Ampeg - Sub Blaster

himister · Post by **himister** » 14 Nov 2009, 20:09

I was thinking today about values printed on the pots and there's one more reason to believe that pot values are actually 10k
middle value of 70-103-47 confirms it. Only thing that we need is the which type they are. Simple test would be to try as they were suggested on the posted schematic, that means LOG type.
Audioguy if you plan to desolder them you could try two other pots with the value of 10k log type instead of original to confirm it.
If there would be change in the sound then we'll know more closely which type they are.
Right now I can't think any other way to find out.

And BTW if anyone needs manual here's one.
Cheers

chicago_mike · Post by **chicago_mike** » 14 Nov 2009, 20:36

I was thinking the same thing..

the other numbers are either manufactureer date codes or they also mention if its log or linear.

chicago_mike · Post by **chicago_mike** » 16 Nov 2009, 06:39

We need ampeg knobs for this baby is what we need.

and perhaps a fsb knock off logo of the ampeg A.

chicago_mike · Post by **chicago_mike** » 19 Nov 2009, 12:38

So..theres now the Aguilar Octamizer with a big muff style tone control for the clean and a filter for the octave signal..

What I wonder is this: What type of filter is useful for the lower octave sound? Low pass?

chicago_mike · Post by **chicago_mike** » 29 Nov 2009, 03:53

Well Im soldering this puppy up and should be finished tonight or tomorrow.

I'll take a gander at other octavers and see if I can fake the missing values from those.

chicago_mike · Post by **chicago_mike** » 26 Dec 2009, 08:26

I had an idea...The new flavor of the month octaver is the Aguilar. And what it has is a varible low pass filter for the octave, using it as a fancy tone control. And then for the dry signal it uses a BMP style tone control, but with flat mids so....

I drew this up from ampage for the BMP tone circuit. Now I assume this would go right before the Dry volume pot.

Now..looking at the octave section, it looks like it already has its own LPF, so Im wondering where I might put a pot to sort of make it work like a tone control.

Just before the opamp U1B?

chicago_mike · Post by **chicago_mike** » 26 Dec 2009, 08:54

Then here's another idea... from the EBS black label octaver..

Maybe this can also be hacked into the ampeg unit..

The Range control is part of the octave filter circuit...and looking at the ampeg, something like this should work. Its simple and a trick, but in the ebs unit sounds really good.

Who knows..

chicago_mike · Post by **chicago_mike** » 26 Dec 2009, 08:58

Sorry for the large pic. I just threw this together.

I figure with the range switch i would not need a pot for the lpf as the switch sorta does a similar thing and the pot would be redundant.

Im going to hack up a schematic for this idea tonight I think. I plan to make 2 versions. One with the CD4013 and another with the 74HC74 ( used in the ebs pedal ). But I wonder how different the chips really are.

chicago_mike · Post by **chicago_mike** » 26 Dec 2009, 09:55

OOPS! U1A and U1B IN the previous posts.

chicago_mike · Post by **chicago_mike** » 27 Dec 2009, 02:47

Working on maing her SMD right now...

Bernardduur · Post by **Bernardduur** » 04 Feb 2010, 20:13

I have one in right now;

Do I need to recheck the schematic? Are there any questions?

himister · Post by **himister** » 04 Feb 2010, 20:23

Anything you can do would be really nice!

Also the pot types aren't verified so if you could!
Thanks

Bernardduur · Post by **Bernardduur** » 09 Feb 2010, 23:04

Traced the unit! Found some small errors on the former schematics.

Enjoy!

Schematic

himister · Post by **himister** » 10 Feb 2010, 00:58

Awesome job Bernardd.

Thank you very much!!!

Bernardduur · Post by **Bernardduur** » 10 Feb 2010, 10:48

And a version 1.1

I found some values odd and checked em again.

Schematic v1.1

The 430n to Vb is wrong. The cap is really small compared to the 220n or 47n so it should be lower then that. If I desolder the cap it reads:

NSC
15J

and

KCM
434 (although that last 4 is too small to make out; it is more a point or something)

analogguru · Post by **analogguru** » 10 Feb 2010, 12:29

Depending on the desired characteristic of the filter the value of C6 has to be within 10n and 47n.

analogguru

george giblet · Post by **george giblet** » 13 Feb 2010, 12:05

Re trace: You should check R1. The original photos I used for my trace clearly showed 6k8 not 68k. The 6k8 value, and your fixes to that area, make sense because it's just a copy of the Boss OC-2 values with the resistors 10 times smaller and caps 10 times larger.

