Grundig Mystery Amp, abbasaudio Hybrid Pre-amplifier, Gotham DGS-1

By mrgoodsound 

Earlier this year I had quite the eBay addiction, a terrible thing. It has subsided a bit, but I acquired quite a few pieces of equipment on a whim that I had no preset plan for. 

One of these pieces I am calling the 'Grundig Mystery Amp', a mystery because I do not have much information behind its creation or creator, and Grundig because it proudly displays a matched set of vintage Grundig transformers.

Grundig Mystery Amp

This amplifier came from a kind German seller, who claims his retired engineer friend built it and sold it to him. It is a single ended amplifier using the German EL12 pentode as an output tube and EF12 pentode as a driver tube. The chokes, output and mains transformers are all vintage Grundig units, presumably pulled from a high-end console or radio of the early 60s or late 50s. If you know anything more about these transformers, please leave a comment! Other high quality parts include Siemens capacitors and bridge rectifier. 

The greatest attraction of this unit for me was the fact that the single-chassis construction was entirely dual mono, down to separate power switches for the left and right channels. As a budding monophile, it was nice to know I could use this amplifier in a stereo or mono system without hassle. Finally, the mains transformers had secondaries for the 120 volt AC network we use in North America. Multiple secondaries on power transformers seems to be a common theme for vintage German units, and thanks to the foresight of those engineers we can continue to enjoy German tube audio around the world! I simply had to remove the Euro power plugs and replace them with US ones. 

My initial evaluation of the Grundig amp was driving my Klipsch La Scala's, using the Truth line stage and a Philips CD650 CD player. Unfortunately the EF12>EL12 combo was of moderate to low gain, and the Truth could not provide a satisfactory volume level with the output of my CD player. Though what I heard was extremely promising, I had to put the Grundig amp aside for a few months until I got another pre-amplifier. 

abbasaudio Hybrid Transistor pre-amp/head-amp

A few months ago I placed another order with Abbas from abbasaudio, this time for a hybrid headphone amplifier using germanium transistors, a 7119/ECC182 input stage, and an EZ35 rectifier. The primary motivation was to have a secondary headamp to evaluate low-impedance headphones that my OTL amplifier could not cope with. Thankfully, I had the foresight to ask Abbas to install a pre-out on this unit as well, which proved fortuitous when I realized the Grundig would not play with the Truth. 

Firstly, a brief evaluation of the Hybrid as a headphone amplifier. It is simply excellent. There is nothing for me to say that was not already said in my review of the OTL amplifier (linked above), the two are extremely similar in character, and the Hybrid gives up very little, despite residing in a chassis less than half the size. The Siemens germanium transistors used must be competitive with real triodes in their naturalness and ability to convey emotion! For tubes, I am using Amperex 7119 (made in the USA, I hope to try the Dutch-made variant soon), and a US-made 6ZY5G (an inexpensive, uncommon full-wave rectifier that Abbas suggested as a substitute). 

Next, it was time to try the combination of the Hybrid pre-amp and Grundig amp, a most unique and unlikely pairing if there ever was one. Did I mention I am unsatisfied with mainstream audio? But first I needed a rather long set of interconnects to reach from my headphone station to where the Grundig amp lay. 

Gotham DGS-1 coaxial cable

Doctorjohn was very kind to send me a care package of several wires and tubes (including the aforementioned Amperex 7119, thank you very much!), including a long spool of Gotham DGS-1 coaxial cable. My previous encounter with Gotham was only with their headphone wire, which I used to make a cable for my Sennheiser HD600s. Unfortunately I was not too happy with the result, the wire was immediately impressive with a bright, zippy character and loads of macro-detail; but the overall balance was upset to the detriment of music. The LF and lower middle lacked the proper body and weight, leading to a lean and frantic sound. 

Thankfully the DGS-1 is not like this, though it has some character of its own. I made up some long and short pairs using my favourite Switchcraft RCA connectors and evaluated them first using my headphone system to pick apart the sound character. Again, there is not much I can say that doctorjohn has not already said here, he describes the character of this wire very well. The hue is a bit dark, one might go so far as to think certain HF overtones which would ordinarily cause goosebumps are being lost, but the tone in the MF is simply enchanting. Subtle timing stuff is done well, though the wire is still a little lighter on the LF than I would like. Low piano notes did not have the full resonant weight I would expect.

I recommend this inexpensive cable in a slightly brighter or unruly system, it provides something I would describe as a 'natural dampening' or taming of high frequencies, while preserving or perhaps even enhancing emotion in the middle frequencies. It works rather well for me with the La Scala's. 

All Together

With the pre-amplifier and interconnects ready, I was able to evaluate the Grundig amp proper in the chain below.

DAC: 2008 Mac Pro + abbasaudio DAC2.2SE
Preamp: abbasaudio Hybrid Transistor
Amps: Grundig Mystery Amp
Loudspeakers: Klipsch La Scala

The Grundig mystery amp sounds fantastic! It is thus far the best single-ended amplifier I have heard or owned. I must attribute this in large to the use of vintage transformers, which have a special sound character. I do believe the Germans had already figured out the secrets of making the best sounding transformers long ago, and these arts have been mostly lost to modern manufacturers, at least in the West. 

I have come to realize the best sounding amplifiers seem to be remarkably unremarkable, in that they transmit and convey music and the emotion within intact, without adding too much flair. It seems the high end today, even within the ultra-fi circles concerned with triodes and single-ended amplifiers, are too focused on the delivery of sonic special effects, and the use of increasingly exotic and pricey passive components to achieve this. 

With the Grundig mystery amplifier, I am addicted to listening to historical recordings of famous 20th century performers, as music flows from the speakers in a way that shuts down the brain, with subtle intonations and tone all the listener can really stand to focus on. If I am in a mood to play only monophonic recordings, I simply shut off one channel of the amp and let one speaker sing. The single EL12 per channel is capable of somewhere between 4~5 watts, and has no problem with the La Scala's. These results are being obtained with more common late production 'short bottle' EL12s which I assume are manufactured by RFT, I hope to obtain some early 'tall' EL12 from the firm Telefunken soon. 

I leave some examples of delightful recordings and performances enjoyed from this setup below: