2nd Gen Build

[dbharris]

New FET biased up easy. I set it for just under 3 for the Vdd/Vd ratio. It sounds good, but the volume is lower than the normal channel even with the FET trimmer wide open. I may bring the ratio closer to 2.5 and see if that helps.

I played the amp for a bit just to get a feel. It sounds very nice. A bit more rude than the #102. But impossible to balance the clean and overdrive with medium or more drive dialed in. I'll likely be adjusting the divider leaving V2b at some point.

Gonna take a break for a few hours to clear my head and ears.

-Dan

[martin manning]

New FET biased up easy. I set it for just under 3 for the Vdd/Vd ratio. It sounds good, but the volume is lower than the normal channel even with the FET trimmer wide open. I may bring the ratio closer to 2.5 and see if that helps.

What are the voltages at the top and bottom of the drain resistor?

[dbharris]

New FET biased up easy. I set it for just under 3 for the Vdd/Vd ratio. It sounds good, but the volume is lower than the normal channel even with the FET trimmer wide open. I may bring the ratio closer to 2.5 and see if that helps.

What are the voltages at the top and bottom of the drain resistor?

10.01 and 3.36

[martin manning]

Yes try changing the bias point. The gain should rise sharply at some point and then level off.

[dbharris]

FET is sorted and sounds good.

At some point in testing yesterday, I realized my standby switch was wired incorrectly (essentially like there was no switch in circuit). I easily found the mistake, but for the life of me could not see where the OT CT, choke, and standby were supposed to be tied together on these boards. It looks like HAD used an extra eyelet rather than the hole to loop wires through. So I added an eyelet then moved the connections and everything is good.

Ran out of time to balance the PI. That is next and then I will post a survey of the voltages. Everything seemed to be in normal range.

The smell seems to be almost gone now. Much more faint than before.

Played the amp for a bit with my les paul and a strat. Both through the dumbleator. Sounded great, but the strat really stood out.

Thanks for everyone's help and comments!

-Dan

[Stephen1966]

How is that J201 sounding? Does it or the circuit do anything to raise the sound floor?

[erwin_ve]

FET is sorted and sounds good.

At some point in testing yesterday, I realized my standby switch was wired incorrectly (essentially like there was no switch in circuit). I easily found the mistake, but for the life of me could not see where the OT CT, choke, and standby were supposed to be tied together on these boards. It looks like HAD used an extra eyelet rather than the hole to loop wires through. So I added an eyelet then moved the connections and everything is good.

Ran out of time to balance the PI. That is next and then I will post a survey of the voltages. Everything seemed to be in normal range.

The smell seems to be almost gone now. Much more faint than before.

Played the amp for a bit with my les paul and a strat. Both through the dumbleator. Sounded great, but the strat really stood out.

Thanks for everyone's help and comments!

-Dan

I wired the choke wire directly to the standby switch. But if wanted you can drill a hole and add a eyelet like you did.

[Dr d]

FET is sorted and sounds good.

At some point in testing yesterday, I realized my standby switch was wired incorrectly (essentially like there was no switch in circuit). I easily found the mistake, but for the life of me could not see where the OT CT, choke, and standby were supposed to be tied together on these boards. It looks like HAD used an extra eyelet rather than the hole to loop wires through. So I added an eyelet then moved the connections and everything is good.

Ran out of time to balance the PI. That is next and then I will post a survey of the voltages. Everything seemed to be in normal range.

The smell seems to be almost gone now. Much more faint than before.

Played the amp for a bit with my les paul and a strat. Both through the dumbleator. Sounded great, but the strat really stood out.

Thanks for everyone's help and comments!

-Dan

Thats great Dan. Agreed that strats sound great through this amp, especially through the FET. Balancing the clean with OD is a tough one with these amps and will require a lot of tweaking to get somewhere near, IMO. I think the original owners of these amps might have just used the OD channel and used their guitar volume to clean things up. I added separate volumes like the 2nd gen/bluesmater and find it works perfectly. If you decided to go this route and didn't want to drill another hole on the front, you could sacrifice one of your speaker outputs and place a volume there.
Looking forward to seeing your voltages.

[dbharris]

How is that J201 sounding? Does it or the circuit do anything to raise the sound floor?

I had to pull it and replace with an NTE 452. The J201 wouldn't bias, I think the drain resistor probably needed to be adjusted too. At least for that J201.

-Dan

[dbharris]

FET is sorted and sounds good.

At some point in testing yesterday, I realized my standby switch was wired incorrectly (essentially like there was no switch in circuit). I easily found the mistake, but for the life of me could not see where the OT CT, choke, and standby were supposed to be tied together on these boards. It looks like HAD used an extra eyelet rather than the hole to loop wires through. So I added an eyelet then moved the connections and everything is good.

Ran out of time to balance the PI. That is next and then I will post a survey of the voltages. Everything seemed to be in normal range.

The smell seems to be almost gone now. Much more faint than before.

Played the amp for a bit with my les paul and a strat. Both through the dumbleator. Sounded great, but the strat really stood out.

