joker g1's Avatar
    Join Date
    Feb 2010
    Location
    Canada, somewhere north of Fargo
    Posts
    12,009
    Thumbs Up/Down
    Received: 1,784/24
    Given: 4,584/11
    Rep Power
    23
    One very important thing you have not told us is what setting you have the 'sensitivity' switch on (above the volume pot).
    I just had to replace C2 in my spare, I have it open if we need to verify any measurements.

    1 Not allowed! Not allowed!
    Last edited by g1; 12-09-2019 at 07:59 PM.
    Just because they don't have tubes doesn't mean they don't have feelings! - glebert

  16. #16
    Don't forget the joker g1's Avatar
    Join Date
    Feb 2010
    Location
    Canada, somewhere north of Fargo
    Posts
    12,009
    Thumbs Up/Down
    Received: 1,784/24
    Given: 4,584/11
    Rep Power
    23
    Also, without touching the sensitivity switch, what resistance do you measure from V1 pin 8 to ground.

    0 Not allowed! Not allowed!
    Just because they don't have tubes doesn't mean they don't have feelings! - glebert

  17. #17
    Don't forget the joker g1's Avatar
    Join Date
    Feb 2010
    Location
    Canada, somewhere north of Fargo
    Posts
    12,009
    Thumbs Up/Down
    Received: 1,784/24
    Given: 4,584/11
    Rep Power
    23
    Cleaner version of schematic:
    Attached Files Attached Files

    2 Not allowed! Not allowed!
    Just because they don't have tubes doesn't mean they don't have feelings! - glebert

  18. #18
    Supporting Member
    Join Date
    Mar 2018
    Location
    Germany
    Posts
    2,542
    Thumbs Up/Down
    Received: 1,899/1
    Given: 1,097/2
    Rep Power
    5
    Quote Originally Posted by g1 View Post
    Also, without touching the sensitivity switch, what resistance do you measure from V1 pin 8 to ground.
    6.8K from post #11. Cathode and plate voltage are consistent, so I don't suspect cathode resistance.

    1 Not allowed! Not allowed!
    - Own Opinions Only -

  19. #19
    Don't forget the joker g1's Avatar
    Join Date
    Feb 2010
    Location
    Canada, somewhere north of Fargo
    Posts
    12,009
    Thumbs Up/Down
    Received: 1,784/24
    Given: 4,584/11
    Rep Power
    23
    Quote Originally Posted by Helmholtz View Post
    What happens/changes if you swap V1 and V2?
    Just want to make sure this has been done. Boroman, I know you said you "checked/changed" preamp tubes, I want to verify they are not being checked on a tube tester and put back in the same spots.

    0 Not allowed! Not allowed!
    Just because they don't have tubes doesn't mean they don't have feelings! - glebert

  20. #20
    Member
    Join Date
    Jul 2019
    Location
    boro
    Posts
    66
    Thumbs Up/Down
    Received: 11/0
    Given: 36/0
    Rep Power
    0
    Quote Originally Posted by g1 View Post
    Just want to make sure this has been done. Boroman, I know you said you "checked/changed" preamp tubes, I want to verify they are not being checked on a tube tester and put back in the same spots.
    They all have >90% emission, but yes, I know the actual microphonics and sound can't be measured there. I do have a lot of tubes and put my 60s NOS Mullards there which I always do when testing something that is suspicious. Not the tube for sure. I will start now to remove potentiometer panel to see what's going on there...

    1 Not allowed! Not allowed!

  21. #21
    Supporting Member
    Join Date
    Mar 2018
    Location
    Germany
    Posts
    2,542
    Thumbs Up/Down
    Received: 1,899/1
    Given: 1,097/2
    Rep Power
    5
    Quote Originally Posted by boroman View Post
    They all have >90% emission, but yes, I know the actual microphonics and sound can't be measured there. I do have a lot of tubes and put my 60s NOS Mullards there which I always do when testing something that is suspicious. Not the tube for sure. I will start now to remove potentiometer panel to see what's going on there...
    There seems to be a misunderstanding.

    My intention was to find out what changes regarding DC voltages and amp behaviour with V1 in V2 socket and vice versa.

    0 Not allowed! Not allowed!
    - Own Opinions Only -

  22. #22
    Supporting Member
    Join Date
    Mar 2018
    Location
    Germany
    Posts
    2,542
    Thumbs Up/Down
    Received: 1,899/1
    Given: 1,097/2
    Rep Power
    5
    I was wondering what could cause such asymmetrical channel vol interaction.

