Pre-Classic Tonestacks

[marcos]

Inspired by the recent discussion in the #75 thread, here is my theory of the evolution of the 70s tonestacks:

# 13 tonestack: Treble : 1 MA pot, 510 pF cap, 100K slope
Mid : 250 KA pot, .05 cap
Bass: 1 MA pot, .1 cap, .002 and .02 on the pot ,
10 K tail.

This may the original tonestack, no other info than the #13 schematic.

# 40 tonestack: same as above but 500 KL Treble pot, .010 Mid cap

This is the same as my amp (probably same circuit as #40).
A tech once told me that #19 and many other amps from that time were the same .

3rd generation (like the Karl Ratzer amp): same as above but 250 KL
Treble pot and no .02 cap on the Bass pot (important !)

I have seen one amp done like this(forgot the SNr, it was just a Dumble amp then), and several contributions to this forum lead me to believe that it may be typical for that era (SNrs 60s - 74, toggle swiches)

Lowell George amp: Jelle once mentioned that the Lowell George amp
had 500 K pots for Treble and Bass, no further info.

This adds up to at least four different tonestacks before the Classic,
and looks to me like an evolution.However, some of this is based on
speculation and hearsay, so I would love to learn more

Looking forward to your contributions Marcos

[Max]

Hi marcos,

thanks fort the start and the info you’ve posted.

Here is, what I right now remember without the time to dig deeper at this moment.

2nd generation (current size chassis, sliding switches):

AFAIR the specs of ODR #13 are derived from a hand drawn layout. I even remember, that someone had posted it here some years ago (or parts of it?) but then it was gone again?

So we should perhaps be a bit cautious to take these #13 specs as "confirmed", at least as long as the present owner/keeper of the original of this layout does not chime in and confirms, that he can without doubts read these values as been written down in this layout. I have some doubts e.g. in regard to the .05 mid capacitor, as I have never seen (first hand and pics) such a mid capacitor value in any unmodified 2nd generation amp, neither ODR nor ODS.

But AFAIR all the unmodified 2nd generation ODR I am familiar with, had this 1MA treble pot, too.

(Jelle, what about the Lowell George ODR? Are you sure (first hand, trustworthy source?) about the 500k treble and bass pots, and that this is the still all original and unmodified condition?)

But I have never seen or heard of a 1st, 2nd or 3rd generation ODS with such a 1MA treble pot.

So if my doubts in regard to the .05 mid capacitor of #13 should be confirmed, it may perhaps be, that only the 2nd generation ODR amps have these 1MA treble pots and not the 2nd generation ODS, but all 2nd generation ODS have a 500k linear treble pot?

In this case all still original and unmodified 2nd generation ODS amps would perhaps have indeed the same tone stack:

Treble : 1 KL pot, 510 pF cap, 100K slope
Mid : 250 KA pot, .01 cap
Bass: 1 MA pot, .1 cap, .002 and .02 on the pot, 10 K tail.

And all the 2nd generation ODR, too, with the exception of the 1MA treble pot.


3rd generation (current size chassis, small toggle switches):

I am no longer 100% sure from my own memories, what I have seen myself in or have heard about the tone stack of these 3rd generation ODS amps.

Here is, what I still (hope to) remember in regard to the tone stack of the 3rd generation ODS:

AFAIR all the 3rd generation ODS I have played, had a different tone than the 2nd generation ODS amps I have played. AFAIR a bit less “dark” or “midrangy”, but AFAIR this was a subtle difference, at least not a very prominent one, but it was there.

AFAIR the effects of turning the EQ controls have been different, too.

AFAIR 3rd generation ODS amps had other pot values than the 2nd generation ODS, but I am no longer sure about the precise values, and if all the 3rd generation amps had the same pot values or if there have been differences.

AFAIR all 3rd generation amps had the same EQ capacitor values (510pf, .01, .1) and 100k slope, too.

AFAIR none of the 3rd generation amps I know myself or have heard of still had this .002 and .02 configuration at the bass pot. But I am no longer sure, if the 3rd generation amps had lost both or only one of them, or both, but one of them had been replaced by another value?

Unkown 2nd or 3rd generation specimen:

I can remember with some confidence, that someone has told me some years ago to have seen this configuration in one of the "silverface" 70ies ODS:
Tone stack as in 2nd generation, but one exception: not the .002 and .02 configuration at the bass pot, but a single 5nF capacitor between terminal 2 and 3 of the bass pot.

Can someone confirm such a single 5nF capacitor between terminal 2 and 3 of the bass pot? And if so, in which generation did he find it?

OK, so far what I remember right now. But I will try to dig out more from old notes and my memories.

What do others here know in regard to this topic?

Thanks again for the great and educational start, marcos.

Cheers,

Max

[jelle]

Below my reply to the prevoius tread before I saw this new one.

I do not recall mentioning info on the Lowell amp. I'm not saing I did not. Can you point me to the tread?