Thanks for everyone's help and comments!

-Dan

I wired the choke wire directly to the standby switch. But if wanted you can drill a hole and add a eyelet like you did.

All good Erwin! The boards and chassis are great and it's not a kit after all, but pretty close.

-Dan

[dbharris]

FET is sorted and sounds good.

At some point in testing yesterday, I realized my standby switch was wired incorrectly (essentially like there was no switch in circuit). I easily found the mistake, but for the life of me could not see where the OT CT, choke, and standby were supposed to be tied together on these boards. It looks like HAD used an extra eyelet rather than the hole to loop wires through. So I added an eyelet then moved the connections and everything is good.

Ran out of time to balance the PI. That is next and then I will post a survey of the voltages. Everything seemed to be in normal range.

The smell seems to be almost gone now. Much more faint than before.

Played the amp for a bit with my les paul and a strat. Both through the dumbleator. Sounded great, but the strat really stood out.

Thanks for everyone's help and comments!

-Dan

Thats great Dan. Agreed that strats sound great through this amp, especially through the FET. Balancing the clean with OD is a tough one with these amps and will require a lot of tweaking to get somewhere near, IMO. I think the original owners of these amps might have just used the OD channel and used their guitar volume to clean things up. I added separate volumes like the 2nd gen/bluesmater and find it works perfectly. If you decided to go this route and didn't want to drill another hole on the front, you could sacrifice one of your speaker outputs and place a volume there.
Looking forward to seeing your voltages.

I will try just using OD and riding the volume. I did a bit of that and noticed it cleaned up well. If I can live with it that way and not have to alter the circuit that would be ideal. If not, the dual masters is a good plan. I never run two cabs anyways.

-Dan

[martin manning]

I did a bit of that and noticed it cleaned up well. If I can live with it that way and not have to alter the circuit that would be ideal. If not, the dual masters is a good plan. I never run two cabs anyways.

The only bit of the circuit you would need to modify is between the OD2 coupling cap and OD relay, where the 2nd Gen has a 180k to ground and a series 1Meg. Those two could be replaced by a 250k pot, which gives you the OD Ratio control that the 2nd Gen lacks.

[dbharris]

Thanks, Martin. Bear with me for a minute because I'm just a tax lawyer and the theory and math side of EE is not my strong suit.

I think what Martin is suggesting would be to add a typical 4th/5th Gen ratio control. In all of the Dumble designs I am familiar with there is a series resistor there (immediately after OD2 coupling cap) ahead of the voltage divider. And the voltage divider (ratio pot) matches the resistance of the drive pot, 100K here.

Would it be best to implement this as a 150K series resistor to the input lug of a 100K pot?

I was originally thinking of the bluesmaster implementation, and moving that 180K so it is providing series resistance ahead of a 1M pot (while removing the 1M resistor). Of course the bluesmaster has the HRM tone stack before that 180K series resistance and would provide varies amounts of its own resistance depending on how that network is set.

I see in the 2nd Gen hybrid layout, it keeps the 1M/180K network and the junction of that divider feeds a 1M pot as a separate channel master. Not sure this is something HAD ever implemented?

I am guessing there is something involved with impedance here that is impacted by the size pot, series resistance, and whether you keep a global master or go to separate channel masters. Is that on the right track?

Thanks!

-Dan

[martin manning]

My thought was keep the load similar to the Second Gen to preserve its character, and allow some plus/minus on the level coming out of the OD wrt the fixed divider in the Second Gen layout. The main point is, however you do it, the Ratio control provides for adjustment of the OD output without going to the separate masters of the BM/HRM, which would require some additional rewiring of the clean output. You could do as you suggest and use a 150k into a 100k pot, exactly like the 4th Gen, but I was thinking you might want/need more OD output to get a balanced system. You can always adjust it as needed.

I see in the 2nd Gen hybrid layout, it keeps the 1M/180K network and the junction of that divider feeds a 1M pot as a separate channel master. Not sure this is something HAD ever implemented?

That is another way to go about it, but you would be limited to the same maximum level that the fixed divider in the 2nd Gen produced.

[dbharris]

My thought was keep the load similar to the Second Gen to preserve its character, and allow some plus/minus on the level coming out of the OD wrt the fixed divider in the Second Gen layout. The main point is, however you do it, the Ratio control provides for adjustment of the OD output without going to the separate masters of the BM/HRM, which would require some additional rewiring of the clean output. You could do as you suggest and use a 150k into a 100k pot, exactly like the 4th Gen, but I was thinking you might want/need more OD output to get a balanced system. You can always adjust it as needed.

I see in the 2nd Gen hybrid layout, it keeps the 1M/180K network and the junction of that divider feeds a 1M pot as a separate channel master. Not sure this is something HAD ever implemented?

That is another way to go about it, but you would be limited to the same maximum level that the fixed divider in the 2nd Gen produced.

Thanks, Martin that is helpful. Some experimenting in my future for sure.

-Dan