Re: Tricks for 70's D-ODS Clones

[keithrick]

I have been reading the document titled "Tricks for 70's D-ODS Clones," and have a few questions and observations regarding some of the tweaks.

Changing the coupling caps after the various stages can also fine-tune the sound to your tastes. Using a 0.047uF coupling cap instead of 0.01uF after CL2 will improve the bass response of both the Clean and the OD channels. Using a 0.005uF coupling cap after OD2 seems to improve the blues tones from the amp, while the 0.01uF cap is good for a thicker rock sound. There are many possibilities for the coupling cap after OD1 as seen in different D-ODS amps and clones. The 0.01uF value used in the 70's design could be increased to 0.022uF for a fuller OD signal, although the Skyliner amps decrease the value to 0.0022uF.

I am currently using the .047uf and .005uf coupling caps after CL2 and OD2 respectively per Hybrid A. Also.....

The series resistance after the OD2 coupling cap has a very drastic effect on the overall sound of the OD section. With no resistance at all, the OD section can sound very harsh and brittle. Adding in a 150k resistance for a 0.01uF coupling cap, or a 330k resistance for a 0.005uF coupling cap seems to work really well in shaving off some of the high frequencies while leaving plenty of definition in the sound. But with the 500k trim pot in there (at least temporarily) you can determine the "sweet spot" for your own amp. Once you find the value you prefer you can hard wire in a fixed resistor (or combination of resistors) for that particular resistance.

Does this mean that the Hybrid A values we are using for the .005 coupling cap after OD2 should have a resistence closer to 330K as opposed to 150K which would apply to a .01 coupling cap?

Has anyone wired in the 500K trim pot and tuned your amp this way? Is this the best approach to tuning your OD section, Caps and trim pot?

Just curious what your thoughts were..... and "why?"... as my duaghter always asks!

BTW- Please take these questions as a tool to futher understand how our amps can be tuned to our personal preferences and not as a critique of tweaks and suggestions posted by others.

[dogears]

330k sounds like ass to me. I think this is just an idea that Steve Ahola tossed around. The bigger resistance lowers the knee and the .005 would act like a .01

I have used as high as a 180k fwiw..... HAD used that in some amps as well.

The series resistance after the OD2 coupling cap has a very drastic effect on the overall sound of the OD section. With no resistance at all, the OD section can sound very harsh and brittle. Adding in a 150k resistance for a 0.01uF coupling cap, or a 330k resistance for a 0.005uF coupling cap seems to work really well in shaving off some of the high frequencies while leaving plenty of definition in the sound. But with the 500k trim pot in there (at least temporarily) you can determine the "sweet spot" for your own amp. Once you find the value you prefer you can hard wire in a fixed resistor (or combination of resistors) for that particular resistance.

Does this mean that the Hybrid A values we are using for the .005 coupling cap after OD2 should have a resistence closer to 330K as opposed to 150K which would apply to a .01 coupling cap?

Has anyone wired in the 500K trim pot and tuned your amp this way? Is this the best approach to tuning your OD section, Caps and trim pot?

Just curious what your thoughts were..... and "why?"... as my duaghter always asks!

BTW- Please take these questions as a tool to futher understand how our amps can be tuned to our personal preferences and not as a critique of tweaks and suggestions posted by others.

[keithrick]

Now I know the author, thanks! I have visited his site many times.

I didn't try the 330K but I did try the .01/150k and I agree w/ the ass comment.

With regards to the concepts, is this the way to tune the overdrive circuit?

1. Tone stack changes. (Currently at .047, .1 and .002/390pf)
2. Eliminate any occillations with snubber caps. Lower the PF value to add presence to the circuit.
3. Tune the OD thru the coupling capictors and using series resistance to find the sweet spot.
4. Treble bleed circuit


FWIW:

I recently increased the snubbers to 470pf and on a whim changes the OD2 coupling cap to a .01 leaving the series resistance at 150K to see what the results would be. Well the OD was thicker and the hig end artifacts that are nagging me are reduced BUT.....The amp plays like molasses as well. Not responsive at alland very tight. I did not notice the decrease in the high end artifacts with the increase in the snubbers so I am going back to the 390PF. Then I will evaluate the .01/150K coupling cap resistance array. I also have a feeling I will be reverting to the .005 cap.

But my original question still remains..... Is this artical of Mr. Ahola's a viable approach to tune the amp? He seems to frown on the idea of the treble bleed circuit as a last resort. (A particular importance to me because of the slight shrillness and harshness in the OD tone.

I have the baseline to start tweaking. My amp sounds great, even the wife commented on how great it sounds. But I am still not hearing that last 10-15% improvement that needs to be made.

