UltraPhonix with a few twists

[fred.violleau]

Hey guys,

I am putting together an amp I have not seen yet in the ampgarage archives. Main topology is the Ultraphonix, with a few tweaks. In details it looks like this :
- a UP preamp : 250pf .022/.022 47k slope , 180k and 130k on plates, with 25uf coupling caps values (Am I right to think that the higher value in coupling caps, the more gain, hence distortion, I will get from the tube?)
- local NFB on a switch on V1B
- PAB, mid boost, deep and Bright switches
- Martin Manning’s step filters
- onboard D-lator
- Bluesmaster PI
- Dumble classic power filtering

Using a '66 Super Reverb PT and OT
-switchable tube/SS rectifier

Questions:
1 - Mixing resistor
On the UP schematic, there is a mixing resistor 470k at the entrance of the PI. It is removed on the bluesmaster PI.
I understand this resistor plays an important role if you have two channel mixing, but is it necessary for a single channel amp?
AFAIK wouldn’t it also damp the signal?
All this to say, should I keep it or remove it ?

2 - M.M.’s Step filters
I love the Dumbleland topology and would like to add some filtering on the amp
-where should I put the step filters: before the D-lator, after?
-Do I need to drive the filters with a tube, or can I basically insert these between others parts of the preamp?
- Should I use a post PI cut ala VOX / Two Rock instead?

If any schematic like this has been done, let me know, I have found the Bandmaster UP on the forum, which is a great start.

Ultra Phoenix.gif

I am using this D-lator source as well

Dumbleatorschematicjoost.gif

I am working on an unconventional layout ala SSS.

Thanks for chiming in!

Fred.

[martin manning]

Mixing resistors in that configuration look like a voltage divider at the output of each channel. If you have some level control just before the PI, a 1M master volume for example, you don’t need them.

The filters should be driven from the plate of a gain stage. Think of them as another type of tone stack, which will have losses, and may need to be followed by another gain stage to boost the signal again. As you can see in the schematic, the gain of the driving stage and the filters together is 9-10dB at the middle settings, meaning there is about 20dB of loss.

[Charlie Wilson]

Hello, this may be slightly off topic but I am not so sure the mixing resistors are 470K. If indeed the schematic is taken from this photo.
CW

[martin manning]

I’ve never tried to chase it down, but is there a definitive schematic that describes the Ultraphonix Mods?

[fred.violleau]

@Charlie, Indeed, depending on the schematics you look at, some have 220k for the mixing resistor

Hello, this may be slightly off topic but I am not so sure the mixing resistors are 470K. If indeed the schematic is taken from this photo.
CW

Fred.

[fred.violleau]

Mixing resistors in that configuration look like a voltage divider at the output of each channel. If you have some level control just before the PI, a 1M master volume for example, you don’t need them.

The filters should be driven from the plate of a gain stage. Think of them as another type of tone stack, which will have losses, and may need to be followed by another gain stage to boost the signal again. As you can see in the schematic, the gain of the driving stage and the filters together is 9-10dB at the middle settings, meaning there is about 20dB of loss.

@Martin, this is great news: I planned to add the MV and presence controls, as I think these are great additions to the original topology.

I understand the loss of the added tonestack.
I plan to use the FX loop for reverb and delays, so I could put the filters after the first stage of the D-lator, and before the recovery stage. Would that make sense? Or am I better of with another tube ala SSS?

This implies that the filters must come before the PI.

Thanks !


Fred.

[Charlie Wilson]

@Charlie, Indeed, depending on the schematics you look at, some have 220k for the mixing resistor

Hello, this may be slightly off topic but I am not so sure the mixing resistors are 470K. If indeed the schematic is taken from this photo.
CW

Fred.

I guess what I was getting at is that in the photo, those look more like 47k resistors than 470k.
CW

[fred.violleau]

I guess what I was getting at is that in the photo, those look more like 47k resistors than 470k.
CW

Your knowledge is unvaluable to us !
Thanks for the input Charlie!

Fred.

[fred.violleau]

The filters should be driven from the plate of a gain stage. Think of them as another type of tone stack, which will have losses, and may need to be followed by another gain stage to boost the signal again. As you can see in the schematic, the gain of the driving stage and the filters together is 9-10dB at the middle settings, meaning there is about 20dB of loss.

Topology would then be :
V1a & V1b Clean
V2a & V2b Filters Drive and recovery
V3a & V3b Loop Drive and recovery
V4 PI

Can I drive the filters from V1b as on the SSS#2 schematic? Would that imply to add the CF from V1b to V2b as on the SSS layout?



Thanks for your input!

Fred.

[martin manning]

You can put the filters right after the last preamp stage and have enough signal to drive them, but you will probably need to follow them with a recovery gain stage though.

[fred.violleau]

Thanks Martin!
I will probably put together a schematic to make the conversation easier

Fred.

[beasleybodyshop]

If it were me, I'd put the filters right before the D'lator - And use the cathode follower buffer and makeup stage in that circuit to make the filters work. That's how i'm implementing it in my build. Good Luck! The UP is not entirely set in stone, there are still a few variables to iron out.

[martin manning]

I think that plan is reasonable since you don’t need a high signal level to send out to the FX. The send buffer has high input impedance, and approx unity voltage gain. Even with nothing in the loop you’ll have the recovery gain you need.

[talbany]

Hello, this may be slightly off topic but I am not so sure the mixing resistors are 470K. If indeed the schematic is taken from this photo.
CW

CW
Is there a schematic of this amp handy

Tony

[Charlie Wilson]

Tony, I believe the schematic attached the first post was taken from the photo of the Bandmaster. I’m just not sure of some of the resistor values including those mixing resistors.
CW