Also, the .05 midcap is suspect in these amps with the .002 and .02 caps on the bass pot. I know for a fact that with the .05 mid cap, the mid pot settings do not change the mid content much of the amp, as the low mids are already fixed by the .02 on the bass pot. This leaves only the higher mids to be altered when a .01 mid cap is installed. This could very well be the difference in tonestack behaviour that Max just described. I firmly believe that the .01 mid cap is the correct one. Simulation of this circuit using software confirms what my ears tell me. Hope this helps.

Below my post to the previous tread:

I'd love to but I cannot commit much time to it now. But I'll add some info here.

One question...how are we going to take into consideration that some of the amps were upgraded. I have seen a 70's chassis with full skyline high plate setup. Also the mods to the 70's amps, voicings for specific guitar players....

There's the tmb 1M 250K 1M with the 10K bass tail and the james config (.002 and .02uf) with .1, .05 and 500pF mica with 100k slope.

There's versions of above with mixed 1M and 500K pots for Bass and treble, my guess is that these are mods for certain players, also the james config was altered.

There's the classic early 80's with TMB 250K, 100k, 250k with 1k bass tail, no cap across bass pot and .1, .05 and 270pF ceramic with 100k or 150K slope. I have the impression this was in the early amps too with 100K slope.

Stacks above have a deep switch.

Then in the late seventies, a 'Skyline' was observed in a 50W 70's amp according to a source. I have not seen the amp, just going by the info I received.
Then the classic stack prevailed for a while and was upgraded to Skyline specs which we all know. Bluesmaster specs are well known too.

Anyway, my point is that nowadays, due to all the factors mentioned above, we will observe many types of tonestacks in these silver chassis amps. But I may have answered some of your questions.


Hope this helps,

jelle

[Max]

Jelle, thanks a lot for chiming in and all this info.

Some comments and questions:

I do not recall mentioning info on the Lowell amp. I'm not saing I did not. Can you point me to the tread?

OK, so up to now no all original and unmodified 2nd generation ODR with a 500K treble pot is confirmed. Am I right?

Also, the .05 midcap is suspect in these amps with the .002 and .02 caps on the bass pot. I know for a fact that with the .05 mid cap, the mid pot settings do not change the mid content much of the amp, as the low mids are already fixed by the .02 on the bass pot. This leaves only the higher mids to be altered when a .01 mid cap is installed. This could very well be the difference in tonestack behaviour that Max just described. I firmly believe that the .01 mid cap is the correct one. Simulation of this circuit using software confirms what my ears tell me. Hope this helps.

This is my opinion, too.

One question...how are we going to take into consideration that some of the amps were upgraded. I have seen a 70's chassis with full skyline high plate setup. Also the mods to the 70's amps, voicings for specific guitar players....

My suggestion: Not at all. In this "pre-classic tone stack" thread we should discuss only still all original "pre classic" amps without later modifications. All else will only lead to more confusion (IMO).

There's the tmb 1M 250K 1M with the 10K bass tail and the james config (.002 and .02uf) with .1, .05 and 500pF mica with 100k slope.

Why is this called the "james config."? Did everyone ever meet an original 2nd generation ODS (not ODR!) with this tone stack (1M, 250k, 1M)?

There's versions of above with mixed 1M and 500K pots for Bass and treble, my guess is that these are mods for certain players, also the james config was altered.

Confirmed, trustworthy source, more details, links, series number?

There's the classic early 80's with TMB 250K, 100k, 250k with 1k bass tail, no cap across bass pot and .1, .05 and 270pF ceramic with 100k or 150K slope. I have the impression this was in the early amps too with 100K slope.

What is meant by "270pF ceramic"?: snubbers or treble cap?

Then in the late seventies, a 'Skyline' was observed in a 50W 70's amp according to a source. I have not seen the amp, just going by the info I received.

Confirmed, trustworthy source, more details, links, series number?

Thanks again Jelle!

Have fun and a great day,

Max

[talbany]

The info I have other than what was already posted on 13 and 40 is a later upgrade done on an earlier 50w I believe done in the 80's.. It was the inspiration for the famed Dumble Fender mod posted on Schematic Heaven (axe the Deep) many here asked where this stack came from and if Dumble did actually use it and the answer is yes he did....Same values although my info says 18k bottom of the bass pot not 1k8 (which doesn't do much).. Also the mid pot is wired backwards on the layout.. Other than that and according to most of the info posted so far looks 3rd generation.. Since the amp was upgraded I know doesn't do much in the way of verifying the evolution if there is one but thought I would throw this in there.. As more contribute maybe we can identify which class of stacks this fall into..

FWIW.. This is a very cool stack.. Gives good range on both Jazz/Rock settings works well for both Humbuckers and Singles.. throw this stack in a 100K amp with a Strat and it will scream at you..My minuscule contribution to a wonderful thread so far.. Thanks Max/Marcos/Jelle so far..

