Tweaking Hybrid A, Updated!

[keithrick]

I finally have a fully functioning amp! I hate to ask the same questions because I have read everyones posts....... but thats the the problem I now have information overload!

Here are what the values are- (Think Normster Bassman Layout)
3.3k 5uf
2.2k 1uf
2.7k 5uf
2.2k 5uf

Reverb caps are 4.7uf

.1 Bass
.01 Mid
331pf treble

No 1m resitor on input jack. If that matters.

B+1 448
B+2 444
B+3 427
B+4 308
B+5 305

V1 plates 194,201
V2 plates 204,206

What I need to tweak:

1. Bass is very prominent, (because need bass above 3 to control mids noticably)
2. Mid control is effective between 0-8, Too much low mids or not enough upper mids.
3. Treble is harsh in OD mode. OD channel needs to be smoothed out.
4. OD channel lacks bloom and 3D characteristics. Close though!

Any ideas for a systematic approach to make these adjustments. So I don't get lost in tweakville. I do not have a cap meter but I can get one if needed!

Here is what I am considering:

1. Looking into other ways to wire the mid pot by decoupling it from the bass control and adjusting the bass resistor to ground.

2. Raising the Cathode Bypass caps to 10 uf on CL1,2 per Ayan's pics. Will this increase bass?

3. Adding the resistor/cap combo to ground from OD2, Scott had mentioned in a previous thread.

4. Raising the mid cap to .047 and or the treble cap to .002 per Ayan's pics.

5. Changing the Rock Jazz switch to a Mid boost. Anybody do this? I hesitate to attemp this because my poor understanding of the switching system.

6. Increasing the B+4 & 5 voltages by reducing the 22k droping resister to 13-15K. To get the V1+2 plates closer to 200 and 220 respectively.

Any thoughts...... fire away!

[Darkbluemurder]

The voltages of V1 look good enough to me. V2 is a little low but bringing them up to 220V would probably not smooth the sound.

If you have too much low mid increase the mid cap to 0.022, 0.033 or 0.047.

If you want to turn the bass control past 3 I would not increase the bypass caps from 5F to 10uF. This mod will definitely increase bass. I guess your coupling cap after CL2 is a 0.047uF if it is Hybrid Rev A. Consider a lower value here if you want to reduce bass (I like 0.01uF). However, this will also affect the clean tone.

I don't have the Rock/Jazz switch. One of my amps has the preamp boost, the other has a midboost (820pF in parallel to the 330pF). If you go higher than 820pF I suggest incremental steps to ensure that the bass does not get muddy.

I am yet to experiment with the cap/resistor combo to ground after OD2. Sounds like a good mod. I may sacrifice the presence control for that since I am not satisfied with the way mine works as it gets way too sharp on 10 and does not do anything from 0-8. I don't need it to control the clean tone anyway.

[llemtt]

1. Looking into other ways to wire the mid pot by decoupling it from the bass control and adjusting the bass resistor to ground.

How are your controls wired? The D tone stack has it already decoupled!!

2. Raising the Cathode Bypass caps to 10 uf on CL1,2 per Ayan's pics. Will this increase bass?

Yes, changing from 1u to 10u or 25u in V1b extend low range a lot but sometimes you more feel this instead of earing "more bass".

3. Adding the resistor/cap combo to ground from OD2, Scott had mentioned in a previous thread.

With that you can remove lots of highs from the OD channel but smoothness is a different thing, you can have a smooth OD with lots of highs. IMHO this is a last resort like negative feedback in power amps is, it tries to make better sounding something that inherently doesn't sound good.

4. Raising the mid cap to .047 and or the treble cap to .002 per Ayan's pics.

Mid cap to .047 -> a little less bass, a lot less low mids, more high mids. Treble cap .002 is there for the Mid boost switch where it's series connected to a 390p cap.

5. Changing the Rock Jazz switch to a Mid boost. Anybody do this? I hesitate to attemp this because my poor understanding of the switching system.

See above.