    I think it could work like this:

    Suppose something causes a short between the input of the channel 1 vol pot (where it connects to C3) and the wiper of the channel 2 vol pot.
    This would load the CH2 signal at the vol 2 wiper with another 100k (being the estimated circuit impedance at C3). While this would reduce the max available volume of CH2 by around 50%, it might go unnoticed.

    But for CH1 the signal at C3 would be shorted at zero setting of vol 2.

    0 Not allowed! Not allowed!
    Last edited by Helmholtz; 12-10-2019 at 05:16 PM.
    - Own Opinions Only -

  23. #23
    Member
    Join Date
    Jul 2019
    Location
    boro
    Posts
    66
    Thumbs Up/Down
    Received: 11/0
    Given: 36/0
    Rep Power
    0
    Quote Originally Posted by Helmholtz View Post
    I was wondering what could cause such asymmetrical channel vol interaction.

    I think it could work like this:

    Suppose something causes a short between the input of the channel 1 vol pot (where it connects to C3) and the wiper of the channel 2 vol pot.
    This would load the CH2 signal at the vol 2 wiper with another 100k (being the estimated circuit impedance at C3). While this would reduce the max available volume of CH2 by around 50%, it might go unnoticed.

    But for CH1 the signal at C3 would be shorted at zero setting of vol 2.
    Helmholtz - I will continue with my two new points today. I figured out why I can't measure 5,6M resistor in the input1 jack. Because the jack itself has an open connection - each of the lugs is shorting to eveything else (so, signal is shorted with ground). I desoldered it, desoldered the resistor and it measures okay, but the input jack is trash. Just ordered new one. So this is the first issue.

    Second - I noticed (having at the moment only CH2 soldered to pcb) that sound is loud but not super clear. Even at super low volume you hear distortion. I mean, you can have the level low and you can have it super high, but the "hint" of distortion is there all the time (so not volume dependent). This is actually VERY confusing. Should it be because nothing is connected to CH1 pcb points? I'm trying to understand why

    By the way, the potentiometer board, assembly, solder joints, pots and the boards' components are all okay.

    0 Not allowed! Not allowed!

  24. #24
    Supporting Member
    Join Date
    Mar 2018
    Location
    Germany
    Posts
    2,542
    Thumbs Up/Down
    Received: 1,899/1
    Given: 1,097/2
    Rep Power
    5
    By the way, the potentiometer board, assembly, solder joints, pots and the boards' components are all okay.
    Did you check and clean the "bright" switches? Not sure if the bad input jack explains everything. It would require 3 fault conditions:

    1) CH1 input signal is not connecting to V1.
    2) CH1 connects to CH2 input instead.
    3) CH2 jack is not shorting to ground.

    0 Not allowed! Not allowed!
    Last edited by Helmholtz; 12-10-2019 at 11:51 PM.
    - Own Opinions Only -

  25. #25
    Don't forget the joker g1's Avatar
    Join Date
    Feb 2010
    Location
    Canada, somewhere north of Fargo
    Posts
    12,009
    Thumbs Up/Down
    Received: 1,784/24
    Given: 4,584/11
    Rep Power
    23
    Quote Originally Posted by boroman View Post
    I noticed (having at the moment only CH2 soldered to pcb) that sound is loud but not super clear. Even at super low volume you hear distortion. I mean, you can have the level low and you can have it super high, but the "hint" of distortion is there all the time (so not volume dependent).
    Not sure if this is the problem but if you have the sensitivity switch set on 0db it is fairly easy to overload the first stage which is pre volume control. Someone who likes a real clean sound may not be able to get it without that switch on the -9db setting. A friend of mine using my amp complained about this even with single coils.
    So it will depend on the signal level you are using at the input.