In the meantime I ordered a pair of Red, White and Blues and some sprague 150uf 400v caps for the PS. I am currently using a cab loaded with a Weber Cali and Chicago. I am now wondering whether this speaker combination is a proper match for this amp or I just need more filtering on the front?

Wow it's 3:30am, I should be just DREAMING about my amp at this point!

[paddy]

Hi Keithrick,
I tried wiring a 500k pot as a variable resistor after OD2 and I'm glad I did! My amp was a bit bitey in the top end so I wired in the pot with a .0047uF cap and things improved out of sight.My sweet spot ended up at around 370k.Give it a go,you have nothing to lose.
Cheers
Paddy

[dogears]

Hi Paddy,

If you needed a 370k at that spot, you must have some things upstream hurting the tone. I'd try raising the 100k over the drive pot to 130k-150k. Also try the treble bleed circuit. Make sure you have the 150k at the end of the B+ string. Shoot for the 195v to 205v bogey. Too high voltage will also cause bite.

I've been having good success for a while now using a larger bypass cap on CL2. Try 10uf like the amp in Gil's pics had. I mentioned using big bypass caps the first week the forum opened! It really fattens things and balances those highs.

I have never liked the tone of the large series over the OD level pot as much as the other methods.....

Just my 2C

Hi Keithrick,
I tried wiring a 500k pot as a variable resistor after OD2 and I'm glad I did! My amp was a bit bitey in the top end so I wired in the pot with a .0047uF cap and things improved out of sight.My sweet spot ended up at around 370k.Give it a go,you have nothing to lose.
Cheers
Paddy

[Darkbluemurder]

I have been reading the document titled "Tricks for 70's D-ODS Clones," and have a few questions and observations regarding some of the tweaks.

Changing the coupling caps after the various stages can also fine-tune the sound to your tastes. Using a 0.047uF coupling cap instead of 0.01uF after CL2 will improve the bass response of both the Clean and the OD channels. Using a 0.005uF coupling cap after OD2 seems to improve the blues tones from the amp, while the 0.01uF cap is good for a thicker rock sound. There are many possibilities for the coupling cap after OD1 as seen in different D-ODS amps and clones. The 0.01uF value used in the 70's design could be increased to 0.022uF for a fuller OD signal, although the Skyliner amps decrease the value to 0.0022uF.

I am currently using the .047uf and .005uf coupling caps after CL2 and OD2 respectively per Hybrid A. Also.....

The series resistance after the OD2 coupling cap has a very drastic effect on the overall sound of the OD section. With no resistance at all, the OD section can sound very harsh and brittle. Adding in a 150k resistance for a 0.01uF coupling cap, or a 330k resistance for a 0.005uF coupling cap seems to work really well in shaving off some of the high frequencies while leaving plenty of definition in the sound. But with the 500k trim pot in there (at least temporarily) you can determine the "sweet spot" for your own amp. Once you find the value you prefer you can hard wire in a fixed resistor (or combination of resistors) for that particular resistance.

Does this mean that the Hybrid A values we are using for the .005 coupling cap after OD2 should have a resistence closer to 330K as opposed to 150K which would apply to a .01 coupling cap?

Has anyone wired in the 500K trim pot and tuned your amp this way? Is this the best approach to tuning your OD section, Caps and trim pot?

BTW- Please take these questions as a tool to futher understand how our amps can be tuned to our personal preferences and not as a critique of tweaks and suggestions posted by others.

It is true that the 0.047 after CL 2 increases the bass but I do not think that is an improvement to the OD tone (IMHO).

I tried 100k and 150k before the Drive pot and both sound good to me.

Since I have a 250kA level pot I did not use a series resistor in front of it and used a 220k from the pot wiper to ground to simulate a 150k into a 100kA level pot. That works good for me although the modded Concert gets pretty loud at 2 (1 equals 0 with the Fender knobs).

Personally I prefer 0.02 and 0.01 overdrive coupling caps over 0.01 and 0.0047 - again a matter of taste. They thicken up the OD sound nicely.

I like Steve's article and tried many of his suggestions although I must say that the voltage tips here in the forum got me closer to my tone than anything else. But Steve's article sure helped me understanding the effects of changes in components.

[dogears]

Hi DBM,

Try putting back the .01 and .0047

Then, raise the CL1 and CL2 bypass caps to 10uf. See what you think.......

I have been reading the document titled "Tricks for 70's D-ODS Clones," and have a few questions and observations regarding some of the tweaks.

Changing the coupling caps after the various stages can also fine-tune the sound to your tastes. Using a 0.047uF coupling cap instead of 0.01uF after CL2 will improve the bass response of both the Clean and the OD channels. Using a 0.005uF coupling cap after OD2 seems to improve the blues tones from the amp, while the 0.01uF cap is good for a thicker rock sound. There are many possibilities for the coupling cap after OD1 as seen in different D-ODS amps and clones. The 0.01uF value used in the 70's design could be increased to 0.022uF for a fuller OD signal, although the Skyliner amps decrease the value to 0.0022uF.

