Mod to 2nd/ 3rd generation build

[stevlech]

If I wanted to put a level control in a 70's style build, would I just graft the network from classic/skyliner era ods like this? Just thinkin' out loud...

[Bob-I]

If I wanted to put a level control in a 70's style build, would I just graft the network from classic/skyliner era ods like this? Just thinkin' out loud...

Personally I don't see how the amp would be useful without this. Yes, that would be a great mod.

[mojotom]

IMHO it didn't work for me. It's quite different because loading is different.
I use a 250k drive in mine and I've been thinking about a dual master like the HRM.

[Max]

If I wanted to put a level control in a 70's style build, would I just graft the network from classic/skyliner era ods like this? Just thinkin' out loud...

Personally I don't see how the amp would be useful without this. Yes, that would be a great mod.

Hi stevlech, Hi Bob-I,

I great "mod" I can recommend for the use of a 1st, 2nd and 3rd generation ODS is to equip the guitar that shall be used with a volume control and perhaps to try the higher impedance FET input. The result of the "guitar volume pot mod" is demonstrated here (but into the NOR input): https://tubeamparchive.com/viewtopic.ph ... 117#135117

How these amps without a ratio control can be useful for playing in a band is also demonstrated to some extent by some guys like Lowell George, David Lindley, Ben Harper, Charly Bonat (with Elgam Collective as an example), Graham Nash, Danny Kortchmar etc.

I've attached a pic of one of these amps which Steve Lukather obviously thought to be useful, too.

Have a great weekend,

Max

[marcos]

If I wanted to put a level control in a 70's style build, would I just graft the network from classic/skyliner era ods like this? Just thinkin' out loud...

Hi here´s my 2 cents:
I´ve modded my amp just like that, works great in my 70s amp,
but it is true that the load on V2b changes, so the tone changes a bit.
You could use a 82k resistor in series with a 100k pot to keep close to the 180k load of the original design.Added bonus: a little more range for the ratio control.Hope this helps a bit
Marcos

[wjdunham]

I've been thinking about this as well, the question is what to do with the 1M series resistor that's after the 180K load resistor? I was thinking about putting a 1M OD level pot after the 1M series resistor, just before the 1M Master Pot. This way, V2B sees the same load as the original design - 180K to ground followed by 1M series resistor followed by 1M pot - this network would then feed the 1M master volume. Brandon's 70's amps have an OD level control, and they sound killer, so we know it's possible...
Bill

[talbany]

For what it's worth.. If you can build it first without the ratio and let it sink in before going there do it.. I initially thought the same thing but it sounded so good like it was I didn't go there..Brandon at one point thought the same on his personal amp as well..

Tony

https://tubeamparchive.com/viewtopic.ph ... ht=lindley

My personal amp is the 70's amp with separate Masters and a presence control.

The pre OD network is key, as are the larger couplers in the OD section, and the different PI

Adding presence is easy, just use a 1uf and a 5-10K pot in place of the accent switch.

The "60's" PI setup at Schematic heaven is pretty dead on.

the Overdrive Ratio control is un necessary, out of V2B coupler there is a 180K to ground, and a 1M in series as sort of a pre-set ratio control- Leave it Really.

The last part of the sound that is absoluteley necessary is the FET input, it sounds WONDERFUL with both regular and lap steel guitars.
_________________

[marcos]

Hi Tony,
it seems that Brandon finally changed his mind.FWIW I used my
70s ODS from 1979 until 1986 without the ratio control,and IMO it simply doesn´t work if you want to use the channel switching option.The perceived volume of both channels not only changes with different settings of the Volume and Overdrive controls, but also with different settings of the Master Volume control.Very hard to control.AFAIK players like Rick Vito simply
left the amp in OD mode,choosing to control the amp with the guitar.
This is what I did for a long time,too.If you can live with this you´re fine with
the original design, especially as the amp is very touch sensitive.

Just my experience Marcos

[glasman]

FWIW,

I just built a "70's" style yesterday for testing purposes. I opted for separate Clean and OD level controls.

I just fed the 1Meg to the top of a 1Meg 30% OD level control.

First time I ever tried this style of amp. Definately a rocker. My kid is taking it to a local jam session tonight.

Gary

[stevlech]

Thank you gents for the feedback. I'm prepping a faceplate and I thought about adding a place for a ratio control. I think I'll follow talbany's advice and make it stock first.
Any other recommendations are much appreciated.

[Max]

Hi all,

as you all know my technical knowledge is rather shallow, but I would not be very surprised, if there would be a reason why I don't know of a single 2nd or 3rd generation "pre classic" ODS with their special kind of OD processing (OD entrance, no snubbers etc) with a ratio control. All those I know with a "ratio control update" have been updated to the "trigger" trim pot OD entrance and snubbers etc., too.

Cheers,

Max

[stevlech]

Wow, that was quick, Max. Point taken WRT the od section change.

To anyone - I noticed in Talbany's quote of Brandon that he used seperate Masters. How might I incorporate that?

[Max]

Thank you gents for the feedback. I'm prepping a faceplate and I thought about adding a place for a ratio control. I think I'll follow talbany's advice and make it stock first.
Any other recommendations are much appreciated.

Hi stevlech,

this is exactly what I would recommend, too. In case you later should want a ratio, you could just place it on the back as an example, like on the attached picture of the back of #075, reportedly the first ODS originally made with a ratio control ("effects loop" is a stereo jack, a full size presence control on the front).

Have a nice weekend,

Max

[glasman]

A couple of hints for creating separate masters for Clean and Overdrive.

1. Float the clean master potentiometer off of ground when OD is enabled. THis is very easy to do if you remember that the OD input is grounded when clean mode is enabled. I simply tap the OD input from the relay and connect it to the ground connection of the clean master. This assumes wiring the clean master before the relay.

When OD is selected the Clean master has the same signal on top and bottom and is taken out of the circuit.

2. Adding presence. Just adding a 1uf cap and 10K on the standard PI (820/100 feedback) is going to do bumpkiss. The 100ohm swamps the the pot and it only works when the pot is maxed out.

To overcome this in my amp, I reworked the feedback network for the power amp to 3K3 / 390 to maintain close to the same feedback ratio and then used a 1uf and 2K potentiometer for the presence.

The frequency response with the 820/100 and the 3K3/390 were identical and the break point for presence at max were the same (within 100 hz or so).

The feel of the amp was also the same. YMMV.

Gary

[talbany]

as you all know my technical knowledge is rather shallow, but I would not be very surprised, if there would be a reason why

Hey Max
AFAIK the pre trigger OD entrance design is I would consider a fairly low gain network... much of the signal get's attenuated at the front end and gets attenuated less on the back end of the OD circuit..

Getting the right balance between clean and OD and still have the OD serve up some real gain w/ sustain and bloom is rather difficult at low living room volumes(no FET).. When you get the amp to higher volumes the amp starts to better balance itself clean/OD and really starts to sing..Very Cool!! This is not a living room amp it's a gig amp tuned for slightly higher volumes..(The fet does help with this BTW) Max, Marcos would you agree..

Tony