JHS Morning Glory V4

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drewl
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Post by drewl »

Anyone interested in pix of this while I have it apart trying to find out what's wrong?

Looks a bit different than the schems I saw here.

It uses two 833's, and two ss relays for switching.

I'm getting some weird low end noise, like farting out with the gain switch on.

looks like the gain switch enables the 2nd opamp which has four LED's for clipping, or are lit when gain is on.

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Post by modman »

drewl wrote:Anyone interested in pix?
:popcorn: :thumbsup
Please, support freestompboxes.org on Patreon for just 1 pcb per year! Or donate directly through PayPal

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Matlevo12
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Post by Matlevo12 »

drewl wrote: 20 Feb 2020, 18:32 Anyone interested in pix of this while I have it apart trying to find out what's wrong?

Looks a bit different than the schems I saw here.

It uses two 833's, and two ss relays for switching.

I'm getting some weird low end noise, like farting out with the gain switch on.

looks like the gain switch enables the 2nd opamp which has four LED's for clipping, or are lit when gain is on.
Hi
I'm trying to deal with a noisy morning glory v4 as well.
The schematic I used for reference is this one (which seem to be from a V3)
http://music.codydeschenes.com/wp-conte ... ematic.png
although there are some differences (see end of this post).

Here's what the pedal looks like on the inside (I found it online but will photograph it) : https://images-na.ssl-images-amazon.com ... SY550_.jpg

I tried out a few things:
- use a battery : no weird buzz at all... (i know)
- take all the (NUMEROUS) power filtering caps and using a stabilized power supply : a little better, but still a buzz whenever the pedal is on
- tracing the signal with an audio probe the buzz starts to appear at the output of the first opamp, so I changed it but only had RC4580 or TL072 in my parts box. It the process I might have messed up something since now the normal mode is quiet, no buzz... but gain seems to do nothing much to it, (I probably overheated some of the jfets in the process), and the higher gain mod is just a mess of gated fuzz... I ordered some LM833 and will try again.

Anyway here are the main differences I found between this one and the one on the schem :
- The D3 to D6 diodes in the feedback loop of the second opamp stage on the schem are not there, but instead there are two jfets (top left of the pcb), just two from what I can spot (edit : they are probably "double diode" types like an MMBD4148SE).
- the added ceramic capacitor (on the top left of the pcb) is a 47pf, and it's connected to the second opamp stage, not the first like on the schem
- there is, like drewl said, another dual opamp, a LM833 as well, one side (the left one) if connected to the 4 red leds in the middle and the gain switch, so here's the additional gain+clipping stage, and the other side of them opamp is connected to the 4.5V power supply (+ to the voltage divider, - and output linked together and used as the 4.5 being used in the circuit)

Anyway, I hope that's useful, today or sometimes in the future... and if someone's got a tip on how to make my morning glory alive again I'm all ears :)

See ya !

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Dr.Detroit
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Post by Dr.Detroit »

Some thoughts off the top of my head:

-The 4.5V supply LM833 may be oscillating.
-Despite using a BJT input opamp, JHS used the 1M bias resistor for the 1st audio op amp like the Bluesbreaker (and KOT) it is derived from. Originally the Bluesbreaker used a 072 fet input opamp which doesn't need as much bias current as a BJT opamp. Could reduce this to 100K. (Could also replace 0.047u input cap with 0.470u to preserve input HPF frequency, but changing 1M to 100k here only brings the HPF frequency up to ~33Hz).

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Post by Matlevo12 »

Dr.Detroit wrote: 18 Sep 2020, 19:55 Some thoughts off the top of my head:

-The 4.5V supply LM833 may be oscillating.
-Despite using a BJT input opamp, JHS used the 1M bias resistor for the 1st audio op amp like the Bluesbreaker (and KOT) it is derived from. Originally the Bluesbreaker used a 072 fet input opamp which doesn't need as much bias current as a BJT opamp. Could reduce this to 100K. (Could also replace 0.047u input cap with 0.470u to preserve input HPF frequency, but changing 1M to 100k here only brings the HPF frequency up to ~33Hz).
Thanks a lot !
I'll check as soon as I get the new LM833 to see if I didn't fry something else.

