On the bench Archives - BN1studio

On the Bench: Allison Research Gain Brains & Kepexes

bn1studio — Thu, 15 Aug 2024 21:04:18 +0000

New arrivals include a rack of Gain Brains and Kepexes. These are the original versions. not the later Mk IIs, and the gain Brains are FET-based

These will be stripped down, cleaned, recapped, tested & racked in pairs in 1U cases with internal power supplies and XLR connectors

Email shop@bn1studio.co.uk if you’d like to be informed when they will be for sale

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On the Bench: Shure FP42

bn1studio — Fri, 01 Apr 2022 16:21:19 +0000

The FP42 is a very compact unit, packing multiple circuit boards into a small case. The same size as the earlier M267, the FP42 has way more electronics in the same space, so it’s a challenge to maintain

After firing up the scope the problem was found in under 60 seconds…

See the FP42 in the shop

Shure FP42 on the bench

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On the Bench: Valley 400 Channel Strip

bn1studio — Thu, 23 Sep 2021 21:49:53 +0000

Originally designed as voice preamp / compressor for radio & voiceover work, the Valley International 400 is a rare item in the UK. It has all the features of current channel strips so that’s what I will call it

I’ve spent some time with the 400, working on modifications to make it more flexible. The EQ points don’t work particularly well with music sources so I’ve changed them. I’ve also added a line input

See the Valley 400 in the shop

Valley International 400 Channel Strip

Valley TA-103 Transistor Array

Valley TA-101 Custom VCA

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On the Bench: UREI 565 Little Dipper Filter Set

bn1studio — Tue, 17 Nov 2020 11:40:26 +0000

Classic UREI filter set traditionally seen in broadcast, film & archiving studios for noise & hum filtering. The 565 has sweepable high- and low-pass filters plus two boost / cut notch filters for cutting narrow-bandwidth notches in the audio spectrum. Each filter has a wide, narrow and T-shaped super-narrow notch setting. They’re the secret weapon of a number of engineers who use them to tame ringing snare drums…

These are rare items but I had three on the bench recently!

UREI 565 Filter Set

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On the Bench: Meyer CP-10 Equaliser

bn1studio — Mon, 19 Oct 2020 21:51:11 +0000

I’m a fan of the Meyer CP-10 for many reasons, some of them sonic but others not as obvious. Originally designed for live sound work, the CP-10 is constructed in a completely different way to most other pro audio gear

It uses a backplane with plug-in modules – quite an old-fashioned approach but one that has advantages when the unit is in service & racked up. The EQ is modular, with each band having a dedicated board. This means there are six boards per channel – 5 bands and a filter – plus power supply and input / output board. The filter boards can be removed with the CP-10 still racked & connected – just remove four screws holding the front panel in place, remove the panel then pull out the card

Meyer CP-10 Internal shot

Meyer CP-10 detail of backplane & plug-in cards

The CP-10 uses very high-quality Clarostat sealed plastic pots, high-end capacitors and a power supply with a toroidal transformer – unusual for American gear

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On the bench: UREI 530 Equaliser modifications

bn1studio — Sat, 03 Oct 2020 12:42:24 +0000

UREI was a major manufacturer of equalisers through the 70s, 80s & 90s and the 530 was one of the earlier stereo graphics EQs. It’s a pretty standard opamp-based equaliser with ten octave bands, but it’s liked for the way the EQ bands interact

“Those older Urei graphics are proportional Q designs, great for getting sounds as they extrapolate the curve into a smooth one”. Jim Williams, Audio Upgrades

The one drawback with these older UREI Eqs is sticky pots. JJ Electronics in the USA has a cure for this – a new circuit board to mount replacement Bourns pots. The job is more complex than it sounds, as it requires the pots to be mounted closer to the front panel, but this makes the pots much smoother in operation

We’ve recapped this 530, upgraded the power supply and put larger bipolar caps in the audio path. We’ve done the fader replacement & the EQ tests fine. The original knobs have been replaced with neat soft-touch plastic sleeves from Thonk

