Most versatile "platform" to try out circuits

[VintageCharlie]

Hi folks,

i'm new to the forum, so first i'd like to say hello to everyone!

As it seems impossible to record a true live tone (recorded amps always sound drastically different to what you hear them like on the high volumes they operate at), and as i can't try out many amps live where i live, i am thinking about building a "platform" on which i can test out various amp designs, to make up my mind on which amp suits my needs best.

The most expensive parts of a build are transformers, chassis and tubes. The smaller components don't break the bank. From what i've read (not sure if it's true), it's the schematic that makes the biggest difference in tone (provided you get proper voltages and impedances from the transformers). If this is true, then it might be a good idea to get a big chassis that can accomodate any tube configuration, get trannies that are as versatile as possible (multiple voltage taps for the PT, or some sort of variable PT and multiple primaries for the OT).

The idea would be to not be obliged to buy new trannies/chassis for every build.

Are there some options out there that would fit these needs? I'd be interested in building variations of 2x el84, 4x el84, 2x and 4x various octal tube combinations (e.g. el34, kt66, 6l6, 6v6). Are there any PT's and OT's that would have all or most of the voltages/primaries needed to fit the task? Or maybe i could get two PT's and OT's that can cover all of this ground?

I understand that a perfect clone of a specific design would require a perfectly cloned OT - same materials, winds, etc., but, when talking about Marshalls (in my listening experience), for example, the difference in tone is not THAT drastic when putting Drake or Dagnall OT's in the same amp. Of course, the tone changes, but not THAT much - you get a bit more/less bandwidth, clarity, highs/bass, etc., but even in an A/B comparison the difference isn't jumping out at you. Changing from lead to bass spec, for instance, does change the tone much more. If this holds true to other designs too, then it might be worth to look for such a tranny?

Or would it be a better idea to stick with one type of output stage and just play around with the different preamp circuits?

Has anyone maybe done something like that? I searched around the forum, but didn't find anything (wrong keywords probably).

I'd appreciate any input very much, as i'm not sure if it's that bright of an idea and if it's worth to pursuit it.

Thanks and best regards,


VintageCharlie

p.s. the title was supposed to say "amp shcematics" at the end, but i don't seem to be able to correct it now.

[Structo]

What I did before I built an amp was try to listen to as many clips as I could of recorded amps.
I know it isn't the same as being in the same room with them but you still can get an idea of the tone of the amp.

Maybe you have a favorite professional guitarist you admire their tone and guitar playing style.
Sure a lot of what you here is from their fingers and the way they play but the base tone is still there.

For me it was the Dumble Overdrive Special.
That is what led me to this forum since there are a bunch of guys here that like them as well.

So after studying a lot of the information here I decided to build one.
My first amp in that series was a kit, a sort of lite version.
Then I built a 100w clone.
Lots of fun and it sounds good as well.

Now if you want to just try a bunch of different preamp circuits and plug them into a power amp, you need to decide if you want a Marshall style power amp or a American Fender style.
Sure there are others but those two are broad strokes of tone.

Then just try different preamp styles and experiment with the gain and number of stages, tone stacks, etc. to find your ultimate goal.

[LeftyStrat]

I have what I call my 'Mule.' It is an Electar 30R that wasn't working that someone gave me.

I've modded that amp into so many iterations, I don't think I could list them all; several 18 watt variants, Matchless Lightning 15, Matchless Spitfire, etc.

It's a great way to try various preamp configurations. It's not going to allow you to try out every amp design. But the price was right.

So finding a good mod platform similar to a single topology you're interest in is a great way to go. But I don't think you could ever come up with a universal platform, there are just too many variables. The sound of some old Tweeds are very dependent on the specs of the PSU. So a PT that you could use to build a 100w Marshall just isn't going to get the total feel of the amp.

You're probably better off knowing the specs of several amps you want to build, and keep an eye on eBay for appropriate iron. You can also pick up some good deals at your local ham swap. Another thing to watch for on eBay is old organ amps, "organ donors" as I like to call them.

Over time my collection has grown enough that I can usually find something very close to anything I might build. Of course, when I find something I really like, I'll usually buy proper transformers, chassis, etc. to do a proper build.

You'll also find that once you build one, you'll catch this disease most of us have around here, and will want to keep something you've built, but still have the urge to build "just one more."

[selloutrr]

Try multiple microphones. Ribbon mics will go a long way toward capturing a natural tone of an amplifier. The rest is knowing how to shape the eq to match what your hear with your ears.

Since most recordings have more instruments in the mix then just a single guitar. The full spectrum of the guitar is conflicting with other instruments requiring it to be shaped to fit the final mix. The greater good if you will.

You should be able to listen to albums find the sound you like and with minimal research learn what equipment made that happen. If you are searching for an at home album tone. If the album is with in the last 10 years give up. And buy antfarm or a line6 pod.

