Soursound 1202-84 repro

[playloud]

I know there has been a dearth of companies making accurate transformer replicas in the last few years, so I was excited to see a new entrant pop up recently: Soursound, in Portland.

I now have some experience with Bryan Sours - who has rewound the blown Marstran/Heyboer 1202-84 from my JTM 45/100 clone - and can report that he is a joy to work with and the iron sounds fantastic!

The other good news is that he has copied the winding geometry from this one, so is now able to offer the 1202-84 to others. If you want a nice layer wound OT with attention to detail, I highly recommend it. He is also offering a Dagnall 100w set (C1998/T2562) and working on 18W and JTM45 sets.

Here's the blown Marstran iron I sent him. As you can see, it was wound on a bobbin (rather than being layer wound, like the originals):



Upon receipt, Bryan tore it down and made a few interesting observation:

- The varnish had not managed to fully impregnate the core. Apparently Heyboer submerge their transformers in a vat of varnish, in batches, and basically wait until it stops bubbling/achieves a steady state. Although much less laborious than using a vacuum pump to do it manually, this approach can lead to air pockets, as it clearly did here.
- The 4 ohm secondary wire was really thin. The originals only had 3 taps (100V and 8/16 ohms), and Marstran (like many other builders) had added the extra 4 ohm tap for convenience. However, it isn't possible to remove the 100V winding without significantly affecting the winding geometry apparently, so it was just buried within the transformer (i.e. without an exit wire). Having the additional tap increases the total volume of wire which has to be contained within the transformer, hence the lighter gauge of wire (and increased arc potential).
- The secondaries exited really close to each other, another location for arc potential.
- Apart from the aesthetic layer of paper on the outside, all internal insulation was tape - and this was used inconsistently (i.e. different thickness per layer).

I don't really hold any of this against Heyboer, as they are building to a particular price point (and are still in business!) but do think it's worth noting. Compared to, say, a Merren (layer wound, original spec wire etc.), it's really a different level of construction.

Bryan suggested that he rewind to the original design, without the 4 ohm tap. He also revised the secondary wire colors to make them historically accurate (as shown on the following schematic).

Here are some progress pics he sent me during the rewinding process. It also got some new zinc-plated endbells with a cool patina:








And here it is in the amp, back on the other side of the Pacific. It certainly looks the part!




As for the sound...

I actually had a good recording of the previous OT not long before it blew, together with an input recording that I played through my reamp box (when I was testing out the transparency of the Powerbrake). So I was able to do a pretty much head-to-head comparison of the two OTs (using the same IR, amp settings, input gain and TAE). The only thing that changed was 2 of the GECs and I upped the screen resistors from 470R to 1k (shouldn't make much difference at this level of overdrive).

Here are the results:



I know sound is subjective, but I was quite blown away by how different it sounds! Especially considering that the lamination and winding geometry/turns ratio are the same. Bryan explained the dielectric properties of varnish/wire/insulation all make a difference, primarily via coupling capacitance between the primary and secondary, but it's the kind of difference that most modern transformer winders would consider immaterial. I guess we can decide for ourselves!

I also slapped together a quick mean-spectrogram which confirms what I'm hearing. I'm starting to see why transformer-winding is such a rabbit hole!



Oh, and here's one more clip of me noodling aimlessly to give a better indication of overall tone:



Apologies for the long post, but hopefully this will be helpful to other members!

 

[Whatwhatringrang]

Nicely done. Interesting read about everything ,the info and explaining It . Also cool hearing both.

 

[playloud]

Here's another thing that's interesting (Bryan's suggestion, as I was plotting spectrograms...)



This shows how the OT saturates, at different frequencies. I varied the level of the input signal (the lines in the graph - labelled by output signal volume in Logic), and you can see how quickly each frequency band reaches its maximum. You can see the mids saturate earliest - the sound of rock and roll!

 

[_Steve]

That is seriously cool - especially the top graphs. Im really surprised at the empirical differences!! Thanks for posting

Im trying to get my head around the saturation graph.. Was it in a circuit and/or loaded with a speaker/attenuator or was it an isolated DUT-style test of just the iron?

 

[playloud]

That is seriously cool - especially the top graphs. Im really surprised at the empirical differences!! Thanks for posting

Im trying to get my head around the saturation graph.. Was it in a circuit and/or loaded with a speaker/attenuator or was it an isolated DUT-style test of just the iron?

It was in circuit, loaded with the TAE and recorded with a T1281 IR. All I did was vary the level of the input signal from the reamp box to the head, in stepped increments. Each increment increased the loudness of the resulting signal in Logic, measured in LUFS (from -42.2 to -19.5).

The red line at the top (0 dB reference for each frequency) represents the loudest signal (amp clipping hard), and every other curve is relative to that.

The point is basically to compare the difference between the lowest line (-42.2) and the top at each frequency. In that mid range frequency (~1k), it's only 15dB; compared to almost 25 dB around 7k (note: frequency is on a log scale). My interpretation is that the OT achieves "saturation" earlier at 1k compared to 7k, although I realize there are other factors at play.

Does that sort of make sense?

