Yel­low rock Ca35H Head

Has Yel­low Rock made solid-state sound bet­ter than valves? We take a lis­ten to this new bou­tique brand be­fore the fo­rums start buzzing…

Guitarist - - Contents - Words Nick Guppy Pho­tography Joby Ses­sions

Yel­low Rock’s CA35H head is a new ar­rival on the bou­tique scene, made in Guernsey by founder/de­signer Robert Card, who brings a re­fresh­ingly open-minded ap­proach to his work. Card’s elec­tron­ics back­ground in­cludes stints at the BBC’s leg­endary Equip­ment Depart­ment in Chiswick, work­ing on lo­cal ra­dio broad­cast con­soles, and at Univer­sity Col­lege Lon­don, where he worked in the world-renowned Mullard Space Science Lab, de­sign­ing power sup­plies for satel­lites and space tele­scopes.

Back on earth, the CA35H is a hy­brid de­sign (the H stands for High gain), com­bin­ing a no-frills valve preamp with a unique out­put stage de­sign that Yel­low Rock calls Ana­logue Pen­tode Emu­la­tion, or APEM for short. Ac­cord­ing to Yel­low Rock, APEM not only re­pro­duces the be­hav­iour and clip

Yel­low Rock may just have cracked the holy grail by mak­ing ana­logue solid-state sound as good as, if not bet­ter, than valves

char­ac­ter­is­tics of a valve out­put stage, but also the au­di­ble power. The CA35H looks re­as­sur­ingly con­ven­tional, with a neat ply­wood sleeve sur­round­ing a fully en­closed steel chas­sis and a con­ven­tional re­verb spring. Inside, there are a lot of elec­tron­ics, mostly held on four cus­tom-made through-plated cir­cuit boards that have been hand-loaded with very high-qual­ity com­po­nents. One board also sup­ports a pair of valve sock­ets for the CA35H’s two 12AX7 preamp valves. The front panel con­trols use long-life sealed pots, while the CA35H’s juice comes from a switched mode power sup­ply that takes any stan­dard mains volt­age. There’s also a sub­stan­tial out­put trans­former – some­thing not nor­mally seen on a solid-state power stage. Over­all, the CA35H’s close at­ten­tion to de­tail and pur­pose­ful looks sit com­fort­ably along­side many other top­dol­lar bou­tique de­signs: it’s hand­some, built to last and should han­dle any amount of abuse.

De­spite the elec­tron­ics, the CA35H is a straight­for­ward sin­gle-chan­nel de­sign, with con­trols for gain, bass, tre­ble, mid­dle, ef­fects loop level, re­verb level and a mas­ter vol­ume. There’s a footswitch­able gain boost func­tion, a bright switch Yel­low Rock calls Twang, and a power switch that switches out­put power be­tween 35 watts and eight watts. The sparse rear panel has a pair of speaker out­lets for four- and eight-ohm cab­i­nets and not a lot else. There’s an LED to show when the CA35H is in boost mode, to­gether with a pair of LEDs that in­di­cate when the preamp and power amp stages are clip­ping.

Feel & Sounds

Once switched on, the APEM cir­cuit takes a cou­ple of min­utes to sort out op­ti­mum volt­ages – then the amp is ready to go. The first thing we no­tice is an al­most to­tal lack of noise, mak­ing us won­der for a sec­ond or two if we have a loud­speaker con­nected. Turned up to a de­cent vol­ume and with the gain con­trol at around 12 o’clock, the CA35H pro­vides a warm, vin­tage bite that sits roughly half­way be­tween AC30 and tweed Champ, which is not a bad place to be. The tone con­trols op­er­ate smoothly, and while there isn’t a huge amount of range, it’s enough to dial in most gui­tars, with the Twang bright switch adding a proper snap to mid-bi­ased hum­buck­ers.

Hit­ting the boost adds lots of ex­tra gain, pro­vid­ing plenty of drive for clas­sic rock and blues. We’re im­pressed with the Yel­low Rock’s spring re­verb, too, which has a nice smooth de­cay with none of the splashi­ness that af­fects many re­verb cir­cuits.

But what re­ally sets the CA35H apart is the APEM out­put stage, which not only has the warm, bouncy re­sponse we’ve come to ex­pect from valves, but the power, too. Those 35 APEM watts into a 2x12 speaker cab­i­net are

eas­ily enough to han­dle any size of gig, and even on the eight-watt set­ting it’s more than enough for home use.


For a first en­try into the crowded bou­tique mar­ket, the CA35H has a lot go­ing for it, and con­sid­er­ing the clever in­ter­nals, it’s pretty good value com­pared with other bou­tique heads. The preamp is su­per quiet and takes ef­fects re­ally well, while the clever APEM power stage re­ally does sound like a qual­ity valve cir­cuit, with­out the frus­tra­tions all valve amp users have to con­tend with. Yes, valves sound great, but they’re frag­ile and they wear out, so the sound you get when you switch on to­mor­row will be im­per­cep­ti­bly dif­fer­ent to the great tone you di­alled in to­day, and six months down the road those im­per­cep­ti­ble changes add up to a big dif­fer­ence that may only be cured by new valves. How­ever, if you can use a solid-state amp that sounds – and more im­por­tantly re­sponds – like a valve cir­cuit, with rock-solid re­li­a­bil­ity and con­sis­tent tone night af­ter night, what’s not to like?

Yel­low Rock may have cracked the holy grail by mak­ing ana­logue solid-state sound as good as, if not bet­ter, than valves. For­get your pre­con­cep­tions and check them out.

What re­ally sets the CA35H apart is the APeM out­put stage, which not only has the warm, bouncy re­sponse we’ve come to ex­pect from valves, but the power, too

3 1. The sim­ple con­trol panel is easy to nav­i­gate. It’s also handy to have loop send and re­turns on the front panel along with the Level con­trol 2. The power out­put can be switched from 35 to eight watts, and handy LEDs let you know when the preamp and...




5 5. The CA35’s Twang switch adds a raunchy bite to highs that sounds par­tic­u­larly good with a hum­bucker

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