[Structo]

That is kind of weird on the mid pot.
If I am reading it right, it is showing the right two lugs jumpered then grounded.
Then the wire from the mid cap .047uF on the board connects to the left lug.

Wouldn't that make the pot act backwards?

Because normally the left lug is grounded and the mid cap is connected to the wiper.

[jelle]

Also the mid pot is wired backwards on the layout.

[Structo]

DOh!

That's what happens when you skim read.

[marcos]

Hi guys,
I was suspicious of the .05 mid cap in the #13 schematic,too, but I took
it from the schematic here in the files.I could not really read the value on
the hand drawn layout, but the .01 value would definetely make more sense.
AFAIR the 3rd generation amp I have seen had the configuration Max
mentioned, a .005 in place of the .002 cap, and no cap connected to the tail.I had actually forgotten this, it is of minor importance IMHO.
I will have to look for the thread where the Lowell George amp was mentioned, maybe it wasn´t Jelle´s contribution.However,
a tonestack with 500 K pots for Treble and Bass would make perfect sense.AFAIR the Jim Kelley amps used those values, too.

Marcos

[Max]

AFAIR the 3rd generation amp I have seen had the configuration Max
mentioned, a .005 in place of the .002 cap, and no cap connected to the tail.I had actually forgotten this, it is of minor importance IMHO.

marcos, this confuses me a bit, because in your first post you wrote:

"3rd generation (like the Karl Ratzer amp): same as above but 250 KL
Treble pot and no .02 cap on the Bass pot (important !)"

Why then do you think, that the .005 "is of minor importance"?

Do you still remeber the pot values of this amp with the .005 cap?

Was the one with this .005 cap the "Karl Ratzer amp"?

Thanks again and all the best,

Max

[marcos]

Hi Max,
it could be that the amp I saw and played was the Karl Ratzer amp,
it belonged to a number of players I was in contact with in the 80s/early
90s.I played it side by side with my amp, and got a chance to inspect it
while it was being serviced.I was mostly looking for differences between
this specimen and my amp, so, while I don´t have a full schematic, I remember some of the differences quite clearly.I am quite certain
the tonestack was similar in most respects, i.e. TMB caps, but I remeber
the Treble pot was 250 KL (CTS type) while my amp had 500 KL (big Centralab pot, clearly visible on the #40 pix), and the missing .02 cap on the Bass pot.At the time I thought that maybe it was a mod, but the soldering joints seemed untouched.
The reason I believe the change from .002 cap to .005 is of minor
importance is that it is only active when in Jazz mode, it is shorted
in Rock mode.
What I clearly remember is the difference in tone between the amps
(2nd and 3rd generation): My amp was fairly midrangey, while the other
had way more bass (not a subtle difference at all), a little cleaner treble,
also the treble control on the 3rd generation was fairly ineffective.
The owner at the time was complaining about the somewhat fuzzy
distortion of the amp, which I think is true for many of the 70s amps.
Overall I thought the 3rd generation amp was better sounding,
although it was real easy to mod my amp in that direction.
I only inspected the preamp, so there might be more differences in the
PI and power amp stages.Hope this makes things a little clearer,
thanx for everybody´s input, hope there´ll be some more

Marcos

[Max]

double

[Max]

Marcos, Jelle, Tony, and all others:

to avoid any misunderstandings, and to clarify this with patience and step by step, please let me ask again, if I've got everything right up to now in regard to the tone stack of the 2nd generation ODS amps (not ODR and no other generations and only unmodified amps!):

All 2nd generation ODS amps that are known to you and me first hand or at least from high resolution pictures (and not only from schematics or hearsay!), and that we all are sure about, that at the time we have seen them first hand or the pictures have been taken, they have still been in the same condition as originally built by Alexander and without any later modifications, have this tone stack:

Treble: 500KL pot / 510pF treble cap
100k slope resistor
Mid: 250KA pot / .01 mid cap
Bass: 1 MA pot / .1 bass cap / .002 and .02 cap soldered at the bass pot’s terminals

Do we all agree in this?

Cheers,

Max

[ChrisM]

How about we see some hi-res pics so then we can all see for ourselves and agree.

[marcos]

There's the tmb 1M 250K 1M with the 10K bass tail and the james config (.002 and .02uf) with .1, .05 and 500pF mica with 100k slope.

There's versions of above with mixed 1M and 500K pots for Bass and treble, my guess is that these are mods for certain players, also the james config was altered.

jelle

Hi everybody,
it should be taken into consideration that many of these amps,
were made for the German importer, Applied Acoustics,
so I doubt they were voiced individually.This is definetely true for
all of the amps I have seen.From what I have learned these past few days
it seems that there is a version with a change in the james config with
a .005 cap plus the .02 cap connected to the tail.As I´ve said before,
only a minor point IMHO
Marcos