 

[_Steve]

Yup makes sense thanks. Is it possible that a lot of that observed effect could be explained by the speaker/load impedance curve and the NFB dampening that out as it's pushed harder? As always I could be wrong... Fascinating stuff!

 

[playloud]

Yup makes sense thanks. Is it possible that a lot of that observed effect could be explained by the speaker/load impedance curve and the NFB dampening that out as it's pushed harder? As always I could be wrong... Fascinating stuff!

Honestly, you probably know more than I do. It definitely has to do with those elements. I probably should have phrased it as "how the OT saturates in circuit (with the load impedance + NFB)", but it may be more accurate to say "how the load saturates (with the other two)", as that comes last in the chain.

From the little I know, I believe the coupling inductance (which is similar to the coupling capacitance, in that it would be non-existent in an "ideal transformer" - and affects low frequencies in this case) is related to the actual transformer saturation. Perhaps someone else knows? Sometimes I wish I'd studied physics!

 

[_Steve]

Honestly, you probably know more than I do. It definitely has to do with those elements. I probably should have phrased it as "how the OT saturates in circuit (with the load impedance + NFB)", but it may be more accurate to say "how the load saturates (with the other two)", as that comes last in the chain.

From the little I know, I believe the coupling inductance (which is similar to the coupling capacitance, in that it would be non-existent in an "ideal transformer" - and affects low frequencies in this case) is related to the actual transformer saturation. Perhaps someone else knows? Sometimes I wish I'd studied physics!

It's a topic thats hard to get solid info for on the web. I'd love to learn more about it myself. A while back I was playing with my own wound coils trying to deliberately saturate them with different core materials but it's another half finished project sitting on my garage bench

 

[Marcomel79]

I know there has been a dearth of companies making accurate transformer replicas in the last few years, so I was excited to see a new entrant pop up recently: Soursound, in Portland.

I now have some experience with Bryan Sours - who has rewound the blown Marstran/Heyboer 1202-84 from my JTM 45/100 clone - and can report that he is a joy to work with and the iron sounds fantastic!

The other good news is that he has copied the winding geometry from this one, so is now able to offer the 1202-84 to others. If you want a nice layer wound OT with attention to detail, I highly recommend it. He is also offering a Dagnall 100w set (C1998/T2562) and working on 18W and JTM45 sets.

Here's the blown Marstran iron I sent him. As you can see, it was wound on a bobbin (rather than being layer wound, like the originals):



Upon receipt, Bryan tore it down and made a few interesting observation:

- The varnish had not managed to fully impregnate the core. Apparently Heyboer submerge their transformers in a vat of varnish, in batches, and basically wait until it stops bubbling/achieves a steady state. Although much less laborious than using a vacuum pump to do it manually, this approach can lead to air pockets, as it clearly did here.
- The 4 ohm secondary wire was really thin. The originals only had 3 taps (100V and 8/16 ohms), and Marstran (like many other builders) had added the extra 4 ohm tap for convenience. However, it isn't possible to remove the 100V winding without significantly affecting the winding geometry apparently, so it was just buried within the transformer (i.e. without an exit wire). Having the additional tap increases the total volume of wire which has to be contained within the transformer, hence the lighter gauge of wire (and increased arc potential).
- The secondaries exited really close to each other, another location for arc potential.
- Apart from the aesthetic layer of paper on the outside, all internal insulation was tape - and this was used inconsistently (i.e. different thickness per layer).

I don't really hold any of this against Heyboer, as they are building to a particular price point (and are still in business!) but do think it's worth noting. Compared to, say, a Merren (layer wound, original spec wire etc.), it's really a different level of construction.

Bryan suggested that he rewind to the original design, without the 4 ohm tap. He also revised the secondary wire colors to make them historically accurate (as shown on the following schematic).

Here are some progress pics he sent me during the rewinding process. It also got some new zinc-plated endbells with a cool patina:








And here it is in the amp, back on the other side of the Pacific. It certainly looks the part!




As for the sound...

I actually had a good recording of the previous OT not long before it blew, together with an input recording that I played through my reamp box (when I was testing out the transparency of the Powerbrake). So I was able to do a pretty much head-to-head comparison of the two OTs (using the same IR, amp settings, input gain and TAE). The only thing that changed was 2 of the GECs and I upped the screen resistors from 470R to 1k (shouldn't make much difference at this level of overdrive).

Here are the results:



I know sound is subjective, but I was quite blown away by how different it sounds! Especially considering that the lamination and winding geometry/turns ratio are the same. Bryan explained the dielectric properties of varnish/wire/insulation all make a difference, primarily via coupling capacitance between the primary and secondary, but it's the kind of difference that most modern transformer winders would consider immaterial. I guess we can decide for ourselves!

I also slapped together a quick mean-spectrogram which confirms what I'm hearing. I'm starting to see why transformer-winding is such a rabbit hole!



Oh, and here's one more clip of me noodling aimlessly to give a better indication of overall tone:



Apologies for the long post, but hopefully this will be helpful to other members!

Beautiful workmanship on the transformer. And nice playing and tone too! That amp is a beauty!

 

[Central Scrutinizer]

Thank you for taking the time to break this down for this plebeian.

Nice playing.

 

[Guitar-Rocker]

Did they give you an idea of when the JTM45 iron would be ready to offer?