[Tacosauce]

Hey Now,

Hoping that there's some Mesa gurus on here that can help me out. I'm close to purchasing either a MK1 or MKIIA amp head with the intention of running just the pre amp into my MosValve 962 power amp.

Both of the Mesa's I'm looking at have "slave" outputs. The MK1 has one output jack, the MKII has two of them. I've been googling left and right trying to find something in plain talk that would tell me if these jacks can be used to just run the pre amp, but I haven't been able to find anything definitive. Is that what these outputs are used for, or is it something entirely different?

Two other questions- if that is in fact what the slave outputs are for, is this the most efficient way to run the pre amp out to a separate power amp, or would I be better off having a tech install a dedicated line out for the pre amp? Also, if I use the slave output, would I still need to have a speaker load connected to the amp head (assuming no here?) since the speakers would wind up being connected to the MosValve?

Any wisdom, much appreciated.

Sean

[BoogieMK2]

If you don’t want the power amp, use pre-amp out/ power amp in Part of the circuit. On the MKIIA, there is a jack under the chassis that has this preamp out signal. Note the signal level will be higher than standard inputs and you may need a pad. This is at a level to drive the amp phase inverter. The out/in jack in the back panel is used as the power amp in.

For the IIB, just use the FX loop. I don’t know the MK1, some may have the “loop” as the MKIIA.

In any case, you must leave the speaker connected or have the right load box. With the THD Pi, I need to have the speaker connected, but can totally attenuate. To save space and weight, an 8 ohm power resistor would work but get warm if you were pushing the Boogie power amp. Plus you would need to mount it in some way due heat.

The Slave Out captures the phase inverter, power tubes and output transformer. So, some more tone coloration options especially if you drive the power amp. Would not be a Jerry type setup of Blackface pre-amp to a hifi type amp. But might sound good.

You can try both and see what you get. Makes me realize I need to do what you are doing, going into my ART SLA2 and 2x12 open back pine cab.

[BoogieMK2]

The G-LAB ALA-1 is a great buffer box. You can attenuate the large voltage Boogie preamp signal. Either to feed a rig like you are thinking about or to make a standard loop. The other half will boost the loop to the Boogie preamp out level.

But, you have to find it used

https://glab.com.pl/wp-content/uploads/ ... 102009.pdf

[kludge]

Keep in mind the original Mk1 did not have preamp out/power amp in (aka effects loop in later amps). Slave out only. You can drop some $$ and get a load box for it if you want to run silently.

Also, those early Boogies (all Boogies, really) are biased very cold. The sort of Vox/Marshall/Tweed idea of “overdriving the power tubes” is a lot harder to pull off and probably not necessary anyway. After living with a Mk1 for ages, one thing I’ve learned is that none of the knobs should ever be turned all the way to 10. Dialing in an old Boogie takes restraint and careful listening. It ain’t a blackface Fender or Marshall that always sounds good at any setting.