KT88 Tube amp mods

[arny1]

Hi all, first post and looking for some advice.

I have a KT88 integrated (6SN7/KT88) that I want to use in a bi-amp setup driving the mid/tweeter section. They are DIY speakers so no xover, I am going to use a minidsp to set these up with the seperate woof speakers(no xover here either).

Is there some surgery I can do to the integrated so I can use the input/volume controls and send these to a minidsp/KT88 and another amp for biamping.

Thanks in advance, arny1.

[ozmillsy]

Integrated's are difficult for this task.

Seperate preamp/power amp setup is what you need.

[tuyen]

Need internal photos to be able to give exact advice.

But essentially, you could disconnect the selector switch and volume pot from the circuit and just have one of the rca sockets go straight into the amp (ie. converting it into a power amp).   Then wire the output of the volume pot into 2 pairs of the rcas, this will basically create a 'passive preamp' circuit inside your amp with 2 outputs..   sorry if it is a bit confusing, but in a diagram, it is quite easy.   Still really depends on how many inputs/outputs your amp has.

Tuyen

[arny1]

Hi ozmillzy, yes it would be easier and  I have a separate pre/amp. Trouble is, that amp is what I will need to use for the LP section. I need to make use of the gear I have until permission is granted to get more.

Tuyen, I am at work tonight so I will try to do a diagram in a day or so. I hope this works because the valves on the mid/tweeter  section sounds much nicer.

Thanks, arny1.

[ozmillsy]

But essentially, you could disconnect the selector switch and volume pot from the circuit and just have one of the rca sockets go straight into the amp (ie. converting it into a power amp).   Then wire the output of the volume pot into 2 pairs of the rcas, this will basically create a 'passive preamp' circuit inside your amp with 2 outputs..   sorry if it is a bit confusing, but in a diagram, it is quite easy.   Still really depends on how many inputs/outputs your amp has.

T,  

In an active setup, the volume control needs to sit in this sequence....

Source(s) -> Volume Control -> Active Xover -> Multiple Power amps

[ozmillsy]

Hi ozmillzy, yes it would be easier and  I have a separate pre/amp. Trouble is, that amp is what I will need to use for the LP section. I need to make use of the gear I have until permission is granted to get more.

No worries Arny.  That's great.   Since you already have another standalone preamp, then use that 1 for VC.

You can still use this integrated amp as a power amp.   Just set the volume setting to a 1:1 gain setting, often 12oclock., and away you go.   And if using it as a pure power amp permanently, bypassing the internal VC and selector switch could be something worth investigating that may yield an improvement in performance.

[arny1]

Ok, just quickly before I knock off work. The amp is point to point wiring, 4 pairs of RCA for input, wired to selector switch, to volume pot (a 100K log), direct to 6SN7 valve.
  My worry is that going from the pot to a Minidsp will not work with the resistances etc.

Thanks, Derek.

[tuyen]

But essentially, you could disconnect the selector switch and volume pot from the circuit and just have one of the rca sockets go straight into the amp (ie. converting it into a power amp).   Then wire the output of the volume pot into 2 pairs of the rcas, this will basically create a 'passive preamp' circuit inside your amp with 2 outputs..   sorry if it is a bit confusing, but in a diagram, it is quite easy.   Still really depends on how many inputs/outputs your amp has.

T,  

In an active setup, the volume control needs to sit in this sequence....

Source(s) -> Volume Control -> Active Xover -> Multiple Power amps

I know that oz. hence why showing how to conver his amp into a power amp and setup basically a passive preamp/volume controller 'inside' the amp that can be used as a master volume controller.  Of course it would be easier and less confusing if he had an external preamp. But thought he was doing it on the cheap and only able to use the bits available.

[ozmillsy]

I know that oz. hence why showing how to conver his amp into a power amp and setup basically a passive preamp/volume controller 'inside' the amp that can be used as a master volume controller.  Of course it would be easier and less confusing if he had an external preamp. But thought he was doing it on the cheap and only able to use the bits available.

No worries.

You're up early,,,, have you pulled an allnighter?

[tuyen]

Ok, just quickly before I knock off work. The amp is point to point wiring, 4 pairs of RCA for input, wired to selector switch, to volume pot (a 100K log), direct to 6SN7 valve.
  My worry is that going from the pot to a Minidsp will not work with the resistances etc.

Thanks, Derek.

It will be fine Derek. Have played around with the minidsp myself. Great value bit of kit and very flexible. Have fun!

[tuyen]

I know that oz. hence why showing how to conver his amp into a power amp and setup basically a passive preamp/volume controller 'inside' the amp that can be used as a master volume controller.  Of course it would be easier and less confusing if he had an external preamp. But thought he was doing it on the cheap and only able to use the bits available.

No worries.

You're up early,,,, have you pulled an allnighter?

Nah just woke up mate. Im an early riser, can never sleep in!

[arny1]

Thanks guys, the KT88 just sounds nicer driving the full range speaker, and am quite happy to use it like that. But, I have built a pair of helper woofs for when you just need more, and will use the Adcom amp to drive them. I just want to set up a xover with the dsp for bi-amping, then i may play with PLLXO, don't know yet, it depends if sound quality suffers with the dsp.

OK, if the passive pot will drive the minidsp I will order one tonight. Wifes given the OK, she wants the TT back in the system and for me stop messing with the system.

Thanks, will let you know how it goes.

[ozmillsy]

OK, if the passive pot will drive the minidsp I will order one tonight. Wifes given the OK, she wants the TT back in the system and for me stop messing with the system.

Thanks, will let you know how it goes.

passive pot + 4 new rca's fitted to the back.

Are you sure you dont want to try this first with your separate preamp, before going to town with mods?

[arny1]

Hi ozmillsy, I tried with the pre I have but it knocks the sound around too much in the vocal range. I will just re use the existing RCAs with a bit of rewiring that can be changed back if needed.

[ozmillsy]

Leverage rca's intended for other inputs, ok.

With the other preamp, I assume this issue with the vocals was without the miniDSP in the loop yet?

[arny1]

Sure is, I have not got the dsp yet, it's in the post i hope. The Adcom pre is really killing mids, the full ranger with the KT88 is pin point and clear but sweet at the same time, I don't have the words to describe it. Besides, I have only a rudimentary xover set up for crossing between them. I hope the dsp unit is suitable but if not I should be able to use it to help integrate the speakers for designing a PLLXO.

This DIY stuff is interesting and consumes too much of my time, or so I have been told (a LOt), I am thinking about doing a passive external pre/selector box to minimise changing the amp too much, we will see.

[ozmillsy]

Well the adcom might be compromising the sound.    But you could still use it to make an initial assessment of how much the miniDSP further compromises things.

If the miniDSP is seemless in combination with the fairly limiting Adcom,   then move onto other options that take the Adcom out of the equation.

But if the miniDSP adds its own compromises, you might not want to mess about with preamps - and focus on a passive XO  ?