Q for the expert amp folk

TimmyO

When people talk of custom built amps with a clean channel based on (say) a Blackface and a crunch channel based on (say) a Plexi/JTM - just how good of a mix is possible? given a single set of transformers, valves, speakers, subjectively speaking how sensible/achievable are those things? 

Yours, intrigued of Wiltshire

martinw

I'm not sure if you'd want me to answer this or not! I will anyway......

It depends on the target amps you choose to some extent, and choices made during the design. Obviously all 2 channel amps like this will involve some compromise;  everything from the phase inverter on is common to both amps. However, in many cases the differences between power stages of the target amps

• are quite small to begin with
• have little noticeable effect on the sound in a large part of the output range of the amp
• can be minimised in some ways
• and any remaining compromise can be accepted by the user as producing an overall great sounding amp

The preamps can be completely independent, given no valve sharing, so the authenticity of those is not compromised. In the case you mentioned, the output stages of a pair of 6L6s versus a pair of KT66/EL34 will sound surprisingly similar for much of the operating range of the amp.

No-one is ever going to pretend that you're getting 2 amps in one box. As you've intimated, the output stage architecture and detail circuit choices and components are different, and things like the ideal speaker type will be different from type to type. Only a Twin and a Plexi will sound like a Twin and  Plexi.

However, what you can end up with (speaking for myself only here of course) is an amp, which has it's own character, and the basic tonal character of each of the target amps in each channel. What I generally do is bias one or other channel to the customer's preferred option, so that it's, say, a bang-on accurate SLO on the OD channel, with a 'proper' clean channel added on; typically a Twin circuit, which actually makes great sense given the SLO output stage of 4 x 6L6.

TimmyO

martinw said:

I'm not sure if you'd want me to answer this or not! I will anyway......

Of course I do! :-) 

martinw said:

I'm not sure if you'd want me to answer this or not! I will anyway......

It depends on the target amps you choose to some extent, and choices made during the design. Obviously all 2 channel amps like this will involve some compromise;  everything from the phase inverter on is common to both amps. However, in many cases the differences between power stages of the target amps

• are quite small to begin with
• have little noticeable effect on the sound in a large part of the output range of the amp
• can be minimised in some ways
• and any remaining compromise can be accepted by the user as producing an overall great sounding amp

The preamps can be completely independent, given no valve sharing, so the authenticity of those is not compromised. In the case you mentioned, the output stages of a pair of 6L6s versus a pair of KT66/EL34 will sound surprisingly similar for much of the operating range of the amp.

No-one is ever going to pretend that you're getting 2 amps in one box. As you've intimated, the output stage architecture and detail circuit choices and components are different, and things like the ideal speaker type will be different from type to type. Only a Twin and a Plexi will sound like a Twin and  Plexi.

However, what you can end up with (speaking for myself only here of course) is an amp, which has it's own character, and the basic tonal character of each of the target amps in each channel. What I generally do is bias one or other channel to the customer's preferred option, so that it's, say, a bang-on accurate SLO on the OD channel, with a 'proper' clean channel added on; typically a Twin circuit, which actually makes great sense given the SLO output stage of 4 x 6L6.

Awesome post - thanks 

Modulus_Amps

so if I answer this does that make me an expert?

it is a compromise you either take a blackface and plexi amp to your gigs to get the proper tones, or you get an amp with with channel switching that will get you close enough, or you get a digital modelling amp that gets a bit further away or you get a line 6 pod, plug direct into the sound board and play with in ears and who cares anyway as long as the punters drink enough beer to pay the bills....

Thing about real blackface and plexi amps is, as they don't have master volume controls, much of the drive tones are generated in the power section and that is the small part of the output range where it does matter how the power section is configured and what speakers you are pushing, if you are playing with the power section running cleanly then like Martin said it is a good enough compromise.

thomasross20

I'm getting exactly this from Martin. Don't want to spoil the whole spec but it's going to have fender clean and plexi/jcm for channel 2 / boost.

I considered a Marshall type clean but I love fender cleans... and I can always dirty it up a bit, even with pedals.

Can't wait!