I am currently using the .047uf and .005uf coupling caps after CL2 and OD2 respectively per Hybrid A. Also.....

The series resistance after the OD2 coupling cap has a very drastic effect on the overall sound of the OD section. With no resistance at all, the OD section can sound very harsh and brittle. Adding in a 150k resistance for a 0.01uF coupling cap, or a 330k resistance for a 0.005uF coupling cap seems to work really well in shaving off some of the high frequencies while leaving plenty of definition in the sound. But with the 500k trim pot in there (at least temporarily) you can determine the "sweet spot" for your own amp. Once you find the value you prefer you can hard wire in a fixed resistor (or combination of resistors) for that particular resistance.

Does this mean that the Hybrid A values we are using for the .005 coupling cap after OD2 should have a resistence closer to 330K as opposed to 150K which would apply to a .01 coupling cap?

Has anyone wired in the 500K trim pot and tuned your amp this way? Is this the best approach to tuning your OD section, Caps and trim pot?

BTW- Please take these questions as a tool to futher understand how our amps can be tuned to our personal preferences and not as a critique of tweaks and suggestions posted by others.

It is true that the 0.047 after CL 2 increases the bass but I do not think that is an improvement to the OD tone (IMHO).

I tried 100k and 150k before the Drive pot and both sound good to me.

Since I have a 250kA level pot I did not use a series resistor in front of it and used a 220k from the pot wiper to ground to simulate a 150k into a 100kA level pot. That works good for me although the modded Concert gets pretty loud at 2 (1 equals 0 with the Fender knobs).

Personally I prefer 0.02 and 0.01 overdrive coupling caps over 0.01 and 0.0047 - again a matter of taste. They thicken up the OD sound nicely.

I like Steve's article and tried many of his suggestions although I must say that the voltage tips here in the forum got me closer to my tone than anything else. But Steve's article sure helped me understanding the effects of changes in components.

[Darkbluemurder]

Hi DBM,

Try putting back the .01 and .0047

Then, raise the CL1 and CL2 bypass caps to 10uf. See what you think.......

Hi dogears,

I had .01 and .005 in there before. In another amp I had 10uF for the CL 1 bypass cap. I thought it made the OD sound muddy but by listening to various soundclips posted here I realize that I play at higher gain levels (Vol. at 6 - 1 o'clock, Drive at 8 - 3 to 4 o'clock) and probably at slightly lower overall volume levels than most folks here (Level between 2 and 3 - 8 to 9 o'clock on the small amp and 2 - 8 o'clock with the big amp). So I tend to reduce bass in the early stages and voice the amp for more bass in the later stages. I am sure your suggestion works great for mid to lower gain sounds and I certainly will try it next time I have the amp open.

BTW - I revisited the HRM design on my Bandmaster doing the voltages and many of your suggestions and it is now my favorite amp for home playing. I feel with the PAB and OD engaged this is the closest that I can come to Carlton's tone on "Last Nite". But it also does a very nice Allman Brothers tone. I cannot thank you enough for the help. I just need to put different speakers into the combo cab as I don't like the Weber 10s in there - I'm looking into the Jensen Neo 10s or Emi Ragin Cajuns or Ramrods.

[dogears]

Try 10uf on CL2 only. That is what I have.

You are welcome btw.....

Btw, try removing the clean master bright cap on the HRM amp.... See how the OD improves

Hi DBM,

Try putting back the .01 and .0047

Then, raise the CL1 and CL2 bypass caps to 10uf. See what you think.......

Hi dogears,

I had .01 and .005 in there before. In another amp I had 10uF for the CL 1 bypass cap. I thought it made the OD sound muddy but by listening to various soundclips posted here I realize that I play at higher gain levels (Vol. at 6 - 1 o'clock, Drive at 8 - 3 to 4 o'clock) and probably at slightly lower overall volume levels than most folks here (Level between 2 and 3 - 8 to 9 o'clock on the small amp and 2 - 8 o'clock with the big amp). So I tend to reduce bass in the early stages and voice the amp for more bass in the later stages. I am sure your suggestion works great for mid to lower gain sounds and I certainly will try it next time I have the amp open.

BTW - I revisited the HRM design on my Bandmaster doing the voltages and many of your suggestions and it is now my favorite amp for home playing. I feel with the PAB and OD engaged this is the closest that I can come to Carlton's tone on "Last Nite". But it also does a very nice Allman Brothers tone. I cannot thank you enough for the help. I just need to put different speakers into the combo cab as I don't like the Weber 10s in there - I'm looking into the Jensen Neo 10s or Emi Ragin Cajuns or Ramrods.