[VintageCharlie]

Thanks for the tips guys!

I do have some amp modelers and i use them with redwirez impulse response cab sims + altiverb for ambience/reverb/room simulation. It gives me quite good results, very "pretty" and pleasing and endlessly modifiable. BUT, when i run a DI signal of my real 45/100 (through the hot plates line out) through the same digital chain, it's obvious that the modelers can't approach the harmonic detail, full and punchy midrange and some of the werid stuff that happens to real tubes, when they are pushed over their limits. For approaching my "heroes" tone i did just that - most of them play big marshalls, so i built a JTM 45/100, which i love for what it does (except the bit of ghosting, that i hope to get rid of at some point, without increasing filtering).

But this time i'm looking for "my own" tone. I've heard great clips of many different amps and they seem to be the right thing. But i had an experience with an 18w marshall - great clips, but i couldn't live with the tone i got in my room - no bottom, fuzzy mids and too spikey in the highs. I too got infected by the GAS caused by Greg V's fantastic clips, but i got wiser after my 18w marshall experience from years ago (not connected to Greg V's demos at that instance) - besides terrific playing, the way it is recorded has also a very dramatic effect on tone. Hence i thought such a "tour" through various schematic designs based on the same platform (PT, OT), might be worth a try. In worst case it might be 2 platfroms - one for say 2x or 4x el84 style amps and one for octal output stage, or maybe, as suggested, one for british, one for american style tones.

On the other hand, i think it is a good argument to look for some cheaper trannies for various purposes on eBay, as, if i change the circuit from one to the next, i can't a/b the various designs anymore and would have to rely on the recorded tones of my experiments again, which would kind of defy the whole purpose again.

In your experience, is it enough to change the preamp, tone stack, etc., but stick with the same oputput stage, to approximate different amp sounds? Would a marshall circuit sound ANYTHING like a marshall through a 2x 6L6 black face type output stage and vice versa? Would an ac30 tone stack, preamp sound anything like a vox through a 2x 6L6 or EL34 output stage? (looking into the direction of Structo's advice).

As for Marshalls, my guess is that one could get a good approximation, as most of the character seems to build up until the phase inverter, which is a reason for PPIMV working rather good in this circuit? But i guess that it's not the case for all amp desings?

(sorry for the long posts!)

[sliberty]

Triode carries a power transformer that allows you to hook up for several different voltages. And Hammond makes so-called Universal Output Transformers, but only in low watt configurations. The 125E should allow you to do sever different 15 watt amps though due to its configurable primary.

[VintageCharlie]

Thanks sliberty! I guess this is the one you mean:

http://triodeelectronics.com/the-conver ... ormer.html

That seems to be EXACTLY what i was looking for. I guess it could be used for, say, super reverb, 50w dumble types, etc.?
Only problem is that it only has the 120v primary for US, if i understand it correctly. I'm in Europe, so i'd need something like that, just with a 240v primary.

Having one of these in 240v would be a great starting point for further explorations. So, i'd narrow the platfrom down to ~30-50w amps (i'd be after something practical and rather mobile anyway).

[sliberty]

Not sure if this is the same transofrmer or not, but the one listed on the Magnetic Components site appears to support 240V among others.

http://www.classictone.net/40-18069.html

See the various connections on page 2 of the pdf:

http://www.classictone.net/40-18069.pdf

[VintageCharlie]

After digging through the net and looking at various options, i think this is what i might go with. Ingo in germany offers a 45/50w PT with taps for 350v and 325v and a 36w pt with taps for 290v and 275v. His prices are very fair and i would end up roughly at the same spendings with both of these trannies as when i'd get one of the 3-tap PT's from triode or classictone in US (due to all the postage and tax hassle). And then i'd have 2 speperate PT's for 2 amps, which can't be bad.
Both of these PT's have 6.3v and 5v (tube rec) supplies.
So this would cover 275v, 290v, 325v, 350v. From looking at most amp design specs - including vox, marshall, fender, trainwreck and others, it seems like this would allow me to make nearly any 30-50w amp imagineable - is this correct?
One thing though - it wouldn't be possible to do a 2x el84 amp with a 36w spec PT, or would it be no problem?

For the OT, which is a far more delicate matter, i might start out with something at about 4k primary (in this case the 3.5k of a JMP-50 style OT). It seems to me like this 3.5k (hopefully close enough to 4k?) primary would be most versatile, as i see it on ac30, Super Reverb and most other black face era Fenders, most 50w marshalls (3.4-3.6k to be precise) and probably lots of others. Of course, the size, thickness and windings of the respective OT's have all an effect on the tone - the OT seems to be like a bottle neck for the whole amp, which decides on the frequency bandwidth. But besides that, techncially speaking, the ~3.5k primary would work well with all the designs, that ask for a 4k primary?
As most of the classic amps had undersized OT's (even more undersized as the Drake on the 50w marshalls), it might do ok for many of the designs (except that it might have a wider bandwidth than say an ac30 OT or a Super Reverb OT, for instance)?