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Matlevo12
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Post by Matlevo12 »

Hi,

Here's what I traced on my unit.
I checked a few times but it was late so it might not be 100% accurate... but I'm pretty confident about it. Tell me if I should check something or it something looks weird.
The parts are numbered differently on the v4 (at least the one I have) than on the older schematic. There are a few other differences as well, I noted them somewhere in case someone's interested, but apart from some resistor values the main differences are :
- the first stage of the V4 uses pins 5/6/7 of the U1 LM833, and the stage stage uses 1/2/3 , not the other way around
- there's a 47p ceramic cap between pins 1 and 2, so between the inverting input and the output of the second stage (and fyi I checked and there still is a 47p cap, smd this time, at the same place in the first stage as well)
- there isn't any resistor before the gate of the volume control JFET, it goes directly from cap to gate

Anyway, here's my schem for the added parts between V3 and V4 :
Image
NB : The mode switch controls a non latching relay, I represented it as a DPDT switch on the schem

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Matlevo12
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Post by Matlevo12 »

Something is looking weird to me, but I checked it again...

Isn't it strange that when the normal mode is engaged the non-inverting input of the extra (not used soundwise in this mode) opamp is connected to the 4.5V ? What could it add ?

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mauman
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Post by mauman »

That half of the op amp is being used to buffer the VB supply, providing a low impedance source. For example, see viewtopic.php?p=279166#p279166

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Matlevo12
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Post by Matlevo12 »

mauman wrote: 24 Sep 2020, 17:25 That half of the op amp is being used to buffer the VB supply, providing a low impedance source. For example, see viewtopic.php?p=279166#p279166
Hi.
Thanks.
Just to make sure that we're talking about the qame thing :
I thought that the pins 1/2/3 were doing the Vb buffer. I'm talking about the other half of the opamp, pins 5/6/7, and the fact that when it's "off" (meaning not used in the circuit sound-wise) pin 5 is connected to +4.5V, whereas when it's used it's connected to the end of the previous gain stages.

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mauman
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Post by mauman »

Your schematic of the extra V4 op amp has both halves numbered with pins 1-2-3, but I assume you mean the left half that's providing the added gain stage (U2.1)? If so, my guess is that JHS is switching VB to the non-inverting input to keep it running in idle mode when it's out of the circuit, so it doesn't make noise when it's switched in. This is the recommended way to set up the idle half of an op amp on a single supply, with non-inverting input to VB and inverting input tied to the output. https://www.ti.com/lit/an/sboa204a/sboa204a.pdf

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Matlevo12
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Post by Matlevo12 »

mauman wrote: 25 Sep 2020, 03:58 Your schematic of the extra V4 op amp has both halves numbered with pins 1-2-3, but I assume you mean the left half that's providing the added gain stage (U2.1)? If so, my guess is that JHS is switching VB to the non-inverting input to keep it running in idle mode when it's out of the circuit, so it doesn't make noise when it's switched in. This is the recommended way to set up the idle half of an op amp on a single supply, with non-inverting input to VB and inverting input tied to the output. https://www.ti.com/lit/an/sboa204a/sboa204a.pdf
Oh yeah sorry, wrong numeration of the opamp pins... here's the correct version.
Image

And thanks a lot for the explanation, that's perfect.

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Post by bmxguitarsbmx »

It is strange that relay K1.1 would not only switch signal path but, also switch between bias points. During the switch transition, this op-amp would be unbiased and should hit one of the rails and make a loud pop (Necessitating pop mute circuitry).

The conection of the LEDs is quite interesting however. Essentially the outputs of both op-amps are connected together by these LED's. I would assume, depending on signal level, the current limitations of the op-amps would be exceeded and distort, which may have some interesting tonal effects. Or, the circuit is wrong.

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Post by Matlevo12 »

bmxguitarsbmx wrote: 26 Sep 2020, 17:51 ... Or, the circuit is wrong.
Haha, yes, that's a possibility, for sure.
If I manage to fix this thing I'll double check, I can post some pictures of it as well.

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Post by Matlevo12 »

bmxguitarsbmx wrote: 26 Sep 2020, 17:51 It is strange that relay K1.1 would not only switch signal path but, also switch between bias points. During the switch transition, this op-amp would be unbiased and should hit one of the rails and make a loud pop (Necessitating pop mute circuitry).

