Bogner - La Grange  [traced]

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Chewbacca
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Post by Chewbacca »

Thank you Manfred for the capacitor clarification - something new to learn every day. :D
I did some testing with the gain pot.
With the 25K pot you have only max 25K +47R separating the signal from ground so you loose some gain right there.
I found that max gain can be achieved with around 65K to ground so a 50K pot or even a 100K pot would work better (and would also make more sense with the expression pedal as most of these have 100K pots).
(With this much gain even the red LED in the COT part light up :D .)
The pot also needs to be logarithmic. With a linear pot everything happens in the first quarter.
I could not find an A50K so I used an A100K with 47K across the lugs and this gives me a steady gain increase up to about 3 o'clock.
I also skipped the 47R. This is just to make sure you can't kill the signal completely with the gain pot.
This also solves the boost riddle.
With more gain up front you don't need the boost as another gain stage and it makes a lot more sense as a volume boost behind the BOR part.
Last edited by Chewbacca on 29 Jan 2017, 13:08, edited 2 times in total.

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Post by Manfred »

Thank you Chewbacca for sharing your gain pot experience, this sounds pretty good. :thumbsup

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Post by FeVeR2112 »

Chewbacca: Do you have the boost section at the beginning or at the end in your circuit?

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maoriente
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Post by maoriente »

Manfred and Chewy, thanks for your notes on the Gain and Boost pots, my experience had been exactly the same.

The gain and boost pots were acting more like switches, either nothing or full on.

I have also upped the Gain pot to 50k log and the response and available gain is much improved.

I was still struggling with the boost pot though, was going to just eliminate it, but now will give your suggestion a try.

Thanks again!

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Post by maoriente »

The re-wiring of the boost control per the manfred schematic update seems to be an improvement. Thanks again.

I just noticed I'm getting a loud squeal with the gain switch in either outer position, in the center off position sounds fine. Squeal changes tone when in 18v mode, but gain, quiet in the center off position.

Would someone mind posting the voltages you have on the the gain switch's BS170 DGS pins?

In 9v mode, gain switch in center position, I have:
D 7.63v
G 3.70v
S 1.65v

Gain switch in high gain mode (1k resistor shunted to ground)
D 5,69v
G 2.82v
S 0.59v

Gain switch in max gain mode (100R shunted to ground)
D 4.74v
G 2.27v
S 0.08v

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Manfred
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Post by Manfred »

The bias point will dramaticly shiftet due to the gain switch postion.
Perhaps it may be necessary to have decouple capacitor of e.g 22 Microfarads for both gain resistors.
GainMod.JPG

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Chewbacca
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Post by Chewbacca »

FeVeR2112 wrote:Chewbacca: Do you have the boost section at the beginning or at the end in your circuit?
Yes the boost definitely needs to be at the end. With the Gain switch and the 18V switch you have more than enough gain at the front end. The Booster in front will increase gain, of course, but the thing will start squealing pretty soon as it is just too much.

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Post by Chewbacca »

maoriente wrote: I just noticed I'm getting a loud squeal with the gain switch in either outer position, in the center off position sounds fine. Squeal changes tone when in 18v mode, but gain, quiet in the center off position.
With 18V engaged and the gain and presence switches on high there is a lot of gain. I used shielded wires for everything longer than an inch. That'll tame it a bit. I also put the +/- 9V and the +18 V circuits on separate daughter boards and placed them as far as possible from the main board. The +18V circuit also needed 100 uF instead of 47 uF at the 18V end. I used an LT1054 for the 18V circuit and a ICL7660S for the -9V. The "squeal" you are hearing is probably from the 18V voltage doubler. Move it around, try a1044 or 1054 chip.

I am finished with mine now and I am pretty satisfied. Tons of gain and the booster really adds some bite, not only volume boost.
The LaGrange does not really do clean, but in the lower gain settings it reacts well to dynamic playing.
One other change I recommend is a C1K instead of the B1k for the Blend. Try it - it makes more sense.

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Post by maoriente »

Thanks again,

I have the LT1054 for the 18v, and tried a 2nd LT1054 in the 9v position. No change.

I also shielded all the wiring, again no change.

I have to think there is a component error or a wrong value somewhere in my build because it squeals like crazy with the gain switch in either "on" position, regardless of the other switches or knob control settings. Except when I have the gain pot turned down to about 1k resistance, then the "lesser" of the 2 gain switch position will quiet down. The higher gain position continues to squeal.

Maybe to much gain already feeding that section?

The pedal is really quiet without the gain switch engaged. I don't get it.

It is a weird kind of squeal, not so much a typical feedback squeal, it does interact with the guitar's volume control, maybe it is related to the power supply ICs, not sure. Seem's strange the power would be the problem as the pedal is quiet with the gain switch in the "off" position.

Here is a sound sample of the squealing:



I have not tried to separate out the power supplies yet, may do so if component values check out and manfred's decoupling cap doesn't do the trick. Or I may just ditch the gain switch on this one and try again...Who am I kidding, I won't sleep well until I get it figured out!

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Post by maoriente »

Not luck so far.

