Ampeg VH140C

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Ampeg VH140C

Alex
This post was updated on .
This was a request from an unknown schematic.
Not sure about pots orientation.
I've added a bipolar voltage converter with voltage regulators to achieve the +/- 15V this circuit needs.
Hope it works!
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Re: Ampeg VH140C

Hozy31
The man's a genius
"Red velvet lines the black box"
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Re: Ampeg VH140C

TheChaplain
In reply to this post by Alex
This is killer! From what I'm seeing the part values match the schematic.

I wanted it to act more as an added amp channel more than as a distortion pedal sort of like what the Van Weelden Royal Overdrive does. I miss my VH140C like crazy but I sold it because it really only does one tone well and that doesn't cut it for me.

For what its worth, according to the service manual:
D1-2 = 1N754
D3-4 = 1N5393
The journey will answer questions that, in the beginning, you never thought to ask.
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Re: Ampeg VH140C

strassercaster
In reply to this post by Alex
very nice layout. i had one for a while . i loved it but it didnt cut through the mix. great for playing satriani and vai .i loved the clean channel too. i am friends with several of the st louis music engineers. when i was building my first tagboard chorus pedal and getting lfo tick one of them told me the original prototype had the same issue it delayed production  and the first run had to have revisions / mods done on the assembly line.

Crate actually applied for patent for the assymetrical diode clipping with zeners. at the time boss had the assymetrical patent for it via the super overdrive. ibanez sued and won some years ago . its funny i was checking one out on craigslist today .man i have a bench full of half built pedals some waiting for chips others waiting for boxing .if someone doesnt verify this soon i will . i a
was wished this amp had a tube power section for more punch. ill bet it will sound killer on my low input  jmp marshall for some extra punch in the mix.Alex your the superstar pumping them out "
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Re: Ampeg VH140C

TheChaplain
In reply to this post by Alex
built it and I'm not getting anything to come out. I measured the 7660S:

Battery- 9.41v

1- 8.98
2- 5.16
3- .3mV
4- -3.64
5- -8.6
6- 4.13
7- 5.59
8- 8.98

The journey will answer questions that, in the beginning, you never thought to ask.
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Re: Ampeg VH140C

TheChaplain
In reply to this post by Alex
Ok ok ok, first off:

VERIFIED  

The circuit does work but mine sounds a bit chunky and off.

For the diodes:
6.8vz = 1N5235BTR
3.3vz = 1N746ATR
12vz = 1N5242BTR

My initial problem was with the 1N746s. The band is actually anode so I put them in backwards.

Voltages:

Battery = 9.04V (8.89 when connected)

TC7660SCPA
1. 8.47V      8. 8.44V
2. 4.82V      7. 5.06V
3. 2.1mV     6. 3.61V
4. -3.24V     5. -7.66V

JRC4558D (right upper)
1. 3.2mV     8. 14.28V
2. 5.1mV     7. 4.7mV
3. 4.1mV     6. 6.0mV
4. -14.03V   5. 5.2mV

JRC4558D (left upper)
1. 2.9mV     8. 14.21
2. 2.9mV     7. 6.5mV
3. 1.6mV     6. 2.3mV
4. -13.98V   5. 1.7mV

JRC4558D (left lower)
1. -0.6mV    8. 14.13V
2. 1.3mV     7. 1.01V
3. 2.07V      6. 3.9mV
4. -13.95     5. 3.0mV

I've made all my off board connections on a breadboard (minus the pots) to avoid having to work with this inside a box for now.
The journey will answer questions that, in the beginning, you never thought to ask.
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Re: Ampeg VH140C

Alex
Cool but I think there is something weird with those voltages.
Regulators should give you + & - 15V.
7660S pin 3 should be 0 cause it's connected to ground.
Same thing for pin 3 & 5 of JRC4558D (left upper)
May have to look for bridges somewhere and maybe test it with a 9V power supply instead of batteries.
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Re: Ampeg VH140C

TheChaplain
Definitely some serious weirdness! After troubleshooting until I was swearing at inanimate objects I decided to got a real schematic for the amp.

This is the one I submitted (not my own work)



This is from SLM Electronics (duh) showing the entire preamp section of the amp complete with some test points.



- IC1 is split between the two channels. Why? Shouldn't it be included in the schematic?

- The SLC one has JFETs. There are diodes in the input also.

- Pots (read top to bottom or left to right)
  Gain: 100K rev. audio     CW-C-CCW
  Ultramid: 50KB               CCW-C-CW
  High: 50KL                     CW-C-CCW
  Low: 250KL                    CCW-C-CW
  Vol: 10KL                       CW-C-CCW

- What does IC7A do?

- What does IC5B do?

Sorry for the annoying questions. Im pretty passionate about getting this thing to run
 
The journey will answer questions that, in the beginning, you never thought to ask.
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Re: Ampeg VH140C

Alex
Can't read the schematic properly but it's a bit too complicated for me.
Better adding it to the debugging section.
Where did you get the other schematic?
Still that doesn't explain those voltages.
Even the -0.6mV at JRC4558D (left lower) pin 1.
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Re: Ampeg VH140C

TheChaplain
You wouldn't happen to have a schematic for that power supply would you?
The journey will answer questions that, in the beginning, you never thought to ask.
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Re: Ampeg VH140C

Hozy31
Looking at the top schematic you posted the only issue i see with Alex's build is a missing 47n cap at the input. I might give this a build come the weekend as i'm off for Xmas as i have holidays i have to take or i lose them.
"Red velvet lines the black box"
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Re: Ampeg VH140C

Alex
Well spotted! I've completely forgotten about this layout.
I've added the missing cap.
Let me know if it works!
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Re: Ampeg VH140C

Hozy31
I also count 59 cuts. Just marking out board.
"Red velvet lines the black box"
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Re: Ampeg VH140C

TheChaplain
In reply to this post by Alex
You forgot about this behemoth of a layout?!

I got frustrated with the whole thing and put it in the back of my mind (again) for way to long. I was just going to start breadboarding things based off the original schematic and work from there section by section...and try to keep those voltage control attenuator jfets in there.

Thats why I was asking about the power supply schematic. Getting +/-15v from a 9vdc input is something I've been trying to research and understand but I just can't seem to get there.
The journey will answer questions that, in the beginning, you never thought to ask.
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Re: Ampeg VH140C

Hozy31
Ok it works and sounds close, but i think its over clipping. Are the Zeners involved in clipping?, if so i'm tempted to change them out for something less brutal.
"Red velvet lines the black box"