Re the filter caps: If I saw 15J I would expect a 15pF 5% cap, but it is definitely NOT 15pF. You could also suspect 15nF. This value isn't unreasonable at all, but it's a best guess. The filter seems way off the Boss circuit so I wouldn't like to guess but the values AnalogGuru suggest are reasonable (but cover a large range).

The best thing to do is to measure it. I suspect you don't have a capacitance meter since you would have already measured it! There two ways to whip up a quick test.

1) - Generate a 1kHz sinewave using the line out or headphone out, on your PC, crank the out.
- Take the output and feed it through a 22k resistor, then to your meter set to AC.
- Measure the voltage on your meter
- Now, with that configuration in place, connect the cap across the meter terminal. The output will drop. Read the value. Try not to change ranges on the meter.

2) If you have a Frequency range on your meter then you can wire up an NE555, go to this page and scroll down about 1/3 to the ASTABLE circuit,

http://www.kpsec.freeuk.com/555timer.htm

Wire the circuit with R1 = 2.2k and R2 = 47k, and the unknown cap to C1.

Measure the frequency at pin 3.

In both case you can calculate the capacitance (I can give you equations if you want to do it). As a check, I suggest sticking a known cap with that value into the test circuit as see if it produces the same values. In fact you can just poke a few caps into the test jig until you find the same measurement as the unknown cap without doing any calculations.

Bernardduur · Post by **Bernardduur** » 13 Feb 2010, 12:45

george giblet wrote:Re trace: You should check R1. The original photos I used for my trace clearly showed 6k8 not 68k. The 6k8 value, and your fixes to that area, make sense because it's just a copy of the Boss OC-2 values with the resistors 10 times smaller and caps 10 times larger.

Re the filter caps: If I saw 15J I would expect a 15pF 5% cap, but it is definitely NOT 15pF. You could also suspect 15nF. This value isn't unreasonable at all, but it's a best guess. The filter seems way off the Boss circuit so I wouldn't like to guess but the values AnalogGuru suggest are reasonable (but cover a large range).

The best thing to do is to measure it. I suspect you don't have a capacitance meter since you would have already measured it! There two ways to whip up a quick test.

1) - Generate a 1kHz sinewave using the line out or headphone out, on your PC, crank the out.
- Take the output and feed it through a 22k resistor, then to your meter set to AC.
- Measure the voltage on your meter
- Now, with that configuration in place, connect the cap across the meter terminal. The output will drop. Read the value. Try not to change ranges on the meter.

2) If you have a Frequency range on your meter then you can wire up an NE555, go to this page and scroll down about 1/3 to the ASTABLE circuit,

http://www.kpsec.freeuk.com/555timer.htm

Wire the circuit with R1 = 2.2k and R2 = 47k, and the unknown cap to C1.

Measure the frequency at pin 3.

In both case you can calculate the capacitance (I can give you equations if you want to do it). As a check, I suggest sticking a known cap with that value into the test circuit as see if it produces the same values. In fact you can just poke a few caps into the test jig until you find the same measurement as the unknown cap without doing any calculations.

Hey man!

The resistor is 6k8; I overlooked a band. It was R24 btw??????

The cap is 47n. Looked at it with a magnifing glass and that made it all clear. The dot I overlooked as a 4 turns out to be a 'n'.

Schematic v1.2

george giblet · Post by **george giblet** » 13 Feb 2010, 13:55

> The cap is 47n.

Cool!

Finally those unknown parts are nailed.

Not sure what is going on with the part designators. Some of the designators on your schematic don't match-up with my old schematic. I tried to get the designators to match the PCB but a few were unidentified and some were wrong.

If you look at lohstar's gut-shot pics (board is dated 2005) the 6k8 is R1, it's located centrally at the top of the board, between U5 and U6. R24 is the 100k is in the middle of the board between two caps, which are between U3 and U6.

On your schematic the 6k8 *is* R24.

Bernardduur · Post by **Bernardduur** » 13 Feb 2010, 14:02

george giblet wrote:> The cap is 47n.

Cool!

Finally those unknown parts are nailed.

Not sure what is going on with the part designators. Some of the designators on your schematic don't match-up with my old schematic. I tried to get the designators to match the PCB but a few were unidentified and some were wrong.

If you look at lohstar's gut-shot pics (board is dated 2005) the 6k8 is R1, it's located centrally at the top of the board, between U5 and U6. R24 is the 100k is in the middle of the board between two caps, which are between U3 and U6.

On your schematic the 6k8 *is* R24.

Maybe my resdef went wrong as there are 2 r24's in the schematic and no R1. I check again!

Ampeg - Sub Blaster [schematic]