For completeness regarding the gain switch hookup:

I have one end of the 1k and 100R resistors tied to the source of BS170, the other ends are on lugs 1 and 3 of an on/off/on switch, with lug 2 tied to ground. The resistance from the source to ground is 5k1 in the center postiion, 900R with the 1k shorted to ground and 97R with the 100R shorted to ground. I also tried inserting a 22uf cap from lug 3 to lug 2 and lug 1 to lug 2 with the switch in the center position. no change, still squeals when connecting the cap to ground.

Using an audio probe, and with the tip of the input jack grounded, I found the squeal enters at the 100n side of the input's 68k resistor. The input jack side of that resister is quiet.

The squeal goes away if I remove that BS170, the 2n5088 or the OPA132. (I tried swapping all three, and tried a TL071 too)

I also tried powering with a 9v battery, however at the same time I inadvertently left the input jack ground floating and there was a similar squeal, even in the center switch position.

So it seems the loss of the input ground causes this same squeal. That must mean something, but what? A bad ground somewhere?

I'm at a loss, the pedal is fairly quiet with the gain switch in the off position. Squeals like crazy in either gain position.

And how does a squeal occur with the input signal grounded and/or with an un-grounded input jack?

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Post by Frank_NH »

I looked at the schematic and believe that the 53 ohm source resistor (in the MOSFET stage right after the Presence control) must be wrong (it's not even a standard value). You're probably getting a huge gain from that stage, which may be resulting in the squealing. Try 5.1K (or 510 ohm) and see if that sounds better.

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Post by FeVeR2112 »

For the squeal... check the 7660S and which one you are using... CPAZ or IPAZ... another builder had posted that changing this lost the "whistle" he was getting.

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Post by FeVeR2112 »

also from the same site...

"The 7660S tend to add high frequency whine when they are used as +/- voltage supply or voltage doublers. Sometimes the problem can be solved by putting them on a daughter board and placing this away from the main board or shield it with some foil. But I have found that the LT1054 works much better and rarely produces any noise. You can use the same socket, just make sure you don't connect PIN 1 (clip or bend out of the way)."

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Post by maoriente »

As always, thanks for the help guys.

I agree 53R seems like a suspect value, but surprised no one else has mentioned it...or the squeal I had actually placed a 82R and 150R in parallel to achieve the 53R.

Will try a higher value tonight. I have a gut feeling this will resolve the issue. Thank you in advance!!!

If so, I'll up the value until the squeal goes away in the 100R gain position, Then maybe add 10% or 20% more. In fact, maybe I'll temporarily use a 5k pot to see how this affects the overall gain/tone.

Also, I'm currently using LT1054s with pin 1 lifted in both positions. I have heard the 7660 whine before, this noise is more of a squeal than a whine, but if all fails tonight I will power with 2 batteries just to eliminate the LT1054s for sure.

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Post by bmxguitarsbmx »

Chewbacca wrote:...
The LaGrange does not really do clean...
Another hint to 53R possibly being wrong to the original, as it seems the original will do clean.

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Post by Frank_NH »

maoriente - let us know if upping the 53 ohm resistor works. I have a handy, dandy MOSFET gain calculator spreadsheet, and for the 5.1K drain resistor and a 510 ohm source resistor, you'll get gain (Vout/Vin) of about 9, whereas 53 ohms gives you a gain of 45! Don't use 5.1K as that just gives you unity gain. I'm not sure why they have two identical gain stages in series - maybe that's part of the secret mojo. :D But with the second stage in there (with a 330 ohm source resistor) you get a combined gain for the two stages of about 117! You'll have to experiment to see what sounds best.

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Post by FeVeR2112 »

Would you share the worksheet or add a link to where you found it?

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Post by Frank_NH »

Here you go. Type in the resistor values for Rd, Rs, R1, R2 and the spreadsheet calculates the gain for the unbypassed and cap bypassed source resistor. There are three different MOSFET gain stage circuits to choose from using the tabs. Have fun! :D
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MOSFET Calculator 1.0.xlsx
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Post by FeVeR2112 »

Frank_NH: Thanks!

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Post by maoriente »

" I'm not sure why they have two identical gain stages in series - maybe that's part of the secret mojo."

That was going to be my next question...why identical gain stages in series?

But some progress:

(circuit was in my test rig and exposed, not boxed up or fully shielded. Boost mode was not engaged)

I replaced the 53R with a (temporary) 5k pot and with the variac switch set at 9v I was able to easily dial out the squeal in the mid gain switch position.

The high gain setting still had some squeal, it would be triggered with the gain control on full, also with some settings with the presence switch on, and also with the tone control maxed, and even with the blend control maxed.

Seems like dialing in to much high end triggered the squealing.

In 18v mode, I could not get rid of the squeal at all in the high gain setting, unless I had the gain control backed all the way down. In the mid gain position, some settings were ok, but the squeal was easily triggered when adjusting switches and controls as mentioned above.

Need to box it up to complete the shielding and do some additional sound tests, but it seems 5k1 may actually be the proper value...at least in my build :0)

Maybe unity gain followed by the 330R gain stage = mojo

I did notice, increasing the 53R value to 5k had a huge effect on the different amounts of gain available with the switch settings. Low gain was extremely low, mid gain was about right(for me), and high gain was over the top and flubby.

I'll report back once I have it boxed up and properly shielded.

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