We can supply XLR pigtails to suit the terminal strips

Removing the old pots, old movies in the background

Laying out the parts – new JJ circuit boards closest to the camera

Test fitting with nylon stand-offs and 40mm M3 bolts

Close up of new board mounted closer to the front panel

Making up wire links to link to the original board

Main circuit board partially recapped

Bigger power supply caps with bypass caps mounted under the board

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On the bench: Effectrons

bn1studio — Tue, 08 Sep 2020 21:36:45 +0000

Today was Day of the Effectrons as the newly repaired & tested delays were prepped for sale

Switched to 220 volt, power supplies upgraded & recapped, pots & switches cleaned before audio testing & packing for shipment…

This is a Deltalab Effectron II ADM 1024 with 512 Kb RAM which gives around half a second delay at full bandwidth and 1 second at half bandwidth. It has “Infinite Repeat” mode which loops the sample in the delat line with no degradation. While looping the modulation section is active – allowing some weird wobbling noises – and the delay time pot sweeps the sample up & down in pitch

[This post contains video, click to play]

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On the Bench: Projects & Prep

bn1studio — Thu, 07 May 2020 12:49:08 +0000

Despite the lockdown, I’m still working in my little workshop at Brighton Electric, making progress with new arrivals & projects that have been on the back burner:

Moog MKPE & Moog MKG

Recapped & upgraded power supply. The two units are constructed in the same way and have similar power supplies

Moog MKPE internal shot

Moog MKPE eq board showing pots

TC Electronic 1220 preamp / equaliser

TC Electronic 1220 eq board with pots

TC Electronic 1220 input / output board before recapping

CBS Audimax 4450 stereo compressor

CBS Audimax 4450 compressor board 4450 – deep 1U box with lots of seperate circuit boards

CBS Audimax 4450 internal shot shows power supply, control board plus left & right compressor boards. The grey encapsulated units are proprietary CBS timing modules

CBS Audimax 4450 compressor board

CBS Audimax 4450 control board & power supply before recapping

CBS Audimax 4450 front panel preset pots – to be replaced with regular pots & knobs

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On the bench: CBS Audimax 4450 Stereo Compressor / Leveller

bn1studio — Fri, 17 Apr 2020 20:31:55 +0000

The Audimax range was developed by CBS for AM & FM radio broadcasting. It’s a compressor / leveller designed to create a consistent level from mixed sources and less-than professional operators. But it can be creatively abused to dramatic effect: ” I noticed that excessive input creates huge compression density and also makes these things pump like mad!”

The Audimax was often paired with a CBS Volumax limiter which was used to drive the radio transmitter to peak modulation – but not over. Overmodulated transmitters could cause interference in other bands and the FCC levied hefty fines for offenders

At the time broadcasters vied for the loudest signal in their area and there was a constant struggle to achieve the loudest, punchiest signal. The Audimax and Volumax – dubbed “The Max Brothers” – were the CBS way of achieving this

Levellers like the 4450 use a slow release time to avoid pumping. Later models, like this one, had an internal three-way switch to select release times. I’ve modified this to have much more aggressive release times to accentuate the effect

Attack times were set by the CBS compression module, an encapsulated “secret” module developed by their engineers. Schematics are now available

There’s a fair amount of background info available for these:

https://broadcastengineering.info/viewtopic.php?t=2964

http://www.steampoweredradio.com/pdf/cbs%20laboratories/cbs%20model%204440a%204450a%20audimax%20manual.pdf

CBS Audimax 4450 compressor board 4450 – deep 1U box with lots of separate circuit boards

CBS Audimax 4450 internal shot shows power supply, control board plus left & right compressor boards. The grey encapsulated units are proprietary CBS timing modules

CBS Audimax 4450 compressor board

CBS Audimax 4450 control board & power supply before recapping

CBS Audimax 4450 front panel preset pots – to be replaced with regular pots & knobs

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On the bench: UREI LA4 Compressors

bn1studio — Sun, 15 Mar 2020 23:34:55 +0000

I’ve just finished refurbishing a tidy pair of LA4 compressors. They are late-model silver-face LA4s with the chrome UREI badge so the same kind of age as the 1176 Rev G & H and 1178 stereo compressor

I fitted a new set of incandescent meter bulbs so they give that classic UREI orangey glow when powered up

They’ve been recapped with bigger reservoir caps in the power supply and higher-value bipolar caps in the audio path. They’ve been aligned in standalone and stereo-linked modes and will come with a stereo link cable and a set of new XLR pigtails

UREI LA4 stereo pair, set #20

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