6. Increasing the B+4 & 5 voltages by reducing the 22k droping resister to 13-15K. To get the V1+2 plates closer to 200 and 220 respectively.

Any thoughts...... fire away!

Voltages seems ok, I think is not your problem. If you can try this: run your preamp output into another "good sounding" power amp, is your OD now smooth? Bass is ok?

teo

[Bob-I]

I finally have a fully functioning amp! I hate to ask the same questions because I have read everyones posts....... but thats the the problem I now have information overload!

Here are what the values are- (Think Normster Bassman Layout)
3.3k 5uf
2.2k 1uf
2.7k 5uf
2.2k 5uf

What are the plate load resistors?

No 1m resitor on input jack. If that matters.

Yes that matters. Without that load the amp won't work. Where is the 1M load resistor if it's not on the input jack?

V1 plates 194,201
V2 plates 204,206

These voltages are good. Increasing the V2 plates voltage will make the amp more harsh IMO. I wouldn't change the voltages.

What I need to tweak:

1. Bass is very prominent, (because need bass above 3 to control mids noticably)

The don't increase the bypass caps. You might try lowering V1a from 5uF to 4.7uF or even lower.

2. Mid control is effective between 0-8, Too much low mids or not enough upper mids.

I'd try a .047uF mid cap. If that goes too far towards the upper mids then .022.

3. Treble is harsh in OD mode. OD channel needs to be smoothed out.

What are your snubbers on the V2 plate to cathode? You can raise these and smooth out the harshness in OD mode. Also, connect a .0022uF cap from the junction of the .01uF after OD2, through a 1M trim pot to ground. Basically you'll drop some of the ice pick highs to ground just before the OD level control.

4. OD channel lacks bloom and 3D characteristics. Close though!

The correct snubbers will help this.

1. Looking into other ways to wire the mid pot by decoupling it from the bass control and adjusting the bass resistor to ground.

Double check your wiring of the tone stack. It should already be de-coupled with that 10K resistor.

2. Raising the Cathode Bypass caps to 10 uf on CL1,2 per Ayan's pics. Will this increase bass?

Yes it will increase bass. If you're already bass heavy, don't do it, you'll make the amp flubby.

3. Adding the resistor/cap combo to ground from OD2, Scott had mentioned in a previous thread.

Yep, do that and use a trim pot so you can adjust it.

4. Raising the mid cap to .047 and or the treble cap to .002 per Ayan's pics.

Mid cap yes, treble cap no. That's a mid boost cap. I like a .005uF on a switch for mid boost.

5. Changing the Rock Jazz switch to a Mid boost. Anybody do this? I hesitate to attemp this because my poor understanding of the switching system.

Yes, I did this. I like it so much I'm putting it on a relay so I can foot switch it.

6. Increasing the B+4 & 5 voltages by reducing the 22k droping resister to 13-15K. To get the V1+2 plates closer to 200 and 220 respectively.

I wouldn't. That might make it harsh. Focus on the snubbers first. Increase the 390pF to 470pF or even 500pF and see what you think.

Any thoughts...... fire away!

[dogears]

Bob has good suggestions..... My .01 midcap amps sound great though. I suspect your issue is elsewhere.

What cabling did you use. I found the tone to be harsh with crap shielded cable. As you reduce the cpacitance, the tone gets sweeter and more open. IMO.

Try bypassing the reverb as a test. Maybe that is hurting the tone. Go right from the master to the PI.

Shoot me a PM with your # and we can discuss.....

[Normster]

1. Bass is very prominent, (because need bass above 3 to control mids noticably)
2. Mid control is effective between 0-8, Too much low mids or not enough upper mids.
3. Treble is harsh in OD mode. OD channel needs to be smoothed out.
4. OD channel lacks bloom and 3D characteristics. Close though!

For the first 2 items, do what Dogears (and a few others) do...record a clip, EQ to taste with multi-band equalizer, note the frequencies that need tweaking. Then go into Duncan's tone stack calculator and experiment with different values to see what effects the range you need to enhance. With my gear, the .047 mid cap with a 270pF treble cap sounds just about right. However, depending on your guitar, pick attack, style, etc., you may find you need completely different values to get YOUR sound.