[Darkbluemurder]

Try 10uf on CL2 only. That is what I have.

You are welcome btw.....

Btw, try removing the clean master bright cap on the HRM amp.... See how the OD improves

dogears,

Do you mean the bright cap on the 1MA level control? I don't have one there at all.
I have one at the 1MA Clean Master but that control is out of the signal path in the OD mode - I don't see how removing the bright cap there could affect the OD sound. I'm planning to remove it anyway because it makes the clean tone too brittle and does not sound too nice with OD pedals.

[dogears]

Are you sure the clean master is out of the circuit??? Do you break its ground or just the wiper?? If you left it grounded, the bright cap is a treble bleed!

Try 10uf on CL2 only. That is what I have.

You are welcome btw.....

Btw, try removing the clean master bright cap on the HRM amp.... See how the OD improves

dogears,

Do you mean the bright cap on the 1MA level control? I don't have one there at all.
I have one at the 1MA Clean Master but that control is out of the signal path in the OD mode - I don't see how removing the bright cap there could affect the OD sound. I'm planning to remove it anyway because it makes the clean tone too brittle and does not sound too nice with OD pedals.

[Darkbluemurder]

Are you sure the clean master is out of the circuit??? Do you break its ground or just the wiper?? If you left it grounded, the bright cap is a treble bleed!

The channel switch is a manual DPDT (relay tbd). The signal from the CL 2 coupling cap goes to the switch input (middle left contact). In the clean mode the signal is routed from the bottom left contact to the clean master (with a 47pf between input and wiper) and from there back to the bottom right contact of the switch. The middle right contact goes to the Reverb section, followed by the Tremelo section and PI/output section.
In the OD mode the signal goes from the top left contact of the DPDT to the OD input and following circuitry. From the OD level control it goes back to the top right contact of the switch.

So the clean master is definitely out of the circuit when the OD mode is engaged since the signal path to it is interrupted at its input and its output. Therefore it should not matter to the OD sound whether the clean master has a 47pf or not. Please correct me if I am wrong.

[dogears]

So you are switching it much differently than the Dumble schematic.... That shows the pot before the switch and the switch breaking the wiper from the clean master and also grounding out the OD section when not in use..... Take a look and you'll see what I mean.

I've been told it is a bad idea to not ground out the OD when not in use.

Are you sure the clean master is out of the circuit??? Do you break its ground or just the wiper?? If you left it grounded, the bright cap is a treble bleed!

The channel switch is a manual DPDT (relay tbd). The signal from the CL 2 coupling cap goes to the switch input (middle left contact). In the clean mode the signal is routed from the bottom left contact to the clean master (with a 47pf between input and wiper) and from there back to the bottom right contact of the switch. The middle right contact goes to the Reverb section, followed by the Tremelo section and PI/output section.
In the OD mode the signal goes from the top left contact of the DPDT to the OD input and following circuitry. From the OD level control it goes back to the top right contact of the switch.

So the clean master is definitely out of the circuit when the OD mode is engaged since the signal path to it is interrupted at its input and its output. Therefore it should not matter to the OD sound whether the clean master has a 47pf or not. Please correct me if I am wrong.

[Darkbluemurder]

So you are switching it much differently than the Dumble schematic.... That shows the pot before the switch and the switch breaking the wiper from the clean master and also grounding out the OD section when not in use..... Take a look and you'll see what I mean.

I've been told it is a bad idea to not ground out the OD when not in use.

I see - yes I did it differently then. That means that with the 47pf on the clean master the clean master with the cap acts as variable treble bleed in the schematic wiring. Removing the cap would then just have the effect that the clean master acts as 1M resistor to ground in the OD mode.

Indeed best practice in channel switching is to mute both input and output of the OD channel. This is done to keep the noise down in the clean mode. I will correct that when I put in the relay as it's not final anyway.

[skyboltone]

I tried 100k and 150k before the Drive pot and both sound good to me.

Since I have a 250kA level pot I did not use a series resistor in front of it and used a 220k from the pot wiper to ground to simulate a 150k into a 100kA level pot. That works good for me although the modded Concert gets pretty loud at 2 (1 equals 0 with the Fender knobs).

I bought West's 250KA "Worlds Best" pots(?!?) and intend to put 168K resestor across the pot to bring it to 100K. I'm interested in how much of the audio curve remains after this mod, and may well experiment with a ten turn calibrated knob I have to see how the resistance stacks up to regular audio curve. I don't have the scheme handy but I'm not sure how you've simulated a 100K pot with what you describe. You may want to try the other approach to get a somewhat more usable drive control.

FWIW
Dan