    0 Not allowed! Not allowed!
    Just because they don't have tubes doesn't mean they don't have feelings! - glebert

  26. #26
    Member
    Join Date
    Jul 2019
    Location
    boro
    Posts
    66
    Thumbs Up/Down
    Received: 11/0
    Given: 36/0
    Rep Power
    0
    Yes, the switches are clean, they all work well beside one thing. the ULTRA HI switch has 3 settings: (-) then (0) then (+). It does not go to the (+) setting. Switch does, but it sounds like it's back to minus, so like - / 0 / - rather than - / 0/ +

    1) CH1 input signal is not connecting to V1.
    2) CH1 connects to CH2 input instead.
    3) CH2 jack is not shorting to ground.
    1) As I see on the amp, the positive wire from input jack CH1 goes from its place on pcb to PIN7 of V1. I checked it now and there is a flow between them, so no need for the jumper.
    2) I have only one working jack now, when I solder it to CH1 pcb and leave CH2 unsoldered I have a lot of strange buzz in the amp - like something is wrong with the transformer. That buzz you want to shut the amp down in a second.
    3) It's shorting to ground (checked now). The PCB point of CH1 also shorts to ground.

    Not sure if this is the problem but if you have the sensitivity switch set on 0db it is fairly easy to overload the first stage which is pre volume control. Someone who likes a real clean sound may not be able to get it without that switch on the -9db setting. A friend of mine using my amp complained about this even with single coils.
    So it will depend on the signal level you are using at the input.
    I know these amps, I've been playing through V4B (the other one) for about 10 years now. they are overloading on about 11o'clock, but not a hint of distortion on lower volumes. This behaves like it has that 10% overdrive on each volume setting you play. Like its an added from dist. pedal and mixed with the clean. The same proportion, not matter if you're on 1 or 10 in the vol. scale. I might record it but waiting for the new input jack first.


    and BTW, R4 measures like 2-3 Ohm (desoldered is ok at 33k). Is it other components of circuit interacting?

    0 Not allowed! Not allowed!
    Last edited by boroman; 12-11-2019 at 09:45 AM.

  27. #27
    Member
    Join Date
    Mar 2018
    Location
    Sweden
    Posts
    35
    Thumbs Up/Down
    Received: 6/0
    Given: 1/0
    Rep Power
    0
    Quote Originally Posted by boroman View Post
    1) As I see on the amp, the positive wire from input jack CH1 goes from its place on pcb to PIN7 of V1. I checked it now and there is a flow between them, so no need for the jumper.
    2) I have only one working jack now, when I solder it to CH1 pcb and leave CH2 unsoldered I have a lot of strange buzz in the amp - like something is wrong with the transformer. That buzz you want to shut the amp down in a second.
    3) It's shorting to ground (checked now). The PCB point of CH1 also shorts to ground.
    Looking at the schematics and your picture of the input jacks I'd presume you've lost R8 5.6M resistor from the ch 2 input circuit since it's located on the input jack.

    0 Not allowed! Not allowed!

  28. #28
    Supporting Member
    Join Date
    Mar 2018
    Location
    Germany
    Posts
    2,542
    Thumbs Up/Down
    Received: 1,899/1
    Given: 1,097/2
    Rep Power
    5
    R4 measures like 2-3 Ohm (desoldered is ok at 33k). Is it other components of circuit interacting?
    Yes, it's supposed to be shorted by the sensitivity switch at max setting.

    1 Not allowed! Not allowed!
    - Own Opinions Only -

  29. #29
    Supporting Member
    Join Date
    Mar 2018
    Location
    Germany
    Posts
    2,542
    Thumbs Up/Down
    Received: 1,899/1
    Given: 1,097/2
    Rep Power
    5
    Yes, the switches are clean, they all work well beside one thing. the ULTRA HI switch has 3 settings: (-) then (0) then (+). It does not go to the (+) setting. Switch does, but it sounds like it's back to minus, so like - / 0 / - rather than - / 0/ +
    .

    That makes the Ultra Hi switch suspicious. The unwanted coupling between the channels I indicated in post #22 might actually be happening inside this defective switch.

    If the new input jack doesn't solve your problem, I would inspect/disassembly the Ultra Hi switch.

    1 Not allowed! Not allowed!
    - Own Opinions Only -

  30. #30
    Member
    Join Date
    Jul 2019
    Location
    boro
    Posts
    66
    Thumbs Up/Down
    Received: 11/0
    Given: 36/0
    Rep Power
    0
    Quote Originally Posted by doombass View Post
    Looking at the schematics and your picture of the input jacks I'd presume you've lost R8 5.6M resistor from the ch 2 input circuit since it's located on the input jack.
    It's there. And measures okay. Today I'm going to solder new jack for the V1 and we'll see again what's going on. If it does not help, I'm lost with ideas...