Another nice candidate for such a task seems to be the Radiospares OT with 6.6k, 8k and 9k primaries, which is really on the small side of things, but should do well at aping the various undersized OT's of the days gone by. It lacks the 4k (or 3.5k) primary though.

What would you think of this approach? Totally bogus, or worth considering? (i'm simply not sure if it is technically as simple as i'm trying to imagine all of this).

[LeftyStrat]

For experimenting, remember you can always mismatch speaker impedance. So you can get 3k to 12k from 6k by using different taps.

Not sure where you're located (you should update your profile), but I love Dynaco OT's. The A470 is 4.3k and originals can sometimes be had cheap on eBay. Reproductions are available from Triode Electronics http://www.triodestore.com/noname.html

[overtone]

What would you think of this approach? Totally bogus, or worth considering? (i'm simply not sure if it is technically as simple as i'm trying to imagine all of this).

It is not quite clear to me if you want to test the exact circuits or just get close enough? I am assuming just close enough.

Regarding the PT:
1. If you are in Europe, my advice is to run with the two IG PTs, but are you paying attention to the current ratings for what you intend to do? For instance the PTs for TW circuits tend to be 300mA. You may well get away with less.
2. You can always use the 36W PT for the 18W amps, the voltage should be the same + you will have current in reserve. Some amps were under specified for current and if you really need to starve your circuit you could consider using a suitable valve rectifier to create a bottle neck.

Regarding the OT:
1. 4k = 3k5 for "just close enough".
2. Consider mismatching as suggested by LeftyStrat above, or "fudging" as Merlin calls it.
3. Some builders, way more experienced than me, call the OT the "tone control".
4. Personally I cannot really talk about "tone", but the IG OTs do have clarity of response. I think that is relevant to your OP.
5. Where are you sourcing the Radiospares OT with 6.6k, 8k and 9k primaries? You have me interested in that one.

Finally, I would like to suggest that you read the post from selloutrr again.
You will certainly gain a lot of knowledge with your project as you have described, but I am not sure it really will answer the question in your OP.
In the end, when recording, the sound engineer is more important than the choice of amp, OT, PT etc.
If you really want to get a decent recorded sound with the energy of playing live, take a deep look into the art of recording guitar amps. It really is an art.

Best, tony

[rdjones]

5. Where are you sourcing the Radiospares OT with 6.6k, 8k and 9k primaries? You have me interested in that one.

Here's one (not mine ...)

http://www.ebay.com/itm/220896030428

http://www.mercurymagnetics.com/images/ ... 45RS-L.pdf

[VintageCharlie]

Thanks overtone!

I was looking into these: http://www.marstran.com/JTM45%20RS%20Ou ... former.htm

From Marstran. But, yes Mercury magnetics does them too and quite a few others do a 6.6k and 8k version.

As i've been quite a bit into the Marshall clone cork-sniffing field, have read loads of stuff on various Marshall trannies. The Marstran version seems to be a favorite among mosty of the guys who have tried many different clones of the same Radiospares OT - but, as always, that's a highly subjective thing. The original was made by Radiospares and was used in early JTM-45's and early 4-hole AC30's too. It iss supposed to be a rather cheap hi-fi OT, but it was a high quality OT (Parmeko being one of the rumored suppliers for those).

[VintageCharlie]

Overtone, of course i missed the 300mA rating on the trainwreck PT. Will take a more thorough look at the mA ratings. of various PT's.

But, yes, the idea is to get "close enough" to as many circuits as possible, to be able to test them (or close approximations of them) out. Would you consider +/- 5-15v "close enough", or would these voltage differences cause major tonal differences too?

Another thing i can think of in regard to the PT would be involving some sort of variac, but in a way that it effects only the high voltage tap, leaving 5v and 6.3v alone. I guess that might be possible in theory, but not very practical, as i'd have to take some PT wires out of the amp and then back in?

Thanks and regards,

Karlis

[overtone]

Karlis,

5% of 300V is 15V, so I would not get too worried about that kind of difference. Most guitar amps were made to wider tolerances than that.

When you research each amp, you may come across some kind of "Holy Voltage" opinion for a certain part of the circuit. If you see that, then by all means try to aim for it. But don't get too hung up about it. Usually you can get each section or node easily to within 5V of the target by adjusting the dropping resistors. In fact any "off" voltages may be even more to your own taste. You just have to try it out and be creative.

Variacs are kind of useful when cooking up an amp. I don't really care for them in a finished amp. You can use a separate transformer for your 6,3V and 5V by the way. Someone is going to mention VVR, I'm sure. There, I just did!

Best, tony