missing midrange clarity

[paddes53]

Hi all,
Since this is my first post I?d like to say hello to all of you guys on the forum. I just recently finished my first clone as per the ods-101 non hrm schematic. I've already done some tweaking and am actually quite happy with it. The thing which strikes me though is that somehow it is missing brightness in the mid register. I'm sorry but don't know exactly how to describe it. The brightness, high end that is, is there, but there seems to be something strange about the midrange, just like there was a blanket over the speaker for that particular frequency range.
Here are some of my values, so you know where you're at:

V1 voltages are spot on at 200V
V2 voltages are at 213/214V
CL2 cap is a 0,047 which I prefer over a 0,02 value
OD1 input is 180K over 100k trim (also tried 150 and 220 which I didn't like that much)
OD1 .01 coupler over 100k (tried up to 150k here but didn't like it)
100kl Ldrive pot to 180k then OD2
OD2 coupler is a .0047 to 150k then 47k/47k combination to a 1M od master volume
snubbers are both 270p

I also installed the .0012 /250k pot combination on OD2 to get rid of the extreme harshness, which really works out ok, unfortunately it also adds a little of this unwanted midrange mushiness.

If anybody has any idea where to tune to get the midrange clarity back, I would really appreciate it.

I also try to record some clips of the amp as soon as I get my recording equip installed.

best regards,
Patrick

[Pete]

It sounds to me like you are missing some of the "fatness" or "fullness" in the mid-upper mid area.

I could be wrong but I seem to have noticed this myself in my amps while experimenting with plate resistors (with corresponding cathode resistor) for V1 & V2 . I may change my mind, but I think I get an improvement with the old "standard Fender" values of 100k w/ 1.5k. I haven't heard many comments on this around here, and it may be that most prefer the values typical to the 101 schem.

I would be curious to know the findings of others, or if there is any technical reasons for this. If you do any experimenting in this area please post your observations (I guess I'd like to know if I'm way off on this)

Just my two cents
Pete

[Bob-I]

Are you using ceramics for the treble and snubber caps? If you're using silver mica you'll get the symptoms you describe. Also, the plate resistors should be hi-fi metal films, Vishay Dale RN65's.

I've tried the 47k/47k divider into a 1M pot and don't like it. I found that a 100K as a "ratio" control into the global master at 1M just somehow sounds better.

[tictac]

Could it be the mid cap in your tone stack? Are you using a .01?

That will give you less of a mid range dip and can sound too midrangy with certain guitars.

I like .02 in that position myself, it's a compromise between the .047 old Dumble/ Fender value and the Skyliner value of .01

I have a 100K mid pot with a pull switch so I can switch between .047 and .02 values.

My .02

[Funkalicousgroove]

I'd say do the following:

If you have silver mica's in your treble cap or anywhere in your signal path GET RID OF THEM, use Ceramics, If you have M150's anywhere in your signal path GET RID OF THEM.

Now, I like type PS od's and type 225p od's in the signal path, I've also had good luck mixing a couple 715's in here and there as well as a couple Solens.

I'd drop your plate voltages on V1 and V2 to anywhere in the 165-190 volt range, that should help with the "Brashness", and will allow you to ditch the internal "tone" control.

Keep in mind that these amps need 40+ hours on them before they "open up."

Can you post some pics?

[paddes53]

thanks alot for the suggestions.

I will try to go back to the standart 100k level with a global 1m master just to see if i like it.
Also I'm using xicon mpp couplers. I tried the od ps but I prefer the xicons. Pf value caps are ceramic, only the snubbers are parallel polystyrene/ceramic. Maybe I should giveceramics a try in this position as well.
Midcap is a .01 right now, I changed back from .02 a while ago and liked it better, but then again, I was using another guitar with the amp.
Plate resistors are already the Vishay/Dale RN.

Ok I will try replacing the od master 1m pot with a 100k and also use ceramics as snubbers. I'll report my findings.

cheers,
Patrick

[Bob-I]

It sounds like you have all the right components. What about the speaker, what are you using?

[paddes53]

Right now I'm using a 2x12 open back with Tone Tubby Ceramics which aren't completely broken in yet, so I'll have to get some more hours on them.

Before I was using the same 2x12 open back with celestion g12h which actually sounded alright. Unfortunately I moved into a new flat with less space and I had to leave the celestions behind in our rehearsal room.