    0 Not allowed! Not allowed!

  31. #31
    Don't forget the joker g1's Avatar
    Join Date
    Feb 2010
    Location
    Canada, somewhere north of Fargo
    Posts
    12,009
    Thumbs Up/Down
    Received: 1,784/24
    Given: 4,584/11
    Rep Power
    23
    Quote Originally Posted by boroman View Post
    I know these amps, I've been playing through V4B (the other one) for about 10 years now. they are overloading on about 11o'clock, but not a hint of distortion on lower volumes.
    The V4B does not have the sensitivity switch so it has less gain in the first stage. If you have the sensitivity on the V4 set to -9db then you can compare the two models as far as the volume settings.

    0 Not allowed! Not allowed!
    Just because they don't have tubes doesn't mean they don't have feelings! - glebert

  32. #32
    Member
    Join Date
    Jul 2019
    Location
    boro
    Posts
    66
    Thumbs Up/Down
    Received: 11/0
    Given: 36/0
    Rep Power
    0
    I give up..



    I have changed two jacks as both of them were not shorting to ground when the instrument jack was released. I also changed one of the resistors which measured a little higher (7.5Mohm vs 5,6mohm). Having a bit of time, I also replaced diodes and added bias pot...

    And I'm in the beginning. The same behaviour like in the first post. I don't get it. I have tried to measure all the caps and resistors near V1/V2 and all looks/measures close to its specs. No bad traces, no overlapping solder joints. I have got some photos of previous work on other V4's and it PCB/wiring looks the same. I have no idea what to do now. Maybe it'll be "spare parts" V4 for some new projects.

    0 Not allowed! Not allowed!

  33. #33
    Member
    Join Date
    Jul 2019
    Location
    boro
    Posts
    66
    Thumbs Up/Down
    Received: 11/0
    Given: 36/0
    Rep Power
    0
    OKAY,

    One more thing which I do not underrstand. In the attachment photo there's a shot of the original jack wiring. All of the lugs are shorted with each other, so ground is shorting with signal???

    Click image for larger version. 

Name:	aaa.jpg 
Views:	11 
Size:	489.8 KB 
ID:	56327

    1 - solid wire jumper to 2 position
    2 - negative (black) from pcb + resistor leg2
    3 - positive (white) from pcb + resistor leg1
    4 - tip (=2)

    So from this picture everything is connected with everything. Resistor between 2 and 3, jumper wire between 1 and 2. So there's no way that we have separate ground here

    Confused.

    0 Not allowed! Not allowed!

  34. #34
    Supporting Member
    Join Date
    Mar 2018
    Location
    Germany
    Posts
    2,542
    Thumbs Up/Down
    Received: 1,899/1
    Given: 1,097/2
    Rep Power
    5
    All of the lugs are shorted with each other, so ground is shorting with signal???
    Yes, that's the way it's supposed to be: Everything grounded as long as no plug is inserted.

    0 Not allowed! Not allowed!
    - Own Opinions Only -

  35. #35
    Member
    Join Date
    Jul 2019
    Location
    boro
    Posts
    66
    Thumbs Up/Down
    Received: 11/0
    Given: 36/0
    Rep Power
    0
    Quote Originally Posted by Helmholtz View Post
    Yes, that's the way it's supposed to be: Everything grounded as long as no plug is inserted.
    If the plug is inserted, everything is shorted too.
    That's why I dont get it.

    All lugs are connected to each other, so there will be shorting with the jack inserted and without it too. Am I missing something?

    0 Not allowed! Not allowed!

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. Ampeg G-212 Hiss in Channel 2
    By RWood in forum Maintenance, Troubleshooting & Repair
    Replies: 27
    Last Post: 10-04-2017, 10:03 PM
  2. Ampeg SVT-5 pro channel problems
    By tonepumpamps in forum Music Electronics
    Replies: 1
    Last Post: 06-04-2016, 03:37 PM
  3. Ampeg B5R: Overdrive channel always on
    By decades in forum Maintenance, Troubleshooting & Repair
    Replies: 29
    Last Post: 03-03-2013, 06:37 AM
  4. Independent vs interacting volume - please help.
    By slidincharlie (Carlo P) in forum Guitar Tech
    Replies: 8
    Last Post: 05-25-2010, 02:34 AM
  5. This Is Wierd....
    By acorkos in forum Maintenance, Troubleshooting & Repair
    Replies: 5
    Last Post: 03-12-2008, 10:10 AM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •