D'lite HRM daughterboard...

[Bob Simpson]

Can it be switched out, or around maybe?

Put it on a relay for HRM/non-HRM?

Bob

[ampdork]

You could make a new board and use this scheme to switch out the hrm (or in).
Put a relay on the board and associated parts shown here. Use a 100k trim pot for the "ratio" for the non hrm side.

Of course there are numerous other things you can incorporate (and should imo) here and this shows nothing more then the hrm stack being used or bypassed. I am aware of all the rest that this does not address in regards to the difference between the circuits.

This basic idea does work just fine for the hrm switching but of course I am sure the people around here could find fault in it or do it better.....after all I am just another AMPDORK! ;O)
The other stuff could probably be easily figured out....well in fact I know it can. This one is a bit trickier then most of the rest and it is simple and obvious.....So the rest should be able to be hashed out in discussion to get both modes singing nicely.
I am in fact astounded this is not old hat around here...Maybe I ought to have said something sooner?

If one goes deeper another hint is that when switching the V1 nfb put the cap one the plate before the relay....that should be obvious but ...
Keep on in this direction of thought and the results can be well worth it!!

OR....you can do it the other way....that is wait around for dumble to do it first and reverse it. ;O)

Hope it helps. Mileage may vary. I accept no responsibility for the kludging of anyones amp. Use at own risk (cause it can be too cool) and ENJOY!

http://img25.imageshack.us/img25/8533/hrmtrick.gif

[dogears]

Good post Shad.

For the record, Glaswerks has been completely and effectively switching every facet of non HRM to HRM for years. Don't forget that the clean master is seperate and the bright cap (which always is better there IMO) needs to be designed so it is not a bleed to ground when non HRM is on.

Also, seperate pre-od networks with seperate trimmers.

V2B coupling size changes, as does the impedence it drives (250K vs 100K pot). You can short things in series to get approximate values. You can use a 250Ka pot, like the HRM, but you can jumper around the 100K feeding it. Better yet, try a 100K pot, scraped up to 160K or so. Then use two resistors in series to get the impedences correct. You need series caps as well. Short one to get the bigger non HRM value. Use a larger one in HRM if you need work with lower impedence than the 350K standard. Best solution is a custom tweaked dual gang pot with bioth 100KB and 250KA elements.

Lastly no snubbers always sounds better on HRM to me.

So, you need several relays to make it work best.

Your schematic is good though. No fault there!

You said it was not old hat, but for some it is. Now that Gary is doing the SODII where he has a dedicated non HRM and HRM preamp tube and circuitry, I can post this. THe new solution, seperate discrete circuits with no shared controls, is the superlative way IMO. Nobody waited to reverse engineer anything. The original switching design was the result of at least 12 months of collaboration between Gary and I. We did not feel like sharing so that certain foreign schematic trollers would pinch it.

You could make a new board and use this scheme to switch out the hrm (or in).
Put a relay on the board and associated parts shown here. Use a 100k trim pot for the "ratio" for the non hrm side.

Of course there are numerous other things you can incorporate (and should imo) here and this shows nothing more then the hrm stack being used or bypassed. I am aware of all the rest that this does not address in regards to the difference between the circuits.

This basic idea does work just fine for the hrm switching but of course I am sure the people around here could find fault in it or do it better.....after all I am just another AMPDORK! ;O)
The other stuff could probably be easily figured out....well in fact I know it can. This one is a bit trickier then most of the rest and it is simple and obvious.....So the rest should be able to be hashed out in discussion to get both modes singing nicely.
I am in fact astounded this is not old hat around here...Maybe I ought to have said something sooner?

If one goes deeper another hint is that when switching the V1 nfb put the cap one the plate before the relay....that should be obvious but ...
Keep on in this direction of thought and the results can be well worth it!!

OR....you can do it the other way....that is wait around for dumble to do it first and reverse it. ;O)

Hope it helps. Mileage may vary. I accept no responsibility for the kludging of anyones amp. Use at own risk (cause it can be too cool) and ENJOY!

http://img25.imageshack.us/img25/8533/hrmtrick.gif

[heisthl]

The biggest obstacle to switching is the snubbers, separate tubes let you do that.

[Funkalicousgroove]

I've seen HRM's with Snubbers:

[Bob-I]

I've seen HRM's with Snubbers:

And I've tried it. I'm with Scott here, HRM's sound better without it.

IMHO this is a lot of effort for not much return. In a live situation pick one and stick to, in a recording situation switch heads. JMO.

[Funkalicousgroove]

I guess to each their own, that Pic is a Dumble #185 not a clone.

I totally agree to just pick one way or the other-

[dogears]

That one sounds great I am sure.....

Different super secret probation HRM circuit though. I was referring to snubs on the standard HRM everyone here is familiar with.

I guess to each their own, that Pic is a Dumble #185 not a clone.

I totally agree to just pick one way or the other-

[Funkalicousgroove]

You know that amp is in Maine right? you can totally go hear it- No edges on that one at all!!

[dogears]

I'll hop in my car after work and drive up! I'd be there sometime tomorrow!

You know that amp is in Maine right? you can totally go hear it- No edges on that one at all!!

[Funkalicousgroove]

Well, that's not what I meant- It's just alot closer than Denver! LOL!

[BobW]

This sounds like a great project for my Bassman ODS. thanks.