Log/ Lin Bass Pot (DlxRev).

[Sea Chief]

G'day. Got a new build p-to-p DR (TAD effectively).

The bass is a real burden. I find to get a 'normal, balanced single coil sound' I cant turn the bass more than 1.75. At 2 it starts to be overbearing (as IMO it shouldn't with single coils).. & at 5 its ridiculous. It sounds so fat & full to me thats more akin to a cello, or a small bass gtr. The treble I find no less than 7.5 or it seems lost too.

Now Im not too familiar with the DR circuit, but did read about it being a bright amp so Im confused. Now, my wem with the bright switched on & a big 15" celestion.. I DO get a 'normal, balanced sound' bass 4 treb 6: just how I'd expect for my slight treb-emphasis I like. I thought a 15" would be bassier than twin 10's (why I bought these two) so, maybe I got that wrong?

Im wondering about the bass pot taper. Whether I have it right, whether a typo. Or how if I do have A250K as I read is correct, would changing to a B250K change the sound.. feasable idea?

Thanks SC.

[frus]

linear would be even worse

[Sea Chief]

Right so Ive got that curve of the audio taper thinking-wrong then have I?

Is the AB763 meant to be bassy then by default? just read a few things about bass at 3 max when dimed.. but Im using at lower vols generally.

[frus]

maybe your pot is not-so-much-audio taper
try to measure the resistance (lower lug to wiper) when you turn the pot half way
if it's more than, say, 10% then it will be bassy soon, yes

[pdf64]

Just to note that 'A' is a manufacturer, not industry standard, code, ie it can mean linear; usually applies to European made pots.
Maybe the treble and bass pots would work better in the other's role? The RI audio tapers are 10% on bass, 30% for treble, which I think confirms with the 60s BF Fender arrangement.

[Sea Chief]

maybe your pot is not-so-much-audio taper
try to measure the resistance (lower lug to wiper) when you turn the pot half way
if it's more than, say, 10% then it will be bassy soon, yes

10% of the max I read on the pot (call it 230k as it may be) at halfway rotation?

[Sea Chief]

Just to note that 'A' is a manufacturer, not industry standard, code, ie it can mean linear; usually applies to European made pots.
Maybe the treble and bass pots would work better in the other's role? The RI audio tapers are 10% on bass, 30% for treble, which I think confirms with the 60s BF Fender arrangement.

pdf64 hi, its not the RI though. The pots are all large alpha (and some cts). Pro chap got for me & I asked for A250k for the tone pots.. so Id guess they are correct taper.

Damn I was hoping a linear taper might suit/ IE the bass would come on strong at the tail end of the pot maybe, which would suit. Maybe I need to start looking at major cap value changes to reduce the bass by half say, what an arse.

Fwiw when the amp was an RI (before) I had the same bass issue. Even tried changing from a fender oxfart speaker (a twin one, not alas the great DR ones some say are the best for the DR) to a pair of 10" but I couldnt hear any difference whatsoever/ I cant even discern there are two spkrs rather than one, let alone smaller & one being an alnico, or any sonic difference (ok maybe the slightest hint more mid honk with twin 10's.. but I maybe kidding myself; the bass tho still same).

[Jazz P Bass]

Is the problem on both the Normal & the Vibrato channels?

Try lowering the capacitance value of the first stage cathode bypass capacitor.
(Either channel for a test)

Stock is 25uf.

Try a 10uf.

[Dave H]

Maybe I need to start looking at major cap value changes to reduce the bass by half say

Only minor cap value changes really, just a bit of fine tuning. It does have a lot of low bass boost in the tone stack and the only bass roll off is the 1n cap on the PI input. Try changing that to 470p or lower. You could also change the 0.1u and 0.047u caps in the tone stack to 0.022u to roll off the low bass. I guess it's not quite a typical Blackface sound if the tone stack caps are changed but you may prefer it with less muddy low end.

[Sea Chief]

Thanks Dave H, JazzP. I will tentatively give this some thought and maybe a tweak of caps you mentioned. Not liking the idea of 'not typical blackface', although as of yet Ive no knowledge of what exactly consitutes a blackface sound aprt form a brownface, or silverface; I cannot distinguish/ but I guess that takes alot of time or something to hear the difference.. so in that case I might be ok changing.

BTW are the brownface, or SF any different or pe4ceived to be different, in terms of the bassiness to a BF? is there any value changes ingerrant in thes models in the area in Q (bass/ tonestack etc)?

[Sea Chief]

Same both cahnnels, similar if not same as in its RI guise before I rewired it p-to-p JP.

So if I use the Vibrato ch2 as most do 99%, I change this '1st stage' cap too, or is the 1st physically (with a 1.5K bypassing it, is the one in Q?) on the board the one only to change-?

[pdf64]

So if I use the Vibrato ch2 as most do 99%, I change this '1st stage' cap too, or is the 1st physically (with a 1.5K bypassing it, is the one in Q?) on the board the one only to change-?

The input stage is that which the input (the fx / vibrato / ch2 channel in the above case) connects to; so, assuming a regular DR board, eg p2 of http://bmamps.com/Schematics/fender/...b763_schem.pdf the 2nd from the right.

It's quite valid (ie not a bizarre modification) to use a 470pF cap at the input to the phase splitter, as Dave H suggests; Fender tended to use that value for amps which may be used with closed back cabs, eg http://bmamps.com/Schematics/fender/...b763_schem.pdf which tend to have a greater bass output.
Modern speakers tend to have bigger magnets / magnetic flux than typical speakers used for the DR in the 60s, which may tend to greater bass output than may have been envisaged.