ayan wrote:The HRM tone stack will make a huge difference in signal level, as you've already found out. How did you measure your OD master volume pot, you disconnected say the ground connection from the circuit and measured it? If you didn't do something along those lines, your measurement would be off.
Gil
norburybrook wrote:Gil, the HRM board you mean? would that have much effect on the level? I suppose thinking about it that's what the boost does and that makes a difference.
I did find that there wasn't a lot of noticeable difference tweaking the HRM trim pots, should they have a 'big' effect?
Marcus
edit; just tested my 1M Od volume pot and it's only measuring 335K
so that would do it....if it's a knackered pot then that also could have been the problem I had earlier as well!!
right time to get a new pot in there.
ah....I didn't disconnect the ground. I measured the other pots first in situ and they all ready perfectly, why is the Od volume different?
marcus
edit..... yes you were right
also 2 of my trimmer pot's work backwards, so that tainted my impression. I'll knock them all back from midway position( that's clockwise for me) to reduce the level.
Other than the Middle pot, the Bass pot when the amp is not in Jazz mode and the presence pot, the rest of the pots are wired as voltage dividers and not variable resistors -- look at a schematic. That being the case, one simply can't neglect the effects of the circuit loading the pot. The smaller the pot's value, the less effect a given network would have on it. In the case of the OD pot, the value is 1 Meg and the HRM tone stack hanging on one end of it is a hog...hence your reading.
Gil
norburybrook wrote:
ayan wrote:The HRM tone stack will make a huge difference in signal level, as you've already found out. How did you measure your OD master volume pot, you disconnected say the ground connection from the circuit and measured it? If you didn't do something along those lines, your measurement would be off.
Gil
norburybrook wrote:Gil, the HRM board you mean? would that have much effect on the level? I suppose thinking about it that's what the boost does and that makes a difference.
I did find that there wasn't a lot of noticeable difference tweaking the HRM trim pots, should they have a 'big' effect?
Marcus
edit; just tested my 1M Od volume pot and it's only measuring 335K
so that would do it....if it's a knackered pot then that also could have been the problem I had earlier as well!!
right time to get a new pot in there.
ah....I didn't disconnect the ground. I measured the other pots pots first in situ and they all ready perfectly, why is the Od volume different?
I've already got it closer in volume now. It's quite hard to decide on what settings to leave it on, as when it's set up for humbuckers it's a bit thin on single coils, also the OD trim pot comes into play as well so there's 4 trim pots to balance the OD sound.
a tweakers delight
I don't like too much choice generally with things....
ah well when I get my half volume switch in I can then put it back in it's cab and forget about it
I hear ya, and that's the reason I ultimately got rid of my BM.... Although some people try to fool themselves into thinking otherwise, those bloody controls belong on the outside of the chassis! That's the beauty of the non HRM amps, they're a total compromise as well, but there isn't too much one can do about them... so we just play the guitar instead of tweaking the amp to death.
Gil
norburybrook wrote:thanks Gil,
I've already got it closer in volume now. It's quite hard to decide on what settings to leave it on, as when it's set up for humbuckers it's a bit thin on single coils, also the OD trim pot comes into play as well so there's 4 trim pots to balance the OD sound.
a tweakers delight
I don't like too much choice generally with things....
ah well when I get my half volume switch in I can then put it back in it's cab and forget about it
ayan wrote:I hear ya, and that's the reason I ultimately got rid of my BM.... Although some people try to fool themselves into thinking otherwise, those bloody controls belong on the outside of the chassis!
Gil
Hey I resemble that remark lol. Sorry Gil I couldn't resist.
glasman wrote: Hey I resemble that remark lol. Sorry Gil I couldn't resist.
Is there any particular tweaks you did to give the tonestack use-able sweep on the front panel?
I've tried a bunch of panel mounted HRM circuits, full amps and tube preamps and I ended up with the Plexi like tonestack. Using the same pot values and Coupling caps/slope resistor, with the normal 220k off the treble pot into the master vol. Adding a high cut circuit off the V2 grid helped too.
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glasman wrote: Hey I resemble that remark lol. Sorry Gil I couldn't resist.
Is there any particular tweaks you did to give the tonestack use-able sweep on the front panel?
I've tried a bunch of panel mounted HRM circuits, full amps and tube preamps and I ended up with the Plexi like tonestack. Using the same pot values and Coupling caps/slope resistor, with the normal 220k off the treble pot into the master vol. Adding a high cut circuit off the V2 grid helped too.
Yes I changed the taper of the pots. Makes it a LOT easier to dial in.
Treble = 30%
Middle = 15%
Bass = 15%
BTW, very clean preamp!! I have thought about building one, but never have got to it as of yet. Thinking a 2 space double decker, twin clean channels driving twin OD channels, digital stereo effects with low impedance outputs to directly a mixer.
Make it three space and I can build my Fendumshall amp. Gil do you remember this concept from a few years ago.
Located in the St Croix River Valley- Afton, MN
About 5 miles south of I-94
aka K0GWA, K0 Glas Werks Amplification www.glaswerks.com
ayan wrote:I hear ya, and that's the reason I ultimately got rid of my BM.... Although some people try to fool themselves into thinking otherwise, those bloody controls belong on the outside of the chassis!
Gil
Hey I resemble that remark lol. Sorry Gil I couldn't resist.
M Fowler wrote:Gary enjoy the small town feel while still in a large Metro area
I love the place, so funny still have to drive 20 miles to get to anywhere, same as where I live now.
NOt sure whats up with Minnesota lol, I bought a Hammond M-3 at goodwill for $2.50 on my last trip to see the wife and saw another for sale at the Brooklyn Center Goodwin for $5.95.
Now looking for a Goodwill B-3...
Gary
Located in the St Croix River Valley- Afton, MN
About 5 miles south of I-94
aka K0GWA, K0 Glas Werks Amplification www.glaswerks.com
I've removed the HT fuse today and fitted a DPDT on/on switch in it's place.
Now I'm having a bit of difficulty understanding the half power switching.
1: does the LED matter apart form a visual clue?
2: the 1R resistors I have to ground from pin 8 for bias measurement are not shown in the schematic/Layouts I've seen. Do they just go in line straight to the switch?
3: looking at the schematic it seems whichever way the switch is the signal always goes to ground , it's either direct to ground or via the 10k resistor. How does this shut off 1 pair of valves?
norburybrook wrote:I've removed the HT fuse today and fitted a DPDT on/on switch in it's place.
Now I'm having a bit of difficulty understanding the half power switching.
1: does the LED matter apart form a visual clue?
2: the 1R resistors I have to ground from pin 8 for bias measurement are not shown in the schematic/Layouts I've seen. Do they just go in line straight to the switch?
3: looking at the schematic it seems whichever way the switch is the signal always goes to ground , it's either direct to ground or via the 10k resistor. How does this shut off 1 pair of valves?
Thanks
Marcus
The 10K resistor cannot pass enough current to allow its two tubes to do anything useful, so essentially, those two tubes have been taken out of the circuit when the switch is open.
yes you were right
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