Eastern Transmission Audio Preamp II 6J4 6P3P Solen Wima

Click pics to enlarge.

Review: Eastern Transmission Preamp, Part II

Cheap Mods: My Two Preamps

Letter from Shenzhen (23-8): Materialistic Does Not Equate Costly

Note: 12/4/23: Due to the recent Failure of the ETA Volume Pot, this Preamp is now not recommended!

Eastern Transmission Audio Preamp, Part I

Part III, however, covers a serious failure of the volume pot. Highly annoying!

Part IV, on JAN GE 5670 tubes and more. Pot fixed.

In Part I, I mentioned I was contemplating mods. Indeed, even after I was pleasantly surprised by the very good results I was getting then, I still proceeded with my plans.

Since I had been using the thin, soft and excellent (dirt cheap too) Canare L-2B2AT as interconnect (here), I resorted to changing out the signal cables in both my Preamps with this Cable. BOTH Preamps employ generic Chinese shielded cables that are very thin (this makes them very easy to work with and solder). The Canare is already a very thin 25 AWG, so I estimate the ones in the preamps to be 30-32 AWG or more. This doesn't mean thinner is worse, but there's a limit, and quality of copper matters.

Eastern Transmission Audio Preamp (ETA)(Original Review here)

• Transformer Shock Absorption I refer you to my previous Dynaco PAS3 mod on how important it is to isolate transformer vibration. I don’t have much around, so I put 2 slabs of Heat Shrink between the 2 Power Trans screw terminals and the chassis.

• Cable Change I changed out the Input Signal Cables, the Cables from the pot to the board and from the board to the Output. For the first 2, I had to work around the Tiny Volume Pot, which is more prone to heat damage than larger pots. I incidentally found out the pot is 50K. While application of solder to the prongs is quick, I quickly learned it’s better to pre-tin the wires and the prongs before welding them together.

As soon as the first notes sounded, I knew the change was ALL for the better, and I should have done it earlier. As anticipated, sound was freer and fuller, more fleshed out in the mid-range, and bass was fuller too! Remarkable!

• Capacitor Change I procrastinated on this. The stock is (supposedly) red Wima (0.33, 400V). What the hell, I decided to buy some to try out as it’s not difficult to do. I bought 2 used 0.33 400V vintage TRW (RMB 17 including postage). Despite never having been a Solen fan, I also bought several “Solen”. At RMB 1.5 each (and RMB 8 postage), they cannot be the real thing, but they do look the part. The 0.33 pair I bought is 630V (but one is quite a bit larger than the other); I also bought 2 pairs of 400V ones, 0.22 and 0.47). When I loosened the Circuit Board, I noticed it said 0.22. I’m not sure if this board is from ETA. However, 0.33 shall give a fuller bass, which suits this amp. I thought about it and finally decided to install the 0.33 “Solen”.

Well, well, sound was just as expected. Sound became not only fuller, but more subtle and flowing in a way. In fact, bass now was quite awesome, tight and with heft. There was a downside. Treble was slightly rolled off compared to the Wima, partly due to slightly slower transients. But this SRPP circuit can take that. In fact, the Solen and Wima, real or not, seem to be both fine and similar in signature to the real things that I know well (e.g., the plainer sound of Wima and heftier bass of Solen). I’d think the 0.22 “Solen” and the vintage TRW would be both worth a try. When I get the urge perhaps...Right now, I’m satisfied! This is now a completely different amp from when I received it. And I don’t even have the urge to change the cheap Russian 6N3P, so finely detailed and musical it is now.

A few days later, I moved on to my other Preamp.

6J4 6P3P Preamp (Original Review here)

• Transformer Shock Isolation This Power Trans is larger and has 4 screws. So, I threaded a sliver of PVC cable skin (harvested from Mogami) onto each screw and re-bolted the trannie to the chassis.

• Cable Change This Routing was more complicated in this case. As noted from the Addendum to the article above, in contrast to the schematic, the Volume Pot is actually put last, before the Output. I saw no need to change all 4 Inputs, so I just changed one, from the Input to the Selector. Then, the Cable to the 6J4; then the cable from the 6V6 to the Volume Pot and finally from the Volume Pot to the Output.

Although both have high gains, this preamp has a diametrically opposite sound signature to the ETA. Nonetheless, the sound was also definitely significantly improved. In this case, it brought more clarity and detail and tempered a little the occasional over-luscious sound. Transient speed was also definitely improved. I’m very satisfied.

• Capacitor Change? Yes, I shall do it soon. But this circuit is more complicated and I’m not sure which cap would have the biggest effect. I shall inquire the builder. I’d think one of the 0.22 caps (stocks are generic; I’m thinking of using the Wima removed from the ETA for the job - wouldn’t that be just perfect recycling?)

Conclusions:

• 1. Cable change makes a big difference. And combined experience (not just these 2 preamps, also my FU-50 amp!) shows the Canare L-2B2AT does a very fine, even tempered, job. If your preamp sounds too dull or too bright (like many DIY efforts that use awful, silver-plated wires), it may just help. Highly recommended to all. I’d like to do the same with my APPL amp, but all the soldering joints are topped with some kind of red sealant that removal might be a problem (see pic in review article).

• 2. Cheap caps can sound good! In fact, I have heard just too many esoteric and crazily high-priced caps sound bad (in my considerable experience listening to DIY products, the more overloaded it is with boutique components, the more the tendency to sound wayward). Despite the stock cheap capacitors (mostly generic, with a few Wima, Bennic etc) in these 2 preamps, they sound reasonable, and the designers have voiced them within a budget. After the necessary cable change, caps could be icing on the cake. But keep in mind a pair of the 0.33 Mundorf caps would equal the price of the ETA preamp! Maybe cheap for you, but I’d like to maintain my sense of scale. Now, I don't actually encourage you to buy the cheap "Solen" caps except as experiment and with an open mind. If you have the time and curiosity, however, I'd welcome your feedback.

• 3. I didn’t test out the singular effect of transformer isolation as I have written about it before (see PAS3 article quoted above). I’m not the only firm believer, read the many positive comments left by the readers!