If the OD is still harsh after the tonestack mods, you can raise the snubber values. If it's "fizzy" then the treble bleed circuit may work better. Hopefully Dogears will jump in here with some sage advice.

Bloom and 3D characteristics don't really display themselves well at bedroom levels. My amp doesn't really start to sweeten up until the master is at 9 o'clock. At 10 o'clock or above it really starts singing. I only bring this up because I went through a long period of disappointment with my amp because I'd only played it at bedroom levels (8 o'clock). The first time I played it at gig volumes, I was blown away.

[keithrick]

Thanks for everyones reply's. To answer a few questions:

1. OK, the bass is decoupled from the mid pot by 10K resistor. I thought that decoupling was to run the 10K from bass pot to ground.

2. Plate load resistors are Vishay dales:

3.3k / 221k 5uf
2.2k / 150K 1uf
2.7k / 182k 5uf
2.2k / 150k 5uf

3. Snubbers are the 391pf.

Question: to eliminate the Rock/Jazz switch from Normsters layout I remove the .0047cap and 100K (Jazz side) resistor feeding the volume control and route the wire from the bass cap (.1) through the common (middle) of the PAB boost switch to the bass pot, left tab. Has anyone drawn this?

4. Not set up to record clips.

5. I used MIL-C-RG174-U for shielded cable in two places

a. From the 100K resistor on the board off of OD1 side to the drive pot (right side terminal) if looking from the back.

b. From the 150K resistor on the board off of OD2 side to the level pot right side terminal if looking from the back.

I was considering removing! What do you think?

Norm, I am getting the fizziness with the pick attack. I will admit that my pick attack needs work though!

Scott, PM sent.

Edit: After speaking with Scott, I am going to add the 1 meg resistor on the input jack, I omitted, and look into isolating the reverb tube and transformer with a reisistor/cap combination. See Dogears post!

[Bob-I]

2. Plate load resistors are Vishay dales:

3.3k / 221k 5uf
2.2k / 150K 1uf
2.7k / 182k 5uf
2.2k / 150k 5uf

Looks good

3. Snubbers are the 391pf.

You might try increasing these to 470pF.

5. I used MIL-C-RG174-U for shielded cable in two places

Just try replacing with an unshielded wire, leave the shielded in place in case the tone doesn't improve.

a. From the 100K resistor on the board off of OD1 side to the drive pot (right side terminal) if looking from the back.

b. From the 150K resistor on the board off of OD2 side to the level pot right side terminal if looking from the back.

I was considering removing! What do you think?

No, that'll only make it harsher. These series resistors are critical to the Dumble tone.

[keithrick]

Update:

I replaced the shielded cable from my input jack to V1 and added the 1M resistor to ground. The result was a slight improvement in tone with no noticable increase in the noise floor!


Next I also added a 22K resistor in line with my reverb transformer to partialy isolate it from B+2. No noticeable change in tone. I am getting the 10uf and 20uf filter caps today to add.


Question: With the current .01, .1, 330pf tone stack would a .001 cap be the proper mid boost cap?

[Darkbluemurder]

Question: With the current .01, .1, 330pf tone stack would a .001 cap be the proper mid boost cap?

.001 would be the equivalent to 1000pf. That value is not far away from the 820pf I use with good results. Try it. If it makes the bass muddy, try 750pf or 820pf. With lower values the effect will be very subtle. If the boost is not enough, try 1200pf or even 1500pf. Higher values such as 2200 pf make the sound very middy.

[Bob-I]

Update:

I replaced the shielded cable from my input jack to V1 and added the 1M resistor to ground. The result was a slight improvement in tone with no noticable increase in the noise floor!

Cool. I use shielded only when I can't kill the noise any other way.

Question: With the current .01, .1, 330pf tone stack would a .001 cap be the proper mid boost cap?

That works fine, but I've gone as high as .005uF for a HUGE boost.