The conection of the LEDs is quite interesting however. Essentially the outputs of both op-amps are connected together by these LED's. I would assume, depending on signal level, the current limitations of the op-amps would be exceeded and distort, which may have some interesting tonal effects. Or, the circuit is wrong.
Hi. Some very helpful people in a french facebook group helped me get the circuit.
After the second opamp (IC1B in my shcem) there are no caps, meaning that 4.5 is "virtual ground" on the added part in v4. The person who helped me redrew the circuit in a different way, and I did the same on mine, if that's any clearer.
I alos corrected the part numbers so that they match the V4, and added C4, a cap that I forgot about in the last versions (but it's yet another 100n between 9V and ground).

Here it is :
Image

Since mine had a problem and I ended up changing the opamps I had a "synth fuzz" problem on the red mode (more gain) whenever the gain was high (but also related to the high cut switch, volume and tone). The person who helped me solved this problem by adding a 10n cap in the third opamp loop, if that can help someone one day.

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Post by mauman »

Thanks for this. Just a couple of thoughts: C5 is not marked, but it's usually 10n. Increase to 20n or 30n to add some bass. You have a question mark @ C14, I think V3 used 2.2 uF, but a 1 uF or higher should maintain the same low-end frequency response. Mike

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Post by bmxguitarsbmx »

Still surprised that U2.1 would float it's (+) input during relay transition. Just seems like it is going to pop like no other.

The LED's connected to it's output are also interesting. With out a dropping resistor, the current through the LED's is only limited by the current capability of the LM833. Maybe this sounds cool.

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Matlevo12
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Post by Matlevo12 »

bmxguitarsbmx wrote: 04 Dec 2020, 21:41 Still surprised that U2.1 would float it's (+) input during relay transition. Just seems like it is going to pop like no other.

The LED's connected to it's output are also interesting. With out a dropping resistor, the current through the LED's is only limited by the current capability of the LM833. Maybe this sounds cool.
I'll triple check next week, but I'm pretty sure about this one.
I checked and I'm correct about this one.

From the information i managed to gather jhs switched to another version of the v4, with a new pcb, somewhere before/around 2018. I found a pic of this pcb but it's not clear enough to find out about the differences. There are now at least 3 (dual, probably) opamps now.

If someone here has or knows someone with a recent morning glory v4 it's be really helpful!

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Post by Matlevo12 »

Well... I finally found someone whith a "newer" morning v4, he very nicely lent it to me so I can have a look, and it's really interesting.

But before sharing what I traced (if I ever manage to do it), I have a question for you well experienced and wonderful pedal electronics wizards, if you don't mind helping me, pretty please.
I'm affraid I d'ont have the knowledge to understand the inner schematic of the datasheet of an LM833...

It's like a riddle : what does an opamp do when it's not powered ?
Something like this, for exemple :
Image

If that can help, here's the schem of an LM833 :
Image

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Post by deltafred »

Matlevo12 wrote: 09 Jan 2021, 14:16 It's like a riddle : what does an opamp do when it's not powered ?
It's not a question that has kept me awake at night as it is not how you would use an opamp.

My guess is either nothing or if you crank the input sufficiently it might pass a rather distorted much attenuated signal (due to the PN junctions acting as diodes).

If you do try it don't be surprised if you toast your opamp if you input too high a voltage.

Disclaimer - I accept no liability for any damage to persons, equipment or property caused by anyone pursuing this line of investigation. :lol:
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Post by Matlevo12 »

deltafred wrote: 09 Jan 2021, 20:00
Matlevo12 wrote: 09 Jan 2021, 14:16 It's like a riddle : what does an opamp do when it's not powered ?
It's not a question that has kept me awake at night as it is not how you would use an opamp.
[...]
Disclaimer - I accept no liability for any damage to persons, equipment or property caused by anyone pursuing this line of investigation. :lol:
:)
Thanks a lot for your answer.

The truth lies elsewhere... and like all very weird theories that seem like something you might want to believe just because of they offer an sensational explanation to a question you have, it's almost always something more logical.
I probably ignored it because... that involves me having damaged something AGAIN. This whole morning glory experience feels like a curse so far, haha !
I'll be back soon with the rest of the schem, if that ever interests someone !

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