V1 through V5 question for 5:50

[vbf]

If this has been answered in another post somewhere, or is available in the manual somewhere, my apologies for being redundant.

I've always wondered what each valve does and would be grateful for a dumbed down explanation. For example, is V1 the gain stage and V4 the reverb stage? (I'm not even sure if I'm using the correct terminology) Thank you in advance!!

 

[Anonymous]

The manual has a description on page 25. Keep in mind the 12AX7's are dual triodes, you can think of them like 2 valves in one. Each half is like one valve, and can be assigned to whatever function the designer chooses. In hifi amps, usually each 12AX7 performs one function, across two channels. In guitar amps, as they have only one channel, the functions can vary widely by valve. Boogie labels each preamp tube section A or B to differentiate between the two "halves" of the dual triode.

I'm not 100% clear on the "flow" as the descriptions in the Boogie manual are a little vague. V2 is definitely the first preamp tube in the chain, with V2A the "1st Gain Stage" and V2B the "1st Gain Stage Cln/2nd Stage OD." V1A is "Channel 2 3rd gain stage" and V1B is "Channel 1 2nd Gain Stage." V3A is markes as "4th Gain Stage, both channels" and the second triode half of V3 is used for the FX loop. V4 is used as a driver for the power tubes (and should be well balanced between triode halves), and V5 is the reverb tube.

Here's my guess of flow, which is only an interpretation:
Clean: V2B > V1B > V4 > power tubes
Crunch: V2B > V1B > V3A > V4 > power tubes
Blues: V2A > V2B > V1A > V4 > power tubes
Burn: V2A > V2B > V1A > V3A > V4 > power tubes

Just my guesses based upon the sound of the channels, and the description in the manual. Hopefully someone with a schematic can help clear up the mystery!

 

[Don]

I don't know exactly what each tube does, but signal always passes through V3A and V3B.

I think this would be more correct-
Clean: V2B > V1B > V3 > V4 > power tubes
Crunch: V2B > V1B > V3 > V4 > power tubes
Blues: V2A > V2B > V1A > V3 > V4 > power tubes
Burn: V2A > V2B > V1A > V3 > V4 > power tubes


The difference between the modes on each channel appears to be more related to preamp tube bias and bias bypass caps than gain stages.

 

[MrMarkIII]

If this has been answered in another post somewhere, or is available in the manual somewhere, my apologies for being redundant.

I've always wondered what each valve does and would be grateful for a dumbed down explanation. For example, is V1 the gain stage and V4 the reverb stage? (I'm not even sure if I'm using the correct terminology) Thank you in advance!!

You might check the other thread you posted in:
http://forum.grailtone.com/viewtopic.php?f=30&t=45737

 

[vbf]

Thanks guys...appreciate it

 

[Anonymous]

An interesting aside: I can confirm the "Clean" voicing goes through V3A. Yesterday I was swapping in various preamp tubes from my stock, and swapped in an old Telefunken 12AX7 into V3. The sound on the clean channel was VERY quiet, you could barely hear the notes even when sitting next to the amp.

Interestingly, the Blues channel sounded relatively normal, although perhaps a bit thin. It's hard for me to tell right now as I have a head cold. So maybe it had enough gain already to not need the V3A gain, or maybe that channel isn't going through V3A at all...

 

[Don]

So maybe it had enough gain already to not need the V3A gain, or maybe that channel isn't going through V3A at all...

Both channels are going through V3a as well as V3b. I've seen the schematic.

 

[Anonymous]

So it was the former, then. Interesting.

I recall at one point having a tube go somewhat microphonic, but only in one mode on one channel. This supports the notion that tube operating points perhaps are the main differentiators in the sonic differences between voicings.

Are the schematics public, something anyone can get a hold of? I'd love to have a peek.

 

[Don]

Are the schematics public, something anyone can get a hold of? I'd love to have a peek.

Unfortunately, the schematic is not available to the public.

 

[TenCentHat]

New Boogie Board member here. Hi everyone!

I'm interested in what's happening with the gain stages as well, as I like to use two different amps side by side for added texture. From what you guys have described here, it looks like we have an even number of gain stages in clean/crunch channel, and an odd number in blues/burn. Assuming that each gain stage inverts the polarity of the signal (flips phase), is it safe to assume that by switching channels on the express, and not the other amp, I would be introducing frequency cancellation between the amps? Not good if they are to be blended mono at the FOH board!

Please correct me if I'm wrong.

Thanks.
Scott.

 

[J.J]

I don't know the exact answer to your question, but not all the stages are necessarily all inverting output. If channel 1 has a cathode follower and channel 2 doesn't then the output phase could still be the same. I would expect that the phase won't reverse between channels. Next time I have my amp on the bench I'll test the phase and see.

Actually I have tried running my old Bjr and the Express side by side and didn't notice anything out of order.

 

[TenCentHat]

Thanks for the insight, JJ. Since I don't have a scope to visually analyze the phase, I'm hoping to get a chance to DI both amps into our mixing board. I could then do a crude audible check by panning both to centre, have one amp at unity, and slowly bring the second up. If the bottom starts to disappear, I'm assuming that means their polarities are reversed. I could then try swiching channels and do the same.

In case you missed it, the point of all this is to have one amp fairly clean and the other fairly dirty, to maintain clarity... plus I find it actually helps keep stage volume down as the spread is better and everyone can hear it better. The added bonus is the stereo effects. I like to run everything through the amp inputs.

At the risk of being slightly off-topic, I did have a chance to try something very interesting, with surprisingly great results. Instead of using the Traynor YCV (the second amp in this case), on a whim I bought one of those Vox Amplug AC30 doohickeys. I plugged it right into the second output of my GT-8 and directly into the mixing desk. You wouldn't believe it. A slight bit of eq at the board, and you're rocking. Still didn't have a chance to check the phase relationship with the 5:50 though.

Thanks again.
Scott.

 

[J.J]

I'm sure by playing around you will find a setup you like and possbily other interesting things that you didn't expect. If you do end up loosing bass you can always turn the bass down on one amp and up on the other. That should prevent the cancelation and compensate for it too.

 

[EtherealWidow]

I talked with Marcus Daniel a while back about the circuitry of the Express because someone had brought up Russian tubes often failing in cathode follower positions. He said that by looking at it, he didn't think that there was a cathode follower in the Express. That being said, he's not a tech.