I'd got to admit that I got a certain favor for open back cabs, but I don't know if they are really the right choice for this circuit.

[Funkalicousgroove]

You need to break those speakers in!!

sounds like you have all the right stuff in there, I don't know your level of experience in building amps so please forgive me if I am covering redundant things, How is your lead dress? are plate wires long? grid wires short? how much shielded cable do you have in there? do any of your plate wires run in paralell with any of your grid wires?

the v2 snubbers shouldn't have that big of an effect being mica/polystyrene

Have you tried disconnecting the feedback on v1b? some like it with, some like it without.

[paddes53]

I already have quite some experience with amps, so I guess lead dress isn't an issue. I'd have to say that I used quite a lot of shielded cable but it is RG59 coax which only has about 14p/feet.
I just recently shielded the wire to the drive pot and the one to the od master and it didn't take away any high end, at least not that I could notice, so I guess the shielding isn't the issue
I will try disconnecting local feedback at V1b, maybe I like it better without it.

Don't get me wrong, this is already a superb sounding amp as is, but it's just that the last little magic touch is somehow missing, and I suspect it to be in the midrange. Well the amp has a maximum of 4 hours on it, so I guess I'll just change the od master 1m pot to a 100k just to see if I like it and just keep it like that until it is properly broken in

[Bob-I]

I already have quite some experience with amps, so I guess lead dress isn't an issue. I'd have to say that I used quite a lot of shielded cable but it is RG59 coax which only has about 14p/feet.
I just recently shielded the wire to the drive pot and the one to the od master and it didn't take away any high end, at least not that I could notice, so I guess the shielding isn't the issue

It still may be an issue. I've found that one or 2 runs doesn't make a difference, but 5-6 it drastic. I only use a few runs where absolutley necessary.

I will try disconnecting local feedback at V1b, maybe I like it better without it.

I put a 3 way switch on one of my amps, center off, down 22M up 44M. Subtle but nice changes in tone.

Don't get me wrong, this is already a superb sounding amp as is, but it's just that the last little magic touch is somehow missing, and I suspect it to be in the midrange. Well the amp has a maximum of 4 hours on it, so I guess I'll just change the od master 1m pot to a 100k just to see if I like it and just keep it like that until it is properly broken in

I don't know that the difference is drastic after several hours. Keep plugging away, you'll get it.

[dogears]

1) The 47k/47k feeding a dedicated OD master is fine. It is exactly the same as the ratio pot setup on 1/2 way. Same tone unless there is something else wrong.

2) Try a 10pf bright cap on the OD master. 22pf on the clean master.

3) Try 180k/2.7k plate/cathode resistors on both V1a and V2a

4) Change the 250k trimmer on your bleed to a 500k. Or add a 100k tail. 250k is too much bleed. Setting at 350k is nicer iMHO.

5) .01 midcap is fine. Need to run it up a bit to get that sweet zone.

What bypass cap do you have on V1b??

[paddes53]

Hi,

I did change the 1m od master for a 100k pot with the single
master volume yesterday. I also lowered the voltages on V1 and V2 a bit . I much prefer the amp like that a lot sweeter sounding and the clarity is also much better now.

FWIW I already run a 10p on the global master right now and the bypass caps on all the cathodes are 5uf. I already experimented with caps on the cathodes. I quite liked 10uf on V1b, maybe it would be an idea to make it switchable. Anything less than 5uf just didn't give the right amount of "growl" in the low end.

I will try to add a 100k tail to the bleed circuit just to see if i like it.
I'll also check out 180k/2,7k on V1a and V2a

I also forgot to add that I run the 100k level control almost all the way up. I think any other setting just doesn't sound right. Is this normal ?

[paddes53]

Yesterday I had some time to make a few changements so here's the outcome :

I changed V1a and V2a to 180k/1,8k but I actually didn't notice that much of a difference, so I guess I'll just leave it at that.

I also tried to add a 100k tail to the bleeder circuit but this I didn't like at all, the amp became much more fizzy sounding sout out it went again.

I am actually quite happy with the sound of the amp right now, it's just that somehow I can't really get to the last few percent which are missing.

If you've got any more suggestions I'll be more than welcome to try them out.

cheers,
Patrick

[Funkalicousgroove]

Honestly, Just Play it. I have a Joe pass/herb ellis CD that I run through my amps for about 12 hours before I ever plug a guitar in. They dont get their "tone" until around 40 hours unless you are using old seasoned trannies.