Metropoulos Forum

Here's a video clip:


[youtube]http://www.youtube.com/watch?v=Fcabc00kZ7w[/youtube]


george

And another:


[youtube]http://www.youtube.com/watch?v=SsYBem8obKw[/youtube]

george

Clip #1 starting at 5:20.

Watch the lights and listen.

Spooky.


-bryan

With this latest volley of video clips amp 12380 exhibits more loudness when the volume pot is up half way. This could just simply be from a different taper percentage on the volume pots between the two amps. Nonetheless, under these conditions 12380 exhibits a fuller more complex tone with a bit more articulation or edge if you will. The increased overtones coupled with the perceived additional brightness (upper-mids & lower-high frequencies) makes it sound more "open" or presents more dimension to its tone.

When the volume is full up both amps exhibit the same loudness. In addition, the gain (distortion) between the two amps appears identical. Once again, 12380 seems to present a slightly different tone when it comes to certain chords which is mainly prevalent on the bridge pickup. Chords that seem to highlight this the most are an open A, open D, and open G. To me they sound less bright; more mid orientated. The single string stuff still sound identical to me in tone, dynamics, perceived gain, harmonic complexity, dimension, and loudness for both amps.

So, which one would I choose in a blind test?....Well, if both amps were full tilt on the volume pot I'd go with 12092. If it was a half throttle test I'd choose 12380.

I saw the youtube videos before this thread. I subscribed to George's channel and these popped up.

The similarity in tone is amazing. Only by using the A/B amp switcher could anyone really hear the differences, IMHO.

What I hear is that the vintage amp is a bit more punchy. I don't know what to attribute that to, caps, tubes?

George, if you are willing can you provide some extra information to help the rest of us get to where we want to go with our tone.

When you measured the 820 ohm resistors on V1b and V2a in amps 12093 and 12380 what are the actual readings you acquired?

Also can you offer readings for the power tubes when the voltage is dropped?
Power Tubes V4 through V7:
B+ Vol. _____ dcv (Pin 3),
Screen Vol. _____ dcv (Pin 4),
Bias _____mA (Pin 1),
Heaters _____v (Pins 2&7)

As you know these readings are important to get the brownsound with stock late 60's specs as mentioned in the quote below.

RACKSYSTEMS wrote:The screen voltage measurement was taken with a bias of 30ma to 32ma. At full output power the sag was around 80 volts. Biased to 50 ma while the variac was at 90 volt I believe it was around 354 v on the screens.

Also, you have the virtual variac feature on your replica that offers the best of both worlds. However, if one would just like to keep the dropped voltage sound couldn't this be done with an adequate resistor (i.e. V=I*R, etc.) placed on the incoming wall voltage instead of a variable variac or a dual-tapped PT and dual bias trimmer pots?

Here's an interesting approach I'm trying that should help correlate what we are hearing to actual measured data. Full spectrum sweeps of 12380 and also a 50 watt replica ('68 lead specs). From 10Hz to 50k Hz.

The trace with less lows and more highs is 12380. The trace with more low-mids and less highs is the 50 watt. I want to try adjusting the PI cap to see how that affects the highs overall, but I suspect the difference between 50 and 100 watts is showing up here, for the highs and lows.
I made a probe so I could sweep individual gain stages, which was very revealing. Especially V1. The tone stack was bang on. I tried dozens of values and tweaks there, only to return to standard 33k/500p.

These sweeps definitely don't tell the whole story, they miss THD levels and break up curves. But it's a nice piece of the puzzle.

george

VelvetGeorge wrote:And another:


[youtube]http://www.youtube.com/watch?v=SsYBem8obKw[/youtube]

george

https://dl.dropbox.com/u/64682773/12380 ... 202013.wav" onclick="window.open(this.href);return false;


george

BTW the replica was first in this clip. You can tell if you focus on the extra low mids and lows.

george

Great project! The difference is still discernible though, perhaps build an entirely NOS replica in tandem with the modern/NOS mix parts version, right down to the chicklets, mustards, RS caps and Iskras. I know the chicklets have a more open tone than the .68 mustard's, is that a 1.5uf chicklet in V2A? Also, what is the value and make of the V1A cathode cap in the 12380 amp, those seem to make a subtle difference too and you see them again and again in the old 12xxx's.

Strat78 wrote:Great project! The difference is still discernible though, perhaps build an entirely NOS replica in tandem with the modern/NOS mix parts version, right down to the chicklets, mustards, RS caps and Iskras. I know the chicklets have a more open tone than the .68 mustard's, is that a 1.5uf chicklet in V2A? Also, what is the value and make of the V1A cathode cap in the 12380 amp, those seem to make a subtle difference too and you see them again and again in the old 12xxx's.

What do you want to know (and how soon)?
I have a project lined up (one of too many ) I was going to use the Iskras, mustards F&Ts and Georges trannies with dual B+ so hope to make these comparisons myself as I already have a pair of stock 68SLs.
When I did that before I found that the original had a slightly richer tone but then the build had not been fully burned in.
Decent tubes are a big difference IMO.

Well I was gathering parts for a 50 watt JMP build for awhile, but after seeing these videos I have to have one of George's 68 Super Lead replicas. lol. I've been talking to George and decided to take the plunge (now what am I going to do with all of these amp components? lol). Man I can't believe just how exact the replica and original sound, just incredible.

It's a time machine.

Here's a new spectrum plot of the latest replica, #12094. This one has Sozo VIntage caps and all new production tubes.

12380 is the green curve

12094 is the purple curve

The sound is just what you would expect based on these plots. It sounds spot on. Even cleans up the same. That took a lot of value swapping and balancing what was changed in which part of the circuit.

One thing I noted: the old volume pot has a slightly different taper, it comes on later. The large Mil spec pot reads 1.3M and set to 5 is 1.1M between pin 1 and 2. The CTS in my replica reads exactly 1M and set to 5 is at 900k.
I had to set the replica at 4 and the original at 5 to match gain.


George

Here is a clip of the amps, using the A/B switcher. I switch pickups and roll back the volume on the guitar to show how the replica cleans up the same as the original.

Note, I called the first clip "12380 vs 12094 all on 5", but technically the volume for 12094 was on about 4.25 to match the gain.

https://dl.dropboxusercontent.com/u/646 ... on%205.wav" onclick="window.open(this.href);return false;


Then, tone controls all on 5, Volume on 10:

https://dl.dropboxusercontent.com/u/646 ... n%2010.wav" onclick="window.open(this.href);return false;


Try to guess which is which!


george