[keithrick]

Update:

Scott, couldn't help myself. My latest changes. These were done in the hopes of increasing upper mid range frequency's, reducing the boominess and warming/sweetening the tone. I play my Strat most of the time.

1. Added .002uf treble cap on the board and have the 330pf on the mid boost switch(formerly R/J)
2. Went to the .047 mid cap. My Strat loves this change!
3. 10uf's on CL1,2 like Ayans pics
4. Mid pot is wired like the Dumble Pics.
5. Tried to wire the presence like HAD, couldn't get it to work.
6. 1uf Spraque electrolytic on Presence pot instead of tantalum.

I am not 100% there yet, but I know I am moving in the right direction.

Further tweaks I am considering are:

1. Changing either onboard treble cap to .001uf and/or changing the ceramic on the mid switch to 390pf. With this change I am hoping to increase the upper mids when in boost mode. Mid and boost is getting a little muddy. Suggestions?

2. Change the bright cap to 120pf and/or hardwire the bright cap and use that switch to toggle mid caps.

3. Try .022 or .033 mid cap, this could be the perfect comprimise for single coil or humbuckers or wire a combination in series like the treble cap.

4. Still need to remove shielded cable and see if I truly need it.

5. I am going to slowly move away from the alpha pots. I do not like the taper. The local electronics store sells the PEC's.

Suggestion and Critiques are alway encouraged!

[dogears]

Use a 470pf in conjunction with the 1000pf

120pf is a good bright cap size. Don't hard wire it.....

.022 may be the choice for midcap......

Further tweaks I am considering are:

1. Changing either onboard treble cap to .001uf and/or changing the ceramic on the mid switch to 390pf. With this change I am hoping to increase the upper mids when in boost mode. Mid and boost is getting a little muddy. Suggestions?

2. Change the bright cap to 120pf and/or hardwire the bright cap and use that switch to toggle mid caps.

3. Try .022 or .033 mid cap, this could be the perfect comprimise for single coil or humbuckers or wire a combination in series like the treble cap.

4. Still need to remove shielded cable and see if I truly need it.

5. I am going to slowly move away from the alpha pots. I do not like the taper. The local electronics store sells the PEC's.

Suggestion and Critiques are alway encouraged!

[Bob-I]

Update:

Scott, couldn't help myself. My latest changes. These were done in the hopes of increasing upper mid range frequency's, reducing the boominess and warming/sweetening the tone. I play my Strat most of the time.

1. Added .002uf treble cap on the board and have the 330pf on the mid boost switch(formerly R/J)

I've decided to use a 3 position switch on mine. 330pF, .0022uF and .005uF.

2. Went to the .047 mid cap. My Strat loves this change!

Yes, Strats love that, but Hums hate it. Maybe a switch?

3. 10uf's on CL1,2 like Ayans pics

Really? I found that way too boomy on mine.

Further tweaks I am considering are:

1. Changing either onboard treble cap to .001uf and/or changing the ceramic on the mid switch to 390pf. With this change I am hoping to increase the upper mids when in boost mode. Mid and boost is getting a little muddy. Suggestions?

2. Change the bright cap to 120pf and/or hardwire the bright cap and use that switch to toggle mid caps.

I'd get a push pull pot to add another switch myself.

3. Try .022 or .033 mid cap, this could be the perfect comprimise for single coil or humbuckers or wire a combination in series like the treble cap.

Or switch between the 2 caps so you don't have to compromise.

5. I am going to slowly move away from the alpha pots. I do not like the taper. The local electronics store sells the PEC's.

Funny, I'm having the same issue. I'll be interested to see the results.

[keithrick]

Thanks for the responses, Scott and Bob.

I am going to try the .001 and 470pf combo after I let the dust clear from the mid cap change. That will give me 320pf with the mid boost off correct? Trying to learn the theory as well.

The toggled midcap values are tempting but I have enough switches already, in fact that was my buddies first critizism when trying the amp. .... also that they were too subtle.


But guess what I did do.....just removed the rest of the shielded cable. It truly was like lifting a blanket off the amp. Quite honestly, now I questioning my previous changes. That big off a difference.